**5. Local staging with MRI**

The assessment of the findings obtained with MRI should be based on the TNM system. However, the MRI also provides other essential information, such as the distance of the tumor to the circumferential resection margin (CRM), and the tumoral invasion of the venous structures beyond the muscularis propria (EMVI). This additional information must be included in the report as well.

Multiple studies have proved the added value of structured reporting in rectal cancer [8–10], and resulted in many proforma available online. The diagnosis is ideally carried out using a structured report (SR) like our Structured Report (see Appendix at end of this chapter) for Primary Staging of Rectal Carcinoma at our Imaging Center (www.radiologie-kaufbeuren.de).

The report should include both the appearance of the tumor (e.g. ulcerative growth), as well as its minimum distance from anus. In addition, the craniocaudal tumor extent and the positional relationship of the tumor to the peritoneal fold should be reported. Furthermore, the radius of the carcinoma in the intestinal wall according to lithotomy position (SSL), whether the muscularis propria is infiltrated or whether extramural growth is already present should be reported.

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**Figure 6.**

*F. Bauer, Radiology Kaufbeuren.*

**Figure 5.**

*Imaging and Diagnosis for Planning the Surgical Procedure*

Rectal cancer staging is based on the TNM (tumor, nodes, and metastases) system. In this context, a **stage T1** disease passes through the mucosa and submucosa

A **stage T2** (**Figure 5A**) disease infiltrates additionally the muscularis propria. The more advanced **stage T3** (**Figures 5B, 6,** and **7**) disease infiltrates the muscularis propria and goes beyond into the mesorectum. This stage T3 has been further split into substages **a**, **b**, **c**, and **d** to categorize the depth of extramural invasion, as follows: < 1 mm = T3a; 1–5 mm = T3b; > 5–15 mm = T3c, and > 15 mm = T3d

The last stage, **T4**, also divides into two subclasses, **a,** and **b**. Substage **T4a** is diagnosed when the tumor involves visceral peritoneum or anterior peritoneal reflection, while **T4b** is diagnosed when the tumor invades at least one adjacent

*A. Paraaxial T2w image shows a rectal tumor which invades the muscularis propria (red arrow) but does not penetrate its external margin. Note the fine spiculations towards the mesorectum (yellow star), and the irregular heterogeneous nodes of same signal intensity as the tumor, indicating potential nodal involvement (yellow arrow). Diagnosis: T2, N1, CRM-, EMVI-, which was confirmed by histology (T2 with "desmoplastic reaction" and nodal metastasis). B. Rectal tumor stage T3a. Note the similarity to A: tumor extensions (yellow* 

*Short axis axial high-spatial-resolution T2w images of different sub-classifications of T3 tumors with extramural spread (arrow): A. T3a (<1 mm), B. T3b (1-5 mm), C. T3c (>5-15 mm). Markings: mesorectal involvement (yellow arrow), muscularis propria (red dashed line), and CRM = FMR (green arrow). Source:* 

*arrow) into the mesorectal fat (yellow star). Source: F. Bauer, Radiology Kaufbeuren.*

*DOI: http://dx.doi.org/10.5772/intechopen.93873*

but does not infiltrate the muscularis propria.

**5.1 T-staging**

(**Figures 6** and **7**).

organ, see **Figure 8**.

*Imaging and Diagnosis for Planning the Surgical Procedure DOI: http://dx.doi.org/10.5772/intechopen.93873*

### **5.1 T-staging**

*Colorectal Cancer*

carcinoma [7].

**Figure 4.**

diagnosis of the T category.

**5. Local staging with MRI**

Less rectal tumors, up to 10%, may contain mucin, and mucinous tumors have a poor prognosis and a high risk of spillage during surgery [6]. MRI depicts these

*A. Axial T2w image shows a low-lying mucinous tumor of high signal (red star) disrupting the mesorectal fascia (green arrows) and extending into the dorsal bladder wall (yellow arrow). B. The very large mucinos adenocarcinoma (signet-ring) with a central scar situated in the middle third of the rectum with complete infiltration of the mesorectum, and of the dorsal bladder wall at 12 o'clock. Stage: T4, CRM+, N0, EMVI.* 

As described above, T2-weighted sequences under optimal conditions can differentiate the wall layers of the rectum. The vast majority of carcinomas have a higher signal than the hypointense (not always controllable) mucosa, but a lower signal than the clearly hyperintense submucosa. Exceptions to this are, on the one hand, mucinous carcinoma and on the other hand, sigmoid ring cell

After administration of contrast medium, the entire rectal wall is clearly hyperintense and the individual wall layers can no longer be differentiated from each other. Therefore, the native T2-weighted sequences should be used for the primary

The assessment of the findings obtained with MRI should be based on the TNM system. However, the MRI also provides other essential information, such as the distance of the tumor to the circumferential resection margin (CRM), and the tumoral invasion of the venous structures beyond the muscularis propria (EMVI).

Multiple studies have proved the added value of structured reporting in rectal cancer [8–10], and resulted in many proforma available online. The diagnosis is ideally carried out using a structured report (SR) like our Structured Report (see Appendix at end of this chapter) for Primary Staging of Rectal Carcinoma at our

The report should include both the appearance of the tumor (e.g. ulcerative growth), as well as its minimum distance from anus. In addition, the craniocaudal tumor extent and the positional relationship of the tumor to the peritoneal fold should be reported. Furthermore, the radius of the carcinoma in the intestinal wall according to lithotomy position (SSL), whether the muscularis propria is infiltrated

tumors well on T2w as well delimited high intensity masses, **Figure 4.**

*Histology confirmed this result. Source: F. Bauer, Radiology Kaufbeuren.*

This additional information must be included in the report as well.

or whether extramural growth is already present should be reported.

Imaging Center (www.radiologie-kaufbeuren.de).

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Rectal cancer staging is based on the TNM (tumor, nodes, and metastases) system. In this context, a **stage T1** disease passes through the mucosa and submucosa but does not infiltrate the muscularis propria.

A **stage T2** (**Figure 5A**) disease infiltrates additionally the muscularis propria.

The more advanced **stage T3** (**Figures 5B, 6,** and **7**) disease infiltrates the muscularis propria and goes beyond into the mesorectum. This stage T3 has been further split into substages **a**, **b**, **c**, and **d** to categorize the depth of extramural invasion, as follows: < 1 mm = T3a; 1–5 mm = T3b; > 5–15 mm = T3c, and > 15 mm = T3d (**Figures 6** and **7**).

The last stage, **T4**, also divides into two subclasses, **a,** and **b**. Substage **T4a** is diagnosed when the tumor involves visceral peritoneum or anterior peritoneal reflection, while **T4b** is diagnosed when the tumor invades at least one adjacent organ, see **Figure 8**.

### **Figure 5.**

*A. Paraaxial T2w image shows a rectal tumor which invades the muscularis propria (red arrow) but does not penetrate its external margin. Note the fine spiculations towards the mesorectum (yellow star), and the irregular heterogeneous nodes of same signal intensity as the tumor, indicating potential nodal involvement (yellow arrow). Diagnosis: T2, N1, CRM-, EMVI-, which was confirmed by histology (T2 with "desmoplastic reaction" and nodal metastasis). B. Rectal tumor stage T3a. Note the similarity to A: tumor extensions (yellow arrow) into the mesorectal fat (yellow star). Source: F. Bauer, Radiology Kaufbeuren.*

### **Figure 6.**

*Short axis axial high-spatial-resolution T2w images of different sub-classifications of T3 tumors with extramural spread (arrow): A. T3a (<1 mm), B. T3b (1-5 mm), C. T3c (>5-15 mm). Markings: mesorectal involvement (yellow arrow), muscularis propria (red dashed line), and CRM = FMR (green arrow). Source: F. Bauer, Radiology Kaufbeuren.*

### **Figure 7.**

*Axial T2wi shows a rectal tumor (yellow star) staged: T3d (>15 mm), CRM+, EMVI+, N1). The extramural spread is measured from the level of the supposed muscularis propria (red dashed line) to the maximal point of mesorectal involvement (red arrow). Notice also the invasion of the venous structures (EMVI, blue arrow) and the extramesorectal metastatic node (yellow arrow). This node group will not be removed in a regular TME! CRM = FMR (green arrow). Source: F. Bauer, Radiology Kaufbeuren.*

### **Figure 8.**

*A. Stage T4a tumor involves visceral peritoneum or anterior peritoneal reflection (green arrow). B. Stage T4b tumor involves an adjacent organ, uterus (yellow arrow), and the mesorectum (yellow star). Source: F. Bauer, Radiology Kaufbeuren.*

Several histopathologic studies have shown that T3 tumors with more than 5 mm mesorectal invasion have a cancer-specific 5-year survival rate of approximately 54% [11]. On the other hand, for tumors of 5 mm or less in diameter, the cancer-specific survival exceeds 85% [12, 13]. Therefore, it is crucial to report the depth of extramural spread in detail, with the precise substage **T3a, b, c** or **d**. The overall reported accuracy for T staging using a pelvic phased-array coil ranges from 59% to 95% [12, 13]. Differences in T2 signal intensity between the tumor, submucosa, muscular layer, and mesorectum play the main role while detecting and staging rectal cancers using MRI.

T stage must be assessed on planes strictly perpendicular to the tumor. Incorrect prescription of the acquisition plane leads to blurring of the muscularis propria and may lead to overstaging. When the tumor is not visible on sagittal T2 WI: obtaining high-resolution images of the entire length of the rectum and adding DWI may help localize the mass. The depth of extramural spread must be measured in millimeters beyond the outer edge of the longitudinal muscular layer [13], as depicted in **Figures 5, 6** and **7.**

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*Imaging and Diagnosis for Planning the Surgical Procedure*

diffusion and disruption of muscularis propria [15].

or short term RCT followed by TME.

resection and coloanal anastomosis.

patients who will profit from preoperative CRT.

their signal and contrast medium behavior.

*5.1.2 Specific issues related to low-lying tumors*

Al-Sukhni et al. [9] published a meta-analysis (21 studies between 2000 and 2011) on the diagnostic accuracy of MRI and found a high overall accuracy in the assessment of the T-stage with a sensitivity of 87% and a specificity of 75%.

Differentiation between T2 and borderline T3 lesions is still challenging today. The main issue is to distinguish true mesorectal tumor invasion from desmoplastic reactions [14]. In this case, the inflammatory accompanying reaction in the adjacent mesorectal fat masks the actual tumor spread. In particular, fine spicular extensions in the mesorectum should be evaluated carefully - if these are mistakenly interpreted as a tumor (T3 instead of T2), overstaging and thus

One often error source is the use of thicker sections and lower resolution techniques. Therefore, using fine sections in T2WI should help clarifying such cases. Indeed, desmoplasia associated with ulcerating tumors at the invasive border is typically seen as fine low-signal-intensity spicules on T2WI. These spicules do not show restricted diffusion. Tumor extension into the mesorectum, on the other hand, forms thicker, intermediate signal- intensity nodular bands with restricted

From the therapeutic point of view, the differentiation between T2 and T3a, b stages is not important since the treatment of these lesions is identical: TME alone

Low-rectal tumors are associated with higher rates of positive resection margins, higher local recurrence rates, and poorer survival [16]. This is largely due to anatomic considerations and the fact that the mesorectal envelope tapers and narrows at this level. These rates can be improved by using CRT in locally advanced lowrectal tumors. The results show a good response with higher sphincter preservation rates and disease-free survival [15]. In consequence, a tumor that would have previously required an abdominoperineal excision may instead be treated with ultralow

Our experience has shown that, particularly in the case of low-lying tumors, the primary surgical concept changed relatively often after CRT and restaging. Consequently, tumors that had required abdominoperineal excision before CRT

All these require a very good quality MRI beforehand, to define the location of the tumor relative to the sphincter complex precisely, so that we select correctly the

For the assessment of the anal canal, T1w lipid-saturated T1FS sequences with

Rectal carcinoma usually shows low signal intensity compared to the normal intestinal wall and sphincters. **Stage T3** implies the infiltration of the external sphincter. At **stage T4**, the tumor infiltrates also of the m. levator ani. As a matter of fact, as soon as a rectal carcinoma crosses the mesorectal fascia and infiltrates the visceral peritoneum, the diagnosis is T4. Here, it must be differentiated whether adjacent organs (vagina, uterus, ovaries, prostate, seminal vesicles, bladder and ureter) are reached by the tumor (T4b) or whether only the visceral peritoneum (T4a) is infiltrated **(Figure 8A** and **B).** The contact of the tumor with surrounding

contrast medium are superior to T2w-sequences, since m. levator ani and m. sphincter ani externus are reliably separated from m. sphincter ani internus due to

only needed ultralow resection and coloanal anastomosis after CRT.

*DOI: http://dx.doi.org/10.5772/intechopen.93873*

*5.1.1 Challenges for T-staging*

overtherapy may occur.

Al-Sukhni et al. [9] published a meta-analysis (21 studies between 2000 and 2011) on the diagnostic accuracy of MRI and found a high overall accuracy in the assessment of the T-stage with a sensitivity of 87% and a specificity of 75%.
