How reliable is routine lumbar spine MRI for detection of renal cysts? Correlation with abdominal CT

Background: Incidental renal cysts are a very common finding in routine lumbar spine magnetic resonance imaging (MRI). However, there is no report of the renal cyst detection rate on routine lumbar spine MRI. Purpose: To determine the renal cyst detection rate in routine lumbar spine MRI based on findings of abdominal computed tomography (CT), and to investigate if the largest renal cyst seen by abdominal CT could be also detected by routine lumbar spine MRI. Material and Methods: A retrospective study was conducted of 70 patients who underwent both routine lumbar spine MRI and abdominal CT between December 2011 and January 2014. The detection rate of all renal cysts >5 mm as well as the largest renal cyst seen by abdominal CT were assessed in routine lumbar spine MRI. Results: On routine lumbar spine MRI, the detection rate of renal cysts was 46.5% (73/157) for >5-mm renal cysts and 68.0% (34/50) for >10-mm renal cysts, correlating with abdominal CT. The detection rate of the largest renal cyst seen by abdominal CT was 60.0% (27/45). Non-detection of the largest renal cyst could be caused by upper positioning (n = 7), lateral positioning (n = 6), or relatively small cyst size (n = 5). Conclusion: Approximately half of renal cysts >5 mm and two-thirds of renal cysts >10 mm were detected on routine lumbar spine MRI. However, radiologists should be aware that kidney lesions may not be included in the scan coverage of routine lumbar spine MRI.