Imaging of Perianal Inflammatory Disorders in Ulcerative Colitis

Perianal disease (PAD) sometimes complicates true ulcerative colitis (UC) with an incidence approaching 5 %. Although its pathogenesis is unknown and probably multifactorial, reassessment of clinical, endoscopic, histological, and imaging findings is always recommended to exclude a misdiagnosed Crohn’s disease (CD). Moreover, PAD may occur in UC patients who undergo colectomy with ileal pouch-anal anastomosis (IPAA). Pouch fistulas can be classified into pouch CD-related fistulas, arising in a setting of de novo CD of the pouch, or nonpouch CD-related fistulas, usually representing the later presentation of an initial anastomotic leak. PAD may involve the genital region, mostly in female patients with a 4–12 % incidence rate of ileal pouch-vaginal fistulas. Imaging of the perianal compartment is crucial for prompt and accurate diagnostic assessment of PAD in UC patients, especially for potential candidates for surgery, both in the preoperative and postoperative settings. Magnetic resonance imaging (MRI) is considered the gold standard technique in the assessment and follow-up of PAD, whereas computed tomography (CT) plays a major role in emergency conditions. Transanal and transperineal ultrasound represent low cost and accurate imaging modalities currently used in clinical practice.