Cobra head sign (ureter)

Last revised by Ian Bickle ◉ on 28 Feb 2025

Citation, DOI, disclosures and article data

Citation:

Radswiki T, Bickle I, Niknejad M, et al. Cobra head sign (ureter). Reference article, Radiopaedia.org (Accessed on 23 Mar 2025) https://doi.org/10.53347/rID-12602

DOI:

https://doi.org/10.53347/rID-12602

Permalink:

https://radiopaedia.org/articles/12602?embed_domain=buyreviewer.com%2Fbest-tire-inflator-on-amazon

rID:

12602

Article created:

22 Dec 2010, The Radswiki ◉

Disclosures:

At the time the article was created The Radswiki had no recorded disclosures.

View The Radswiki's current disclosures

Last revised:

28 Feb 2025, Ian Bickle ◉

Disclosures:

At the time the article was last revised Ian Bickle had the following disclosures:

Hexarad, I work for this out sourcing company during non NHS hours (ongoing)

These were assessed during peer review and were determined to not be relevant to the changes that were made.

View Ian Bickle's current disclosures

Revisions:

27 times, by 17 contributors - see full revision history and disclosures

Systems:

Urogenital

Sections:

Signs

Tags:

ureter, bladder, refs

Synonyms:

Adder head sign (ureter)
Cobra-head sign
Adder's head sign
Spring onion sign (ureter)
Cobra's head sign

The cobra head sign, also known as the spring onion sign, refers to dilatation of the distal ureter, surrounded by a thin lucent line seen in patients with an adult-type ureterocele. The cobra head appearance indicates an uncomplicated ureterocele.

During an excretory phase of an intravenous urography, the lucent "hood" of the cobra 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.

Radiologic visualisation can be established using radiographic urography, magnetic resonance urography, computed tomography urography or prenatal ultrasonography regarding fetal patients ³.