Squamous cell carcinoma of the anal canal

Case contributed by Dr Bruno Di Muzio


Anal bleeding and pain.

Patient Data

Age: 50 years
Gender: Male

MRI Anus

Large slightly T2 hyperintense tumor involving the whole length of the anus, with a 5 cm extension proximal to the puborectalis. There is invasion of the levator and puborectalis muscles. The lesion is abutting the posterior aspect of the prostate but no evidence of invasion of the prostate, urethra, bladder or seminal vesicles.  There is no evidence of abnormal lymph nodes in the perirectal region or bilateral groins.

Diffusely decreased T2 intensity is identified in the imaged skeleton, including the sacrum, pelvis and bilateral femoral heads.  No cortical destruction is noted.

Histology report

Microscopy: The sections show fragments of tissue some with the surface stratified squamous mucosa, deep to which there is an infiltrate of severely pleomorphic epithelial cells with very frequent mitoses and a high nuclear to cytoplasmic ratio, showing no evidence of gland formation. There is moderately extensive necrosis of the tumor. Koilocytic atypia and squamous epithelial dysplasia is not seen in the overlying squamous epithelium. Immunoperoxidase shows that the tumor cells are strongly reactive with cytokeratin 7, p63 and 40 and do not react with cytokeratin 20, S-100, or CD45.

Macroscopy: Labeled "Anal lesions".  6 ragged fragments of hemorrhagic, pale grey ragged, friable mucosal tissue and skin ranging from 7 mm to 18 x 8 x 7 mm.  The largest fragment has a smooth pale grey mucosal surface. 

Conclusion: Anal tumor - poorly differentiated squamous cell carcinoma.


Case Discussion

This case illustrates a T3 N0 anal tumor. Biopsy confirmed that it represents squamous cell carcinoma of the anal canal. Remember that, as opposed to rectal cancer, anal tumor staging is mostly based on size and extension, rather than wall invasion.

The systemic spread of anal SCC is uncommon, reported to occur in 5-8% at initial diagnosis, usually seen involving the retroperitoneal para-aortic lymph nodes, liver, lungs, and skin. The abnormal intensity in the skeleton seen in this case is non-specific and, although metastatic disease to bones is unlikely, a bone scan was recommended to rule out metastasis.

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