Cobra head sign
 Discussion of Cobra head sign
- The cobra head sign refers to dilatation of the distal ureter, surrounded by a thin lucent line, which is seen in patients with adult-type ureteroceles.
- The distal ureter dilates in response to restriction of flow at the ureteral orifice in the bladder.
- The lucent hood represents the combined thickness of the ureteral wall and prolapsed bladder mucosa, outlined by contrast material within the bladder lumen.
- This lucent line should be thin and well defined. Any thickening, irregularity, or loss of definition of the cobra’s hood should raise concern for the presence of a pseudoureterocele (a pseudoureterocele can result from edema related to stone impaction or recent stone passage, or more important, tumor overgrowth of the ureteral orifice).
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 References for Cobra head sign
- Raymond B. Dyer, Michael Y. Chen, and Ronald J. Zagoria. Classic Signs in Uroradiology. RadioGraphics 2004 24: S247-280S.