What causes phantom calyx in the renal collecting system on contrast imaging?
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Phantom calyx occurs when a single renal calyx fails to opacify with contrast imaging despite normal opacification of the remaining pelvicalyceal system. This phenomenon arises from an intrarenal pathological process that infiltrates or obliterates the involved calyx or its infundibulum, preventing contrast filling. Common clinical conditions associated with phantom calyx include renal pelvic transitional cell carcinoma, renal tuberculosis, acute pyelonephritis, renal calculi, ischemia, trauma, and congenital anomalies.
Why is it called so?
It is termed phantom calyx because the affected calyx appears “missing” or invisible (like a phantom) on contrast studies due to non-opacification, while surrounding calyces are clearly visible and contrast-filled.
Pathophysiology
The sign develops when a pathological lesion infiltrates or obstructs the calyx or infundibulum, leading to amputation or obliteration of the calyceal space. This obstruction precludes the entry of contrast material, creating the appearance of an absent calyx on imaging. Tumoral infiltration or scarring may replace the urine-filled collecting space, physically blocking opacification.
Alternative names: None.
Other associated named signs: Oncocalyx — where the calyx is filled with tumor but still visible on imaging.
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