What is hiding in the hindgut sac? Looking beyond rectal carcinoma

OBJECTIVES: Although rectal cancer is by far and large the most common pathology involving the rectum that needs imaging, there are many other important but less common pathological conditions affecting anorectal region. The objective of this pictorial review is to discuss the cross-sectional imaging features of less common anorectal and perirectal diseases. RESULTS: Although a specific histological diagnosis cannot usually be made due to considerable overlap in the imaging appearances of anorectal diseases, this review illustrates the cross-sectional imaging findings with emphasis on magnetic resonance imaging (MRI) that can help in narrowing down the differentials to a reasonable extent. TEACHING POINTS: • Variety of pathology exists in the anorectum apart from common rectal carcinoma • Anorectal diseases present as non-specific wall thickening indistinguishable from rectal carcinoma • Computed tomography (CT) and MRI can help in narrowing down the differentials, although often biopsy is warranted.