A 77-year-old man with a 10-day history of chronic constipation and abdominal distension was seen at the emergency room. The patient's medical history included right hemiparesis due to left basal ganglia infarction 8 years prior and systemic hypertension. On physical examination, he had abdominal distension with mild tenderness; however, he did not have rebound tenderness and his bowel sounds were increased. On digital rectal examination, there was an edematous soft mass-like lesion at a one-finger depth from the anal verge which was not tinged with blood. Laboratory studies revealed that the white blood cell count, hemoglobin, electrolytes, and liver function tests were within the normal range. The level of carcinoembryonal antigen was 17.0 ng/mL (normal range, 0 to 6 ng/mL), and that of carbohydrate antigen 19-9 was 99.3 U/mL (normal range, 0 to 37 U/mL). Plain abdominal radiography revealed a mechanical ileus with severe bowel distension (
Fig. 1). A contrast enhanced computed tomography scan was suggestive of rectal cancer with a diffuse wall thickening that was 7 cm in length and was located 5 cm above the anal verge. The small bowel and colon were dilated with fecal retention due to a mechanical obstruction proximal to the mass lesion (
Fig. 2). Colonoscopic findings revealed that the extruding mass was covered with normal mucosa (
Fig. 3). Endoscopic biopsy showed only an inflammatory change; however, we clinically suspected rectal cancer, so additional pelvic magnetic resonance imaging (MRI) was performed. The pelvic MRI revealed a submucosal infiltrating enhanced lesion involving the rectum and containing round and tubular cystic lesions with perirectal fat infiltration (
Fig. 4). A positron emission tomography scan showed rectal cancer because of increased fluorine-18 2-fluoro-2-deoxy-D-glucose uptake (max standardized uptake value, 7.7).
Because of negative biopsy results and radiologic findings that showed a submucosal infiltrating enhanced lesion, we suspected that the tumor was most likely a primary rectal linitis plastica and recommended surgical treatment for the patient. However, the patient declined surgery without pathologic confirmation and chose close observation and symptomatic treatment. One month later, he returned to the emergency room with recurrent abdominal distension and severe constipation. An emergent APR and permanent colostomy was performed due to signs of impending bowel perforation. During surgery which lasted for 5 hours, there were no special events, but pelvic dissection was difficult due to the infiltrative tumor mass and neighboring fibrosis. After surgery, the patient recovered without complications. Pathologic examination of the resected tissue revealed a mucinous adenocarcinoma in the rectal diverticulum involving the rectum (4.2 × 2 × 1.5 cm
3) with extension to perirectal soft tissue; however, no lymphovascular perineural invasion or distant metastasis was detected (
Fig. 5).
The cancer was located within a diverticulum, but the entrance of the diverticulum was not seen during endoscopy (
Fig. 6). The negative endoscopic biopsy result was due to the fact that the mucous membrane was unaffected by the adenocarcinoma within the rectal diverticulum. After surgery, the patient received adjuvant radiation therapy, and no recurrence has been detected for 12 months.