Objectives

To review the following aspects of anal cancer:

- MR staging and protocol

- Post-treatment complications

- Treatment response and recurrence

Background

Although anal cancer is an uncommon disease, its incidence has been continuously rising, with an expected increase in the burden of disease. It is strongly associated with HPV infection, with most tumors being of the squamous cell histologic subtype.

Imaging findings OR Procedure findings

MR is the method of choice for local staging of anal cancer. T2 high-resolution imaging in three planes is mandatory, with axial and coronal slices orthogonal to the anal canal. STIR and post-contrast sequences are not obligatory, but useful if fistulous tracts are present.

Tumors typically show intermediate-high signal on T2 imaging and intermediate-low on T1, with restricted diffusion and avid post-contrast enhancement.

Staging is determined according to TNM 8. T is given by the tumor longest diameter and invasion to adjacent organs. Direct invasion of the rectal wall, sphincter complex or subcutaneous tissue does not upgrade a T3 to T4. Unlike rectal cancer, the location of nodal stations involved determines the N stage for anal cancer. For distant metastasis evaluation a toraco-abdominal CT should be performed.

MR role in tumor response is still controversial. However, MR can document response and recurrent disease, with DWI being increasingly recognized as useful in detecting residual disease.

Radiation proctitis, fistulas and abscesses are the most common complications following radiotherapy.

Conclusion

Due to its rising incidence we are expected to find anal cancers more frequently in our daily practice. Therefore, the radiologist should be familiar with its particularities.

Objectives

To describe the typical features of perianal fistulas in Magnetic Resonance Imaging (MRI) according to their classification;

To review the importance of accurate MRI protocol in perianal fistulas diagnosis.

Background

Perianal fistula is an uncommon inflammatory condition with significant morbidity in the affected population defined as an abnormal communication between the anal canal and the perianal skin or perineum. In patients with Crohn’s disease it is a major problem and affects significantly their quality of life. An appropriate knowledge of the anatomy of the anal sphincter complex and its surrounding structures is crucial for a correct image interpretation. MRI is the method of choice to evaluate perianal fistulas as it provides the visualization of fistula’s relationship with adjacent structure and clarifies the extension of the disease.

Imaging findings OR Procedure findings

Several clinical cases were selected in order to illustrate the typical imaging findings of perianal fistulas according to the St Jame’s University Hospital classification. This classification contemplates important MRI findings and grades the perianal fistulas in five different groups. The primary fistulous track and the presence of abscesses or secondary extensions are the demanding criteria which outline the best treatment decision.

Sequences as T2-weighted with fat-suppression are crucial to recognize fistulous tracts and fluid collections. T1-weighted contrast-enhanced fat-suppressed sequences are important to detecte active fistulas and granulation tissue.

Conclusion

MRI is the gold standard imaging technique to study perianal fistulas once allows the detection of lesions that can be deeply hidden. A structured MRI report is essential for therapeutic management and consequently improves of patient outcome.