Pedunculated sigmoid lipoma causing colo-colonic intussusception

Abstract

This case report describes a 52-year-old man who presented with 2 weeks of left lower quadrant pain and bloody stool. Computed tomography revealed a 4 cm, fat-density mass acting as a lead point for intussusception of the sigmoid colon. Surgical resection was successfully performed, and histologic evaluation confirmed the diagnosis of a pedunculated colonic lipoma. Intussusception of the colon is uncommon in adults and is often associated with malignancy, but other nonmalignant causes such as a lipoma may also present similarly with obstructive symptoms, bloody stool, and/or intermittent abdominal pain. Colonic lipoma should be considered in the differential of a patient with clinical or imaging evidence of intussusception, with primary resection leading to an excellent prognosis.

Colonic lipomas are uncommon benign tumors often found incidentally on colonoscopy.¹ Large (>2 cm) lipomas are more likely to cause symptoms like abdominal pain, bowel habit changes, or bleeding secondary to obstruction.¹ We discuss a case of a 4 cm sigmoid pedunculated colonic lipoma causing colo-colonic intussusception.

CASE REPORT

A 52-year-old man presented to his primary care physician after 2 weeks of abdominal pain and hematochezia. Computed tomography (CT) revealed a fat-containing sigmoid mass with colo-colonic intussusception (Figure 1a). The patient was instructed to go to the emergency department, where he complained of progressive 8/10 cramping left lower quadrant abdominal pain with signs of guarding. A complete blood count demonstrated a normal hemoglobin of 14.2 g/dL and a carcinoembryonic antigen <0.5 ng/mL. The patient’s body mass index was 31.4 kg/m². A colonoscopy identified a large partially obstructing mass in the proximal sigmoid colon measuring 4 cm (Figure 1b). A tattoo was placed proximal and distal to the mass for surgical planning. Due to potential malignancy concerns, the partially obstructive nature of the lesion, and patient symptomatology, an elective laparoscopic partial sigmoidectomy was scheduled. The specimen was extracted through a Pfannenstiel incision (Figure 1c). The patient’s postoperative course was routine, and he was discharged home on postoperative day 2. Pathologic evaluation of the surgical specimen confirmed a pedunculated, submucosal colonic lipoma (Figure 1d).

Figure 1.

(a) Computed tomography of the abdomen and pelvis with contrast, with the sausage-shaped appearance of the intussusceptum into the intussuscipiens depicting colonic intussusception. Low-density lipoma with some internal fat stranding acts as a lead point. No apparent abnormal bowel wall thickening or pericolonic inflammatory changes are identified. (b) Endoscopy showing a partially obstructing polypoid mass. (c) Intraoperative image showing the resected portion of the sigmoid colon and a pedunculated, submucosal lipoma, transected for visualization of the lipomatous content of the mass (circle). (d) Pathology image showing little to no muscularis propria separating the fat from underlying mucosa.

DISCUSSION

While intussusception in children is often due to benign causes, the etiology of intussusception is malignant in 65% of adult cases.² A benign pedunculated colonic lipoma causing intussusception in adults is particularly rare, with <50 documented cases over the last 45 years.^3,4 Mechanistically, an intraluminal lesion is dragged forward during normal peristalsis, resulting in telescoping of the proximal bowel into a section of the distal bowel. Intussusception causes <1% of all intestinal obstructions in adults⁵ but can result in complications such as bowel edema and necrosis due to mesenteric vasculature involvement.

CT is often the first step of diagnosis and is regarded as the most sensitive and specific imaging modality for evaluation of colonic masses and for diagnosis of colo-colonic intussusception.^6,7 Intussusception appears as an abnormal target like bowel in bowel appearance with layers of bowel and fat on axial images and a sausage-shaped mass on longitudinal images. A separate mass or lead point is not always visible due to surrounding edema.^8,9 Uncomplicated lipomas appear as spherical masses with sharp margins and absorption densities of –40 to –120 Hounsfield units.¹⁰

Colonoscopy is the next step, as it allows for direct visualization and possible treatment via snare resection. Endoscopic features indicative of a colonic lipoma include the cushion sign (indent in lipoma after pressure from forceps) and the naked fat sign (extrusion of fat from biopsy site).¹¹ Inconclusive biopsy results can occur due to an overlying necrotic surface and granulation tissue⁶; therefore, endoscopic findings can aid in the diagnosis. Endoscopic resection is employed when the mass is <2 cm, pedunculated with a thin stalk, and when the lesion does not extend into the muscularis propria, which is confirmed via endoscopic ultrasound.^1,12,13 Larger or sessile lesions have increased risk of bleeding and perforation and are often tattooed for surgical planning. Alternatively, when tumor-free margins are not required, some endoscopists will consider a partial resection to reduce the size of a large mass while trying to minimize procedural complications, though the effectiveness of a partial resection vs a complete resection has not been well studied.¹³

Definitive surgical intervention is warranted when the preoperative diagnosis remains unclear or when endoscopic resection is unachievable.⁶ Proper preoperative diagnosis allows for limited resection, when appropriate, compared to an oncologic resection. Therefore, integrated analysis of imaging, histologic, and endoscopic findings should be used to guide operative planning.

This presentation of a rare pedunculated sigmoid lipoma causing colo-colonic intussusception highlights the importance of consideration of this entity in the differential diagnosis for colonic mass in adult intussusception.