Mesial Temporal Lobe Seizures

Mesial temporal lobe seizures are by far the most common seizures originating within the temporal structures and are the single most common seizure type seen in the adult population. They represent the typical complex partial seizure.

Mesial temporal lobe seizure are often preceded by an aura, which not uncommonly also occurs in isolation (54,55). The most common aura are epigastric sensations or abdominal auras, which the patient often describes as a rising sensation, nausea, "butterflies in the stomach," or a feeling like being in an elevator (54,56,57). This type of aura is highly correlated with mesial temporal seizure

Anatomy Temporal Lobe Mri

Anatomy of the temporal lobe shown on MRI. Typical finding of hippocampal atrophy on the right.

onset; however, exact localization within the mesial temporal structures is still controversial (56,58-60). Other auras associated with mesial temporal seizure onset include olfactory sensations, gustatory sensations, ictal fear, déjà-vu, and jamais-vu sensations.

Olfactory sensations can be pleasant or unpleasant (e.g. the smell of burned rubber). They are thought to be associated with seizure onset in the amygdala (61). Gustatory auras are usually described as an unpleasant taste and are associated with insular seizure onset (62) (see also Chapter 10). Ictal fear occurs most often in temporal lobe epilepsy, but is also described with frontal seizure onset (12,63,64). Intracranial EEG recordings and volumetric MRI measurements suggest major involvement of the amygdala in the generation of ictal fear (65,66). However, intracranial EEG recordings have shown that orbitofrontal networks may also play a role (67). Ictal epileptic fear can easily be mistaken as a psychiatric disorder, and the definite relationship to panic disorders remains undefined. It has been reported that a patient with temporal lobe epilepsy have a definite increased incidence of panic disorders (68).

Déjà-vu and jamais-vu sensations are other expe-riental auras associated with temporal lobe epilepsy.

Déjà-vu sensations consist of a strange feeling of familiarity (69). The patient feels like he has lived through the same scene or situation previously. He may describe an intense feeling of familiarity with the situation or a scene. The exact localization of déjà-vu sensations within the temporal lobe remains still controversial, but the parahippocampal gyrus and the neocortical connections were suggested as the generators (70). Some intracranial electrical studies suggest an origin of the lateral temporal neocortex with spread to the mesial temporal structures (69). Other suggest pure mesial temporal onset (71). To distinguish epileptic déjà-vu from psychogenic phenonema, it is often helpful to obtain a clear and definite description from the patient about his sensations. Quite frequently, patients with psychogenic nonepileptic seizures are aware of déjà-vu sensations and list them as one of their symptoms. But they are unable to describe their sensations, or they give descriptions of other sensations. Jamais-vu sensations are related feelings of a sense of unfamiliarity or strangeness in a familiar situation. This is overall a rare occurrence in epileptic disorders. It probably localizes to the same brain structures as déjà-vu sensations.

A typical mesial temporal lobe seizure after an aura progresses to altered consciousness and behavioral arrest. The patient may be partially responsive, but is usually amnestic afterwards. Oroalimentary automatisms consisting of chewing, lip smacking, and lip pursing are common. Manual, semipurposeful automatisms, if unilateral, occur ipsilateral to the side of seizure origin (72). The hand contralateral to the seizure focus may assume a dystonic posture (72,73). Manual automatisms consist of semipurposeful fumbling, picking, or rubbing movements of the hands. Dystonia refers to a forced posturing of the hand with a clear tonic component. Autonomic changes, most often pupillary dilation, may occur. The pupil ipsilateral to the seizure focus is dilated and unresponsive (72). Vocalization is frequent. Vocalization originating in the temporal lobes is less dramatic and emotional than that vocalization originating in the frontal lobes. The patient mumbles or talks without making sense ("gibberish"). Postictally, the patient is confused, and if the seizure originates in the dominant hemisphere, postictal aphasia can be demonstrated. With right temporal seizure onset, the patient can relatively rapidly speak again. With left-sided seizure onset, the patient may, for example, be able to show the purpose of tools or items but is unable to name them. Seizures can secondarily generalize, often out of sleep (34), and have a mean duration of 70 to 90 seconds (72).

Whereas many different lesions in the mesial temporal structure can give rise to mesial temporal lobe seizures, mesial temporal sclerosis is the most commonly observed pathologic finding. Pathologically, pyramidal cell loss occurs in the CA1 and CA3 region of the hippocampal structures, the origin of which is unclear (74). Patients with mesial temporal seizures have similar risk factors for epilepsy, specifically prolonged febrile seizures in early childhood and similar MRI findings. MRI reveals hippocampal atrophy with the affected hippocampus being significantly smaller than the unaffected (Figure 2.6). Temporal lobe seizures associated with mesial temporal sclerosis are considered a specific epilepsy syndrome, referred to as mesial temporal lobe epilepsy (MTLE), and are amenable to epilepsy surgery (75).

Clinically obvious mesial temporal lobe seizures are fairly distinct in their clinical presentation and are highly stereotyped. Therefore, they are easily distinguishable from nonepileptic seizures or other psychiatric disease such as panic attacks. On ictal EEG, a clear build-up of rhythmic theta activity occurs over the affected temporal lobe, so they are unequivocally distinguishable from nonepileptic events. However, differentiation between isolated epileptic auras and panic attacks can be more difficult, because the patient is merely describing subjective sensations, and ictal EEG can be completely normal during epileptic auras. However, auras in isolation as pure manifestation of temporal lobe epilepsy are uncommon and often progress to clinically manifest temporal lobe seizures.

Mesial temporal lobe seizures are also observed with seizure onset in the medial, posterior, orbitofrontal region. This orbitofrontal region is anatomically connected to the mesial temporal structures, and clinical manifestations reflect ictal spread to the mesial temporal structures. It has been shown that the orbitofrontal region may remain clinically silent until spread occurs to the mesial temporal structures (16,76).

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