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Although relatively uncommon, many different infectious, hemorrhagic and neoplastic disease processes may involve the iliac and psoas muscles and are increasingly diagnosed especially in referral hospitals. Furthermore, the iliopsoas compartment may become injured during trauma, percutaneous instrumentation, laparoscopic or open surgical procedures. State-of-the-art cross-sectional imaging including volumetric multidetector CT and multiplanar MRI acquisitions allows prompt detection, comprehensive visualization and confident characterization of most iliopsoas lesions, and the possibility to guide percutaneous biopsy and drainage. The pertinent regional anatomy is reviewed in correlation with disease pathways and imaging modalities. Neoplastic lesions, purulent and mycobacterial iliopsoas infections are discussed with examples. Imaging plays the key role in the differentiation of primary versus secondary abscesses due to intestinal, urinary and musculoskeletal infections, that determines medical therapy and surgical need. The iliopsoas compartment may become involved through direct extension by retroperitoneal, skeletal and pelvic tumors, and should be carefully scrutinized when reviewing oncologic imaging studies since it represents one of the preferred sites of skeletal muscle metastatization. Iliopsoas hemorrhages due to trauma, aortic aneurysms and anticoagulation are reviewed, with a special focus on determining whether the bleeding comes from aneurysmal rupture or from coagulopathy, a critical differentiation to decide about medical or surgical treatment. Postoperative complications involving the iliopsoas compartment are discussed with examples, including retroperitoneal bleeding, infections, urinary leaks and collections following various surgical or instrumentation procedures. Emphasis is placed on choosing the correct imaging modality and technique, particularly to detect active bleeding or urine leakage, and to reduce artifacts related to presence of metallic implants.

Involvement of the urinary tract and genital organs is not uncommon in patients affected with Crohn’s disease (CD). Occurring in both sexes, uro-gynecological complications are often clinically unsuspected because of the dominant intestinal or systemic symptoms. Knowledge of their manifestations and cross-sectional imaging appearances is necessary to recognize and report them, since correct medical or surgical treatment choice with appropriate specialist consultation allows to prevent further complications. Besides uncomplicated urinary tract infections that usually do not require imaging, urolithiasis and pyelonephritis represent the most commonly encountered urinary disorders: although very useful, use of computed tomography (CT) should be avoided whenever possible, to limit lifetime radiation exposure. Hydronephrosis due to ureteral inflammatory entrapment and enterovesical fistulization may result from penetrating CD, and require precise imaging assessment with contrast-enhanced CT to ensure correct surgical planning. Representing the majority of genital complication, ano- and rectovaginal fistulas and abscesses frequently complicate perianal inflammatory CD and are comprehensively investigated with high-resolution perianal MRI acquired with phased-array coils, high-resolution T2-weighted sequences and intravenous contrast. Finally, rare gynecological manifestations including internal genital fistulas, vulvar and male genital involvement are discussed.

Proctocolectomy with ileal pouch-anal anastomosis (IPAA) is the established surgical therapy for familial adenomatous polyposis (FAP) and refractory ulcerative colitis (UC). Despite general patient satisfaction with preserved fecal continence, this procedure is associated with a significant long-term morbidity approaching 70% after 10 years, and with a non-negligible rate of pouch failure leading to removal and permanent ileostomy. Following a concise description of the surgical technique, the normal imaging appearance of the ileal "pouch" reservoir at pelvic CT and MRI is explained. Since awareness of their imaging appearances is needed for a correct diagnosis, we discuss and illustrate common and unusual pouch-related complications, including pouchitis and irritable pouch disease; anastomotic leakages and pelvic abscess collections; fistulas involving the ano-perianal region, urinary bladder, vagina, perineal skin, and subcutaneous planes; anal stenosis and small-bowel obstruction. In our experience, pelvic contrast-enhanced MRI has proven invaluable for the diagnostic assessment of patients with suspected pouch-related complications, allowing differentiation of uncomplicated pouchitis from pelvic sepsis, the latter requiring aggressive therapy and possible even in patients with normal endoscopic findings.