What's This Complication of Crohn's Colitis? - Answer

So Fans of Rob's Radiology - The answer is a fistula from the colon with the subcutaneous tissue and soft tissue abscess.

• Crohn's - named after Dr. Crohn
• Transmural process (mucosa, submucosa, muscularis propria and adventitia) vs Ulcerative Colitis which is primarily mucosal
• One of the diseases included in Inflammatory Bowel Disease (IBD)
• Can involve anywhere from mouth to anus (but usually is either small bowel only, small bowel and colon [45%], or colon only)
• 2 peaks of presentation 15-35 then 50-80
• Risk factors - urban dwellers, whites, Jewish, family history, smoking, OCP, maybe diet
• Presentation - fever, abdominal pain, diarrhea, weight loss, obstruction, rarely blood in stool (usually means colonic involvement)
• Alternating attacks and remissions
• Initially a mucosal process that leads to transmural inflammatory changes with caseating granulomas
• Transmural inflammation leads to strictures, obstruction, fistulas, perforation, malabsorption, abscesses
• Increased risk of adenocarcinoma of colon and small bowel and lymphoma
• Skip lesions - noncontiguous involvement (unlike UC which starts at rectum and travels proximally)
• Early imaging - asymmetric, skip lesions, cobblestonse, aphthous ulcers (partial), linear ulcers, fissuring, mural thickening, inflammatory pseudopolyps
• Early CT - mural thickening, mural enhancement, target or double halo sign
• Subacute to Chronic CT - mural thickening (homogenous and nonenhancing = fibrosis or stricture vs. enhancing wall = reversible inflammatory disease); fibrofatty proliferation (creeping fat), LAD, hypervascularity, inflammatory stranding, phlegmon/abscess
• Comb sign - prominent dilated vasa recta
• Complications - sinus tracts, fistula, abscess, carcinoma
• Extraintestinal -
• Hepatobiliary - steatosis (20-50%), Primary sclerosing cholangitis (1-4%), hepatic abscess
• Pancreatic - pancreatitis
• Musculoskeletal - arthritis; sacroileitis-spondylitis
• GU - nephrolithiasis (2-10%)
• Eyes - uveitis
• Skin - erythema nodosum and erythema gangrenosum
• Lab - positive ASCA (Anti-S Cerevisiae Antibodies) and negative p-ANCA is suggestive of Crohn's while vice versa is suggestive of UC.
• Treatment - ASA, steroids, immunosuppressives for those difficult to control (Azathioprine, 6-Mercaptopurine and Remicade)
• Surgery - for severe strictures, cancer, abscesses or complicated fistulas; in uncomplicated fistulas - often a nuissance and not treated surgically just treat infections. Even after surgery it is common to have recurrence at the site of surgery.
• The above case is a complicated fistula and required surgery.
• Diet is designed based on location and severity of disease.

References - emedicine.com and AFIP Radiologic Pathology Course 7th Edition