Renal subcapsular rim sign: new etiologies and pathogenesis.

Two prior reports have described a cortical rim sign associated with renal infarction from acute renal artery obstruction. This paper adds four additional cases of a thin outer (subcapsular) cortical nephrogram due to renal vein thrombosis (two cases), acute tubular necrosis (one case), and renal artery embolization (one case). An acute vascular compromise from differing etiologic mechanisms appears to be the common denominator of the rim nephrogram. The nephrogram probably represents an intact subcapsular renal cortex (2-4 mm thick) perfused by the perirenal capsular collateral circulation. To date, the rim nephrogram has been visible only on high dose nephrotomography. Its smooth inner margin is sufficiently distinct to differentiate it from the shell nephrogram of severe hydronephrosis.