What causes the spaghetti sign on CT urography?
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Answer:
The spaghetti sign is a coiled, linear, worm-like filling defect lying within the opacified bladder on the excretory phase of CT urography. It is a blood clot cast that has been moulded into a tubular shape as it passed down the ureter, and its presence therefore localises the source of haematuria to the upper tract rather than the bladder, directing attention to the kidney and ureter and prompting a search for tumour, calculus or trauma. It is the usage indexed in the radiology literature. The term is separately used in a textbook sense for the appearance of Ascaris lumbricoides worms in the biliary tree or bowel, where the parasite is seen as a long tubular structure, sometimes with a central lucent line representing its own gut; that usage is descriptive and much less commonly encountered in Western practice. In either setting the finding is one of shape rather than of attenuation, so it is best appreciated on thin-section reformats.
Why is it called so?
The long, thin, coiled tubular defect lying in the contrast-filled bladder looks like a strand of spaghetti.
Pathophysiology
Bleeding from a renal or ureteric source enters the collecting system and clots within the lumen. The ureter continuously moulds the forming clot by peristalsis, so it is extruded as a cast of the ureteric lumen rather than as an amorphous mass, and it retains that tubular shape after it drops into the bladder. Because the clot is of soft-tissue attenuation and the bladder around it is filled with dense excreted contrast, the cast is displayed as a serpiginous negative defect. In the parasitic usage, the shape reflects the worm’s own long cylindrical body rather than any moulding process.
Alternative names: Spaghetti clot, ureteric clot cast
Other associated named signs: Ureteric cast of renal papillary necrosis, the ring sign and lobster claw sign of papillary necrosis, and the inner tube sign
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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