Anterior temporal encephaloceles: Elusive, important, and rewarding to treat.

OBJECTIVE: To investigate the etiology and longitudinal clinical, neuropsychological, psychosocial, and surgical outcome profile of patients with medication refractory epilepsy and temporal encephaloceles with a view to highlight diagnostic clues and management strategies. METHODS: The comprehensive epilepsy program databases at two surgical epilepsy centers from January 2000 to October 2018 were reviewed for this observational study, to identify patients with encephaloceles causing temporal lobe epilepsy (TLE) and treated with surgical resection. Their clinical, radiological, neuropsychological, psychiatric, and surgical data were obtained. Body mass index (BMI) data were also reviewed due to possible correlation between idiopathic intracranial hypertension and encephaloceles. RESULTS: Thirteen patients (eight female) were identified; only three were recognized on initial magnetic resonance imaging (MRI) report. Temporal encephaloceles were identified on the left in eight patients, on the right in three patients, and bilaterally in two patients. One patient had a strong family history of encephaloceles. The median BMI for patients with seizure onset ≤20 years of age was 22.4, whereas for patients with onset >20 years median BMI was 32.6 (P = .06). Five patients underwent a focal lesionectomy, three patients had limited temporal lobectomy, and five patients had standard anterior temporal lobectomy. Median postoperative follow-up was 5.5 years. All but one patient were free of disabling seizures. Nine of ten neuropsychologically tested patients had no discernable cognitive decline postoperatively. Postoperative psychosocial adjustment features were present in four patients. SIGNIFICANCE: Genetic factors and a possible association with idiopathic intracranial hypertension (given female predominance and elevated BMI) may contribute to the causation of temporal lobe encephaloceles. It is notable that a targeted surgical approach in the management of patients with TLE associated with encephaloceles has an excellent long-term clinical and neuropsychological outcome. Subtle encephaloceles should be actively searched for in patients with drug-resistant TLE because they significantly change surgical strategy and prognostication.

Reading difficulty is associated with failure to lateralize temporooccipital function.

OBJECTIVE: Studies of focal epilepsy have revealed abnormalities of language organization; however, little attention has been paid to disorders of reading in this group. We hypothesized that language functional magnetic resonance imaging (fMRI) would reveal differences in language organization between focal epilepsy patients with and without reading difficulties. METHODS: We conducted language fMRI studies of 10 focal epilepsy patients with reading difficulties, 34 focal epilepsy patients without reading difficulties, and 42 healthy controls. RESULTS: We defined regions of interests on the basis of activation patterns on an orthographic lexical retrieval task. Comparison of activations within these ROIs on a second Noun-Verb task revealed epilepsy-related effects (relative to healthy controls: reduced activation in left inferior frontal cortex), as well as greater activation in the right temporooccipital cortex specific to the reading difficulty group. SIGNIFICANCE: These findings identify a focal epilepsy effect in the left frontal region (present in patients with and without reading difficulties), and a functional abnormality specific to the reading difficulty group localized to right temporooccipital cortex-a region implicated in lexicosemantic processing. Our observations suggest a failure of left hemisphere specialization among focal epilepsy patients with reading difficulties.

Impaired verbal associative learning after resection of left perirhinal cortex.

Some patients considered for left temporal lobectomy for epilepsy present with normal verbal learning and no MRI evidence of hippocampal pathology. In order to preserve learning function, the surgical approach in these cases often aims at sparing the hippocampus. Parahippocampal structures, including the left perirhinal region, however, also appear to contribute to some forms of verbal learning. We studied aspects of verbal learning in four patients with left temporal lobe resections that preserved the hippocampus, but which included perirhinal/entorhinal cortices in two cases. Pre- and postoperative T1-weighted MRI scans were spatially normalized and residual mesial temporal structures identified. The two patients whose resection included perirhinal and entorhinal cortices exhibited a marked decrement in the ability to acquire arbitrarily related word pairs that persisted at 12-month follow-up. Word list learning showed an early postoperative impairment, but recovered to normal levels within 12 months. In two patients, resection encompassed anterolateral and inferior temporal neocortex but spared the perirhinal and entorhinal cortices, amygdala and hippocampus. No postoperative change in verbal learning was evident. We concluded that hippocampal-sparing left temporal lobe resections result in task-specific verbal learning deficits when perirhinal/entorhinal tissue is included in the resection.

Differential contributions of the hippocampus and rhinal cortices to verbal memory in epilepsy.

The present study explored the left mesial temporal lobe correlates of verbal memory in patients with temporal lobe epilepsy (TLE). An index of structural integrity, T2 relaxation time, was measured bilaterally in three mesial temporal regions of interest, and correlated with measures of verbal memory. The acquisition of verbal arbitrary relational material was most strongly associated with left perirhinal T2 signal. In contrast, verbal memory consolidation was related to T2 signal in the left hippocampus. Our findings suggest a key role for the left perirhinal region in the uptake of arbitrary linkages that underlie new learning. The hippocampus, on the other hand, is important for protecting newly learned information from the effects of interference. This double dissociation provides a neurocognitive account of the left mesial temporal memory syndrome.

Verbal memory in left temporal lobe epilepsy: evidence for task-related localization.

We explored the hypothesis that components of verbal memory are subserved by separate temporal lobe structures in patients with temporal lobe structures in patients with temporal lobe epilepsy [correction]. Uptake of 18F-fluorodeoxyglucose (FDG) measured by positron emission tomography, hippocampal volume, and memory for arbitrarily and semantically related verbal paired associates were examined in 27 patients with left temporary lobe epilepsy. Scores from memory tests performed outside the scanner were regressed against normalized resting FDG uptake at each voxel. Significant regression was seen in the left perirhinal cortex (Talaraich coordinates x, y, z: -29, 10, -34; p < 0.05) for arbitrarily related word pairs. For semantically related paired associates, significant regression was present in the left inferior temporal gyrus (x, y, z: -48, -18, -24; p < 0.05). In subsequent analyses, mean FDG uptake within a spherical region of interest centered on the perirhinal peak predicted performance on both tasks. Mean FDG uptake in a region of interest centered on the inferior temporal peak made an additional, independent contribution to memory for semantically related pairs. Hippocampal volumes did not explain any additional variance in memory scores. Our findings indicate that heterogeneity in the left temporal lobe structures mediating verbal memory function, and support the view that the perirhinal cortex is an important mnemonic substrate.