Diagnosis:
Crohn's disease with peri-rectal fistula and phlegmon formation

Findings: (Images 1-6)
The rectum is most involved with diffuse rectal wall thickening, granulomatous and mesenteric inflammatory changes and findings quite suspicious for a fistula identified in the lateral aspect of the rectal wall as seen on image 02. In the surrounding perirectal region and ischiorectal fossa, a complex phlegmonous inflammatory process is present with no drainable, mature fluid collection. This is demonstrated on all images.

Discussion:
Crohn's disease can involve any part of the gastrointestinal tract. Complications of Crohn's disease include fistula formation, intramural sinus tracts, abscess, obstruction, and adenocarcinoma. Although adenocarcinoma is thought to occur more frequently in patient's with ulcerative colitis, patient's with Crohn's disease do have a 4-20x increased risk compared to the general population.

When the rectum is involved with Crohn's disease, sinus tracts and fistulas are often present. Abscess collections can secondarily form. This case demonstrates extensive phlegmonous reaction without a drainable abscess.