IN THE NAME OF GOD

Shahram Abootalebi neurologist

localizing and lateralizing value

 Epileptic auras are seizures characterized by subjective sensations experienced by the patient, unaccompanied by any objective clinical manifestations.

 Auras can be characterized by positive or, more rarely, negative sensory phenomena. Paresthesias, visual or auditory hallucinations, a sensation of fear or a feeling of movement when none is occurring are positive phenomena. Numbness of a body part, blindness, deafness or a feeling of inability to move are negative phenomena.  It is now widely accepted that negative as well as positive ictal phenomena are expression of an active seizure discharge.

 aura semiology can still be considered to provide essential clues for the localization and, to a certain extent, lateralization of epileptic seizures.

Aura types Somatosensory auras Somatosensory auras consist of abnormal sensations, involving one or more body parts.Like focal motor seizures, they may migrate from one region to the next, following a somatotopic pattern.

 The most common epileptic somatosensory perceptions are paresthesias (‘tingling’).  Pain and thermal sensations are less frequent.  Sensations referred to the viscera, for example the abdominal aura, and sensations involving the entire body are not classified as somatosensory auras.  The following cortical areas are involved in the generation of somatosensory phenomena:

 Primary somatosensory area (SI)  The primary somatosensory area is located in the postcentral gyrus (Brodmann areas 1, 2, and especially 3b)  The majority of the sensations elicited from SI affect the face, mouth, and hands, less frequently the feet.

 Second sensory area (SII) and insula  The second sensory area is located on the superior bank of the sylvian fissure(inferior frontal gyrus) immediately anterior to the primary face and mouth motor  sensory aura originating in the second sensory area does not differ from the primary sensory region, although they noticed that some patients described a cold sensation.

 The sensations obtained through insular stimulation most often involved the mouth or the upper extremities.  Various types of nonsomatosensory responses (auditory, vegetative, vestibular, olfacto-gustatory, etc.) could only be evoked by insular stimulation.

 Supplementary sensorimotor area (SSMA)  Sensations produced by activation of the SSMA tend to be poorly localized and usually affect more proximal body parts.  They are often bilateral and sometimes described by patients as a whole body aura.

 Localizing value of somatosensory auras:  In patients with somatotopically well-localized somatosensory auras, the epileptogenic zone frequently is in the perirolandic region.

 Since somatosensory auras rarely appear in isolation, the combination with other sensory or motor features and the evolution of subsequent motor patterns can be of help in localization.  The close proximity of second sensory area, insula and temporal lobe explains that sensations produced by activation of these areas are often associated and then progress to motor phenomena of the face or mouth produced by spread into the lower rolandic cortex.

 Sensation of laryngeal constriction with paresthesias affecting large cutaneous territories, eventually followed by dysarthric speech and focal motor symptoms, is highly suggestive of an insular seizure origin.  Somatosensory auras can also occur in temporal lobe epilepsy.

Subtypes of somatosensory auras  Painful auras : primary somatosensory cortex  Thermal auras :They do not provide reliable lateralizing information.  Somatosensory illusions :Somatosensory illusions, such as a sensation of swelling or shrinking of a body part, or a kinesthetic illusion (sensation of movement). Sensations of ocular movement without any objective evidence of movement have been observed in seizures of occipital lobe origin.

Visual auras  Complex visual manifestations that are not the predominant symptom or accompanied by other alterations of perception are better classified as ‘psychic’.  With electrical stimulation, most visual responses can be elicited from the visual areas in the occipital lobe and adjacent border zones with the parietal and temporal lobes.

 Simple visual hallucinations (flashes or static lights) are often produced by activation of the primary visual area (Brodmann area 17).  The surrounding visual association areas (Brodmann areas 18 and 19) are involved in the perception of color, movement and other more complex aspects of vision.

 This subdivision is not exclusive and visual responses can be obtained from many sites along the visual pathways. In a few instances, visual hallucinations have even been evoked by stimulation of the frontal lobe. Simple visual hallucinations, when they are lateralized, always point to an origin in the contralateral hemisphere.

Auditory auras  Auditory auras can manifest as elementary hallucinations of simple sounds (‘ringing’, ‘buzzing’), complex hallucinations like voices or melodies, or auditory illusions in the form of distortion of environmental sounds. Ictal deafness may also occur.  Complex auditory manifestations accompanied by other alterations of perception are better classified as ‘psychic’.

 Auditory phenomena can be produced by stimulation of the primary (Brodmann area 41) and association auditory cortices (Brodmann areas 42 and 22) within the temporal lobe.  It can be assumed that auditory auras, when they are lateralized, are indicative of a contralateral seizure origin.

 In a series of surgical patients with auditory auras, epileptogenic zone was located in the most cases in temporal lobe ( more in neocortex ), but also describe in frontal lobe or the fronto-temporal region.

Vertiginous auras  A variety of symptoms reflecting disturbance of vestibular function (sensation of rotation, sensation of movement in all planes) may occur during epileptic seizures. Typically, they are not accompanied by nystagmus.  There is a strong association with visual and auditory symptoms and this aura, supporting the idea of a symptomatogenic zone close to visual and auditory association areas.

Olfactory auras  Olfactory epileptic auras are rare, constituting about 1% of all auras, and are typically described as unpleasant. They are often associated with other sensory phenomena.  Tumors in the mesial temporal region are the most frequent cause of olfactory auras,but they have been reported to occur also with hippocampal sclerosis or rarely in frontal leison.

 Olfactory sensations can be obtained through electrical Stimulation of amygdala ( the most consistent site), but also seen in stimulation of insula or olfactory bulb.  Olfactory auras have no lateralizing value.

Gustatory auras  Electrical stimulation studies have produced gustatory hallucinations mainly in two areas: the parietal operculum and the anterior mesiobasal part of the temporal lobe.  Gustatory auras are usually not lateralized

Autonomic auras  The term ‘autonomic aura’ refers to sensations suggesting an ictal activation of the autonomic nervous system (e.g., palpitations, difficulty breathing, urinary urge, feeling hot or cold) without objective evidence of altered nervous system function.  The abdominal aura, which likely represents a subtype of autonomic aura, is classified separately because it is one of the most frequent types of aura and often associated with temporal lobe epilepsy.

 Autonomic symptoms can be elicited by electrical stimulation of a number of cortical areas, namely the insula, the anterior portion of the cingulate gyrus, and the SSMA, Structures within the mesial temporal lobe, in particular the amygdala and diencephalon.

 Autonomic auras are frequently observed in seizures arising from the orbitofrontal region, most often due to seizure spread to the temporal lobe.  ictal urinary urge appears to be a lateralizing sign for nondominant temporal lobe epilepsy.  Other types of autonomic auras do not provide lateralizing information.

Abdominal auras  Abdominal (or epigastric) auras are characterized by a sensation of nausea, pain or some kind of undescribable discomfort in the abdominal or periumbilical region.  Electrical stimulation studies suggest that the primary symptomatogenic zone for abdominal auras is located in the insula, even though in other area may also see.( mainly temporal lob).

 Abdominal auras are often thought to be characteristic for patients suffering from mesial temporal sclerosis, but several authors have reported abdominal auras as a manifestation of seizures originating from other brain regions.  The abdominal auras were more frequent in temporal than in extratemporal epilepsy, and more frequent in mesial than in neocortical temporal lobe epilepsy.

 An abdominal aura is associated with temporal lobe epilepsy with a probability of 74%, and the evolution of an abdominal aura into an automotor seizure increases the probability of temporal lobe origin to 98%.  Most patients with extratemporal epilepsies had seizures arising from the frontal lobe. Patients with parieto-occipital lobe epilepsy had abdominal auras associated with visual symptoms, providing an additional clue for localization.

 Painful abdominal auras have been observed in patients with temporal and frontal lobe epilepsies. However, the relative frequency of painful abdominal auras was higher in patients with frontal lobe than in those with temporal lobe seizures.  There is no consensus with regard to lateralization of the abdominal aura.  Exist an abdominal aura combined with ictal vomiting lateralizes to the right hemisphere.

Psychic auras  They can be subdivided into three broad categories, although symptoms often overlap: 1- emotional or affective manifestations (fear, anxiety or elation) 2- distortions of familiarity such as the ‘déjà vu’ or the ‘jamais vu’ phenomenon 3- multisensorial hallucinations including the revocation of complex memories.

 Virtually all psychic reponses were elicited by stimulations of the limbic structures of the temporal lobe.  Forced thoughts, on the other hand, have been attributed to the frontal lobe( forced thinking is a manifestation of expressive language, distinct from experiential phenomena arising from the temporolimbic region.

 Most psychic auras do not provide reliable lateralizing information.  There was no consistent lateralization of psychic phenomena,with the exception of the déjà-vu illusion

Subtypes of psychic auras  Fear :The sensation of fear is said to be characteristic of activation of the amygdala.  Pleasant auras :The localizing value of pleasant ictal sensations such as satisfaction, euphoria, or orgasm-like sensations. Ictal happiness was associated with a discharge in temporal mesiobasal areas. Lateralization in this series was inconclusive. In patient with an orgasmic aura at the start of their seizures, all had temporal lobe epilepsy, and findings suggested a right sided( 83%).

 Distortions of familiarity : Generated by activation of the mesial temporal  Region more precisely the rhinal cortex than by stimulation of other mesial temporal. In particular, déjà vu was associated with stimulation of the entorhinal cortex.  Some evidence suggests that déjà-vu sensations occur (or are reported) more commonly in seizures originating from the nondominant hemisphere.

 Multisensorial hallucinations : It is likely that the revocation of complex multisensorial experiences necessitates activation of a larger cortical network, important parts of which are the mesiobasal limbic cortex, the lateral temporal neocortex and the temporo- parieto-occipital junction.

Nonspecific auras  This term refers to a variety of vague feelings that cannot be readily attributed to one of the previously described aura categories.  Two subtypes of nonspecific auras, cephalic and wholebody auras, have been investigated more in detail.

 Cephalic auras: Cephalic auras include sensations such as nonvertiginous ‘dizziness’, ‘lightheadedness’, an ‘electric shock-like’ feeling, ‘numbness’ or ‘pressure’, which about half of whom had temporal lobe epilepsies.  Cephalic pain did not localize the site of seizure origin and was thought to reflect a vascular mechanism. painful cephalic auras could be seen in patients with seizures originating from any lobe except the perirolandic region.

 Whole-body auras:were able to elicit generalized body sensations from the second sensory area as well as the supplementary sensorimotor area.  whole-body auras occurred in patients with frontal, temporal and multifocal epilepsies.  Whole body auras have no known lateralizing features.

Summary and conclusions  Since it is usually the first symptom to appear in the course of a seizure, the aura is still the best available clinical indicator of the possible location of an epileptogenic zone.  The localization of a presumed epileptogenic zone can only be accomplished through a combination of several semiological, morphological and electrographic pieces of information, of which aura semiology is just one, albeit important element.