The cobra head sign

Abstract

A 39-year-old man presented with complaints of long standing lower abdominal pain and episodic left renal colic, associated with urgency, frequency and dysuria. His physical exam, urinalysis and blood tests were unremarkable. Images from the contrast enhanced computed tomographic (CECT) scan of abdomen demonstrated the “cobra-head sign”(A,B), consistent with diagnosis of intravesical ureterocoele. Endoscopic incision of the ureterocoele was successfully performed and complete resolution of symptoms achieved. Ureterocoeles result from incomplete dissolution of the primitive membrane separating the ureteric bud from the developing urogenital sinus. Intravesical ureterocoele is defined as a cystic out-pouching of the distal ureter within the bladder, arising from a ureter with a normal insertion into the trigone-“orthotopic ureterocoele”. This type of ureterocoele is usually diagnosed in adults; hence, it is also called adult-type ureterocoele. Most intravesical ureterocoeles are incidental findings in asymptomatic adult patients, but may cause infections or calculi. Larger ones may cause bladder neck obstruction, along with obstruction of the ipsilateral ureter, which seems to have happened in our patient (B, C). However, he had neither hydronephrosis nor delay in the function of the left kidney (D). On contrast studies, they appear as a bulbous dilatation within the bladder, surrounded by a radiolucent halo-the 'cobra-head sign'. The lucent rim represents the combined thickness of the ureteral wall and prolapsed bladder mucosa, outlined by contrast material within bladder lumen. Also known as the “spring onion sign”, this cobra-head deformity is seen in only 50% of cases. It is important to distinguish ureterocoele (with thin and well defined lucent rim) from a pseudo-ureterocoele (with thick, irregular, or less well-defined lucent rim), as the latter can be caused by distal ureteric obstruction from a tumor or impacted calculus.