Intussusception is a condition where one segment of the intestine telescopes, or slides, into an adjacent segment, much like the parts of a collapsible telescope. This unusual folding can lead to an obstruction, preventing food and fluids from passing through the digestive tract. While intussusception is a common cause of intestinal blockage in young children, it is considerably less frequent in adults, accounting for less than 5% of all bowel obstructions in this population. In adult cases, this phenomenon is almost always linked to an identifiable underlying medical condition, which prompts the intestinal telescoping.
Key Differences in Adult Intussusception
A fundamental distinction exists between intussusception in adults and its pediatric counterpart. In children, the cause is often not identified, and the condition may resolve spontaneously. In contrast, adult intussusception is typically triggered by a “lead point,” which is a pathological lesion or an anatomical abnormality within the bowel. This lead point acts as a physical mass that the intestine’s normal wave-like contractions, known as peristalsis, can grab onto and pull into the adjacent segment, initiating the telescoping process.
Identifying this lead point is crucial for both diagnosis and treatment in adults. Unlike in children, where non-surgical methods like enemas are often effective, adult intussusception frequently necessitates surgical intervention to address the underlying cause. The presence of a lead point in adults means the condition is rarely transient and often requires treatment to prevent complications like bowel obstruction, reduced blood supply, or tissue death.
Common Underlying Causes in Adults
The majority of adult intussusception cases, approximately 70% to 90%, are secondary to a distinct pathological finding acting as a lead point. These lead points can be categorized into several types, with varying prevalence depending on the location within the digestive tract.
Benign lesions represent a significant proportion of lead points, particularly in the small intestine. These non-cancerous growths include polyps, abnormal tissue growths on the inner lining of the bowel. Other benign tumors like lipomas (fatty tumors), leiomyomas (smooth muscle tumors), and hamartomas can also serve as lead points. The size or specific location of these lesions can disrupt normal intestinal movement, making them susceptible to being pulled into an adjacent bowel segment.
Malignant lesions are a common cause of intussusception in adults, accounting for a substantial percentage of cases. They are more frequently associated with colonic intussusception (about 66% of cases) than small bowel intussusception (around 14% to 30%). Colorectal adenocarcinoma is the most common malignant lead point in the large intestine. Other cancerous causes include lymphoma and metastatic tumors that have spread from other parts of the body. These aggressive growths provide a fixed point of traction that initiates the telescoping.
Inflammatory conditions can also act as lead points by causing thickening, scarring, or masses within the intestinal wall. Crohn’s disease can lead to intussusception due to inflammation, ulceration, or fibrous strictures that disrupt normal peristalsis. Other inflammatory processes, such as celiac disease, post-surgical adhesions, or severe appendicitis, can create areas of altered tissue that serve as lead points. Meckel’s diverticulum can also initiate intussusception.
Less common causes of adult intussusception include vascular malformations or the presence of foreign bodies within the intestine. Though rare, these can similarly create a focal point that triggers the invagination process. Diverticula may also act as lead points.
Cases Without a Clear Cause
While the vast majority of adult intussusception cases have an identifiable lead point, a smaller proportion, typically ranging from 10% to 20%, are classified as idiopathic, meaning no clear cause is found. For small bowel intussusception, this idiopathic rate can be as high as 16%, while for large bowel intussusception, it is less common, around 5%.
In these rare idiopathic instances, the exact mechanism behind the telescoping remains unclear. It is hypothesized that very small or transient lead points or subtle functional issues with intestinal motility might be present but are undetectable. Despite the absence of a visible lead point, a comprehensive medical evaluation is always performed to rule out any subtle or underlying serious conditions. Even in idiopathic cases, symptoms often lead to medical attention due to the potential for complications.