Diagnostic Ultrasound - Abdomen and Pelvis

Intussusception
TERMINOLOGY
Definitions
• Invagination or telescoping of 1 segment of
gastrointestinal tract and its mesentery (intussusceptum)
into lumen of adjacent distal segment (intussuscipiens)
IMAGING
General Features
• Best diagnostic clue
○ Sausage-shaped mass (longitudinal) and target or
doughnut appearance (transverse) on cross section
• Location
○ Occurs anywhere from stomach to rectum
○ Tends to occur at junctions between free-moving and
fixed segments (retroperitoneum or adhesional)
○ Categories: Enteric, ileocolic, ileocecal, colonic
○ Adults: Most commonly enteroenteric and ileocolic
○ Children: Most commonly ileocolic (75%)
• Morphology
○ "Bowel within bowel" appearance
○ Adults: 90% have pathological trigger (lead point or
predisposing condition)
○ Children: 95% idiopathic (lymphoid hyperplasia in
mesenteric adenitis)
○ Transient intussusception: Nonobstructing, self-limiting
Ultrasonographic Findings
• Grayscale ultrasound
○ High sensitivity (98-100%) & specificity (88-100%)
○ Particularly useful in pediatric population (gold standard)
– Diagnostic and therapeutic, avoiding radiation
– Usually subhepatic complex structure, > 5 cm,
displacing bowel loops
○ Transverse
– Concentric parallel rings of bowel wall (target,
doughnut, or bull's-eye sign)
– Hypoechoic outer layer of edematous bowel
– Layering of hypoechoic fluid trapped between
compressed bowel segments
– Echogenic crescent of intussuscepted mesenteric fat
(crescent within doughnut sign)
○ Longitudinal
– Multiple parallel, hypoechoic, and echogenic stripes
(sandwich sign)
– Curved with eccentric fat or imaged obliquely, giving
rise to pseudokidney sign
– Enlarged hypoechoic mesenteric lymph nodes give
appearance of renal medullary pyramids
○ Additional features
– Central lead point lesion or lymph nodes
– Small volume of free fluid (common)
– Perforation: Large-volume ascites, debris, and free gas
○ US-guided hydrostatic nonsurgical reduction (NSR)
– Increasing use of saline solution under ultrasound
guidance; avoids ionizing radiation
– Limited by presence of excessive bowel gas,
depending on site of intussusception
– Outer wall thickness < 1 cm, lymph nodes < 1 cm
within intussusception & minimal internal trapped
fluid associated with higher success rate of NSR
○ Transient intussusception
– No significant bowel edema, fat, or lymph nodes;
segment involved often shorter and smaller diameter
– Spontaneous resolution may be observed on US,
particularly in pediatric population in small bowel
intussusception (SBI), so-called benign SBIs
• Color Doppler
○ Mesenteric vessels trapped between entering and
returning limbs of intussusceptum
○ Reduced or absent mural vascularity of intussusceptum
indicative of vascular compromise, ischemia with risk of
infarction and perforation
○ Absence of vascularity in intussusceptum is good
predictor of irreducibility
Radiographic Findings
• Radiography
○ Elongated soft tissue mass
○ Intraluminal air between walls of intussusceptum and
intussuscipiens, air crescent sign
Fluoroscopic Findings
• Fluoroscopic contrast enema
○ No longer gold standard investigation in children;
therapeutic use only
○ Edematous mucosal folds of returning limb outlined by
contrast in lumen, giving rise to coiled spring appearance
○ Contraindicated in perforation
• Fluoroscopic-guided hydrostatic/contrast/pneumatic NSR
○ Water-soluble contrast, barium, or air enema
CT Findings
• Multiplanar viewing essential and confirms presence or
absence of lead point
○ Soft tissue sausage-shaped mass (longitudinal)
○ "Bowel within bowel" configuration with concentric rings
axial to plane of intussusception, ultrasound equivalent
of target sign
○ Complications: Signs of ischemia/infarct (variable wall
enhancement, edema), perforation (free gas, fluid)
○ Transient intussusception may be incidental finding
Imaging Recommendations
• Best imaging tool
○ Ultrasound: 1st modality in pediatrics but operator
dependent and limited by distended bowel
○ CT: Often 1st investigation in adults presenting acutely;
high sensitivity and specificity and accessible
DIFFERENTIAL DIAGNOSIS
Tumor
• Bowel-related masses
○ Malignant: Adenocarcinoma, carcinoid tumor,
lymphoma, GIST
○ Benign: Lipoma & adenoma
○ Metastases to bowel
– Antimesenteric border of small bowel
– From malignant melanoma, lung, and breast cancer
Diagnoses: Bowel
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