PROTON MAGNETIC-RESONANCE SPECTROSCOPY FOR DETECTION OF AXONAL INJURYIN THE SPLENIUM OF THE CORPUS-CALLOSUM OF BRAIN-INJURED PATIENTS

Object. This study was conducted to determine whether proton magnetic resonance spectroscopy (MRS) is a sensitive method for detecting diffu se axonal injury, which is a primary sequela of traumatic brain injury (TBI). Diffuse axonal injury is characterized by selective damage to white matter tracts that is caused in part by the severe inertial stra in created by rotational acceleration and deceleration, which is often associated with motor vehicle accidents. This axonal injury is typica lly difficult to detect by using conventional imaging techniques becau se it is microscopic in nature. The splenium was selected because it i s a site vulnerable to shearing forces that product diffuse axonal inj ury. Methods. The authors used proton MRS to evaluate the splenium, th e posterior commissure of the corpus callosum, in normal control volun teers and in patients with TBI. Proton MRS provided an index of neuron al and axonal viability by measuring levels of N-acetyl aspartate (NAA ). Conclusions. A majority of mildly brain injured patients, as well a s those more severely injured, showed diminished NAA/creatine (Cr) lev els in the splenium compared with normal control volunteers. The patie nts displaying lowered NAA/Cr in the splenium were also likely to exhi bit lowered NAA/Cr in lobar white matter. Also. the levels of NAA/Cr i n the splenium of normal volunteers were higher compared with those fo und in lobar white matter. Decreases in NAA/Cr levels in the splenium may be a marker for diffuse injury. A proton MRS examination may be pa rticularly useful in evaluating mildly injured patients with unexplain ed neurological and cognitive deficits. It is concluded that MRS is a sensitive tool in detecting axonal injury.