Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic Resonance Images

*Pilar Giraldo Castellano and Mercedes Roca Espiau*

### **Abstract**

Magnetic resonance imaging (MRI) is the gold standard for evaluating bone marrow (BM). The information provided is a useful tool for obtaining a global map of the contents of the medullary cavity. The applications of this technique to the study of different processes affecting the bone marrow are of great importance to know the extension of disease, to distinguish by image different entities, and to evaluate response to therapies. Actually, machine learning tools aid in the interpretation of images and patterns that are not visible or are unfamiliar to the observer. In addition, integrating clinical, biological, and therapeutic data with imaging using artificial intelligence methods applied to these studies provides a broad perspective and tool that can predict the risk of complications. The systematic inclusion of structured bone marrow MRI reporting is useful to standardize the collected data collaborate in developed algorithms to learning model, and facilitate clinical management and academics collaboration.

**Keywords:** bone marrow, MRI, infiltration patterns, lysosomal disorders, structured reports, machine learning

### **1. Introduction**

This chapter reviews the information provided by magnetic resonance imaging (MRI) as a useful tool to obtain a global map of the content of the medullary cavity and the applications of the technique to the study of different processes affecting bone marrow.

The daily clinical practice involves resolving situations of uncertainty in order to obtain the most accurate diagnosis possible and initiate therapeutic measures quickly. In this sense, the exchange of information and collaboration between the clinical physician and the MRI specialist is essential to answer questions regarding the global or focal involvement of the bone marrow in various pathological situations.

MRI, as a useful imaging technique to distinguish differences and anomalies in different tissues, bases its resolution on reflecting the balance between the medullary fatty component and the hematopoietic cellular component, providing an image of the variations that occur between these components within the bone cavity [1].

Artificial intelligence (AI) models based on deep learning algorithms offer actually diagnostic assessment and follow-up assistance for low-frequency entities, with findings to date suggesting that the diagnostic performance of such systems is equivalent to that of health-care professionals [2].

### **2. Rational basis of magnetic resonance imaging**

The physical basis of the procedure is due to the property possessed by some atomic nuclei of orientation in a magnetic field and the emission of a signal when subjected to an electromagnetic wave of an appropriate frequency. The basis is sending a sound signal on a magnetized object, developing macroscopic magnetization phases, which disturb the state of equilibrium due to the sound signal and collection of the MR signal and the return to the state of equilibrium or relaxation. This signal of a return to equilibrium or relaxation is the MR signal [3].

Some notions to keep in mind are the following:


*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

characterization. A DWI sequence may be helpful for lesion detection, but its utility in evaluating and characterizing focal bone marrow lesions is unknown. MR Spectroscopy. MRS is useful for fat quantification, and bone marrow studies have primarily focused on its use in the imaging of osteoporosis [4].

### **3. Applications of magnetic resonance imaging to the study of bone marrow**

In general, bone marrow involvement is easy to detect and interpret by MRI without requiring sophisticated sequences; it is very useful to obtain a map of hematopoietic marrow distribution and infiltration.

#### **3.1 Normal bone marrow distribution**

In children, bone marrow occupies 85% of the bone and accounts for 5% of the body weight. In the adult, red marrow is located in vertebrae, sternum, ribs, epiphyses of long bones, and iliac crests.

The bone marrow content in adults is 70% water and 30% fat. Hematopoietic marrow (red) consists of 40% water, 40% fat, and 20% protein. The fatty marrow (yellow) is made up of 15% water, 85% fat, and 5% protein.

Normal bone always contains both fat and red marrow, the percentage depending on age and anatomical region (**Figure 1**). However, it undergoes variations in its fatty composition/hematopoietic cellularity as part of a transformation phenomenon and in dependence on cellular requirements. Fat tissue is very labile and can be replaced by hematopoietic tissue under the influence of appropriate stimuli. Anatomically,

#### **Figure 1.**

*Distribution of red marrow and fat. A in the child. Red bone marrow is distributed in 85% of the bones. B in the adult, the red bone marrow is located in vertebrae, sternum, ribs, epiphyses of long bones, and iliac crests.*

medullary repopulation occurs in the reverse direction of regression, i.e., from proximal to distal areas.

MRI is able to reflect the ratio between the medullary fatty and hematopoietic components, through the changes that occur within the bone cavity [5, 6].

Marrow fat has a signal analogous to subcutaneous fat, the signal intensity is high due to its high proton content, expressing itself with a short T1 and a long T2 with high signal intensity in T1 and T2. As we have said, normal bone marrow contains 70% water and 30% fat and is hypointense in T1 and T2. T1 is the fundamental sequence for the study of bone marrow. The bone cortex has low proton content and small signal intensity.

Fat has a high signal in T1 and T2. Red marrow has an intermediate signal lower than fat and higher than muscle. The alterations that can occur are reconversion, infiltration, depletion, edema, and ischemia [7].

### **3.2 Patterns of bone marrow infiltration by MRI**

The distribution of bone marrow involvement may be diffuse or focal. Several distribution patterns have been described according to the images that appear on magnetic resonance imaging. **Table 1** shows the patterns described by Moulopoulos et al. [8] in the study of the bone marrow in patients with bone marrow involvement and the one described by our group [9] (**Figure 2**).

### **3.3 Hematological entities with preferential involvement of bone marrow**

#### *3.3.1 Multiple myeloma (MM)*

Eighty percent of patients with multiple myeloma present osteolytic lesions or demineralization at the time of diagnosis [10]. When these lesions become evident on radiography, more than 50% of the bone is already occupied.

There are three described patterns of infiltration in MM by MRI [11]:



**Table 1.** *Patterns of bone marrow infiltration by MRI.* *Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

**Figure 2.**

*Bone marrow infiltration. MRI patterns described by Roca-Espiau et al. 2007. Three MRI patterns were defined: Normal, homogeneous, and nonhomogeneous infiltration subtypes reticular, mottled, and diffuse.*

#### **Figure 3.**

*Sagital spin echo (SE) T1 (A) focal pattern in spine in multiple myeloma. It is the most frequent lesions and corresponds to lytic images in plain radiology. SE T1 (B) and T2 (C) spine with diffuse infiltration. The MR signal is hypointense in T1.*

3.Mottled or variegated pattern, with hypointense foci in T1 and generally hyperintense in T2 and STIR with contrast uptake (**Figure 4**). Libshitz et al. [12] describe diffuse involvement as areas where myeloma cells mix with hematopoietic cells, producing a displacement of hematopoiesis caused by nodular accumulations formed mainly by plasma cells. For this reason, the appearance of MRI is variable.

A strong association between diffuse infiltration and disease progression has been described. Diffuse infiltration is an unfavorable prognostic factor in patients with

#### **Figure 4.**

*Sagital spin echo (SE) T1 (A) and T2 (B) mottled or variegated pattern in multiple myeloma, with hypointense foci in T1 and hyperintense in T2.*

normal bone radiology [13]. Approximately 15% of patients are asymptomatic at the time of diagnosis, but bone marrow infiltration can already be detected in up to 29–50% of patients [11–14]. Patients with focal and diffuse MR patterns tend to progress more rapidly than patients with mottled patterns. Following these criteria, MR infiltration imaging helps to identify patients who are at higher risk of complications and to predict disease progression [15, 16]. However, in the current diagnostic criteria for MM, only the focal pattern on MRI (> 1) is considered as a criterion for multiple myeloma (previously called symptomatic myeloma) and, therefore, an indication for treatment [16, 17].

MRI is probably not the most sensitive imaging procedure in the follow-up of the response in MM, since bone lesions will persist over time, and it is not possible to delimit whether it is an active lesion. It is, however, useful for comparative assessment of lesion progression [18, 19].

In the variety of light chain multiple myeloma, a different MRI pattern of mottled appearance with hypointense foci in both T1 and T2 have been described, analogous to the pattern that appears in Gaucher disease [20]. The diagnosis of solitary plasmacytoma requires histologic demonstration of plasma cell infiltration. Although radiotherapy can eradicate this lesion, most patients progress to multiple myeloma, which has been attributed to occult disease growth [21].

For this reason, MRI is important in the extension study, since it detects unsuspected lesions, especially at the vertebral level. Currently, the accepted treatment for these lesions is radiotherapy covering at least 2 cm outside the tumor, and for this purpose, it is recommended to perform a previous MRI of the plasmacytoma area.

*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

The consensus panel (International Myeloma Workshop 2011) [22] recommends MRI in three situations:


#### *3.3.2 Non-Hodgkin's lymphoma and Hodgkin's lymphoma*

Bone marrow infiltration occurs in 5–15% of patients with Hodgkin's lymphoma and in 25–40% of patients diagnosed with non-Hodgkin's lymphoma. In T1, the pattern of involvement is heterogeneous diffuse, with focal infiltration being less frequent. In T2, hypersignal is observed, as well as contrast uptake after gadolinium injection. This aspect is nonspecific and indistinguishable from other spinal cord infiltration of other origins, and there is no difference in the MRI pattern between the different histological types of lymphoma [23, 24] (**Figure 5**).

Due to the permeative nature of lymphomas, tumor extension can be observed in the form of a soft tissue mass without rupture of the bone cortex. Although it is not pathognomonic, since it can exist in other malignant lesions, especially in small cell tumors, its detection, and evaluation with MRI is highly suggestive of lymphoma [25].

#### *3.3.3 Chronic myeloproliferative neoplasms*

#### *3.3.3.1 Polycythemia vera*

In polycythemia rubra vera, the bone marrow of the axial skeleton appears hypointense in T1 with a diffuse and homogeneous character in MRI studies, being

#### **Figure 5.**

*Coronal pelvis spin echo (SE) T1 (A), T1 Gadolinio (B), and T2 FSat (C) in non-Hodgkin lymphoma. Pattern heterogeneous diffuse in T1, hyperintensity of signal in T2, contrast uptake after gadolinium injection.*

**Figure 6.**

*Sagital spin echo (SE) T1 (A) and T2 (B) diffuse pattern in chronic myeloproliferative neoplasia (polycythemia rubra vera (PRV)). (C) Macroscopic section of spine with red infiltration PRV (right image) versus normal (left image).*

indistinguishable from the diffuse involvement observed in other myeloproliferative neoplasia. When the reconversion is pronounced, the proximal epiphyses of the femur and humerus and the greater trochanter, also participate in the reconversion showing hyposignal in T1. In T2, the behavior can be variable depending on the cellularity, the extent of reticulin fibrosis, and the paramagnetic effect of iron if hemosiderosis is present (**Figure 6**). The assessment in the proximal femur can be quantified according to the involvement of the femoral head and greater trochanter. The greater trochanter is more resistant to reconversion than the epiphyses. Patients with infiltration of both have higher disease activity [26, 27].

### *3.3.3.2 Myelofibrosis*

The fibrotic medulla, typical of primary or secondary myelofibrosis, is visualized in MRI as low signal areas in all sequences, but its appearance is nonspecific as in the rest of hematologic diseases and does not differentiate primary from secondary myelofibrosis. There is usually contrast uptake due to increased capillaries, large sinusoids, and increased vascular permeability [28]. Our group has performed a comparative study in patients diagnosed with primary or secondary myelofibrosis between histological findings and the pattern of bone marrow involvement by MRI. The results showed that the bone marrow patterns defined from lesser to a greater degree of involvement were: normal patterns according to age (NP), hematopoietic hyperplasia (HHP), reticular infiltration pattern (RP), mottled infiltration pattern (MP), diffuse heterogeneous infiltration pattern (DHI) and diffuse homogeneous infiltration pattern (HP) [29] (**Figure 7**).

*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

#### **Figure 7.**

*Sagital spin echo (SE) T1 (A) mottled pattern, coronal SET1 (B) reticular pattern in chronic myeloproliferative neoplasia (myelofibrosis). (C) Bone marrow histological section (reticulin staining) showed reticular fibers. (D) Collagen fibers.*

#### *3.3.3.3 Systemic mastocytosis*

Systemic mastocytosis is also a rare disease (less than 10% of mastocytosis), which usually affects adults and presents bone alterations in 70% of patients [26]. It has a special tropism for the axial skeleton, and although it can be silent, about 28% of patients report pain. The changes observed in simple radiology are small lytic or sclerotic lesions of focal or diffuse character (**Figure 8**). Mast cell proliferation in the

#### **Figure 8.**

*Coronal spin echo (SE) T1 (A) fémurs heterogeneous reticular pattern in systemic mastocytosis. (B) Plain radiology of the femur (C). Bone marrow histological section (hematoxylin–eosin staining. HE×4). Showed mast cell nodules.*

bone marrow stimulates fibroblastic activity with granulomatous reaction, resulting in trabecular destruction with replacement by neoformed bone. Soft tissue masses and deformities secondary to fractures may also be observed. MRI shows hypointense lesions in all sequences with diffuse distribution and homogeneous or mottled character that affect the axial skeleton and may extend to femurs and proximal humerus [30]. In any case, the infiltration presents a nonspecific signal, although sometimes it is not detectable by other diagnostic means [31].

#### *3.3.4 Bone marrow aplasia and hypoplasia*

Acquired aplasia is of unknown cause and may be secondary to chemical agents, drugs, or infectious agents. Some cases are irreversible. Biopsy is usually diagnostic, demonstrating the absence of cells or marked hypocellularity with the predominance of fatty marrow and fibrosis [32]. It should be kept in mind that areas of increased hematopoiesis may coexist with hypo- or acellular marrow, so that bone marrow biopsy from the iliac crest is a sample that does not always reflect the true state of marrow function. The marrow findings in cases of aplasia secondary to chemotherapy or irradiation may be diffuse or focal in cases of selective irradiation [33].

Hypocellular or aplastic marrow is characterized by a diffuse or mottled hyperintense pattern in T1, which corresponds to cellular replacement by fatty marrow. This signal enhancement is more appreciable in areas that normally contain red marrow remnants such as the proximal femur or vertebrae. In the appendicular skeleton, it is more difficult to appreciate this variation.

When there is a response to treatment, a heterogeneous pattern is observed in the vertebral bodies formed by hypointense foci in T1 and T2 that represent foci of hematopoiesis. MRI is a good method for assessing response to treatment [34, 35], taking into account that sometimes, these foci appear in vertebrae and are not seen in the pelvis, where the biopsy is normally performed if the patient recovers completely from his aplasia, the marrow returns to the normal appearance and distribution for his age.

The administration of erythropoiesis-stimulating factors as an adjuvant to chemotherapy treatment produces a patchy pattern in MRI showing hypointense foci in T1, which in T2 present identical or slightly increased signal, similar to hematopoietic foci in their behavior but located in areas where fatty marrow is normally present.

The depletion of medullary cellularity also occurs during ionizing irradiation at therapeutic doses. In vertebral irradiation, no signal changes are usually observed two weeks after treatment. Between the third and sixth week, most of the red marrow elements disappear, and there is central fatty infiltration in the vertebral body, or even a heterogeneous appearance pattern may be seen, resulting from the partial elimination of red marrow cellular elements. After six weeks, all patients will show hypersignal in T1. During the first year of irradiation with low doses (less than 30 Gy), there is marrow regeneration, but above 50 Gy, there is no recovery, with the MRI showing the limits between the zone of fatty infiltration and the zone of normal marrow. In case of irradiation at low doses, marrow regeneration in MRI could be confused with cellular infiltration of another type. Irradiation doses higher than 50 Gy are associated with complete replacement by fatty marrow due to irreversible marrow extinction [34].

#### *3.3.5 Hematopoietic stem cell transplant*

Knowing the normal MRI appearance of bone marrow repopulation after transplantation (BMT) is essential to be able to distinguish normal marrow repopulation from

#### *Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

tumor infiltration. The pretransplant MRI examination may show a normal appearance of the bone marrow in the spine and pelvis or an abnormal signal corresponding to infiltration, since the examination is performed prior to myeloablative treatment. In case of obtaining an MRI in this previous phase, a tendency to decrease signal in T1 and increase in STIR is observed, a modification that may be related to cellular necrosis and bone marrow edema induced by radiation and/or chemotherapy [35].

Until the third month after allo-TMO, no changes are observed in MRI in relation to the pretransplant examination. From the sixth month onwards, the changes are due to medullary colonization after induced aplasia, with the appearance of a heterogeneous signal alternating areas of hypo- and hyperintensity in T1 or a banded appearance. This characteristic appearance observed in the vertebral bodies corresponds to cellular hypointensity in the peripheral areas below the vertebral plats and a central zone of hyperintense fatty signal. Histologically, the peripheral zones correspond to hypercellular areas of hematopoietic repopulation, while the central zone is poorly cellular and rich in fat. The distribution depends on the vascularization system of the vertebral body [36].

In addition to assessing cellularity in BMT patients, MRI can be used to study metabolic alterations derived from cytotoxic treatment or immunological processes using QSCI (chemical shift selective imaging techniques) [37].

#### *3.3.6 Lysosomal storage diseases. Gaucher disease*

In metabolic storage diseases, MRI detects the changes produced in the bone marrow due to the combination of cellular infiltration, edema, and ischemia phenomena. Cellular infiltration causes hypointense areas in T1 and T2, starting at early stages in the vertebrae (**Table 2**) and progressing from the axial to the appendicular skeleton, affecting pelvis, hips, and lower extremities [37], with proximal predominance. The typical pattern shows homogeneous signal decrease in T1 and T2 in vertebral bodies and nonhomogeneous in proximal segments of lower extremities, with preserved epiphyses in most cases.

Vascular involvement causes infarcts, avascular necrosis, and pseudosteomyelitis or bone crises. Avascular necrosis is due to chronic infarcts produced by arteriolar occlusion following progressive cellular infiltration of the marrow and episodes of vasospasm and thrombosis. In the initial phase, the marrow is isointense, and the transition between normal and necrotic tissue is a low signal band in all sequences. Subsequently, the signal of the necrotic bone decreases and fractures appear due to cortical collapse [38].

Bone infarcts are visualized as low signal foci in all sequences of intramedullary diaphyseal location and sometimes bilateral. The bone crises that appear in 30–40% of patients with Gaucher disease are caused by acute intraosseous vascular obstruction. Due to edema, the marrow appears hypointense on T1 and hyperintense on T2. Sometimes subperiosteal hyperintensity is observed on T1 due to subacute phase hematoma or hemorrhage. Control studies show recovery of the physiological signal after the episode of bone crisis.

Gaucher disease causes alterations in the vertebrae due to increased intramedullary pressure due to cellular accumulation in the form of cortical endosteal resorption and vascular occlusive phenomena. Flat vertebrae are due to necrosis and compression fractures with the widening of the disc space.

Both enzyme replacement therapy and substrate reduction therapy cause a decrease in intramedullary lipid storage already visible in some patients after six


**Table 2.**

*Indications for bone marrow MRI and degree of usefulness in relation to the disease.*

months, with clearance and recovery of the physiological signal in MRI, as well as the disappearance of edema in bone crises [39] (**Figure 9**). In addition, in the examination of the bone marrow by MRI, other alterations not related to Gaucher disease are detected, such as vertebral hemangiomas, discopathies, etc., which stand out for their frequency in these patients [40].

#### **3.4 Posttreatment evaluation in hematological malignancies**

The initial applications of MRI in hematology were aimed at defining the presence of lesions not detectable by other imaging procedures, the maximum exponent being the assessment of intraosseous involvement in multiple myeloma. With the incorporation of BMT, MRI acquired a new dimension for the clinician, as an instrument to define the status of the BM in patients requiring this procedure, particularly in the case of bone marrow aplasia.

MRI, due to its sensitivity in the detection of cellular infiltration, is useful in the initial phase as an assessment of the extent of the disease. This quantitative extension study will also be important, together with the rest of the tests, when considering

*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

#### **Figure 9.**

*Coronal spin echo (SE) T1 (A) pelvis and femurs nonhomogeneous mottled pattern with infarcts in Gaucher disease before and after therapy. The therapy causes a decrease in intramedullary lipid storage with clearance and recovery of the physiological signal. Nevertheless, complications such as infarcts or necrosis are irreversible and more visible in MRI once the infiltration has been cleared. (B) Coronal spin echo (SE) T1 femurs and tibias nonhomogeneous mottled pattern with large infarct-necrosis in Gaucher disease before and after therapy.*

therapy. In the evaluation of the therapeutic response, MRI can show the degree of bone marrow involvement, being complementary to the methods that assess the progression of bone mineralization.

### **4. Practical considerations**

MRI has proved to be a useful tool for obtaining a global map of the contents of the bone marrow cavity and the applications of the technique to the study of different processes. Assessment of bone marrow is often complex due to the presence of multiple patterns and their evolutionary change with age and disease.

Structured reports are the result of applying a logical structure to the radiological report, and the rules of elaboration comprise several criteria: (I) using a uniform language. The standardization of terminology avoids ambiguity in reporting and makes it easier to compare reports. (II) Accurately describe the radiological findings, following a prescribed order with review questions and answers. (III) Drafting using diagnostic screening tables. (IV) Respect the radiologists' workflow by facilitating the work and not hindering it [41].

The creation of structured radiological reports for the study of bone marrow is of great relevance in order to unify terms and provide the most objective assessment possible. Our group has recently published a structured report based on eight items (demographic data, diagnostic suspicion, technical data, type of exam initial or


#### **Figure 10.**

*Structured report for MRI bone marrow exam. Roca-Espiau et al. 2022.*

control, patterns and involvement distribution, complications and their location, and summarized comments). It has been designed to provide guidance for radiologists when reporting protocol assessments to unified criteria, allow comparisons and decrease inter observers' variability [42] (**Figure 10**).

The structured radiological reports provide an answer in daily clinical practice, where situations of uncertainty are generated due to the lack of knowledge of the radiological semiology of the bone marrow, technical limitations in an extensive organ, and variability in the maturation of the bone marrow tissue and its pathological affectation. This involves both diagnosis and follow-up in the face of differentiated therapeutic approaches.

Nowadays, machine learning is revolutionizing the way data are analyzed in clinics and is helping to develop digital tools for diagnosis, disease progression prediction, and treatment responses. In our experience, using machine learning in rare diseases provides an opportunity to analyze agglomerated and heterogeneous data to create quality predictive models and identify risk features [43].

In the case of bone marrow diseases, these tools can be especially useful to speed the diagnosis and obtain better prognosis assessments and personalized care in our recently published work regarding the application of machine learning tools (random forest models) in a homogeneous Gaucher group of patients with different degrees of bone marrow infiltration and complications evaluated by MRI in order to identify features that can predict the risk of bone complications defined by the presence of intraosseous ischemic events (bone crisis, infarcts, avascular necrosis) during the follow-up. We have obtained the following information shown in **Figure 11**, model A includes all variables described as significant in a previously published study [43],

*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

#### **Figure 11.**

*ROC models. A model includes all variables. ROC B model considers whether any treatment was applied or not and features the importance of model B using the mean decrease in accuracy. ROC C model did not contain the S-MRI score and had a substantial drop in accuracy of 74.29% and an f1-score of 69.92%. The most important features for these models to predict the severity of bone affectation in Gaucher disease were the S-MRI, the age at first treatment, and the treatment used.*

model B considered whether a specific treatment was applied or not, and model C ignored the degree of infiltration according to the S-MRI punctuation score [44]. The results muestran la relevancia del grado de infiltración de medulla ósea y la localización para estimar el riesgo de desarrollar complicaciones [45].

More recently, radiomics has been incorporated, which is the science of noninvasively studying features of medical images imperceptible to the human eye by applying automated algorithms to associate them with specific physiological states. Integrating clinical, biological, and therapeutic data with imaging by applying artificial intelligence methods to these studies provides a broad perspective and models that can predict the risk of complications. Today Radiomics is a science Radiomics converts medical images into mineable data by extracting quantitative characteristics [46].

The main goal is to transform imaging into actionable predictions. Programs through imaging and address healthcare issues by creating image-based predictive AI models. This outcome will allow when evaluating an MRI acquired after treatment, to assess the evolution of the patient's bone marrow involvement and to predict how they are responding to treatment. The integration of clinical, biological and/or molecular data in the classification method will be evaluated to optimize and increase its performance.

The field in which most studies are being carried out is oncology. Thanks to radiomics, diagnostic and prognostic biomarkers have been identified, associated with the development of metastases and overall patient survival in different types of cancer [47, 48].

In conclusion, in the area of bone marrow diseases, the use of machine learning provides an opportunity to analyze agglomerated and heterogeneous data to create quality predictive models and identify risk features. And it can provide important digital solutions to empower physicians to achieve health objectives [49]. Nevertheless, validation is required prior to widespread adoption in clinical practice. *New Advances in Magnetic Resonance Imaging*

### **Author details**

Pilar Giraldo Castellano1 \* and Mercedes Roca Espiau2

1 Hematology, Hospital Quironsalud, FEETEG, Zaragoza, Spain

2 Radiology, FEETEG, Zaragoza, Spain

\*Address all correspondence to: giraldocastellano@gmail.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Advantages of Digital Technology in the Assessment of Bone Marrow Involvement by Magnetic… DOI: http://dx.doi.org/10.5772/intechopen.111964*

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### **Chapter 7**

## Current Topics on Knee MRI

*Jorge Rolando Ortiz, Juliana Gonzalez and Juan Sebastian Herrera*

### **Abstract**

Knee pathology is one of the most common complaints worldwide. Among the most common complaints is ligamentous and meniscal injuries, for which MRI is the main diagnostic tool. Advances in MRI have improved the accuracy of detecting Anterior Cruciate Ligament (ACL), posterior cruciate ligament (PCL) and meniscal tears, which have helped orthopedic surgeons treat and classify injuries accordingly. Understanding the anatomy, different protocols and the advances will help orthopedic surgeons to deliver better patient care. MRI is especially important in ACL pathology due to its implication in femoral and tibial tunnel positioning; the more anatomically we can reconstruct the ACL, the better the functional outcomes. This is true for most of the ligamentous pathology of the knee. This chapter will review the current indication and further research areas in knee pathologies.

**Keywords:** ACL, posteromedial corner, posterolateral corner, postoperative meniscus, isotropic three-dimensional MRI

### **1. Introduction**

Magnetic resonance (MR) is the preferred non-invasive imaging method to assess knee musculoskeletal injuries due to its high soft tissue resolution, and it is considered the reference standard with the additional benefit of avoiding exposition to ionizing radiation [1]. New advances in magnetic field and gradient strength allow the development of sequences for ultrastructure imaging and even postoperative ligament reconstructions or meniscal repair, which has represented a challenge to date.

Isotropic three-dimensional MR imaging has a thin slice of less than 1 mm and less partial volume artifacts with the use of thin continuous sections and oblique planes that are helpful for complex structure analysis like static and dynamic knee stabilizers with their tissue-osseous relationships [2]. These advances will be tools for preoperative planning and clinical decisions in patients with ligament and meniscal injuries.

### **2. Current topics in anterior cruciate ligament on MRI**

The three-dimensional configuration of the anterior cruciate ligament is important to determine different conditions in association with the prognostic of the anterior cruciate ligament reconstruction, as parameters related to the most anatomical

possible position. Ortiz et al. described the orientation of the anterior cruciate ligament in resonance, proposing a triplane trigonometric method; as a result, they found that the mean angle in sagittal, coronal and axial projection were 76.95, 81.65 and 33.17 degrees, respectively. It is expected that this method may be applicable for planning anterior cruciate ligament reconstruction, using the position of the anterior cruciate ligament of the uninjured knee as a reference [3].

In the evaluation of an acute lesion of the anterior cruciate ligament in MRI, there are different signs that can help with the diagnosis, the most sensitive being the discontinuity of the fibers or irregularity, increased signal on T2, bone bruises and abnormal orientation of the fibers. Secondary findings include bone lesions mainly at the level of the external femoral condyle and external tibial plateau, and it is less common to present lesions at the internal femoral condyle and tibial plateau; other findings are the anterior translation of the tibia and uncovering of the posterior horn of the lateral meniscus greater than 3.5 mm [2].

The normal appearance of the anterior cruciate ligament is characterized by a uniform caliber with a course parallel to Blumensaat's line, a high or intermediate signal on T1 and T2, and some signs of fluid between the fibers [4].

### **2.1 Indirect MRI signs related to anterior cruciate ligament injury**

The lateral femoral notch sign is a radiographic phenomenon defined as an impaction greater than 2 mm of the lateral femoral condyle, and it may result from a traumatic episode in which the lateral femoral condyle collides with the proximal tibia, causing a defect in the lateral femoral condyle with high signal on T1 (**Figure 1**) [5, 6].

Haluk Yaka validated a posterior base measurement of the medial and lateral meniscus, defined as a line passing through the tibial edge of the meniscus and a line passing through the capsular edge on the sagittal side of the posterior horn of the meniscus based on the previous studies performed by Hohman where the relation of the posterior angle of the base of the meniscus and its relationship with the anterior cruciate ligament injury was discussed, it was concluded that the medial and lateral angles above 84.5 and 93.15, respectively are an indirect finding of anterior cruciate ligament injury (**Figure 2**) [7].

**Figure 1.** *Lateral Femoral Condylar Notch, Indirect Sign of Anterior Cruciate Ligament Injury.*

#### **Figure 2.**

*Posterior base meniscus angle, a line through the base of the meniscus and a line through de posterior aspect of the meniscus in the sagittal plane.*

#### **2.2 Location of anterior cruciate ligament injury point in MRI**

Within the management protocol for anterior cruciate ligament injuries, there is the option of performing primary repair in cases in which the injury is proximal near the insertion of the femur and a contained injury with good tissue. In order to validate this condition, Sherman classified injuries into five types, been I and II types the proximal tears, in which a primary ACL repair can be considered. Now, before performing an arthroscopy, it is important to know if the patient is a candidate for repair or not; it could change the treatment and rehabilitation approach. For this purpose, it has been described in recent years to resonance as a method that allows us to know the location of the rupture of the anterior cruciate ligament [8, 9].

In a study carried out by Guillien et al. at the University of Rennes, they evaluated the correlation between the anterior cruciate ligament lesion point determined in MRI in comparison with the findings in arthroscopy, and this study was based on the Sherman classification (**Figure 3**). It was identified that the correlation in relation to the position of the lesion is approximately 70%; it was not the same for the evaluation of the quality of the ligament determined in resonance, in which the correlation was 50%. In another work carried out by Vanderlist, the predictive capacity of preoperative resonance is evaluated in relation to anterior cruciate ligament repair in Sherman type I and II injuries, finding that in 90% of the cases that a lesion was diagnosed pre-surgical type I repair of the ACL was performed and in 88% of type II [4].

As mentioned previously, the complex three-dimensional ACL orientation does not allow for the complete visualization of the ligament in a single image. ACL runs obliquely through the intercondylar notch; this is why various MRI techniques including oblique planes have been investigated (**Figure 4**) [3].

Kwon et al. from the Department of Radiology and Center for Imaging Science and Department of Orthopedic Surgery of Samsung Medical Center, Seoul, Korea, published a study whose purpose was to evaluate the diagnostic role of additional use of oblique coronal and oblique sagittal imaging for an ACL injury [10]. The study

 **Figure 3.**  *Anterior cruciate ligament tear in the proximal third of the ligament.* 

#### **Figure 4.**

 *A 55-year-old female left knee. Oblique coronal PD FSE MR images, performed using a 1.5 T system with 1.2 mm thickness (A) anterior bundles of ACL (arrow) and it is possible evaluate posterior meniscal roots (red open arrows). (B) Posterior bundles of ACL (arrow).* 

population consisted of 101 patients with a mean age of 35 +/− 12.6 years who required knee arthroscopy for suspected of having a torn ACL on MRI examination with both orthogonal and oblique images using 1.5 MRI system conventional protocol sequences with section thickness 3 mm, TR/TE 2000–3800/20-30 ms and additional oblique coronal/sagittal proton density-weighted imaging. The oblique sagittal image was made in the plane parallel to the medial border of the lateral femoral condyle on an orthogonal coronal image and the oblique coronal image was obtained in plane parallel to course of the femoral intercondylar roof using a sagittal *Current Topics on Knee MRI DOI: http://dx.doi.org/10.5772/intechopen.114124*

image. Two musculoskeletal radiologists analyzed the knees MRI retrospectively, without knowledge about arthroscopic results, then determined intact, probable tear or definite ACL tear. They evaluated sequences by using four methods (*M*), *MA*: orthogonal images only, *MB*: orthogonal and oblique coronal, *MC*: orthogonal and oblique sagittal, and *MD*: orthogonal, oblique coronal and sagittal images.

Diagnostic performance with sensitivities, specificities and accuracies of each method respect arthroscopy (partial or complete ACL tear) as a gold standard was as follows respectively, MA 95%, 83.6%, 88.1%, MB 97.5%, 95.1%, 96%, MC 97.5%, 95.1%, 96% and MD 97.5%, 98.4%, 98%, meaning that specificities and accuracies for methods B, C D were statistically significantly higher than method A. No difference was found between methods B, C and D. This study concludes that some oblique imaging added to standard MRI sequences improves the ability to diagnose ACL tears [10].

#### **2.3 Mucoid degeneration of the anterior cruciate ligament**

A topic of interest in recent years has been mucoid degeneration of the anterior cruciate ligament as a rare entity, which can be confused with an ACL lesion, being difficult to diagnose. Bergins et al. described an incidence of 1.8% in an analysis of 4221 patients, in addition to describing different aspects that can help diagnose mucoid degeneration of the anterior cruciate ligament, which includes the presence of a uniform thickening with a bulging ligament, semiologically described as "celery stalk," increased intermediate intraligamentary signal on T1, and hyperintensity on T2, maintaining orientation and continuity of the anterior cruciate ligament fibers. More recently, Cilengir et al. described MRI findings that can help differentiate mucoid degeneration of the anterior cruciate ligament from injury and found an increased prevalence of intraosseous femoral cysts being part of the mucoid degeneration. Other authors have described anatomical conditions in resonance that can be associated with mucoid degeneration of the anterior cruciate ligament, such as an increase in the angle of the tibial slope, a decrease in the width of the intercondylar groove, male sex [11–13].

### **3. MRI accuracy of posterolateral and posteromedial corners injuries**

#### **3.1 Normal anatomy of the posterolateral corner**

Posterolateral corner (PLC) is currently a diagnostic challenge.

PLC structures are grouped into primary stabilizers, which are statics, and secondary stabilizers, which are static and dynamic [14]. PLC structures are the main mechanism to protect against knee varus stress and posterolateral rotation of the tibia with respect to the femur [15–17].

**Table 1** shows all the PLC structures with their respective origins and insertions, and the graphic scheme of the structures is shown in **Figure 5**.

The three primary stabilizers are the fibular collateral ligament (FCL), popliteus tendon (PLT) and popliteofibular ligament (PFL). FCL is the main stabilizer with varus stress, and PLT acts as a stabilizer regarding tibial external rotation.

On magnetic resonance (MR) imaging FCL is visualized on axial and coronal plane as low signal-intensity band extending from the lateral epicondyle to the lateral aspect of the proximal fibula. The PLT is seen as a low-signal-intensity structure on axial or sagittal sequences [18].


#### **Table 1.**

*Components of the posterolateral corner.*

The PFL has an anterior and posterior bundle that embraces the popliteus myotendinous junction, and it is best seen as a low-T2-signal structure on coronal and sagittal planes, deep to the inferior lateral genicular vessels. However, the PFL is not currently described in conventional MR imaging. Coronal oblique sequences and isotropic 3D MR improve visualization of these tissues (**Figure 6**) [19, 20].

Secondary stabilizers include the mid-third lateral capsular ligament (ALT), popliteomeniscal fascicles (PMF), lateral gastrocnemius tendon (LG), fabellofibular ligament (FFL), arcuate ligament, biceps femoris tendon and iliotibial band.

The ALT that is a thickening of the lateral capsule of the knee is seen on isotropic 3D MR axial images [20].

The popliteomeniscal fascicles form the roof and floor of the popliteus hiatus. They are visible in 60–94% of patients and can be seen on sagittal images of isotropic 3D MR.

FFL is best seen on sagittal and coronal MR imaging posterior to the lateral inferior genicular artery; however, this ligament is visible in 33–48% of patients.

Arcuate ligament is also inconsistent, but it may be identified as a thin band overlying the PLT on axial sequences [20].

 **Figure 5.**  *Scheme of the structures of the posterolateral corner.* 

#### **Figure 6.**

 *MR images of a left knee of a 40-years old female patient. (A) Axial fat-saturated T2 weighted sequence demonstrates posterolateral structures. Popliteus tendon (PLT), fibular collateral ligament (FCL), biceps femoris tendon (BF), lateral capsular ligament (ALT), iliotibial band (ITB). (B) Sagittal proton densityweighted image lateral knee with popliteus hiatus formed by popliteomeniscal fascicles (red open arrows) and Popliteofibular ligament (PFL) located anterior to lateral inferior genicular artery (LIGA). (C) Coronal T1 image that shows PFL and its association with respect to LIGA.* 

 Biceps femoris tendon (BFT) is composed of multiple distal insertion arms that may not be easily distinguishable but just long and short arms ( **Figure 6** ).

#### **3.2 Posterolateral corner injuries and MR imaging**

 Injuries to the PLC most commonly occur with varus forces, particularly to a hyperextended knee or associated with knee dislocation. Diagnosis may be difficult in the setting of acute trauma because of the patient's joint effusion. However, prompt diagnosis and management are important, as unrecognized PLC injuries may result in chronic instability and premature osteoarthritis [ 21 ]. Therefore, it would be desirable

to predict not only by clinical testing but also by imaging. **Figure 7** shows PLC injury patterns on MR imaging.

A meta-analysis established that 1.5-T or 3.0-T MRI offers high diagnostic accuracy for evaluating injuries involving the meniscus, anterior cruciate and posterior cruciate ligaments. However, in multi-ligament injured knees, MRI had been found to have lower accuracy for the detection of PLC ligament tears [22].

A recent retrospective study from the Ottawa Hospital Research Institute and Department of Radiology determined the diagnostic performance of preoperative MRI for diagnosing PLC injuries of patients with knee dislocations compared to intraoperative findings [21]. They included 39 patients who required repair/reconstruction of the posterolateral corner between May 2005 and April 2020. Preoperative MRI of these patients was on 1.5 T or 3.0 T scanners, and all protocols included sequences in standard imaging planes.

The fibular collateral ligament, bicep femoris and popliteus tendon were categorized as normal, partial tear or complete tear. The posterolateral ligamento-capsule complex (LCC) was evaluated as a single unit that includes popliteofibular and fabellofibular ligaments. This complex and posterolateral capsule was classified as intact or torn; the same classification was used for intraoperative findings.

The *diagnostic performance* of MRI was a sensitivity (Se) of 95% and specificity (Sp) of 100% for detecting fibular collateral ligament (FCL) tears, Se of 100% and Sp of 77% for BFT tears, Se of 88% and Sp of 71% for PLT injuries and Se of 97% and Sp of 33% for LCC tears. The correlation between surgical findings and magnetic resonance of PLC structures was strongest for the BFT and weakest for the LCC.

This study reports accuracy ranging from 82 to 95% for detecting PLC injuries with MR imaging, even higher than other previous studies [23], probably associated with MRI evolution in the last few years.

Longer time between injury and surgery may allow some injuries to heal and can be found intact at surgery but still presenting with abnormal signals at MRI, leading to higher false positive counts; obtaining MR images closer to the time of injury may

#### **Figure 7.**

*MR images of a 23-year-old man with left knee PLC injury caused in a motorcycle accident. (A) Coronal protondensity weighted fat-saturated T2 sequence with popliteomeniscal fascicles disruption (red open arrow) and complete tear of fibular collateral ligament (FCL) and popliteus tendon (PLT). Lateral inferior genicular artery (LIGA), fibular styloid (FS). (B) Sagittal proton-density weighted fat-saturated T2 image with PLT tear and disruption of posterolateral ligamento-capsule complex (LCC) and evident disruption of poplitemeniscal fascicles (red open arrow). (C) Axial proton-density weighted fat-saturated T2 sequence with posterolateral capsule injury, midthird lateral capsular ligament (ALT).*

#### *Current Topics on Knee MRI DOI: http://dx.doi.org/10.5772/intechopen.114124*

make their interpretation more challenging due to inflammatory process also affecting the radiologist reading [24].

Finally, this study concludes that despite the challenges of evaluating knee posterolateral corners, MRI has an acceptable accuracy for detecting their injuries.

Statistically, up to 20% of MRIs made in patients with an Anterior Cruciate Ligament (ACL) tear may reveal PLC injuries. A Swiss retrospective cohort study of The University of Zurich determined the diagnostic performance of different MR imaging findings for helping to predict posterolateral instability in patients with acute complete ACL tears by performing a decision tree analysis [25]. Their sample comprises 162 patients who underwent ACL reconstruction with or without concomitant posterolateral corner reconstruction. Clinical diagnosis of PLC instability requiring reconstruction served as gold standard, and there were obtained conventional MRI of all patients. Results demonstrated a low sensitivity and high specificity for posterior cruciate ligament, biceps femoris, popliteus tendon and lateral collateral ligament. Decision tree analysis results showed that a complete tear or fibular avulsion of the FCL was the most statistically significant finding to help predict posterolateral instability. These results are shared with other studies that affirm it is sufficient to assess the FCL, BFT and PLT to predict PLC instability [26].

With respect to small structures, this study confirms variable visibility of popliteofibular ligament, fabellofibular ligament and popliteomeniscal fascicles, which are not always observed at conventional two-dimensional MRI.

Limitations of this study are sample of patients limited to ACL reconstruction, MRI performed in the acute trauma 10 days or less, and it was different protocol and scanners to take images like in many other studies.

In the next years, the use of isotropic three-dimensional high-resolution sequences could allow for oblique reconstructions and individual examination for each patient. A retrospective study performed at Gachon University of South Korea aimed to document the appearance of PLC structures on 3D isotropic and routine two-dimensional MR images and to determine the significance of pathologic findings in patients with confirmed posterolateral instability. They evaluate conventional 3.0 T MRI of 25 patients with surgery indication as the gold standard and also of 25 control patients with any radiological or clinical finding, but in addition to standard sequences 3D isotropic SPACE (Sampling perfection with Application optimized Contrasts using different flip angle Evolution) images were obtained until adequate visualization of posterolateral corner. Their findings were the following:


A disadvantage of 3D isotropic imaging is the lack of fat suppression that may underestimate slightly altered ligament signals.

Despite these limitations, 3D isotropic SPACE MRI could be an interesting examination method in institutes interested in multiligamentary knee reconstruction [26].

### **3.3 Normal anatomy of the posteromedial corner**

The posteromedial corner (PMC) contains the structures lying between the posterior margin of the superficial medial collateral ligament (MCL) and the medial border of the posterior cruciate ligament (PCL). These structures avoid anteromedial rotational instability and provide restraint to valgus stress. Although some authors do not consider MCL to be part of posteromedial corner, recently, an international expert consensus panel has included it [27, 28]. **Figure 8** illustrates the borders of the PMC, **Table 2** shows PMC structures with their respective origins and insertions, and **Table 3**, **Figures 9** and **10** describe normal MR imaging of PMC.

### **3.4 Posteromedial corner injuries and MR imaging**

The semimembranosus is the main dynamic stabilizer of the PMC; without its dynamic support, the remaining PMC structures fail over time and lead to instability that affects the anterior cruciate ligament or posterior cruciate ligament [32].

MR imaging is the modality of choice for PMC injury assessment; however, at present, there are no specific studies that have evaluated the sensitivity and specificity of PMC structure injuries on MR imaging, unlike PLC structures.

A retrospective study of patients with symptomatic anteromedial rotational instability who were treated with ligament reconstruction and based on surgical descriptions found injury of the posterior oblique ligament (POL) in 99% of the cases, injury to the semimembranosus in 70% and peripheral meniscal detachment in 30% [33].

Tears in these three structures are well defined on MRI with an established classification system for each one of the ligament structure injuries.

House et al. have proposed the same classification used for the MCL injuries in the POL injuries, and it is grade I, intact ligament with edema surrounding it (T2

**Figure 8.** *Axial fat-saturated MR image of a left knee illustrated the borders of the PMC (green outline).*


#### **Table 2.**

*Components of the posteromedial corner.*


#### **Table 3.** *Normal MR imaging of PMC structures.*

#### **Figure 9.**

*Axial proton density weighted fat-saturated MR images of a normal knee, proximal to distal. (A) At the level of the femoral condyles illustrates medial collateral ligament (MCL), posterior oblique ligament (POL) and semimembranosus tendon (Sm). (B) At the level of joint space, oblique popliteal ligament (OPL). (C) At tibial plateau level, tibial semimembranosus expansion (TSm), inferior arm (ISm) and direct arm (DSm).*

#### **Figure 10.**

*Coronal proton-density weighted fat-saturated images and sagittal proton density images of a normal left knee. (A) Posterior oblique ligament (POL), anterior expansion of semimembranosus (ASm). (B) Inferior semimembranosus arm (ISm). (C) Oblique popliteal ligament (OPL), (D) Tibial and inferior expansions of semimembranosus.*

high signal). Grade II thickening of the ligament with partial disruption of fibers and Grade III with complete disruption of the ligament [34]. The coronal plane allowed for visualization of the POL; however, the coronal oblique plane, in combination with the axial plane, improved the analysis of the POL. In case of doubt, the addition of intraarticular contrast material can optimize the visualization of the POL and capsular layers in the axial plane as these structures are displaced away from the femur (**Figure 11**) [35].

With respect to medial meniscocapsular injuries, a "reverse Segond fracture" represents meniscotibial ligament osseous avulsion, also associated with posterior cruciate ligament rupture. Meniscocapsular separation is best visualized in the sagittal sequences. When there is increased signal intensity and thickening of the capsule, it may

#### **Figure 11.**

*MRI of a 53-year-old man with right knee PMC injury caused in a twisting knee injury. (A) (B) axial proton density weighted fat-saturated sequence at the level of joint space and at tibial plateau level respectively illustrate OPL partial tear, POL, MCL complete tears and capsular separation (red open arrow). (C) Axial T1 fatsaturated image shows tibial (TSm) and inferior (ISm) semimembranosus arms injuries. (D) Coronal protondensity weighted fat-saturated image with POL complete tear.*

be associated with capsule sprain, but it could be a ruptured popliteal cyst, too. Hence, it is important to interpret according to clinical history and other imaging features.

### **4. MR imaging of the postoperative meniscus**

Meniscal surgery is a frequent orthopedic procedure [36]. Clinical examination and MR imaging are both the current way to assess patients who complaint about knee pain after meniscectomy or meniscus repair. However, the evaluation after surgery can be difficult and represents a challenge to date.

The normal medial and lateral meniscus are hypointense on T1- and T2-weighted MR images. On axial plane, they are like C-shape; on sagittal images, they appear as a wedge configuration; on coronal plane, they are seen as a right-triangular with a free edge oriented to intercondylar notch [37–39].

Sagittal and coronal images of intermediate and/or T1-weightened sequences of conventional MRI are the method of choice to assess signal changes in nonoperative meniscus, however after meniscal surgical procedure, it is the T2-to-intermediateweighted fluid-sensitive images in sagittal and coronal planes to detect synovial fluid signal extending into the substance of the meniscus indicating that the articular surface has been breached due to a new retear [39].

In regard to magnetic resonance with contrast, direct magnetic resonance arthrography (MRA) is useful to evaluate recurrent tears or unhealed repair when there is an extension of contrast into a meniscus substance. Disadvantages of this examination include other invasive procedures, infection, bleeding and allergic reactions. If there is fluoroscopic-guided injection, radiation exposure is another risk and finally entails more costs. In some countries, it is considered an off-label use of gadolinium-based contrast agents, according to FDA [40].

Indirect MR arthrography involves the intravenous administration of gadoliniumbased contrast; it allows the identification of sites of hyperemic synovitis associated with vascular tissue enhancement. Nevertheless, the stable healed granulation tissue, as expected after meniscus surgery, may be difficult to differentiate from a residual tear, and it may result in potential false positives. Disadvantages are costs, patient time and adverse reaction to contrast agents [40].

### **4.1 Imaging findings after meniscectomy**

Low signal linear fibrotic tissue in Hoffa fat pad is. A sign of precious arthroscopic knee surgery [39, 40]. With respect to partial or total meniscectomy, it could be found:

Diminution of meniscal tissue, ranging from a large portion of the meniscus being removed to mild blunting of the apical margin [39].

Baker et al. reviewed PubMed published evidence from 1990 to 2017 about recurrent tears after partial meniscectomy imaging. They found nine studies that reported the accuracy of conventional MRI, direct MRA and indirect MR arthrography compared to second-look arthroscopy. Conventional MRI had accuracy ranging from 57 to 80%, direct MRA from 85 to 93% and indirect MRA from 81 to 93% [40]. However, some other studies, specifically a randomized cohort study made by White et al., published in Radiology Journal compare the accuracy of conventional MRI, direct MRA and indirect MRA, with inconclusive results that do not find statistical differences among the three techniques in the setting of a recurrent meniscal tear, although there was a trend toward increased diagnostic performance for both direct and indirect MRA [41].

Intermediate-signal intensity extending to the articular surface of the postoperative meniscus on fluid-sensitive sequences has been the most specific sign of retear [41], meaning that its absence could be a negative predictive sign of an intact meniscus after surgery (**Figure 12**) [39, 42].

#### **4.2 MRI findings after meniscal repair surgery**

In this kind of surgery, intrinsic high signal may be seen on intermediate and T2 MRI such as the features of preoperative meniscal injury.

A cohort study performed by the Institute of Sports Medicine of Peking University evaluated the diagnostic performance of MRI compared with second-look arthroscopy as the gold standard in 81 patients to evaluate the healing of the repaired meniscus. They found T2-weighted sagittal and coronal sequences had higher specificity (89.6–98.7%, respectively) and accuracy (85.4–91%), while T1 and proton density had higher sensitivity, 91.7% and 75%-83–3%, respectively. The diagnostic value could be improved by a combined application of different sequences [43].

#### **Figure 12.**

*(A) A 62-year-old man following partial medial meniscectomy, sagittal fat-saturated T2 and sagittal proton density images respectively that show diminutive body and posterior horn of medial meniscus (orange arrows) and (B) fibrotic stranding in Hoffa fat pad (arrowhead). (C) and (B) same patient. Sagittal fat-saturated T2-weighted image illustrates surfacing intermediate signal extending to the apical meniscal articular surface characteristic of a new tear.*

*Current Topics on Knee MRI DOI: http://dx.doi.org/10.5772/intechopen.114124*

The same study by Pekin University also demonstrated that approximately 50% of the patients with intact menisci in diagnostic arthroscopy illustrating features of surfacing increased intermediate-weighted linear signal at the healed repair site [43].

On MRA, one of the findings that may represent a partially healed repair or a partial thickness recurrent tear is the extension of intraarticular contrast through the meniscal repair site from one articular surface to another [39].

As a clinical care point, MRI or direct and indirect MR arthrography is the examination of choice for patients with suspected meniscus retear. However, those methods can be challenging because conventional diagnostic criteria of a meniscal tear may be normal findings postoperatively.

### **5. Three-dimensional isotropic MRI of radial and root tear of meniscus**

Almost all meniscal injuries have suggested that the sagittal imaging sequences are the most accurate for detecting them; however, the radial and the root tears could be missed on conventional 2D images due to thicker slices of axial sequences, which is the preferred plane to evaluate both. Several studies describe thin-Section 3D FSE sequences such as Volume isotropic turbo spin echo acquisition (VISTA), CUBE and SPACE to analyze menisci injuries with better quality image of peripheral and radial tears (**Figure 13**) [44].

Daekeon Lim et al. from Yonsei University College of Medicine, Seoul, Korea, assessed the diagnostic value of FS 3D VISTA (*Volume isotropic turbo spin echo acquisition*) protocol imaging compared to 2D standard imaging in detecting arthroscopyconfirmed (gold standard) radial and root tears. Their results reported sensitivity and specificity of 96% and 96% with VISTA protocol imaging, respectively, versus 87% and 91% with 2D imaging. They found higher sensitivity and specificity with isotropic 3D imaging and excellent interobserver agreement for detecting meniscal radial and root tears. Some limitations and bias were retrospective study design, size

#### **Figure 13.**

*A 45-year-old female left knee. MRI were performed using a 3.0 T system with 2 mm thickness (A) PD FSE FS axial 2D image with suspected tear of posterior root of medial meniscus (arrow). (B) Multiplanar reformatted axial 3D VISTA (volume isotropic turbo spin echo acquisition) image of 0.5 mm slice thickness with better delineation of posterior root tear (arrow).*

of sample, and MRI readers were aware that patients had undergone arthroscopic surgery that could overestimate the lesions [44].

## **6. Conclusions**

The advances in magnetic resonance research imaging have made it possible to achieve greater detail in the diagnosis of knee joint pathologies. Different protocols and MRI sequences have been described, as well as clinical signs for different conditions such as posterolateral corner lesions and mucoid degeneration of the anterior cruciate ligament. These tools should be used as part of the clinical approach to patients with traumatic knee injuries.

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Jorge Rolando Ortiz1,2\* † , Juliana Gonzalez1† and Juan Sebastian Herrera1†

1 Department of Trauma and Orthopedics, Universidad Nacional de Colombia, Colombia

2 Hospital Universitario Nacional de Colombia, Colombia

\*Address all correspondence to: jrortizmo@unal.edu.co

† These authors contributed equally.

© 2024 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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### **Chapter 8**
