Cobra Head Sign

A descriptive term for the appearance of the ureterovesicular junction in adult-type ureterocele of the urinary bladder, as seen on an excretory urogram; a thin outer membrane, which corresponds to the ureteral walls appears as a dark halo, and encloses a cystically-dilated distal intravesicular ureter that protrudes into the bladder, and opacified urine pools in both the dilated ureter and the bladder; simple ureteroceles in adults are associated with stenosis of the ureteral orifice and prolapse of the distal ureter into the bladder, possibly due to the persistence of Chiralla’s membrane and blockage of the ureteral orifice