What causes faceless kidney sign on CT?
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Answer:
Faceless kidney sign: Absence of the normal central renal sinus complex (renal sinus fat, vessels, and collecting system) on an axial CT section through the kidney, seen when the scan plane passes through the junction of a duplicated (duplex) collecting system — i.e., between the upper and lower moieties — so the section shows only featureless renal cortex and medulla (“no face”), which can otherwise be mistaken for a renal mass.
Why is it called so?:
Named because the imaged section lacks the “face” of the kidney — the central sinus containing fat, vessels, pelvis, and calyces — appearing as a homogeneous, featureless renal parenchymal disc.
Pathophysiology:
In a duplex kidney, each moiety has its own separate renal sinus. A transverse CT section taken at the level where the two moieties are fused/juxtaposed (interpolar zone) can pass entirely through parenchyma, missing both sinuses, so the sinus fat, vessels, and pelvicalyceal elements are not seen on that slice — producing the “faceless” appearance. Reviewing adjacent sections above and below reveals the normal sinus of each moiety, confirming the underlying duplication rather than a mass.
Alternative names: None widely used.
Other associated named signs: Drooping lily sign (displaced, compressed lower pole moiety in an obstructed duplex system), cobra head sign (ureterocele of an ectopic upper-pole ureter).
References
Access all radiology signs posted so far: https://radiogyan.com/radiology-signs/
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