Abstracts

Selective amygdalohippocampectomy (SAH) has emerged as a tissue sparing surgical alternative to standard anterior temporal lobectomy for patients with medically refractory mesial temporal lobe epilepsy. Successful use of this procedure demands a higher standard of certainty that mesial temporal structures represent the epileptogenic region. Magnetic resonance spectroscopic imaging (MRSI) may demonstrate metabolite abnormalities that correlate with the epileptogenic zone. More widespread abnormalities may indicate bitemporal disease or the presence of more widespread subtle developmental disorders. We performed temporal lobe MRSI in patients who were seizure free (SzF) or had persistent seizures (PSz) following SAH to study the spatial distribution of metabolic abnormalities as pilot work for a prospective study of MRSI in SAH candidates.
11 healthy controls (CON) and 14 post-SAH patients (10 SzF, 4 PSz) underwent 1H MRSI of both temporal lobes in the plane of the hippocampus, performed on a 1.5T GE scanner using TR/TE 1500/144, NEX=2, 15mm thick, FOV=20 cm,16x16 phase encoding steps, zero filled to 32x32 (nominal voxel size 0.59cc). The metabolite ratio NAA/Cr (N-acetyl aspartate/creatine) was calculated for six regions of interest (ROI), each comprising 3-6 voxels, in each temporal lobe (anterior, mid, and posterior hippocampus; anterior mid and posterior temporal lobe) using LCModel. For patient groups, hippocampal measurements were not made on the operated side. NAA/Cr for each ROI in patients was defined as abnormal if the value was [gt]2SD below control mean for that region. No patient had seizures within 24 hours of MRSI.[table1]
Overall mean temporal lobe NAA/Cr was lower in PSz compared with CON (p[lt].0007). Comparing PSz to SzF, there were significantly more abnormal total ROIs (p[lt].0001), abnormal (contralateral) hippocampal ROIs (p[lt].0016), and abnormal total lateral temporal ROIs (p[lt].0034) in the PSz group (Fisher[rsquo]s exact test). PSz (compared with SzF) patients had significantly more abnormal lateral temporal ROI ipsilateral (p[lt].0275) but not contralateral (p[lt].25) to the operated side.
MRSI demonstrates lower temporal lobe NAA/Cr in patients who have persistent seizures following SAH compared with controls. Patients with persistent seizures following SAH have more widespread abnormalities of NAA/Cr in the contralateral hippocampus and ipsilateral (but not contralateral) temporal lobe compared with patients who are seizure free. Future prospective studies will address the contributions of preoperative spectroscopic abnormalities vs. postoperative dynamic changes in producing these differences.
[Supported by: Medical Research Foundation of Oregon]