Assessment of the cortical rim sign in posttraumatic renal infarction

Purpose: The cortical rim sign has frequently been described as a sign of renal infarction. It is reported to be present in ~50% of focal or global infarcts and is thought to be due to an intact renal collateral circulation. This study evaluates the incidence and temporal development of the cortical rim sign in posttraumatic renal vascular compromise. Method: This retrospective study included 20 patients who were diagnosed by contrast- enhanced CT to have posttraumatic focal or global infarcts. The CT scans were reviewed to evaluate the size of infarcts and the presence and appearance of the rim sign. Medical records were reviewed to identify the timing of trauma in relation to the CT examination. Results: Eight patients had multiple CT examinations and 12 had a single CT study. For all cases that demonstrated a rim sign (n = 14, 8 of which had more than one CT), the earliest appearance of the rim sign was 8 h (median time to appearance was 7 days). All cases with no rim sign (n = 6) were evaluated within 10 h of trauma, with a median time of 4 h. Conclusion: This study suggests that in spite of the presence of renal collateral circulation, it takes a minimum period of 8 h after trauma for this circulation to expand and become apparent on CT. CT demonstrated a rim sign in all cases performed after 1 week.