Imaging of axonal damage in vivo in Rasmussen's syndrome.

We obtained magnetic resonance spectroscopic images (MRSIs) in three patients with Rasmussen's syndrome. The relative resonance intensity of N-acetylaspartate (NAA) to creatine (NAA:Cr), an index of neuronal loss or damage, was determined for various regions within the brain, and the affected:unaffected hemisphere asymmetry ratio was determined. All three patients had decreased relative NAA signal intensity over the entire affected hemisphere. The decrease in NAA:Cr involved cortex and white matter, was most prominent in the anterior periventricular region, and showed a tendency to be worse in patients with longer duration of disease. 1 year follow-up MRSI showed further reduction of the relative NAA signal in all patients, indicating progression of the disease. All patients were free of seizures for at least 48 h before the first MRSI, but two of them had epilepsia partialis continua (EPC) during the follow-up examination. There was no significant increase of the lactate resonance intensity, except in the two MRSIs performed during EPC. This indicates that lactate accumulation results from repetitive seizures rather than from the disease process itself. The spatial distribution of the metabolic abnormality on MRSI was more widespread than that of the structural abnormality on MRI. The relative NAA resonance intensity was not reduced in the contralateral hemisphere. Our findings indicate that MRSI can identify and quantify neuronal damage and loss throughout the affected hemisphere of patients with Rasmussen's syndrome, including areas that appear normal on conventional MRI.