ª Springer Science+Business Media New York 2014

Abdominal Imaging

Abdom Imaging (2014) DOI: 10.1007/s00261-014-0269-8

The cobra head sign Philippe A. Tirman, Raymond B. Dyer Department of Radiology, Wake Forest Baptist Medical Center, Wake Forest University School of Medicine, Medical Center Blvd, Winston-Salem, NC 27157, USA

Unlike the deadly reptile for which it is named (Fig. 1), the cobra head sign is used to describe the usually incidental and benign finding of an orthotopic, intravesical ureterocele (previously referred as a ‘‘simple’’ ureterocele) [1]. When opacified with contrast material, the ureterocele mimics the cobra’s head protruding into the urinary bladder lumen, with the upstream ureter serving as the snake’s body (Fig. 2). Although the sign was originally described on standard radiographic images, it may appear on MR or CT urography (Fig. 3, 4). For those that relate more to botany than herpetology, this appearance has also been referred as the ‘‘spring onion sign’’ (Fig. 5) [4]. As the term intravesical implies, both the ureterocele and ureteral orifice are positioned within the bladder lumen; as the urinary bladder fills with contrast, a thin and uniform ureterocele wall should become apparent as a rounded and relatively radiolucent ‘‘halo’’ outlining the ureterocele. In contrast to the classic ectopic ureterocele seen in children with duplex renal collecting systems, intravesical ureteroceles more commonly seen in asymptomatic adults are usually associated with a single ureter which normally inserts into the urinary bladder trigone; these may be unilateral or bilateral [1, 2]. When found on imaging it is important to ensure that the ureterocele wall, comprised of a thin muscular layer lined internally by ureteral uroepithelium and externally by bladder uroepithelium, is thin and uniform in appearance [2]. A thickened, irregular, or illdefined wall may indicate a more sinister pathology, such as an infiltrating carcinoma or edema from a stone that is obstructing the intramural ureter (referred to as a pseudoureterocele) [1, 3, 5].

Correspondence to: Philippe A. Tirman; email: [email protected]

Although commonly asymptomatic, intravesical ureteroceles can be associated with varying degrees of upstream (proximal) ureteral obstruction. When large, ureteroceles can also result in an outlet obstruction of the urinary bladder. Stasis of urine within the intravesical ureterocele can also predispose the patient to the formation of ureterolithiasis and recurrent urinary tract infections [1, 2].

Fig. 1. Cobra snake (courtesy of Michael Allen Smith; https://creativecommons.org/licenses/by-sa/2.0/).

P. A. Tirman, R. B. Dyer: The cobra head sign

Fig. 4. MR axial image (T2-weighted FS) of the pelvis with an incidental intravesical ureterocele on the left (

The cobra head sign.

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