Magnetic resonance imaging in the management of resistant focal epilepsy: pathological case report and experience of 12 cases

Magnetic resonance features of the feline hippocampus in epileptic and non-epileptic cats: a blinded, retrospective, multi-observer study

BACKGROUND

Hippocampal necrosis in cats has been reported to be associated with epileptic seizures. Magnetic resonance imaging (MRI) features of temporal lobe (TL) abnormalities in epileptic cats have been described but MR images from epileptic and non-epileptic individuals have not yet been systematically compared. TL abnormalities are highly variable in shape, size and signal, and therefore may lead to varying evaluations by different specialists. The aim of this study was to investigate whether there were differences in the appearance of the TL between epileptic and non-epileptic cats, and whether there were any relationships between TL abnormalities and seizure semiologies or other clinical findings. We also investigated interobserver agreement among three specialists.

METHODS

The MR images of 46 cats were reviewed independently by three observers, who were blinded to patient data, examination findings and the review of the other observers. Images were evaluated using a multiparametric scoring system developed for this study. Mann-Whitney U-tests and chi-square were used to analyse the differences between observers' evaluations. The kappa coefficient (k) and Fleiss' kappa coefficient were used to quantify interobserver agreement.

RESULTS

The overall interobserver agreement was moderate to good (k =0.405 to 0.615). The MR scores between epileptic and non-epileptic cats did not differ significantly. However, there was a significant difference between the MR scores of epileptic cats with and without orofacial involvement according to all three observers. Likewise, MR scores of cats with cluster seizures were higher than those of cats without clusters.

CONCLUSION

Cats presenting with recurrent epileptic seizures with orofacial involvement are more likely to have hippocampal pathologies, which suggests that TL abnormalities are not merely unspecific epileptic findings, but are associated with a certain type of epilepsy. TL signal alterations are more likely to be detected on FLAIR sequences. In contrast to severe changes in the TL which were described similarly among specialists, mild TL abnormalities may be difficult to interpret, thus leading to different assessments among observers.

High signal intensity on T2-weighted MRI correlates with hypoperfusion in temporal lobe epilepsy

Single-photon emission computed tomography (SPECT) and [99mTc]HMPAO were used to assess the functional significance of nonspecific magnetic resonance imaging (MRI) abnormalities observed in patients with temporal lobe epilepsy and no focal lesion on CT scan. We studied 18 patients whose MRI was normal or showed high signal intensity on T2-weighted images (T2WIs) at the site of the EEG focus in 11 and 7 cases, respectively. EEG was monitored during regional cerebral blood flow (rCBF) study. Lateralized hypoperfusion was present in 7 of 17 interictal (41%) and in one postictal cases; it was located in the temporal lobe on the side of the EEG focus in all, and was significantly more frequent in patients with high signal intensity on T2WI (86%) than in patients with a normal MRI (18%). The degree of temporal perfusion asymmetry measured in each individual was higher in patients whose MRI was abnormal.

Lateralization of epileptic foci by magnetic resonance imaging in temporal lobe epilepsy

A retrospective single-blind study was carried out to assess the reliability of magnetic resonance imaging (MRI) for determining lateralization of the electrographic focus in 45 patients with intractable temporal lobe epilepsy. With strictly defined MRI diagnostic criteria, the electroencephalographic (EEG) focus was correctly lateralized in 86% of patients. Excluding patients with structural lesions, the criteria provided for correct lateralization of the epileptogenic focus in 78% and false lateralization in 5%. Hippocampal atrophy on T1-weighted images and increased signal intensity from mesial structures on T2-weighted scans were highly reliable for lateralization. Postoperative outcome did not differ between the patients with normal and those with abnormal findings on MRI, but the group sample was inadequate to assess the issue of surgical outcome. These findings suggest that with appropriate techniques and strictly defined diagnostic criteria, MRI can provide reliable seizure lateralization in patients with intractable temporal lobe epilepsy.

Hippocampal sclerosis in temporal lobe epilepsy demonstrated by magnetic resonance imaging

The value of magnetic resonance imaging in the detection of hippocampal sclerosis has been controversial. We studied 10 patients aged 22.5 +/- 6.0 years with intractable temporal lobe epilepsy selected because of a history of a prolonged childhood convulsion, which is characteristic of a group of patients in whom hippocampal sclerosis is a constant finding. All 10 patients showed reduction in size of one hippocampus associated with increased signal intensity on T2-weighted magnetic resonance images. These changes were reliably detected on coronal spin-echo images, perpendicular to the long axis of the hippocampus. Appreciation of the normal imaging anatomy of the hippocampus allowed correct interpretation of the relative changes in signal intensities of the hippocampus and adjacent temporal horn on sequential echo images. The side of the abnormal hippocampus on magnetic resonance imaging accorded with the electroencephalographic localization in all 10 patients, and with the lateralization of the early convulsions in all 6 patients where this was known. Temporal lobectomy was performed in all 10 patients. Hippocampal sclerosis was confirmed in the 3 patients in whom hippocampal tissue was available for histological examination. The value of this technique was reinforced by the excellent postoperative results, with 80% being seizure free at a mean follow-up time of 33 +/- 4 months.

Magnetic resonance imaging of the brain and spine

The efficacy of magnetic resonance imaging (MRI) in the diagnosis of diseases of the central nervous system is reviewed. MRI, computed tomography (CT) and certain radionuclide studies are compared in the evaluation of intracranial tumours, cerebral vascular disease, multiple sclerosis and other white matter diseases, dementia, head injury, infection, epilepsy, spinal lesions and in paediatric central nervous system disorders. The measurement of cerebrospinal fluid volumes and dynamics by MRI is discussed. MRI most clearly has advantages where CT is degraded by bone hardening and streak artefacts (spine, skull base, posterior and temporal fossa, sella and parasellar regions) and in diseases in which the X-ray attenuation of the suspected lesion differs little from normal parenchyma (paediatric brain disorders, demyelination and dysmyelination, early oedema associated with infarction, infection or low-grade infiltrating neoplasm, subacute and chronic haemorrhage and lesions in the spinal subarachnoid space and cord). Elsewhere MRI and CT should be seen as complementary rather than competitive methods of imaging. In spite of an absence of information about the contribution of MRI to management decisions and a lack of rigorous, prospective controlled trials, MRI will play an increasing role in the diagnosis of diseases of the central nervous system.