Neuronal migration disorders: MRI, SPECT and PET findings

ABSTRACT

BACKGROUND: With the aid of high-resolution MRI, the identification of neuronal migration disorder(NMDs) is increasing and NMDs are considered as one of the major causes of extrahippocampal epilepsy. However, MRI has some limitatons in detecting small cortical lesion of NMDs. We have studied the diagnostic value and findings of brain SPECT and PET in the patients with NMDs. METHODS: Nineteen NMD patient with intrac table and partial epilepsy were studied. Diagnosis of NMDs was based on neuroimaging and pathology. Proton, Tl and T2-weighted axial, saggital and coronal MR image were obtained by 1.5 Tesla unit. Interictal and ictal SPFCT and PET imagings were performed with 99mTc-HMPAO and 18F-fluorodeoxyglucose. RESULT: Focal cortical dysplasia (FCD) and schizencephaly were detected in 4 patients, heterotopias in 3(one with 3 isolated lesions and one with bilateral temporal lobe lesions), polymicrogyria in 3, hemi-megalencephaly in 2, pachygyria in 2, forme fruste of tuberculous sclerosis(FFTS) in 1. Heterotopia was also combined with other lesions as schizencephaly, FFS and pachygyria. The MRI detected the lesions in 14 patients(73.7%). Of the 5 patients without definite abnormalities on MRI, 3 had focal polymicrogyda and 2 had FCD on pathologic examination. The interictal SPECT revealed abnormalities in 9 of 12 patients(75.0%), but could not detect 2 FCDs and one heterotopia. The ictal SPECT detected the lesions in all 11 patients. PET showed the compatible abnormalities in 17 patients(89.5%), but there was no abnormal finding in 2(1 with FCD and 1 with heterotopia). The abnormal lesions in PET were more extensive than those in MRI in the 8 patients with focal NMDs. Heterotopia showed cortical gray matter activity on PET in 6 out of 11 lesions. All other NMDs showed hypometabolism or metabolic detect in the interictal SPECT and PET. CONCLUSION: Functional imaging as SPECT & PET may be more selective than MRI to detect focal cortical lesions in NMD. NMDs show, variable metabolic pattern on functional imagings and in general the derangement in the functional imaging is more widespread than the lesions detected by MRI. We recommend the functional neuroimaging in the patients who are suspected to have partial seizure of neocortical origin and have no abnormal findings on brain MRI.