**3. Primary benign bone tumors by tissue type**

Cystic bone lesions:

Adult:

diagnosis.

Epiphysis:

Chondroblastoma. Giant cell tumor. Metaphysis:

Enchondroma.

Osteochondroma. Simple bone cyst. Diaphysis:

Fibrous dysplasia.

Osteochondroma. Osteofibrous dysplasia. Simple bone cyst. Aneurysmal bone cyst.

Enchondroma.

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Aneurysmal bone cyst. Chondromyxoid fibroma.

Enchondroma. Giant cell tumor. Osteoblastoma.

Brown Tumor (Hyperparathyroidism).

*Recent Advances in Bone Tumours and Osteoarthritis*

Nonossifying fibroma/fibrous cortical defect.

Nonossifying fibroma/fibrous cortical defect.

Brown tumors (hyperparathyroidism). Cystic angiomatosis/lymphangiomatosis.

Osteochondroma (Diaphyseal Aclasis).

Expansion of bone from slow growth. Smooth periosteal new bone formation. Absence of an associated soft tissue mass.

whether the lesion is aggressive or nonaggressive.

Infiltrate myofibromatosis. Langerhans cell histiocytosis.

Enchondroma (Ollier disease, Maffucci syndrome). Fibrous dysplasia (McCune-Albright syndrome).

Nonossifying fibroma (Jaffe-Campanacci Syndrome).

Chronic recurrent multifocal osteomyelitis (CRMO).

and help differentiate from aggressive malignant bone lesions: Well-defined margins with a narrow zone of transition.

The location of the lesion in the bone can help narrow down the differential

Pediatric benign bone tumors based on location in the long bones:

Some lesions are solitary, and others are multifocal at presentation. The

The following features are characteristic for nonaggressive benign bone lesions

Some benign bone tumors are adequately defined by radiographs and do not require any further imaging for diagnosis or treatment. However, most bone tumors require additional imaging; this may be in the form of CT, MRI, scintigraphy, PET scanning, and rarely ultrasound. The choice of imaging for a given tumor depends on the differential diagnostic considerations, possible treatment options, and

Classification of pediatric bone tumors according to matrix or tissue type:

following are the examples of multifocal pediatric benign bone lesions:

1.Simple bone cyst:

A simple bone cyst is also called a solitary cyst or unicameral bone cyst (UBC). A simple bone cyst is a common benign nonneoplastic lucent bony lesion mainly seen in childhood and typically asymptomatic. Approximately 85% of unicameral bone cysts occur in children and adolescents [1]. There is 2–3:1 male predominance [2]. During the active phase, the cyst increases in size and remains close to the physis. The latent phase cysts are found farther from the physis and usually do not continue to grow. Cysts may appear to migrate into diaphysis, but actually, it is the growth plate that migrates away from the cyst. The lesions are usually asymptomatic and found incidentally, although the adjacent joint's pain, swelling, and stiffness can also occur. The most frequent complication is a pathologic fracture, and this is usually the cause of presentation. 75% of patients come in with a pathologic fracture [3]. Pathologically, the cysts contain clear serosanguineous fluid surrounded by fibrous membranous lining. The proximal humerus is the most common location (in 50–60% of cases) [4]. The second most common location is the proximal femur.

On radiography, bone cysts are located centrally in the medullary cavity within the metaphysis. Most cysts are less than 3 cm in short-axis diameter but may be much larger in the long axis. The cyst wall is well-defined and sclerotic; the overlying cortex is thinned, and the lesion may be mildly expansile (**Figures 1A, 2A**). Following a fracture, a fragment of bone may be seen dependently within the cyst, called a fallen fragment sign, considered pathognomonic for a simple bone cyst [5] (**Figure 3A**).

Computed Tomography (CT) scan and Magnetic Resonance Imaging (MRI) can help exclude other entities that can potentially mimic a simple bone cyst such as an intraosseous lipoma, fibrous dysplasia, eosinophilic granuloma, giant cell tumor, nonossifying fibroma, or aneurysmal bone cyst. The CT scan helps to delineate the cyst and confirms a fallen fragment. MRI confirms the cystic nature of the lesion. The fluid contents are low signal on T1 and high signal on T2-weighted imaging (**Figure 1B** and **C**). In contrast, the cyst lining enhances, but the contents do not (**Figures 1D, 2C**). Occasionally, when presenting with intralesional hemorrhage from fracture, fluid–fluid levels may be seen representing internal degraded blood products. The internal hemorrhage may evolve into septations that can be demonstrated on MRI (**Figure 2B**).

On scintigraphy, the unicameral bone cyst appears as a focus of photopenia (cold spot). It may have increased uptake peripherally, and a photopenic center sometimes referred to as a doughnut sign. However, a pathologic fracture would cause an increased radioisotope activity.

#### **Figure 1.**

*Simple Bone Cyst: Frontal radiograph of the right femur demonstrates a well-circumscribed, lytic, proximal metadiaphyseal lesion (white arrow) with a narrow zone of transition and represents a simple bone cyst (A). There is no fracture. On the coronal MR sequences (B–D), the simple bone cyst (white arrows) shows an intermediate signal on T1-weighted sequence (B), a homogeneous increased signal on T2-weighted imaging (C), and peripheral rim enhancement on the post-contrast T1-weighted fat-saturated imaging (D). A simple bone cyst is treated by bone grafting. Fluoroscopic spot image of the right femur (E) confirms that the osteolytic lesion is cemented by the bone graft material (white asterisk).*

The larger cysts with or without fracture are usually treated with curettage and bone grafting [6] (**Figures 1E, 3B**). The fractured cyst tends to heal spontaneously. The prognosis is excellent, although 25% of bone cysts recur

sclerotherapy has also been used for treatment. Intervention is usually not

An aneurysmal bone cyst is a benign, radiolucent, expansile, and hemorrhagic lesion of uncertain etiology. Pathologically, the lesion comprises numerous blood-filled nonendothelialized channels separated by connective tissue of bone or osteoid tissue and osteoclastic giant cells. Aneurysmal bone cyst affects 0.14 per 1,00,000 of the population [8]. There may be a slight female predominance. 75–90% of cases occurred before the age of 20 [9]. The patient usually presents with nonspecific pain and swelling, and a minority of patients (approximately 10%) present with pathological fractures. The lesions are most commonly located in the metaphysis of long bones, the craniofacial bones, and

The aneurysmal bone cysts are sharply defined on radiographs and appear as expansile osteolytic lesions with thin sclerotic margins, frequently termed a soap bubble lesion [10] (**Figures 4A, 5A**). If the lesion is wider than the affected normal bone, an ABC should be considered. ABCs are typically multiloculated, and the cortex is usually intact but maybe markedly thinned to the point of being invisible, and the periosteal new bone may be present. CT scan demonstrates these findings better and accurately assesses cortical breach and extension to the soft tissues (**Figure 5C**). Additionally, the CT and MRI

demonstrate fluid–fluid levels, which are characteristic of the lesion (**Figures 4C, 5B**). Fluid–fluid levels are due to the dependent location of degraded blood products, especially methemoglobin, which has a much shorter T1 relaxation time than hemoglobin. Fluid–fluid levels may be single

after curettage [7]. Cyst aspiration with corticosteroid injection or

*Simple Bone Cyst: Frontal radiograph of the right femur (A) demonstrates a pathological fracture (thick arrows) through a circumscribed expansile lytic proximal meta-diaphyseal lesion (white arrow). It represents a simple bone cyst with the characteristic fallen-fragment sign (yellow arrow). A follow-up post-treatment frontal radiograph of the right femur (B) shows graft material (white asterisk) cementing the bone cyst and a*

the spine; spinal lesions occur in the posterior elements.

required for an asymptomatic lesion.

*transfixed healing fracture with good periosteal reaction (black arrow).*

2.Aneurysmal bone cyst:

*Imaging of Pediatric Benign Bone Tumors DOI: http://dx.doi.org/10.5772/intechopen.99021*

**Figure 3.**

**27**

#### **Figure 2.**

*Simple Bone Cyst: Frontal radiograph of the right humerus (A) demonstrates an expansile circumscribed lytic lesion (white arrow) in the proximal diaphysis with a narrow zone of transition. It has scalloped margins, suggesting chronicity. No cortical breach is demonstrated. Coronal T2-weighted fat-saturated MR image (B) reveals heterogeneous hyperintense signal of the simple bone cyst (white arrow) with a few thin linear T2 hypointensities (septations; black arrow) within. The bone cyst (white arrow) demonstrates peripheral rim enhancement on the post-contrast T1-weighted fat-saturated image (C).*

#### **Figure 3.**

On scintigraphy, the unicameral bone cyst appears as a focus of photopenia (cold spot). It may have increased uptake peripherally, and a photopenic center sometimes referred to as a doughnut sign. However, a pathologic

*Simple Bone Cyst: Frontal radiograph of the right femur demonstrates a well-circumscribed, lytic, proximal metadiaphyseal lesion (white arrow) with a narrow zone of transition and represents a simple bone cyst (A). There is no fracture. On the coronal MR sequences (B–D), the simple bone cyst (white arrows) shows an intermediate signal on T1-weighted sequence (B), a homogeneous increased signal on T2-weighted imaging (C), and peripheral rim enhancement on the post-contrast T1-weighted fat-saturated imaging (D). A simple bone cyst is treated by bone grafting. Fluoroscopic spot image of the right femur (E) confirms that the osteolytic lesion*

*Simple Bone Cyst: Frontal radiograph of the right humerus (A) demonstrates an expansile circumscribed lytic lesion (white arrow) in the proximal diaphysis with a narrow zone of transition. It has scalloped margins, suggesting chronicity. No cortical breach is demonstrated. Coronal T2-weighted fat-saturated MR image (B) reveals heterogeneous hyperintense signal of the simple bone cyst (white arrow) with a few thin linear T2 hypointensities (septations; black arrow) within. The bone cyst (white arrow) demonstrates peripheral rim*

*enhancement on the post-contrast T1-weighted fat-saturated image (C).*

fracture would cause an increased radioisotope activity.

*Recent Advances in Bone Tumours and Osteoarthritis*

**Figure 2.**

**26**

**Figure 1.**

*is cemented by the bone graft material (white asterisk).*

*Simple Bone Cyst: Frontal radiograph of the right femur (A) demonstrates a pathological fracture (thick arrows) through a circumscribed expansile lytic proximal meta-diaphyseal lesion (white arrow). It represents a simple bone cyst with the characteristic fallen-fragment sign (yellow arrow). A follow-up post-treatment frontal radiograph of the right femur (B) shows graft material (white asterisk) cementing the bone cyst and a transfixed healing fracture with good periosteal reaction (black arrow).*

The larger cysts with or without fracture are usually treated with curettage and bone grafting [6] (**Figures 1E, 3B**). The fractured cyst tends to heal spontaneously. The prognosis is excellent, although 25% of bone cysts recur after curettage [7]. Cyst aspiration with corticosteroid injection or sclerotherapy has also been used for treatment. Intervention is usually not required for an asymptomatic lesion.

2.Aneurysmal bone cyst:

An aneurysmal bone cyst is a benign, radiolucent, expansile, and hemorrhagic lesion of uncertain etiology. Pathologically, the lesion comprises numerous blood-filled nonendothelialized channels separated by connective tissue of bone or osteoid tissue and osteoclastic giant cells. Aneurysmal bone cyst affects 0.14 per 1,00,000 of the population [8]. There may be a slight female predominance. 75–90% of cases occurred before the age of 20 [9]. The patient usually presents with nonspecific pain and swelling, and a minority of patients (approximately 10%) present with pathological fractures. The lesions are most commonly located in the metaphysis of long bones, the craniofacial bones, and the spine; spinal lesions occur in the posterior elements.

The aneurysmal bone cysts are sharply defined on radiographs and appear as expansile osteolytic lesions with thin sclerotic margins, frequently termed a soap bubble lesion [10] (**Figures 4A, 5A**). If the lesion is wider than the affected normal bone, an ABC should be considered. ABCs are typically multiloculated, and the cortex is usually intact but maybe markedly thinned to the point of being invisible, and the periosteal new bone may be present. CT scan demonstrates these findings better and accurately assesses cortical breach and extension to the soft tissues (**Figure 5C**). Additionally, the CT and MRI demonstrate fluid–fluid levels, which are characteristic of the lesion (**Figures 4C, 5B**). Fluid–fluid levels are due to the dependent location of degraded blood products, especially methemoglobin, which has a much shorter T1 relaxation time than hemoglobin. Fluid–fluid levels may be single

or multiple and may be seen as varying horizontal levels within the separate loculations [11]. The signal characteristics of the cyst contents depend on the relative age and concentration of blood components. Abundant hemosiderin

hypointense (**Figure 4B**). Cyst contents do not enhance, but the septations

may produce areas of low signal. On T1, the cyst is predominantly

It may not be possible to differentiate primary and secondary ABCs. Approximately 30% ABC's are secondary [12]. According to one study, the most common reasons for secondary ABC are chondroblastoma and giant cell

tumor [13]. Secondary ABC can also be found in other lesions such as osteoblastoma, chondromyxoid fibroma, fibrous dysplasia, and nonossifying

Treatment: Most ABCs are treated with curettage and bone grafting. Recurrence rate is approximately 12–30% after initial treatment [14].

Enostosis, also known as the bone island, is a benign focus of compact (cortical) bone located within the cancellous bone (medullary cavity). The bone island is most commonly found incidentally. Pathologically, a bone island is a normal cortical bone containing Haversian canals. There are radiations of cortical bone blending into the normal cancellous bone at the periphery of the lesion. The bone island is likely developmental, a normal cortical bone that fails to resolve during the growth process of endochondral ossification. The bone island is seen in adults far more frequently than children. There is no gender predilection. The bone island is generally a radiographic diagnosis. The bone island is a homogeneously dense lesion on radiography, fading at the periphery and merging into normal marrow. The periphery of the bone island is described as brush-like; may appear somewhat

stellate [16] (**Figure 6A**). There is no associated cortical destruction. Polyostotic bone islands concentrated in the metaphyseal region are termed

*Enostosis: Frontal radiograph of left humerus (A) shows a circumscribed focal sclerosis (white arrow) in the proximal epiphysis with peripheral brush border extensions into the normal adjacent bone. Axial T1-weighted (B) and T2-weighted fat-saturated (C) images reveal marked hypointense signal of the bone island.*

components which can guide the surgeon for biopsy.

Bone lesions containing osteoid matrix:

Percutaneous treatment with fibrosing agents has also been performed, either in isolation or as a precursor to surgical excision. According to one institution's experience, many ABCs can be treated with polidocanol sclerotherapy [15]. Vascular embolization has also been used. MRI is helpful to identify any solid

and wall do (**Figure 5D**).

*Imaging of Pediatric Benign Bone Tumors DOI: http://dx.doi.org/10.5772/intechopen.99021*

fibroma.

1.Enostosis:

**Figure 6.**

**29**

#### **Figure 4.**

*Aneurysmal Bone Cyst: Lateral radiograph of the left tibia (A) shows a well-circumscribed, expansile, lytic lesion (white arrow) involving the proximal tibial metadiaphysis. It demonstrates internal heterogeneity and has a narrow zone of transition. Coronal T1-weighted image (B) reveals the multiloculated appearance of the lesion (white arrow) and a predominantly intermediate T1 signal. No associated soft tissue swelling is noted. Sagittal fat-saturated T2-weighted image (C) shows multiple fluid-fluid levels within the lesion (yellow arrows), a characteristic imaging feature of an aneurysmal bone cyst.*

#### **Figure 5.**

*Aneurysmal Bone Cyst: Lateral radiograph of the pelvis (A) shows an expansile, circumscribed, lytic, proximal femoral metaphyseal lesion (white arrow) with scalloped margins. On axial fat-saturated T2-weighted imaging (B), the lesion shows multiple fluid-fluid levels within (yellow arrow), suggesting an aneurysmal bone cyst. C and D are images of an aneurysmal bone cyst in the left pubic bone in a different patient. The aneurysmal bone cyst appears as a well-circumscribed lytic lesion on CT (C). Coronal T1-weighted fatsaturated post-contrast image (D) depicts heterogeneous and peripheral enhancement of the aneurysmal bone cyst.*

or multiple and may be seen as varying horizontal levels within the separate loculations [11]. The signal characteristics of the cyst contents depend on the relative age and concentration of blood components. Abundant hemosiderin may produce areas of low signal. On T1, the cyst is predominantly hypointense (**Figure 4B**). Cyst contents do not enhance, but the septations and wall do (**Figure 5D**).

It may not be possible to differentiate primary and secondary ABCs. Approximately 30% ABC's are secondary [12]. According to one study, the most common reasons for secondary ABC are chondroblastoma and giant cell tumor [13]. Secondary ABC can also be found in other lesions such as osteoblastoma, chondromyxoid fibroma, fibrous dysplasia, and nonossifying fibroma.

Treatment: Most ABCs are treated with curettage and bone grafting. Recurrence rate is approximately 12–30% after initial treatment [14]. Percutaneous treatment with fibrosing agents has also been performed, either in isolation or as a precursor to surgical excision. According to one institution's experience, many ABCs can be treated with polidocanol sclerotherapy [15]. Vascular embolization has also been used. MRI is helpful to identify any solid components which can guide the surgeon for biopsy.

Bone lesions containing osteoid matrix:
