What causes the coiled spring sign on contrast enema and ultrasound?
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Answer:
The coiled spring sign is the appearance produced when contrast or fluid becomes trapped between the stretched, oedematous mucosal folds of the intussusceptum and the surrounding intussuscipiens, giving a series of closely spaced transverse lines resembling a coiled spring. It is a classic finding of intussusception, seen on contrast enema and in the longitudinal plane on ultrasound, where the transverse counterpart is the target or doughnut sign of concentric rings and the longitudinal appearance is also called the pseudokidney sign. Ultrasound is the first-line investigation in children, with very high sensitivity and specificity, and the report should describe the location, the diameter, the presence of trapped fluid, wall thickening, absent mural Doppler flow and free fluid, all of which predict failure of reduction or ischaemia, and any pathological lead point. In children under 2 years the cause is usually idiopathic lymphoid hyperplasia after a viral illness; a lead point such as a Meckel diverticulum, duplication cyst, polyp, Henoch-Schönlein purpura haematoma or lymphoma becomes more likely with increasing age and mandates a careful search. Treatment in children is image-guided pneumatic or hydrostatic reduction, contraindicated by perforation, peritonitis or shock. In adults intussusception is uncommon, is usually due to a tumour, and is managed surgically with resection rather than reduction.
Why is it called so?
The regularly spaced lines of contrast between the mucosal folds resemble the turns of a coiled spring.
Pathophysiology
Intussusception occurs when one segment of bowel telescopes into the segment beyond it, dragging its mesentery with it. The invaginated segment obstructs venous and lymphatic return first, so its wall becomes congested and oedematous and its valvulae conniventes or haustral folds thicken and stretch. Contrast introduced from below, or fluid trapped between the layers, outlines the spaces between these compressed folds and produces the regularly repeating transverse striations. Continued compression eventually compromises arterial supply, leading to ischaemia, necrosis and perforation, which is why the interval to treatment matters and why absent Doppler flow within the intussusceptum is an ominous finding.
Alternative names: Coil spring appearance; stacked coin appearance
Other associated named signs: Target sign and doughnut sign on transverse ultrasound and the pseudokidney sign in the longitudinal plane
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