Magnetic resonance imaging of anal cancer

The purpose of this study was to evaluate the magnetic resonance imaging (MRI) appearances of primary and recurrent anal carcinoma, and to demonstrate the commonest patterns of local and distant disease spread.

A retrospective review was performed of 27 cases of biopsy-proven anal carcinoma, where MRI was used for primary staging (9 patients) or suspected recurrence (18 patients). Two oncological radiologists reviewed the MR images, following a standardized approach. The size, extent and signal characteristics of the anal tumour were documented. Metastatic disease spread to lymph nodes, viscera and bone was recorded. In all, 7 patients with recurrent disease underwent surgery and subsequent histological correlation was performed.

Primary and recurrent tumours were of high signal intensity relative to skeletal muscle on T2-weighted images (T2WI), and of low to intermediate signal intensity on T1-weighted images (T1WI). Lymph node metastases were of similar signal intensity to the anal cancer. Recurrent tumours were more locally advanced than primary tumours and extended into adjacent organs and the pelvic skeleton. Recurrent lymph node disease involved perirectal, presacral and internal iliac nodes more commonly than did primary lymph node disease.

MRI can be useful in the primary staging of bulky tumours or of those with a long craniocaudal extent. MR has a role in the preoperative evaluation and surgical planning of cases of recurrent disease following radiotherapy.