Author: David De Gruyter

Institute: Senior Radiographer - Medical Imaging Campbelltown

Patient Presentation

A 37 year old male presents with abdominal pain, nausea and vomiting, and less frequently melena, weight loss, fever and constipation. On examination the patient complains of long duration constipation (several weeks to several months), although the patient may occasionally present with an acute abdomen. The Physical examination demonstrated localized abdominal tenderness, but is often unremarkable.

Anatomy

Pathophysiology:

Intussusception can be classified according to location (small bowel or colon) or according to the underlying aetiology (neoplastic (benign or malignant), non-neoplastic or idiopathic).

About 80–90% of intussusceptions in adults are secondary to an underlying pathology, with approximately 65% due to benign or malignant neoplasm. Non-neoplastic processes constitute 15–25% of cases, while idiopathic or primary intussusceptions account for about 10%.

Intussusception arises in the small bowel in two-thirds of cases. The aetiology of intussusception in the small bowel and the colon is quite different.

Small bowel
Most intussusceptions in the small bowel are secondary to benign lesions. These include benign neoplasms (lipoma, leiomyoma, haemangioma, neurofibroma), adhesions, Meckel's diverticulum, lymphoid hyperplasia and adenitis, trauma, coeliac disease, intestinal duplication and Henoch–Schonlein purpura. Malignant lesions causing intussusception in the small intestine account for about 15% of cases and are most often metastatic, melanoma being by far the most common metastasis to cause intussusception. Idiopathic intussusception accounts for about 20% of all small bowel intussusceptions.

Colon
Intussusception in the large bowel is more likely to have a malignant aetiology (50–60%). This reflects the greater prevalence of malignant tumours in the colon compared with the small bowel. Primary malignant lesions (adenocarcinoma and lymphoma) are the most common underlying malignant lesions in the colon. Benign lesions constitute about 30% and include neoplasms such as lipoma, leiomyoma, adenomatous polyp, endometriosis (appendiceal) and previous anastomosis. Idiopathic intussusception occurs less often than in the small bowel (about 10%).

Intussusception occurs when a mass in the bowel is pulled forward by normal peristalsis, with resultant invagination of the involved wall. In the absence of a mass, intussusception may be caused by functional disturbances without gross mural abnormality, such as in coeliac disease. In these cases the loss of normal tone in the small bowel owing to the toxic effect of gluten causes flaccid, dilated bowel loops that are more prone to non-obstructing intussusception.

A significant incidence of intussusception has been reported in patients with acquired immune deficiency syndrome (AIDS). This is due to the association of AIDS with a variety of infectious and neoplastic conditions of the bowel, including infectious enteritis, lymphoid hyperplasia, Kaposi's sarcoma and non-Hodgkin's lymphoma of the bowel. Intussusception should therefore be considered in the differential diagnosis of prolonged abdominal pain in patients with AIDS.

Intussusception following abdominal surgery may be related to a variety of predisposing factors, including intestinal anastomotic suture lines, previous jejunostomy site, adhesions, submucosal bowel oedema, intestinal dysmotility and electrolyte imbalance. Long intestinal tubes are known to cause telescoping of the bowel.

Transient intussusception has been observed on small bowel barium follow-through studies in patients with adult coeliac disease. This phenomenon has more recently been noted on CT in patients with Crohn's disease, malabsorption syndromes, intestinal tumours and even in the absence of either malabsorption syndromes or an organic lesion. It has been attributed to dysrhythmic contractions. Transient intussusception is more common in the proximal small bowel where the peristaltic activity is normally greater.

Previously, data regarding the aetiology of intussusception were based on surgical findings or a coded diagnosis on discharge. In contrast, a recent study reported substantially different data regarding the underlying pathology. This study included 33 patients diagnosed on CT. A neoplastic lead point was found in only 10 patients (7 malignant, 3 benign) but in none of the other 23 patients, all with enteroenteric intussusception. A possible predisposing condition for the intussusception was found in only 7 of these 23 patients and the intussusception was classified as idiopathic in the other 16 (48.5% of all patients). These authors suggested that intussusception in the small bowel, encountered on CT, may on occasion be innocuous and transient and does not necessarily need extensive evaluation in the absence of severe abdominal symptoms.

Intussusception can be confidently diagnosed on CT because of its virtually pathognomonic appearance. It appears as a complex soft tissue mass, consisting of the outer intussuscipiens and the central intussusceptum. There is often an eccentric area of fat density within the mass representing the intussuscepted mesenteric fat, and the mesenteric vessels are often visible within it. A rim of orally administered contrast medium is sometimes seen encircling the intussusceptum, representing coating of the opposing walls of the intussusceptum and the intussuscipiens. The intussusception will appear as a sausage-shaped mass when the CT beam is parallel to its longitudinal axis, but will appear as a "target" mass when the beam is perpendicular to the longitudinal axis of the intussusception.

While the appearance of intussusception is characteristic on CT, its aetiology cannot usually be established. Exceptions are lipoma, a long intestinal tube and known abdominal metastatic disease. A lipoma serving as a lead point is identified as a mass of fat density that does not contain blood vessels. Mesenteric fat entrapped in an intussusception also has fat density but has blood vessels coursing through it, and can thus be distinguished from lipoma. A long intestinal tube visualized in the centre of the intussusception is an obvious cause. When other masses are seen in addition to the intussusception, one may conclude that the intussusception is due to metastatic disease. The same level has to be examined either at the same session or later to establish the diagnosis of transient intussusception.

Warshauer and Lee found that intussusceptions seen on CT that had a neoplastic lead point were significantly longer and had a significantly larger diameter than non-neoplastic ones. They also found proximal dilatation of small bowel to be significantly more common in intussusceptions with a neoplastic lead point.

The bowel loops proximal to the intussusception are usually of normal calibre and are only occasionally dilated, since intussusception in adults only rarely presents as intestinal obstruction. Although intussusception in adults may be diagnosed by many other imaging modalities, including barium enema, upper gastrointestinal series and ultrasound, CT is clearly superior. In contrast to ultrasound, CT is not affected by the presence of gas in the bowel and will clearly demonstrate the intussusception, whether in the small bowel or in the colon. Additional valuable information such as metastases or lymphadenopathy is readily obtained by CT and may point to an underlying pathology.

The most important factor for establishing the diagnosis is awareness of the possibility of intussusception occurring in an adult patient with abdominal symptoms, especially those with prior episodes of partial intestinal obstruction. CT is then the examination of choice.

Causes

In most infants and toddlers with intussusception, the etiology is unclear. This group is believed to have idiopathic intussusception. One theory about the etiology of idiopathic intussusception is that it occurs because of an enlarged Peyer patch; this hypothesis is derived from 3 observations: (1) often, the illness is preceded by an upper respiratory infection, (2) the ileocolic region has the highest concentration of lymph nodes in the mesentery, and (3) enlarged lymph nodes are often observed in patients who require surgery. Whether the enlarged Peyer patch is a reaction to the intussusception or a cause of it is unclear.

• In approximately 2-12% of children with intussusception, a surgical lead point is found. Occurrence of surgical lead points increases with age and indicates that the probability of nonoperative reduction is highly unlikely. Examples of lead points are as follows:
• • Meckel diverticulum
  • Enlarged mesenteric lymph node
  • Benign or malignant tumors of the mesentery or of the intestine, including lymphoma, polyps, and hamartomas associated with Peutz-Jeghers syndrome
  • Mesenteric or duplication cysts
  • Submucosal hematomas, which can occur in patients with HSP and coagulation dyscrasias
  • Ectopic pancreatic and gastric rests
  • Inverted appendiceal stumps
  • Sutures and staples along an anastomosis
• Other theories have implicated a viral etiology; however, no theory has proven to be reliable.
• • A seasonal variation in the incidence of intussusception that corresponds to the peaks in frequency of gastroenteritis (spring and summer) and respiratory illnesses (midwinter) has been described but has not been corroborated universally.
  • An association was found between the administration of a rotavirus vaccine (RotaShield) and the development of intussusception.¹ RotaShield has since been removed from the market. These patients were younger than usual with idiopathic intussusception and were more likely to require operative reduction. The vaccine is hypothesized to cause a reactive lymphoid hyperplasia, acting as a lead point.
  • In February 2006, a new rotavirus vaccine (RotaTeq) was approved by the US Food and Drug Administration (FDA) and did not show an increased risk compared with placebo in clinical trials. A study that involved more than 63,000 patients who received Rotarix or placebo at age 2 months and age 4 months reported a decreased risk of intussusception for those patients receiving Rotarix.² The intussusception data was determined over a 31-day observation period (inpatient or outpatient) after each dose of the Rotarix vaccine; this also included a 100-day surveillance period for all serious adverse events.
• Familial occurrence of intussusception has been reported in a few cases. Intussusception in dizygotic twins has been reported; however, these reports are extremely rare

Scanning Technique

Oral Technique is Gastrograffin - 1.2 L 1 hour prior

Images

Diagnosis

A Transaxial multidetector CT scan of the abdomen was performed. There is an obvious intersussception in the small bowel predominatly at the region of the ilium. There is an obious contrast filling in the intersusscepted bowel with bowel wall thickening.