Mesial Frontal Epilepsy

Epikpsia, 39(Suppl. 4):S49-S61. 1998 Lippincon-Raven Publishers, Philadelphia 0 International League Against Epilepsy Mesial Frontal Epilepsy Norman K. So Oregon Comprehensive Epilepsy Program, Legacy Portland Hospitals, Portland, Oregon, U.S.A. Summary: The mesiofrontal cortex comprises a number of occur. The task of localization of the epileptogenic zone can be distinct anatomic and functional areas. Structural lesions and challenging, whether EEG or imaging methods are used. Suc- cortical dysgenesis are recognized causes of mesial frontal epi- cessful localization can lead to a rewarding outcome after epilepsy, but a specific gene defect may also be important, as seen lepsy surgery, particularly in those with an imaged lesion. in some forms of familial frontal lobe epilepsy. The predomi- Key Words: Mesial frontal epilepsy-cingulate gyrus- nant seizure manifestations, which are not necessarily strictly Supplementary motor area-Absence seizure-Hypermotor correlated with a specific ictal onset zone, are absence, hyper- seizure-Postural tonic seizure-Epilepsy surgery. motor, and postural tonic seizures. Other seizure types also FUNCTIONAL ANATOMY convolution. Traditional cytoarchitectonics have further subdivided this anterior frontal region. The frontal pole The frontal lobe is the largest lobe in the brain, ac- refers to the anterior most portion of the frontal lobe, but counting for one-third to one-half of total brain volume there is little consensus on how far back this extends. and weight. On the medial surface, the most important One or more curved.sulci are seen anterior and inferior to landmark is the cingulate sulcus (Fig. 1). This runs as an the cingulate sulcus, called the superior and inferior ros- inverted “C” following the contour of the corpus callo- tral sulci. The most inferior band of medial frontal cortex sum. Starting at the region opposite the lamina terminalis is contiguous with the orbital surface of the frontal lobe below the rostrum of the corpus callosum is the subcal- and the various orbital gyri, and can be regarded as part losal area. This merges with the anteriormost extent of of the orbitofrontal cortex. the cingulate gyrus, the long band of cortex lying be- The functional areas on the medial frontal surface that tween the callosal and cingulate sulci. The cingulate gy- have been best studied and defined are the anterior cin- NS curves posteriorly beyond the confines of the frontal lobe with its posterior portion in the parietal lobe, and gulate cortex and the supplementary motor area (SMA). continues around the splenium of the corpus callosum to The anterior cingulate cortex comprises cytoarchitec- become continuous with the parahippocampal gyrus. As tonic area 24, and functionally includes area 32, which is the cingulate sulcus is followed posteriorly, it turns up- immediately dorsal, and subcallosal area 25 (1,2). It has wards into the marginal ramus and reaches the superior the pattern of frontal agranular cortex with prominent convexity. The central sulcus indents the superior surface layer V neurons. Afferent connections are predominant of the brain anterior to the marginal ramus, thus defining from the anterior, dorsomedial, midline, and intralaminar the pre- and postcentral parts of the paracentral lobule. thalamic nuclei, and efferent projections are widespread The paracentral lobule is limited anteriorly by the para- to the primary motor cortex, dorsal and ventral striatum, central sulcus, a short ascending sulcus arising from the the amygdala, thalamus, and periaqueductal gray in mid- cingulate sulcus. , brain tegmentum. Stimulation studies evoke autonomic, The medial frontal gyrus situated in front of the para- visceromotor, or affective sensations, and simple to com- central lobule and beyond the cingulate gyrus is exten- plex movement patterns (3). Motor functions found in sive and is marked by many irregular gyrations. It can the midportion of cingulate gym probably overlap with also be considered the medial surface of the first frontal those of the supplementary motor area. Lesions of the anterior cingulate cortex produce affective and motor neglect, clinically apparent as apathy and akinetic mut- Address correspondence and reprint requests to Dr. N. K. So at Neu- rological Clinic, 1040 NW 22nd Street, Suite 420, Portland, OR 97210, ism, and can lead to relief of chronic pain and obsessive U.S.A. compulsions (1). The posterior cingulate cortex has dif- s49 S50 N. K. SO A FIG. 1. A: Medial surface of the cerebral hemisphere. B: Cyto- architectonic areas on the medial surface of the human cerebral hemisphere after Brodmann (1909). (Reproduced with permission from Gray’s Anatomy 36th ed., Williams PL and Warwick R, Churchill Livingstone, 1980.) ferent cytoarchitectonics and connectivity and appears to limit of this functional area is variable and may overlap participate more in visuospatial and memory functions. with and extend into the cingulate gym. Superiorly, it (4). can extend to the convexity of the superior frontal gyms. The supplementary motor (and sensory) area, or sup- Afferent connections derive from thalamic nuclei ven- plementary sensorimotor area (SSMA), is best viewed as tralis anterior and lateralis and from the dorsomedial a functional rather than a strictly anatomically defined nucleus. Projections are found to the putamen, thalamus, region. It is situated around and contiguous with the pri- pontine nuclei, and the spinal cord (5,9). There are also mary motor area for the lower limbs that occupies the extensive reciprocal connections to many cortical areas. precentral part of the paracentral lobule, and extends Cortical stimulation produces proximal, segmental, uni- about 4-5 cm along the medial frontal gym. It includes lateral or bilateral, tonic postural movements as well as a all or most of the Brodmann medial area 6, and possibly range of somatic sensations. Lesions of the SMA can parts of medial area 8 (5,6). A somatotopic organization cause acute mutism, particularly in the speech dominant has now been established in the human (7,8) as in the hemisphere, and contralateral or bilateral weakness that primate brain, in confirmation of Penfield’s model frequently resolve (see below). (Fig. 2). Most anteriorly is a supplementary eye field, The remaining anterior mesial frontal cortex com- probably in the medial portion of area 8. Motor repre- prises Brodmann’s areas 9 to 12 and is considered to be sentations for the upper limbs precede those for the lower a part of the prefrontal cortex. There are extensive affer- limbs. The supplementary sensory areas are most poste- ent and reciprocal connections to the dorsomedial tha- riorly situated in the medioparietal cortex. The inferior lamic nucleus and efferent projections to other cortical MESIAL FRONTAL EPILEPSY S51 series), followed by gliosis (33%, 33%), and cortical dysgenesis (7.5%, 15.5%). The frequency of tumors in frontal lobe epilepsy treated surgically is probably a good deal higher than the figures above. In a group of 18 patients with SMA epilepsy treated surgically, seven had a tumor, five had evidence of cortical dysgenesis, and three exhibited changes of encephalomalacia (14). Head trauma much more commonly damages the anterior polar or orbitofrontal regions of the frontal lobe rather than its medial surfaces. As cerebral imaging techniques ad- vance, small areas of cortical dysgenesis are increasingly MOTOR recognized in patients with partial epilepsy (15). Until the recent definition of familial forms of tempo- ral and frontal lobe epilepsies with autosomal dominant patterns of inheritance, it has been assumed that partial epilepsies persisting into adulthood are usually symp- tomatic in nature. Although well recognized, the benign partial epilepsies of childhood are conceived of as idio- pathic localization-related epilepsy syndromes unique to childhood, which run a benign course with frequent re- mission later in life. A benign frontal lobe epilepsy of childhood had been proposed (16), akin to benign child- SEN SO RV \( hood epilepsy with centrotemporal spikes. More re- FIG. 2. Somatotopic’organization of the primary and supplemen- cently, children with seizure characteristics similar to tary motor and sensory areas according to Penfield and Jasper (47). (Reproduced from ref. 47 with permission.) those of SMA epilepsy (17), or of suspected medial frontal origin (18) have been described. The affected children exhibited a relatively benign clinical course, and a posi- areas, the basal ganglia, hypothalamus, and periaqueduc- tive family history of epilepsy was common. They very tal gray in the midbrain tegmentum. likely represent the early presentation of autosomal dom- All areas of the mesial frontal cortex have extensive inant frontal lobe epilepsy (19,20). In affected families, connections with the opposite hemisphere via callosal clinical seizure semiology is stereotyped, with features to commissural fibers and with other cortical areas via ar- be discussed below, that are strongly suggestive of sei- cuate fibers. The SMA have relatively dense callosal zures of mesial frontal origin. Scalp ictal EEGs have connections compared to the primary motor cortex. been difficult to localize or are obscured by artifacts. Single shock stimulation studies (10) evoked shorter Interictal PET and SPECT studies confiied regional transcallosal latencies on the order of 10 ms between hypometabolism or hypoperfusion, while ictal SPECT homologous SMA sites compared with longer latencies showed regional

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