Intussusception is a condition where one segment of the intestine telescopes into the immediately adjacent segment. While this phenomenon is a relatively common cause of intestinal blockage in children, its occurrence in adults is rare, accounting for only 5% of all intussusception cases and a small fraction of adult bowel obstructions. Unlike pediatric cases, which often resolve spontaneously, the adult form is frequently linked to a structural abnormality within the bowel. This difference in underlying cause leads to a high potential for severe complications, demanding a prompt and often surgical response.
The Mechanism of Adult Intussusception
The physical process involves the proximal segment of the bowel, called the intussusceptum, sliding into the lumen of the distal segment, the intussuscipiens. This telescoping action pulls the mesenteric tissue, which contains the blood vessels, nerves, and lymphatics, along with the inner segment of the bowel. The mechanism itself creates a mass that obstructs the normal passage of digestive contents.
Intussusception is classified into four main types based on the location where this telescoping occurs:
- Enteroenteric type, confined entirely to the small intestine.
- Colocolic type, restricted to the large intestine.
- Ileocolic intussusception, describing the terminal ileum prolapsing into the ascending colon.
- Ileocecal intussusception, occurring when the ileocecal valve itself acts as the leading edge.
Identifying the Pathological Lead Points
A pathological lead point is present in nearly 90% of adult intussusception cases. A lead point is a distinct physical abnormality on the bowel wall that is pulled forward by normal peristaltic contractions, initiating the telescoping action. This structural difference from the often idiopathic nature of the condition in children necessitates a more aggressive management approach.
These lead points can be broadly categorized into benign and malignant lesions, with the specific type varying by location in the intestine. In the small bowel, the lead points are more frequently benign, including lipomas, adenomatous polyps, Meckel’s diverticulum, and post-surgical adhesions. Benign lesions account for approximately 50-75% of small bowel intussusceptions.
Intussusceptions located in the large intestine, or colonic types, have a much higher probability of being caused by malignancy. Malignancy is the cause in up to 65% of colonic intussusception cases, with adenocarcinoma being the most common finding. The high incidence of an underlying cancerous growth, particularly in the colon, is the primary reason why adult intussusception is treated as a surgical emergency requiring urgent investigation and definitive treatment.
Acute Risks and Potential Complications
The telescoping of the bowel and the resulting compression of the mesentery create several immediate and life-threatening dangers. The most immediate risk is the development of a complete bowel obstruction, where the intestine becomes fully blocked by the intussuscepted segment. This physical blockage prevents the passage of stool and gas, leading to abdominal distension, severe pain, and vomiting.
A severe complication arises from the entrapment and compression of the mesenteric blood vessels. This compression cuts off the blood supply to the affected portion of the bowel, a condition known as ischemia. If this lack of blood flow is sustained, the tissue will quickly die, leading to bowel infarction or necrosis. Dead bowel tissue is non-functional and can no longer maintain the integrity of the intestinal wall.
The progression from necrosis leads to perforation. When the ischemic tissue tears, the contents of the intestine, including bacteria and digestive enzymes, spill directly into the abdominal cavity. This spillage results in peritonitis, a widespread infection and inflammation of the abdominal lining. Peritonitis can rapidly escalate into systemic sepsis and multi-organ failure.
Diagnosis and Necessary Surgical Management
The diagnosis of adult intussusception is often challenging due to non-specific and intermittent symptoms. Computed tomography (CT) scanning is the preferred and most sensitive diagnostic tool for suspected adult intussusception. The CT image typically reveals a characteristic “target sign” or “sausage-shaped” mass, which is pathognomonic for the condition.
The CT scan is also invaluable because it can often locate the pathological lead point and assess for signs of vascular compromise or obstruction, which guides the necessary treatment plan. Although less sensitive, abdominal ultrasound can also identify the classic “doughnut” or “pseudo-kidney” sign in some cases. An accurate and timely diagnosis is the first step toward preventing the severe complications of tissue death and systemic infection.
For adults, the definitive treatment is surgical resection of the affected bowel segment. Unlike in children, where non-operative reduction via enema is often successful, this technique is contraindicated in adults. The primary reason for avoiding reduction is the high probability of an underlying malignancy, which could potentially be spread by manipulating the tumor during the reduction attempt.
Surgical resection, or removal of the diseased section, is necessary to both resolve the obstruction and obtain a definitive pathological diagnosis of the lead point. For colonic intussusceptions, resection is performed immediately due to the high likelihood of cancer. Even in the small bowel, where benign causes are more common, resection without prior reduction is often performed if the bowel is ischemic or if malignancy cannot be ruled out.