The retrorenal spleen. Implications for percutaneous left renal invasive procedures.

An uncommon but potentially disastrous situation for invasive percutaneous renal procedures is the presence of the spleen behind the upper left kidney. We have termed this anatomic variant "retrorenal spleen." In a computed tomographic (CT) review of 73 patients aged 16 to 86, we found a frequency of retrorenal spleen of 21.1% in the supine and 15.4% in the prone patient. In most individuals with this variant, the spleen was behind the lateral fifth and the superior fourth of the left kidney. The majority (80.0%) of these patients were age 50 or over. However, in only 7.6% would the posterior splenic position pose a risk to posterolateral percutaneous approaches of less than 30 degrees into the upper left collecting system. No patient had retrorenal spleen at the mid-hilar level in either the supine or prone position. Posterolateral approaches up to 40 degrees into the renal hilus are 100% safe from intervening spleen.