Prevalence of MR evidence of diffuse axonal injury in patients with mild head injury and normal head CT findings.

PURPOSE: To assess the prevalence of MR evidence for diffuse axonal injury at 1.5 T in patients with normal head CT findings after mild head injury. METHODS: Twenty consecutive patients with mild head injury (Glasgow Coma Scale, 13 to 15; no subsequent deterioration, loss of consciousness < 20 minutes) and normal head CT findings were examined with MR at 1.5 T. Pulse sequences included a conventional T2-weighted spin-echo sequence (2500-3000/30,80/1[repetition time/echo time/excitations]) and a T2*-weighted gradient-echo sequence (750/40/2, 10 degrees flip angle). Each sequence was read independently by two blinded readers. RESULTS: The readers agreed that abnormalities compatible with diffuse axonal injury were present in the white matter of 6 (30%) of 20 patients (95% confidence interval, 12% to 54%). Both readers agreed that foci of high signal intensity were present on the T2-weighted spin-echo sequence in 3 (15%) of the 20 cases (95% confidence interval, 3% to 38%) and that foci of hypointensity compatible with hemorrhagic shear injury were present on the T2*-weighted sequence in 4 (20%) of the 20 patients (95% confidence interval, 6% to 44%). Both types of abnormality were noted by the readers in one patient. CONCLUSIONS: MR shows evidence of diffuse axonal injury in some patients with normal head CT findings after mild head injury. These lesions may represent the pathologic substrate underlying the postconcussion syndrome that occurs in many patients with moderate to severe head injury.