Prolapsed sigmoid lipoma: a rare cause of adult intussusception

A 70-year-old man, with no significant medical or surgical history, presented to the emergency department with a history of rectal tenesmus, bleeding and anal tumefaction. Physical examination revealed a soft, smooth and erythematous mass that protruded through the anal canal.

Contrast-enhanced Computed Tomography (CT) of the abdomen and pelvis shows sigmoidorectal intussusception through the anal canal, suggested by the presence of the characteristic ‘bowel-within-bowel´ sign and visible mesenteric vessels within the bowel lumen (fig. 1a and 1b). The ‘sausage-shaped‘ soft tissue mass is also present (fig. 1c). Distally, there is an elliptic, well-circumscribed prolapsed fat-density mass (-80 HU), measuring 8.8 x 4.0 x 2.7 cm, highly suggestive of a lipoma (fig. 1c, 1d and 1e). This mass corresponds to the leading point of intussusception.

Parietal oedema of the lower rectum and anal canal, in response to local inflammatory changes.

No evidence of bowel obstruction or signs of bowel ischemia.

No ascites or loculated fluid collection in the pelvis.

Intussusception is defined as a process in which a proximal segment of bowel invaginates into an adjacent distal segment. Well recognized in paediatrics, it is a rare condition among adults, with occurrence reaching nearly 5% of all cases of intussusception. Unlike in children, adult intussusception is rarely idiopathic, having an identifiable aetiology in 90% of cases. The majority of intussusceptions occurring in the large bowel have a malignant aetiology [1-3].

Although being rare, lipomas represent the second most common benign tumour found in the colon, with the highest incidence in the right hemicolon. When large, they have the potential to become a leading point and cause intussusception [2;4-5].

Colonic lipomas are usually asymptomatic but may rarely cause bleeding, obstruction and intussusception, with lipomas larger than 4 cm producing symptoms in 75% of cases. When intussusception develops, symptoms are specific to the intussusception rather than the lipoma itself [4;6].

Diagnosis of adult intussusception is a challenge, owing to the relative rarity of the condition as well as to the nonspecific gastrointestinal symptoms [6-7].

Abdominal CT is the most sensitive diagnostic modality to detect intussusception, with a reported accuracy of 58–100%. The appearance of intussusception on CT is characteristic, with the classical findings being the ‘bowel-within-bowel’ or the ‘sausage-shaped‘ mass. Mesenteric vessels within the bowel lumen are also typically described. CT can often differentiate between non-lead point and lead point intussusception. Moreover, it allows the demonstration of complications, namely bowel obstruction, wall ischemia and perforation. Intussusception may also be diagnosed with ultrasound scanning or barium enema, however with inferior accuracy comparing to CT [2;8].

Lipomas are also usually easy to diagnose on CT on account of their low density, minimal internal soft-tissue component, and well-circumscribed contour.

Adult intussusception is almost always treated surgically. Colonoscopic reduction of the intussusception before resection carries the risk of disseminating malignant cells when underlying malignancy is suspected. However, reduction is acceptable in benign lead point intussusceptions. Although intussusception itself has a very good prognosis, the decisive factor is the cause of the lesion leading to the process [3;6].

Large bowel intussusception in adults is a rare event. Although colonic lipoma is also very rare, it should be considered in the differential diagnosis of adults with intussusception, with CT being the most sensitive diagnostic modality for this condition. Furthermore, it easily allows the identification of fat density in lipomas. Colonoscopy reduction followed by sigmoid resection represents an excellent treatment modality in intussusception secondary to colonic lipoma.