MRI and CT of anal carcinoma: a pictorial review

BACKGROUND: Squamocellular anal carcinoma is increasingly diagnosed in patients with risk factors. METHODS: State-of-the-art imaging with magnetic resonance imaging (MRI) using phased-array coils and volumetric multidetector computed tomography (CT) provides detailed visualisation of anal disorders, identification and extent assessment of neoplastic tissue, detection and characterisation of nodal and visceral metastases. MRI has been recommended by the European Society for Medical Oncology (ESMO) as the preferred modality of choice to stage anal cancer, taking into account the maximum tumour diameter, invasion of adjacent structures and regional lymph node involvement. RESULTS: Cross-sectional imaging techniques allow the identification of coexisting complications, and differentiation from other perineal abnormalities. CONCLUSION: Cross-sectional imaging is useful for planning radiotherapy, surgical drainage or salvage abdomino-perineal resection. After chemo-radiotherapy, MRI follow-up provides confident reassessment of therapeutic response, persistent or recurrent disease. TEACHING POINTS: • Anal carcinoma is increasingly diagnosed in patients with human immunodeficiency virus (HIV), anoreceptive intercourse, chronic inflammatory bowel disease. • An established association exists with human papillomavirus (HPV) infection and premalignant intra-epithelial dysplasia. • Phased-array MRI is recommended as the preferred imaging modality for regional staging. • Imaging allows detection of infectious complications, planning of radiotherapy or salvage surgery. • Follow-up MRI allows reliable assessment of therapeutic response after chemo-radiotherapy.