Atypical “Intramuscular” Colon Lipoma

Abstract

Purpose: A 51 yo male presented for screening colonoscopy. The exam revealed an ∼ 4 cm subepithelial mass in the distal transverse colon region.[figure1] The lesion was diffusely firm to palpation with closed biopsy forceps, and a “cushion sign” was unable to be demonstrated. The lesion was lobulated and endoscopic biopsies revealed only hyperplastic tissue. An abdominal CT demonstrated the lesion to be hypodense, measuring –113 Hounsfield units. The CT radiographic findings suggested the lesion to be a lipoma. One section of the CT scan, however, suggested a non-lipomatous, soft-tissue rim of unclear significance. The patient offered that he had been experiencing vague left upper quadrant distress. Options of expectant management, EUS and surgical resection were discussed. Given that the lesion displayed some characteristics atypical for a lipoma, he opted for surgical resection.FigureLaparoscopic transverse colon resection proceeded uneventfully. Histopathology revealed the lesion to be a lipoma, which was within the muscularis propria layer. [figure2] The unusual histopathology of this lipoma accounted for multiple unique aspects of this case. It is decidedly unusual for a lipoma to be diffusely firm to palpation by biopsy forceps. Also, by CT scan, this lesion appeared to have a soft tissue rim along its border. These findings are likely accounted for by the fact that histopathology revealed the lipoma to be within the muscularis propria. This histopathologic finding may also have contributed to this lipoma's lobulated appearance.FigureColon lipomas can occasionally be associated with atypical colonoscopic and radiographic features. In this case, such atypical findings were likely related to the lipomatous lesion being within the muscularis propria, as opposed to the submucosal layer.