Retroisthmic cleft: a stress fracture of the lamina.

The retroisthmic cleft is a rarely diagnosed defect in the lamina of the lumbar spine. It has always been considered a congenital anomaly. This is the first report we are aware of showing radiological changes in a retroisthmic cleft over a period of time. The follow-up of this patient over a period of 6 years, the radiological and scintigraphic appearances and a review of the literature suggests that the retroisthmic cleft is a stress fracture of the lamina.