A 28-year-old man with a 4-year history of intermittent crampy abdominal pain, low-grade fevers, and non-bloody diarrhea presents with new perianal pain and purulent drainage. Examination reveals fleshy perianal skin tags and multiple cutaneous openings discharging pus. Pelvic MRI shows a transsphincteric fistula with intersphincteric abscess. Colonoscopy reveals the findings marked as **B** in the diagram. Which of the following endoscopic features is MOST characteristic of the condition shown at **B** and helps distinguish it from ulcerative colitis?
A. Solitary deep ulcer on the anterior rectal wall with normal surrounding mucosa
B. Continuous superficial inflammation extending from rectum to sigmoid colon
C. Circumferential transverse ulcers in the ileocecal region with stricturing
D. Skip lesions with intervening normal mucosa and rectal sparing
Explanation
Why "Skip lesions with intervening normal mucosa and rectal sparing" is right
The condition marked B is Crohn disease with perianal fistulizing disease. The endoscopic hallmarks that distinguish Crohn disease from ulcerative colitis are discontinuous (skip) lesions with normal intervening mucosa and rectal sparing. These features reflect the segmental, transmural nature of Crohn disease. The presence of skip lesions, deep linear and serpiginous ulcers with cobblestoning, and rectal sparing are pathognomonic for Crohn disease and are explicitly documented in the colonoscopy findings in this case. (AGA Guidelines on Perianal Crohn Disease 2021; Sabiston 21e)
Why each distractor is wrong
Continuous superficial inflammation extending from rectum to sigmoid colon: This describes ulcerative colitis, not Crohn disease. UC is characterized by continuous inflammation beginning in the rectum and extending proximally without skip lesions, and always involves the rectum.
Solitary deep ulcer on the anterior rectal wall with normal surrounding mucosa: This is the classic presentation of solitary rectal ulcer syndrome (option C in the diagram), not Crohn disease. SRUS is a benign condition unrelated to inflammatory bowel disease.
Circumferential transverse ulcers in the ileocecal region with stricturing: This pattern is characteristic of tuberculous colitis (option D in the diagram), not Crohn disease. TB colitis presents with circumferential ulceration and stricturing in the ileocecal region, but lacks the skip lesions and cobblestoning of Crohn disease.
High-YieldNEET PG
Skip lesions + rectal sparing + deep linear ulcers with cobblestoning = Crohn disease; continuous inflammation from rectum = ulcerative colitis.
AGA Guidelines on Perianal Crohn Disease 2021; Sabiston 21e
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