Intussusception is the telescopic invagination of a bowel segment into the lumen of an adjacent distal segment. In the small bowel, jejunojejunal and jejunoileal intussusception are the most common types. In children, it is usually idiopathic and occurs at the ileocecal region; in adults, an anatomic lead point is present in approximately 90% of cases — such as lipoma, polyp, adenoma, lymphoma, metastasis, or Meckel's diverticulum. Adult intussusception accounts for 1-5% of all bowel obstructions. Clinical presentation includes intermittent abdominal pain, nausea-vomiting, and obstruction findings. CT is the gold standard for diagnosis and is characterized by the 'target sign' or 'sausage sign.' Treatment in adults is usually surgical because the underlying lead point may be malignant.
Age Range
0-80
Peak Age
30
Gender
Equal
Prevalence
Uncommon
Intussusception occurs when a lesion in the bowel wall or dysfunctional peristalsis causes a bowel segment (intussusceptum) to be drawn into the lumen of the adjacent distal segment (intussuscipiens). The lead point is propelled distally by normal peristaltic waves, dragging the following bowel segment along with it. The mesentery and mesenteric vessels are also drawn along with the invaginated segment — this leads to venous compromise, congestion, and edema. In advanced stages, arterial perfusion is also compromised, leading to ischemia, necrosis, and perforation. The 'target sign' on CT results from the concentric layers formed by the telescoped bowel walls on axial imaging — the outer intussuscipiens wall, interposed mesenteric fat, and inner intussusceptum wall are seen at different densities. The 'sausage sign' describes the elongated mass appearance of the invaginated segment on coronal/sagittal views. The dragging of mesenteric fat and vessels is known as the 'mesenteric fat sign' and distinguishes intussusception from other causes of obstruction.
Concentric telescoped bowel wall layers on axial CT (target sign) and elongated sausage-shaped mass on coronal/sagittal sections (sausage sign) — pathognomonic findings of intussusception. Interposed hypodense mesenteric fat between telescoped bowel walls forms the basis of these findings.
Pathognomonic 'target sign' on axial sections — concentric telescoped bowel wall layers create a bull's eye appearance. From outer to inner: intussuscipiens wall (enhancing), interposed hypodense mesenteric fat, intussusceptum wall (enhancing), inner lumen. These four layers at different densities form concentric rings. The lesion is typically 3-5 cm in diameter.
Report Sentence
Target sign with concentric telescoped bowel wall layers and interposed mesenteric fat in the small bowel is consistent with intussusception.
Sausage sign on coronal and sagittal sections — the invaginated bowel segment appears as an elongated, sausage-shaped mass. Mass size varies depending on the lead point size and length of invagination; typically 5-15 cm long. The telescoped bowel walls appear as longitudinal parallel lines. Mesenteric vascular structures can be traced along the invaginated segment.
Report Sentence
Elongated sausage-shaped mass appearance (sausage sign) in the small bowel on coronal/sagittal sections is consistent with intussusception.
Dragging of mesenteric fat and vascular structures into the invaginated segment (mesenteric fat sign) — hypodense fat tissue is seen within the bowel lumen on CT. The lead point may be identified at the distal tip of the invagination as an enhancing or characteristically dense mass: lipoma (fat density -50 to -100 HU), polyp/adenoma (soft tissue density), lymphoma (homogeneous soft tissue). Lead point identification is critical for treatment planning.
Report Sentence
Mesenteric fat dragging within the invaginated small bowel segment with a mass at the distal tip representing a lead point is consistent with intussusception.
Doughnut sign on transverse B-mode US — telescoped bowel walls form concentric hypoechoic and hyperechoic rings. Pseudokidney sign on longitudinal sections — the invaginated segment assumes a kidney-like appearance; peripheral hypoechoic cortex (edematous bowel wall) and central hyperechoic area (mesenteric fat + mucosa) are seen.
Report Sentence
Concentric telescoped bowel wall configuration (doughnut sign) on transverse and pseudokidney sign on longitudinal sections in the small bowel are consistent with intussusception.
Bowel wall thickening and decreased enhancement of the invaginated segment — ischemia findings. Venous congestion leads to wall edema and thickening. In advanced stages, wall enhancement decreases or disappears (ischemia/necrosis). Periintestinal fluid and free fluid may be accompanying. Pneumatosis intestinalis (intramural gas) and portal venous gas are findings of advanced ischemia/necrosis.
Report Sentence
Bowel wall thickening and decreased enhancement in the invaginated small bowel segment are consistent with ischemia findings due to vascular compromise.
Small bowel dilation proximal to the intussusception point — mechanical obstruction findings. Dilated loops are filled with fluid and gas with diameters >3 cm. Distal loops are decompressed. The transition point is at the intussusception point and is evaluated together with target/sausage sign.
Report Sentence
Small bowel dilation proximal to the intussusception point is consistent with mechanical obstruction findings.
Criteria
Invagination of jejunum segment into distal jejunum lumen
Distinct Features
Left upper quadrant location, lipoma or polyp as frequent lead point, lower risk of complete obstruction
Criteria
Invagination of jejunum segment into ileum lumen
Distinct Features
Longer invaginated segment, more prominent obstruction findings, lymphoma or metastasis may be lead point
Criteria
Invagination of ileum segment into distal ileum lumen
Distinct Features
Meckel's diverticulum or lymphoid hyperplasia as frequent lead point, more common in children, right lower quadrant pain
Criteria
Short segment (<3.5 cm), no lead point, spontaneous reduction, mostly incidental finding
Distinct Features
Clinically insignificant, no obstruction findings, resolves on follow-up CT, no treatment needed
Distinguishing Feature
Adhesive SBO does not have bowel-within-bowel appearance (target/sausage sign) at the transition point; abrupt caliber change and 'small bowel feces sign' may be seen. Mesenteric fat dragging (mesenteric fat sign) is specific to intussusception.
Distinguishing Feature
Lymphoma may show segmental wall thickening and aneurysmal dilatation; lymphoma may be a lead point in intussusception but the concentric target sign is absent in lymphoma itself. Sandwich sign (mesenteric LAP) is characteristic of lymphoma.
Distinguishing Feature
Ischemia lacks bowel-within-bowel configuration and mesenteric fat dragging. Ischemia shows SMA/SMV thrombosis, 'paper-thin wall' or pneumatosis. In intussusception, ischemia is a secondary finding and coexists with target sign.
Distinguishing Feature
Crohn's disease shows segmental wall thickening, skip lesions, fistula/abscess, and 'comb sign' (mesenteric vascular congestion). The concentric target sign of intussusception is absent in Crohn's. Crohn usually affects the terminal ileum.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAdult small bowel intussusception is a surgical urgency — a lead point is present in 90% of cases and a significant proportion are malignant. Transient intussusception (<3.5 cm, no lead point) may be managed with observation. In children, ileocecal intussusception can be treated with pneumatic or hydrostatic reduction, but small bowel intussusception usually requires surgery.
In adults, intussusception usually develops with a pathological lead point and requires surgery. In children, it may be idiopathic and air/hydrostatic reduction can be attempted. Transient intussusception without lead point is benign.