Figure 2
MRI, fMRI and SEEG of a patient with epilepsy originating from the parietal lobe who was shown to have right parietal ulegyria and gliosis. The patient was born before term (34 weeks of gestation) with normal delivery. There were no focal neurological deficits, although agnosia digitorum was present with moderate cognitive impairment involving specific deficits in: problem-solving abilities, verbal fluency, visuo-spatial memory, visuo-motor planning, and facial recognition. The patient was ambidextrous. Epilepsy onset occurred at eight months of age, with annual seizures, frequently facilitated by fever and characterized by diffuse hypertonia and staring or eye-head deviation, as well as constant secondary generalization. At the time of the presurgical evaluation at 31 years of age, the seizures had a monthly frequency, and their semiology consisted of an initial tingling-like sensation localized to the fingers of the left hand with a centripetal direction up to the shoulder, and afterwards towards the left foot, followed by eye and head deviation either to the right (more frequently) or to the left, and left arm hypertonia. Interictal EEG showed spike-waves over T4-T6 and P4-T6 and asynchronous spikes over C4-P4, constantly involving Pz, while ictal EEG showed a right temporo-parietal initial rapid discharge. MRI (A)revealed right parietal ulegyria, involving both the inferior parietal lobule and the post-central gyrus, including the underlying white matter (arrow: Rolandic sulcus). fMRI (B) showed an activation of the left primary motor area, the left SMA, and a left post-central area during the finger-tapping (F-T) task of the right (R) hand; an activation of a left post-central area and the primary motor area, bilaterally, with greater extent and intensity on the left, during finger-tapping of the left (L) hand; an activation of the left somatosensory area during brushing of the right hand; and an activation of two small areas, bilaterally, none of which corresponded to the theoretical position of the somatosensory area in the right post-central gyrus during brushing of the left hand. The activated sensorimotor areas did not appear to be contiguous with the ulegyric lesion.
An SEEG investigation of the right centro-parieto-temporal cortex was performed (see stereotactic scheme in [C]; electrodes and corresponding structures investigated are outlined below) demonstrating the presence of:
subcontinous spike-waves (D) involving the post-central gyrus (X12-13), the intermediate-external aspect of the inferior parietal region (external contacts of R and intermediate-external contacts of P) and the posterior part of precuneus (L4-5), and polyspikes in the fusiform gyrus and inferior temporal gyrus (electrode D), while activity in the precentralgyrus (X8-9) was free of interictal abnormalities;
- subclinical paroxysms (E) arising from the inferior parietal area (see fast activity from intermediate-external contacts of electrodes L and P), in the intermediate-external aspect of theparieto-occipital junction (see flattening at electrodes Y and V), but also in the inferior temporal and fusiform gyri (see rhythmic bursts of high-voltage polyspikes at electrode D);
- ictal onset, either similar to the subclinical paroxysms or, more frequently, characterized by a high-voltage spike (F) immediately followed by fast activity of very low voltage involving the majority of electrodes, more pronounced in the intermediate contacts of L, D, P and external contacts of V and R.
Electrical cortical stimulations of the supra marginal gyrus and the post-central gyrus induced the habitual aura, and revealed a normal function of the motor area and a partially functional somatosensory area. Invasive neurophysiological and anatomo-functional findings permitted to delineate an epileptogenic zone localized in the intermediate-external part of the parietal region and involving the post-central gyrus in the superior aspect, as far as the parietal-occipital junction in the inferior aspect (G), the total resection of which leaded to complete seizure freedom (Engel class Ia) without motor-sensitive deficits. Post-operative visual field testing revealed a predicted, incomplete left inferior quadrantanopsia. Histopathological analysis revealed the presence of gliosis. Neuropsychological evaluation at five years of follow-up showed an amelioration of verbal fluency, visuo-motor planning, facial recognition, and problem-solving abilities.
The cerebral structures investigated by each electrode in the stereotactic scheme (C) are listed from mesial to dorsal surfaces; the numbers of each electrode in the trace montage follow the same direction (1 to 15: mesial to dorsal). F1-2: anterior part of paracentral lobule; F3-5: superior part of precentralgyrus; G1-3: posterior part of paracentral lobule; G4-7: superior part of postcentralgyrus; H1-6: anterior part of superior parietal lobule; W1-5: transverse temporal gyrus; W6-7: posterior part of superior temporal gyrus; D1-5: intermediate part of fusiform gyrus; D6-11: posterior part of inferior temporal gyrus; N1-2: posterior part of central gyrus; N9-13: intermediate part of precentralgyrus; S1-2: posterior part of central gyrus; S11-15: inferior part of postcentralgyrus; X1-2: posterior part of paracentral lobule; X7-9: intermediate part of precentralgyrus; X11-14: postcentralgyrus (lesion). P1-2: posterior part of central gyrus; P6-11: lesion; P12-15: supramarginalgyrus; R1-2: posterior part of central gyrus; R10-11: lesion; R12-15: supramarginalgyrus; C1-3: intermediate part of hippocampus; C11: posterior part of middle temporal gyrus; L1-4: posterior part of precuneus; L5-7: lesion; L8-11: posterior part of inferior parietal lobule; V1-2: posterior part of precuneus; V9-15: angular gyrus (lesion); Y1-3: anterior part of cuneus; Y5-6: lesion; Y7-10: superior occipital gyrus.