Temporal lobe epilepsy

The syndrome of medial temporal lobe epilepsy (TLE), which is associated with hippocampal sclerosis, is an example of a surgically remediable syndrome. Approximately 40-67% of these patients have a history of a complicated febrile convulsion (a febrile seizure lasting >30 min). These patients typically present with seizures in late childhood, at which time seizures are well controlled with antiepileptic drugs (AEDs). As the child enters adolescence and early adulthood, the seizures recur and become refractory to multiple medication trials.

Many patients with TLE experience auras, which are simple partial seizures that precede most or all of their complex partial seizures and which often occur in isolation. These auras consist of autonomic phenomena, such as epigastric rising/nausea; olfactory auras, such as a strange taste or odor; or psychic auras, such as fear, déjà vu/jamais vu, depersonalization, or derealization. Secondarily generalized tonic-clonic seizures, when present, are infrequent and easily controlled with AEDs.

These patients are hypothesized to have isolated auras and few generalized seizures because the hippocampus has few connections with the contralateral hippocampus, making seizure propagation slow. Their complex partial seizure consists of behavioral arrest; wide-eyed stare with pupillary dilation; and oral or alimentary automatisms, such as repetitive chewing and lip smacking. Because the hippocampus is involved bilaterally during the complex partial seizure, patients are amnestic for events that occur during the seizure.

Certain clinical features of temporal lobe seizures have lateralizing value. For example, ictal speech usually is associated with nondominant temporal lobe seizure onset. Dystonic limb posturing, when present, is contralateral to the side of temporal lobe seizure onset. This dystonic posturing usually involves flexion of the arm at the elbow with internal or external rotation of the forearm, flexion at the wrist, and extension of the fingers. Some patients may have ipsilateral head turning and contralateral dystonic posturing.

Postictal nose wiping with one hand is defined as wiping of the nose twice in the postictal period. Geyer and colleagues demonstrated that the nose-wiping hand is usually ipsilateral to the temporal lobe of onset. [26] Postictal dysnomia lasting for greater than 2 minutes suggests onset in the dominant temporal lobe. Other lateralizing signs in TLE include postictal thirst, peri-ictal urinary urge, and ictal spitting, which lateralize to the nondominant hemisphere.

Early clonic or tonic activity or an aura suggesting extratemporal onset (eg, unilateral somatosensory aura, visual aura) places the diagnosis of medial TLE in doubt, in that extratemporal foci may propagate to the medial temporal lobe and produce seizure semiology that is indistinguishable from that of medial temporal lobe onset seizures.

Common extratemporal to medial temporal propagation pathways, as described by Ajmone-Marsan and Ralston, [27] include (1) the posterior cingulate gyrus to the medial temporal lobe through the cingulum, (2) the orbitofrontal cortex through the uncinate fasciculus, (3) the parietal lobe, particularly the inferior parietal lobule, through the middle longitudinal fasciculus, and (4) the occipital lobe through the inferior longitudinal fasciculus.

The interictal electroencephalogram (EEG) typically shows anterior to midtemporal epileptiform discharges, which are usually unilateral but may be bilaterally independent in approximately 20-33% of cases. However, bilaterally independent, medial temporal interictal spikes do not necessarily indicate the presence of bilateral epileptogenic regions capable of generating spontaneous seizures. In fact, many patients with bilaterally independent temporal lobe interictal epileptiform abnormalities have their habitual seizure onsets in a single temporal lobe.

Patients with bilaterally independent temporal lobe seizure onsets and lateralizing data from magnetic resonance imaging (MRI) or positron emission tomography (PET) and Wada testing can also be good surgical candidates. Infrequently, a patient with TLE has rare or infrequent interictal epileptiform discharges.

High-resolution MRI using a T1-weighted, spoiled-gradient recall sequence with contiguous slices perpendicular to the long axis of the temporal lobe is most sensitive in detecting unilateral hippocampal atrophy in approximately 85% of patients. Hippocampal atrophy on MRI correlates with the presence of hippocampal sclerosis.

Other MRI findings include increased signal in the hippocampus on conventional spin echo T2-weighted imaging. Clifford Jack and the Mayo Clinic group reported that MRI with fluid-attenuated inversion recovery (FLAIR) shows an even greater sensitivity for detecting signal changes within the abnormal sclerotic hippocampus than conventional spin echo T2-weighted imaging does. [28, 29]

More recent data from Bernasconi and colleagues indicate that some patients may have entorhinal cortex atrophy in the absence of hippocampal atrophy. [30] Other imaging findings include anterior temporal tip atrophy, thinning of the anterior temporal white matter, particularly the temporal stem, or smaller left temporal lobe volume.

Extratemporal lobe epilepsy

Extratemporal lobe epilepsy also may be treated effectively with epilepsy surgery, particularly when a clearly defined lesion is present on high-resolution MRI. In fact, surgical outcome improves from 20% seizure free in patients without a lesion to 70% seizure free in patients with a lesion.

Extratemporal seizures may have variable seizure semiologies that represent seizure propagation patterns rather than the region of onset; however, these regions usually have selected pathways of propagation that may help to narrowly define the potential epileptogenic region.

Frontal lobe epilepsy

Frontal lobe seizures are typically brief, lasting seconds, with minimal postictal state. They usually occur in clusters, and they occur at night or predominantly in the morning. Unlike the semiology of temporal lobe seizures, that of frontal lobe seizures varies depending on the region of onset. For example, frontal lobe seizures propagate so rapidly that the clinical semiology may represent seizure propagation rather than the region of onset.

The semiology of frontal lobe seizure varies according to where the seizure originates: basal frontal (orbital frontal cortex, gyrus rectus), medial frontal (cingulate cortex, supplementary sensorimotor cortex), dorsolateral frontal (lateral frontal lobe extending posteriorly to the precentral sulcus and includes premotor cortex) or primary motor cortex. However, some clinical features of frontal lobe seizures may suggest a particular region of onset.

For example, seizures characterized by agitation with prominent motor activity and thrashing (ie, hypermotor seizure) suggest orbitofrontal onset. Typically, orbitofrontal seizures are clinically silent when the discharge remains there, and the prominent hypermotor activity becomes apparent after propagation to other parts of the frontal lobe, such as the medial frontal lobes. For example, frontal lobe seizures characterized by staring for several seconds or bilateral tonic facial grimacing suggest medial frontal lobe onset (ie, anterior cingulate cortex).

Seizures arising from the supplementary motor region in the medial frontal lobe anterior to the motor strip (area 6) are characterized by asymmetric tonic posturing of bilateral limbs (usually with a figure 4 posture with 1 arm tonically flexed and 1 arm tonically extended), monotonous vocalization, and variable preservation of consciousness; seizure onset is usually contralateral to the tonically extended limb.

Forced head, eye, and body version suggests onset in the dorsolateral frontal lobe. With dorsolateral frontal lobe seizures, forced head and body version is usually contralateral to the hemisphere of onset. However, a cautionary note is that posterior parietal and occipital lobe seizures can also have head and eye turning that may be versive or cursive (nonforced). One study showed that nonforced head turning at ictal onset without a tonic component or hemi-facial clonic twitching was usually ipsilateral to the hemisphere of onset.

Gyratory seizures are defined as a rotation around the body axis during the seizure at least 180 degrees. [31] Gyratory seizures that begin with forced head version are usually contralateral, whereas gyratory seizures without forced head turning are usually ipsilateral to the hemisphere of onset.

Seizures arising from central regions consist of focal clonic, tonic, or tonic-clonic activity of the face, arm, or leg. In the authors’ experience, seizures arising from the pericentral region include tonic extension of the contralateral limb(s) upper, lower and tonic contralateral facial contraction, or both. Seizures arising from the frontal operculum consist of unilateral facial clonic twitching and profuse salivation, immediately followed by tonic posturing of all limbs.

With most frontal lobe epilepsies, except orbitofrontal epilepsy, secondarily generalized tonic-clonic seizures are common because the frontal lobe neocortex has dense connections to other frontal and extrafrontal regions. In addition, the frontal lobe has dense callosal connections to the contralateral frontal lobe, allowing rapid contralateral propagation and subsequent secondary generalization. Auras are uncommon; when present, they are usually nondescript, except with seizure arising in primary motor cortex, where a primary somatosensory aura can be present.

Parietal lobe epilepsy

Parietal lobe seizures may be associated with a lateralized somatosensory phenomenon in the face or limb(s), vertigo, or a sense of motion. [32] Anterior parietal lobe seizures usually mimic frontal lobe seizures because of spread to frontal lobe regions. Posterior parietal lobe seizures often spread to the temporal lobe, producing temporal lobe semiology indistinguishable from that of seizures with primary origin in the temporal lobe.

Seizures arising from the dominant supramarginal gyrus can present with an aura of a “presence” as though someone is in the room with the person experiencing the seizure. Seizures arising from the nondominant supramarginal gyrus can present with autoscopy, described as a feeling of being outside and above one’s body.

Occipital lobe epilepsy

Occipital lobe seizures may be associated with a stereotyped visual aura consisting of unformed elementary visual phenomena, such as the sparkles of light that some patients describe as “television static.” Unlike a migraine aura, which lasts several (usually >5) minutes, an epileptic visual aura is usually brief, lasting several seconds or as long as 1-2 minutes.

In addition, an epileptic visual aura usually does not migrate across the visual field; however, the visual image may rotate in place. It may consist of colorful shapes that are present in the central visual field. Migraine aura also may consist of colorful shapes, but usually these are in the periphery and not in the central visual field.

Postictal blindness, when present, is a highly localizing finding that suggests occipital lobe onset. Although forced bilateral eye blinking during a seizure is nonspecific with regard to localization, it suggests an occipital lobe seizure origin if it occurs at seizure onset.

When an occipital lobe seizure without loss of awareness (aura) evolves into a focal seizure with loss of awareness, it may be indistinguishable from a temporal lobe seizure or a frontal lobe seizure because of spread of the seizure discharge through the inferior longitudinal fasciculus (ie, temporal propagation) or the superior longitudinal fasciculus (ie, frontal propagation).

Eye version in occipital lobe epilepsy can be either ipsilateral or contralateral to the epileptogenic region, and is likely due to propagation of the region for visually guided saccades in the inferior parietal lobule.

The pathologic substrate of extratemporal lobe seizures includes low-grade gliomas: developmental tumors such as gangliogliomas and dysembryoplastic neuroepithelial tumors, arteriovenous malformations (AVMs), cavernous malformations, encephalomalacia, and malformations of cortical development.