Age of seizure onset, functional reorganization, and neuropsychological outcome in temporal lobectomy

Abstract

Patients with early onset seizure disorder tend to have less cognitive decline following surgical resection than patients with late onset seizure disorder. Differential opportunity for presurgical cerebral functional reorganization has been proposed to account for this "age of onset" effect. However, the relationships between age of seizure onset, functional organization, and neuropsychological outcome remain incompletely understood. To shed additional light on these issues, we investigated 66 patients with anterior temporal lobectomies (37 left; 29 right), all of whom completed comprehensive neuropsychological assessment prior to and following surgical resection. The sample was divided into two groups: 34 patients with early onset (EO) epilepsy and 32 patients with late onset (LO) epilepsy. We found the typical age of onset effect: post-surgically, EO patients demonstrated relatively better outcome in multiple neuropsychological domains, especially verbal memory, compared to LO patients. Based on presurgical Wada testing, 23 patients were classified as having traditional cerebral functional organization (TFO) and 35 were classified as having nontraditional cerebral functional organization (NTFO). The NTFO group had an earlier age of seizure onset than the TFO group, and NTFO was more frequent in EO patients (70%) than LO patients (50%). NTFO patients demonstrated relatively better post-surgical outcome in several neuropsychological domains, compared to TFO patients. Our findings are consistent with the notion that functional reorganization may be an explanatory factor for the better neuropsychological outcome of EO epilepsy patients following anterior temporal lobectomy.

Hippocampal volumetry and functional MRI of memory in temporal lobe epilepsy

“…The early onset group (EO) was defined by onset of continuous seizures at or before age nine and the late onset group (LO) was defined by onset of continuous seizures after age nine, in accordance with the use of this variable in the epilepsy literature [21]. …”

“…Early onset may be associated with neural reorganization which can result in use of brain areas that are not optimized for certain cognitive functions, but may also contribute to the better post-surgical outcome due to reduced risk of removing functioning brain tissue. Likewise, later onset may be associated with less reorganization with resulting better pre-surgical performance, but also a greater post-surgical decline due to resection of functional brain regions [18, 21, 22]. Establishing a relationship between these presurgical variables and structural and functional imaging measures would help to establish the role imaging can play in contributing to the pre-surgical evaluation.…”

Recent Innovative Studies of Memory in Temporal Lobe Epilepsy

“…Early temporal lobe lesions, such as hippocampal sclerosis and neural migration disorders, often determine reorganization of brain functions (e.g., atypical distribution or incomplete hemispheric dominance of language competence; Griffin and Tranel 2007;Stafiniak et al 1990). Moreover, temporal lobe regions spared by surgery may remain basically damaged by pre-existing pathology or seizure-induced structural alterations confounding both the preoperative and postoperative localizing contribution of memory patterns (Jones-Gotman et al 1997b).…”

Investigating the Anterior Temporal Lobe With Direct Intracranial Recordings

“…The role of the ATL in naming is most obvious to clinicians since deficient name retrieval is a frequent complaint after language-dominant CAH 24, 25 . The nature of naming dysfunction after language-dominant CAH is well described by numerous studies 6, 7, 23, 26, 27 .…”