RESUMEN
Lateralization of memory by functional MRI (fMRI) may be helpful for surgical planning related to the medial temporal lobe (MTL). Most fMRI memory studies have calculated lateralization indices (LI) in the MTL from suprathreshold voxels only, but the selection of threshold remains highly arbitrary. We hypothesized that LIs could be reliably extracted from the distribution of voxels encompassing all positive T statistical values, each weighted by their own statistical significance. We also hypothesized that patient LIs that are two or more standard deviations (SD) away from the control group mean LI may be more clinically relevant than LIs that are not compared to control group. Thirteen healthy subjects had memory fMRI, and five epilepsy patients had both fMRI and the intracarotid amobarbital procedure (IAP). The fMRI task consisted of encoding patterns, scenes, and words. We found that normal subjects' LIs extracted from whole weighted statistical distributions tended to lateralize to the left for words, to the right for patterns, and intermediately for scenes, consistent with previous research. Weighted LIs were less variable than those calculated from suprathreshold voxels only. Using this approach, all patients had fMRI memory lateralizations consistent with IAP results. The weighted LIs provided a more clear-cut distinction of patients from the normal group (in terms of SDs from the group mean) than the suprathreshold voxel count approach. Our results suggest that using weighted distributions can be a useful strategy for assessing memory lateralization by fMRI in the MTL.
Asunto(s)
Dominancia Cerebral/fisiología , Epilepsia del Lóbulo Temporal/fisiopatología , Hipocampo/fisiopatología , Procesamiento de Imagen Asistido por Computador/métodos , Imagen por Resonancia Magnética/métodos , Cómputos Matemáticos , Memoria/fisiología , Reconocimiento Visual de Modelos/fisiología , Lóbulo Temporal/fisiopatología , Aprendizaje Verbal/fisiología , Adulto , Lobectomía Temporal Anterior , Mapeo Encefálico , Epilepsia del Lóbulo Temporal/cirugía , Femenino , Hipocampo/cirugía , Humanos , Masculino , Persona de Mediana Edad , Valores de Referencia , Programas Informáticos , Lóbulo Temporal/cirugíaRESUMEN
The ability to effectively identify eloquent cortex in close proximity to brain tumours is a critical component of surgical planning prior to resection. The use of electrocortical stimulation testing (ECS) during awake neurosurgical procedures remains the gold standard for mapping functional areas, yet the preoperative use of non-invasive brain imaging techniques such as fMRI are gaining popularity as supplemental surgical planning tools. In addition, the intraoperative three-dimensional display of fMRI findings co-registered to structural imaging data maximizes the utility of the preoperative mapping for the surgeon. Advances in these techniques have the potential to limit the size and duration of craniotomies as well as the strain placed on the patient, but more research accurately demonstrating their efficacy is required. In this paper, we demonstrate the integration of preoperative fMRI within a neuronavigation system to aid in surgical planning, as well as the integration of these fMRI data with intraoperative ECS mapping results into a three-dimensional dataset for the purpose of cross-validation.
Asunto(s)
Neoplasias Encefálicas/cirugía , Corteza Cerebral/cirugía , Imagen por Resonancia Magnética , Neuronavegación , Cirugía Asistida por Computador , Adulto , Mapeo Encefálico , Neoplasias Encefálicas/fisiopatología , Corteza Cerebral/fisiopatología , Estimulación Eléctrica , Femenino , Humanos , Periodo Intraoperatorio , Masculino , Persona de Mediana Edad , Cuidados Preoperatorios , Resultado del TratamientoRESUMEN
The purpose of this study was to assess the cortical representation of sensorimotor functions in patients undergoing perirolandic epilepsy surgery, focusing on somatotopy, mosaicism, and variability of function in relation to the classic motor homunculus. The authors studied 36 patients in whom intraoperative or extraoperative electrical cortical stimulation to map motor functions was performed. A computer program was devised to register electrode number, stimulation parameters, and response to each stimulus. Electrode position was represented graphically whenever a stimulus was delivered. A total of 43 maps from 36 patients were analyzed. The authors found variations in the organization of M1 (primary motor cortex) in seven patients (19.4%). Four patients (11.1%) presented mosaicism (overlapping of functional areas), two (5.6%) presented variability (inverted disposition of M1 functional areas), and one (2.8%) had both. The results of this study challenge the notion of orderly topographic relationships between the human sensorimotor functions and their representation in the primary motor cortex. These results confirm those of other studies with animals and humans using novel imaging techniques, suggesting that the motor homunculus may not always be considered a definite and absolute representation of M1.