Colorectal intussusception is a condition in which a segment of the bowel telescopes into the lumen of an adjacent distal segment. In adults, the vast majority of intussusceptions (65-90%) have an underlying organic cause (lead point), most commonly neoplastic lesions (benign polyps, lipomas, adenocarcinomas, metastases). Two basic patterns are defined: colocolic intussusception (colon-into-colon) and coloanal/rectal intussusception (associated with rectal prolapse). CT is the most sensitive imaging modality for diagnosis, with the characteristic 'target sign' or 'sausage-shaped mass' appearance. In adults, surgical exploration is generally required due to the high rate of malignancy; in children, idiopathic ileocolic type is more common and pneumatic or hydrostatic reduction is the first-line treatment.
Age Range
0-75
Peak Age
30
Gender
Equal
Prevalence
Uncommon
Intussusception occurs when a lesion in the bowel wall (lead point) or abnormal peristaltic activity pushes a bowel segment (intussusceptum) into the lumen of the distal segment (intussuscipiens). In adults, the lead point is typically a polyp, lipoma, adenocarcinoma, or metastatic tumor; these lesions are captured by peristaltic waves and dragged distally. The invaginating segment carries its mesentery along, leading to compression of mesenteric vessels. Venous return is compromised first (venous congestion, wall edema, mucosal hemorrhage); as long as arterial supply continues, ischemia does not develop, but in advanced cases arterial compression leads to transmural ischemia, necrosis, and perforation. The characteristic 'target sign' on CT results from concentric layering of telescoped bowel walls, mesenteric fat, and vessels. The invaginated mesenteric fat corresponds to the hypodense central area on CT, while bowel walls correspond to enhancing concentric rings. Dragging of mesenteric vessels in the invaginated segment ('mesenteric vessel dragging sign') provides additional diagnostic support.
Concentric ring structure on CT axial sections formed by hypodense mesenteric fat between telescoped bowel walls — pathognomonic finding of intussusception.
Concentric ring appearance on axial sections: outermost intussuscipiens wall (enhancing), middle hypodense invaginated mesenteric fat, innermost intussusceptum wall (enhancing). This layering is called 'target sign' or 'bull's eye sign'. Most prominent on sections perpendicular to the long axis of the lesion. Mesenteric fat tissue between invaginated bowel walls forms the hypodense central area (typically -20 to -80 HU).
Report Sentence
A concentric ring pattern 'target sign' appearance is observed in the colon on axial sections with hypodense mesenteric fat tissue between telescoped bowel walls; findings are consistent with colocolic intussusception.
Coronal and sagittal reformats show a sausage-shaped soft tissue mass in the colon elongated along the long axis. This appearance reflects the tubular configuration of the bowel-within-bowel structure on longitudinal sections. The mass length is typically 5-15 cm depending on the extent of intussusception. At both ends of the mass, the bowel lumen narrows abruptly ('meniscus sign' or 'claw sign').
Report Sentence
A sausage-shaped soft tissue mass measuring approximately ... cm is seen in the colon on coronal reformats, with bowel-within-bowel configuration consistent with intussusception.
An enhancing mass lesion may be detected at the distal tip of the intussusceptum (the starting point of invagination). This lead point may be a polyp, lipoma, adenocarcinoma, or metastatic tumor. Lipoma lead points are easily recognized at fat density (-40 to -120 HU). Adenocarcinoma appears as a heterogeneously enhancing, irregularly marginated soft tissue mass. Lead point detection is critical for surgical planning and malignancy risk assessment.
Report Sentence
An enhancing mass lesion (lead point) measuring approximately ... mm is identified at the distal tip of the intussusceptum; histopathological evaluation for malignancy is recommended.
The invaginated bowel segment drags mesenteric vessels and fat tissue along with it. CT shows mesenteric vessels being pulled into the intussusception mass ('mesenteric vessel dragging sign'). These vessels appear as bright linear structures on contrast-enhanced phases and indicate the direction of invagination. The degree of vessel dragging indirectly reflects ischemia risk.
Report Sentence
Mesenteric vessels are seen being dragged into the intussusception mass ('mesenteric vessel dragging sign'); careful evaluation for vascular congestion is recommended.
On ultrasound transverse sections, 'doughnut sign' (ring sign): hypoechoic outer ring (edematous bowel wall) and hyperechoic center (invaginated mesentery and mucosa). On longitudinal sections, 'pseudokidney sign' — kidney-like oval appearance of the invaginated segment. Doppler can assess blood flow in the invaginated mesentery; decreased or absent flow suggests ischemia.
Report Sentence
Ultrasound demonstrates 'doughnut sign' on transverse and 'pseudokidney sign' on longitudinal sections in the colon, consistent with intussusception.
Diffuse thickening and edema of the invaginated bowel wall due to venous congestion. On non-contrast CT, the bowel wall appears thicker than normal (>4 mm). In advanced cases, submucosal edema may produce a 'double wall sign'. When transmural ischemia develops, pneumatosis (intramural air) or mesenteric/portal venous gas may be seen — these findings indicate emergent surgical need.
Report Sentence
Bowel wall thickening and edema are noted in the invaginated segment; pneumatosis or portal venous gas is absent/present.
On MRI T2-weighted images, a multilayered bowel wall structure is seen in the invaginated segment. Edematous submucosa shows hyperintense T2 signal, muscularis shows hypointense T2 signal; these alternating signal intensities create a layering pattern. In cases with ischemia, DWI hyperintensity and low ADC signal are early indicators of bowel wall ischemia.
Report Sentence
MRI T2-weighted images show multilayered bowel wall structure and submucosal edema in the invaginated segment.
Criteria
Invagination of one colon segment into a distal colon segment. Most common type in adults. Usually polyp, lipoma, or adenocarcinoma as lead point. Malignancy rate 40-65%.
Distinct Features
Loss of colonic haustra in invaginated segment, target sign width matching colon caliber, usually left colon or sigmoid location.
Criteria
Invagination of distal ileum into cecum and ascending colon. Most common type in children (>90% idiopathic). In adults, usually triggered by lesion at ileocecal valve.
Distinct Features
Target sign in right lower quadrant at small bowel-colon transition. In children, lead point usually not identified.
Criteria
Invagination of rectal wall into own lumen; internal or external prolapse. Diagnosed on defecography or dynamic MR defecography. Important cause of obstructed defecation syndrome.
Distinct Features
Rectal invagination during straining on defecography or dynamic MRI. Oxford classification Grade I-V.
Criteria
Short-segment (<3.5 cm), no lead point, spontaneous resolution. Resolves on follow-up CT; low clinical significance.
Distinct Features
Short segment involvement, no obstruction signs, minimal wall edema. Confirmed by resolution on follow-up.
Distinguishing Feature
Adenocarcinoma shows annular wall thickening and luminal narrowing; intussusception shows bowel-within-bowel target sign. However, adenocarcinoma may be the lead point.
Distinguishing Feature
Lipoma is homogeneously fat-density (-40 to -120 HU) and one of the most common benign lead point causes. Fat-density lead point within target sign suggests lipoma-related intussusception.
Distinguishing Feature
Lymphoma shows homogeneous hypodense wall thickening with 'aneurysmal dilatation', rarely causes obstruction. Relatively rare as intussusception lead point.
Distinguishing Feature
Colorectal organ metastasis may be the lead point; usually multiple submucosal nodules. Known primary malignancy history is critical in differential.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralColorectal intussusception in adults is a surgical urgency because the underlying malignancy rate is 40-65%. Early surgical exploration (segmental resection) is recommended due to ischemia and perforation risk. Reduction attempts are not recommended in adults. In children, pneumatic/hydrostatic reduction is first-line for ileocolic type. Conservative follow-up is acceptable for transient, short-segment intussusceptions without lead points.
In children, air/hydrostatic enema reduction is attempted. In adults, surgery is usually necessary (due to lead point). Ischemia and gangrene complications require emergency surgery. ~50% of adult intussusceptions have a malignant lead point.