Imaging of anorectal and perineal emergencies - a multimodality review

Acute anorectal and perineal emergencies encompass a wide spectrum of infectious, inflammatory, traumatic, iatrogenic, and neoplastic conditions that often present with nonspecific symptoms but may rapidly progress to significant morbidity if unrecognized. Imaging plays a central role in diagnosis, assessment of disease extent, detection of complications, and treatment planning because clinical examination frequently underestimates involvement of the complex anorectal and perineal spaces. Computed tomography (CT) is the primary imaging modality in the emergency setting owing to its rapid acquisition and ability to detect abscesses, perforation, hemorrhage, extraluminal gas, and deep pelvic extension, whereas magnetic resonance imaging (MRI) provides superior soft-tissue characterization for evaluation of fistulas, sphincteric involvement, and complex inflammatory disease. This review provides an overview of the pertinent anorectal and perineal anatomy, imaging evaluation strategies, and characteristic multimodality imaging features of common anorectal and perineal emergencies. Particular emphasis is placed on key imaging findings, including rim-enhancing abscesses and fistulous tracts, soft-tissue gas with fascial extension in necrotizing infections, bowel wall thickening and perirectal inflammatory changes in proctocolitis, and the presence of extraluminal air or fluid collections associated with rectal perforation and retained foreign bodies. The review also highlights the value of a compartment-based approach in accurately delineating disease extent and guiding clinical management.