What causes the gut signature on ultrasound?
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Answer:
The gut signature is the layered wall architecture of bowel reproduced in the wall of a cystic lesion on ultrasound: an inner echogenic mucosa and an outer hypoechoic muscularis propria. Its presence identifies an enteric duplication cyst, in which the abnormal structure is lined by true gastrointestinal mucosa and invested by smooth muscle. In its two-layer form it is also called the double-wall or muscular rim sign; high-resolution scanning can resolve the full five layers of bowel wall (echogenic mucosa, hypoechoic muscularis mucosae, echogenic submucosa, hypoechoic muscularis propria, echogenic serosa). The differential for a cystic abdominal mass in a child includes mesenteric and omental cysts, ovarian cysts and neoplasms, lymphatic malformation, Meckel diverticulum and choledochal cyst, none of which shows true layering. Specificity improves when all five layers are seen or when the Y-configuration sign is demonstrated, the shared muscularis propria splitting between cyst and adjacent bowel. Haemorrhage or infection can obliterate the layers and give a false negative.
Why is it called so?
The cyst wall reproduces the characteristic layered signature of normal bowel wall.
Pathophysiology
An enteric duplication cyst arises from an error of embryonic recanalisation or from a persistent embryonic diverticulum, so it develops as a genuine segment of gut wall rather than as a simple epithelial-lined cavity. It therefore carries the same concentric histological layers, and because those layers differ in acoustic impedance, ultrasound renders them as alternating echogenic and hypoechoic bands. The cyst most often shares its muscular coat and blood supply with the adjacent native bowel, which is the anatomical basis of the Y-configuration sign and the reason surgical excision usually requires resection of the adjoining segment.
Alternative names: Double wall sign, muscular rim sign, bowel wall signature
Other associated named signs: Y-configuration sign, target sign of intussusception, and the pseudokidney sign
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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