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 in jury at 1.5 T in patients with normal head CT findings after mild head injury. METHODS: Twenty consecutive patients with mild head injury (G lasgow Coma Scale, 13 to 15; no subsequent deterioration, loss of cons ciousness < 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/excitati ons]) and a T2-weighted gradient-echo sequence (750/40/2, 10 degrees flip angle). Each sequence was read independently by two blinded reade rs. RESULTS: The readers agreed that abnormalities compatible with dif fuse axonal injury were present in the white matter of 6 (30%) of 20 p atients (95% confidence interval, 12% to 54%). Both readers agreed tha t foci of high signal intensity were present on the T2-weighted spin-e cho sequence in 3 (15%) of the 20 cases (95% confidence interval, 3% t o 38%) and that foci of hypointensity compatible with hemorrhagic shea r injury were present on the T2-weighted sequence in 4 (20%) of the 2 0 patients (95% confidence interval, 6% to 44%). Both types of abnorma lity were noted by the readers in one patient. CONCLUSIONS: MR shows e vidence of diffuse axonal injury in some patients with normal head CT findings after mild head injury. These lesions may represent the patho logic substrate underlying the postconcussion syndrome that occurs in many patients with moderate to severe head injury.