Colorectal carcinoma is one of the commonest malignancies worldwide . While majority of patients present with symptoms like bleeding per-rectum, weight loss, altered bowel habits, 10–29% of patient with colon cancer can present with the malignant bowel obstruction. Intussusception accounts for 1–2% of adult large bowel obstruction with primary malignancy being the most common cause of a colo-colic intussusception . Sigmoid carcinoma presenting as large bowel obstruction due to the sigmoid-rectal intussusception with rectal prolapse in the ED is rare. Rectal prolapse refers to protrusion of the part of rectum through the anus. Rarely adenocarcinoma, lymphoma and metastasis, and adenoma of the distal large bowel can act as lead point leading to the intussusception with resulting rectal prolapse [4, 5]. The association between rectal prolapse and colorectal cancer is rarely reported. Rashid et al. reported a retrospective study of 70 patients with rectal prolapse. In his study, patients with rectal prolapse had a 4.2-fold increased risk of having colorectal cancer (5.7%), compared with the control group (1.4%) .
Adult intussusception poses a diagnostic dilemma to the clinician due to non- specific clinical presentation and clinical examination findings. Hence, radiology plays a vital role in diagnosis and the management of such cases. Plain abdominal X-rays are usually the first diagnostic tool, demonstrating signs of intestinal obstruction and providing information about probable site of obstruction . Ultrasonography (USG) may demonstrate the typical signs of intussusception . USG is often used in the pediatric population. However, in adults, its utility is limited by air within the bowel lumen and greater depth between the skin and target anatomy.
CT has emerged as a useful imaging modality for diagnosing intussusception in adults and is often performed for primary or secondary assessment of acute and subacute gastrointestinal symptoms of unclear origin. Similar to the USG, CT may also demonstrate target sign, wherein layers of the bowel are duplicated forming concentric rings when imaged at right angles to the lumen. As one image further along the intussusception the mesentery (fat and vessels) will form a crescent of tissue around the compressed inner most lumen, surrounded by the two layers of the outer enveloping bowel. Even further distally the lead point (if present) will be visualised.
In addition, CT provides greater detail in illustrating local and regional anatomy, which can inform operative planning . In cases of rectal prolapse, special MRI procedures like magnetic resonance (MR) defecography may have several advantages over CT. MR defecography due to its intrinsic dynamic nature, allows accurate assessment of the presence of enterocele, rectocele, and anismus, which are often associated with rectal prolapse . Endoscopic investigations such as colonoscopy and sigmoidoscopy also play an important role in evaluating the lead point of intussusceptions and obtaining a histology sample but in an acute setting, as in our case, role of MR defecography and sigmoidoscopy is limited. The most common lead point in an adult intussusception is a malignant mass and therefore a routine resection is advocated. This is also because reduction of an intussusception in the presence of a malignant mass may cause intra luminal seeding and venous embolization .