What causes Cobra head sign in urinary tract on IVU?
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Answer:
Contrast-filled dilated distal ureter within a radiolucent ureterocele, seen in uncomplicated adult-type ureterocele, a submucosal cystic dilatation of the intramural distal ureter protruding into the bladder lumen; associated with urinary tract infections, flank pain, renal scarring, and more common in duplex systems but can occur in single systems.
Why is it called so?
Resembles the flared hood of a cobra head, with the contrast-opacified dilated ureter forming the central body and the thin surrounding radiolucent line (ureteral wall plus prolapsed bladder mucosa) mimicking the cobra’s hood against bladder contrast.
Pathophysiology
Ureterocele causes obstruction and dilatation of the distal ureter; during excretory phase of IVU, contrast fills the dilated ureteral lumen while the thin lucent wall and adjacent bladder mucosa form a well-defined halo, creating the Cobra head sign appearance in uncomplicated cases.
Alternative names: Spring onion sign
Other associated named signs: None
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