Longitudinal stress fractures of the tibia: MRI features in two cases.

Longitudinal stress fractures of the tibia are a recognized but unusual finding in long distance runners. Two cases are presented in which the diagnosis on plain films and scintigraphy (in one case) was not evident. Both patients were referred for MRI. Coronal short tau inversion recovery (STIR) sequences demonstrated extensive hyperintense longitudinal intramedullary signal changes in the tibia. T1-weighted spin-echo scans showed corresponding but less extensive regions of reduced signal intensity. In one case, enhancement of this area was seen following i.v. dimeglumine-gadopentetate (Gd-DTPA). Adjacent soft-tissue abnormality and periosteal reaction was seen in one case but in neither patient was a fracture line identified. Thin section CT with sagittal reformats demonstrated an irregular intracortical longitudinal lucent fracture line which was distinct from the nutrient foramen, establishing the diagnosis.