Obstructing Colonic Mass with Increased Uptake on PET/CT - Benign or Malignant?

Abstract

Purpose: Colonic lipomas are benign tumors that are typically asymptomatic, small, and found incidentally by colonoscopy, surgery, or autopsy. In contrast, large colonic lipomas, seldomly reported, may present with various symptoms that can be misdiagnosed as a more serious pathology, since colonoscopic biopsies may not provide adequate tissue for interpretation. Although PET-CT with 18-fluorodeoxyglucose is often used for detecting cancer and monitoring treatment response, it may fail to distinguish between a malignant and a benign mass. We report a large colonic lipoma presenting as an ulcerated, partially obstructing mass with increased uptake on PET-CT suggesting an invasive malignancy. A 67-year-old male presented with 2 months of hematochezia and diarrhea, but without abdominal pain or weight loss. Past medical and family histories were unremarkable. Physical examination was not significant. Blood tests detected microcytic anemia. Colonoscopy revealed an ulcerated tumor arising from the descending colon, preventing the scope from passing beyond the mass. Biopsy showed inflammatory necrotic tissue with hyperplastic glandular cells. CEA was within normal range. PET-CT imaging indicated increased activity in the distal descending colon, but no other abnormal uptake. Under the impression of colonic malignancy, a laparoscopic-assisted left colectomy was performed. Gross pathology revealed a 4 × 3.7 × 3.5 cm well-circumscribed polypoid mass with a homogeneous yellow cut surface. Final pathology was mucosa overlying lipoma with ulceration and granulation tissues. Nine benign lymph nodes (0/9) were examined. The patient recovered well postoperatively. Colonic lipomas are geneally asymptomatic small benign tumors. However, large colonic lipomas may produce a range of symptoms, leading to misdiagnosis as a more serious pathology. This case presented with an obstructive large colonic tumor with intermittent rectal bleeding and diarrhea, which coupled with increased uptake on a preoperative PET-CT scan. These findings suggested an invasive malignancy resulting in a left colectomy with lymph node dissection. This case revealed the variable presentations of colonic lipomas that can imitate invasive colon adenocarcinoma. Large lipomas should be considered for surgical resection especially if concerning features are present. Non-ulcerated, non-obstructing lipomas can be further evaluated by endoscopic ultrasound or repeat biopsy if clinically suggestive of a benign mass.