Influences of temporal lobe epilepsy and temporal lobe resection on olfaction

Abstract

Although temporal lobe epilepsy (TLE) and resection (TLR) impact olfactory eloquent brain structures, their influences on olfaction remain enigmatic. We sought to more definitively assess the influences of TLE and TLR on olfaction using three well-validated olfactory tests and measuring the tests' associations with the volume of numerous temporal lobe brain structures. The University of Pennsylvania Smell Identification Test and an odor detection threshold test were administered to 71 TLE patients and 71 age- and sex-matched controls; 69 TLE patients and controls received an odor discrimination/memory test. Fifty-seven patients and 57 controls were tested on odor identification and threshold before and after TLR; 27 patients and 27 controls were similarly tested for odor detection/discrimination. Scores were compared using analysis of variance and correlated with pre- and post-operative volumes of the target brain structures. TLE was associated with bilateral deficits in all test measures. TLR further decreased function on the side ipsilateral to resection. The hippocampus and other structures were smaller on the focus side of the TLE subjects. Although post-operative volumetric decreases were evident in most measured brain structures, modest contralateral volumetric increases were observed in some cases. No meaningful correlations were evident pre- or post-operatively between the olfactory test scores and the structural volumes. In conclusion, we demonstrate that smell dysfunction is clearly a key element of both TLE and TLR, impacting odor identification, detection, and discrimination/memory. Whether our novel finding of significant post-operative increases in the volume of brain structures contralateral to the resection side reflects plasticity and compensatory processes requires further study.

Resection of piriform cortex predicts seizure freedom in temporal lobe epilepsy

“…Resection of piriform cortex was safe and there was no impact on neurocognitive performance in regard of extent of resection. Although the role of piriform cortex in initiation and propagation of seizures is well described in animal models, there is little evidence regarding the exact function of piriform cortex in humans 36–38 . Therefore, further research is required to correlate the extent of resection with both seizure as well as neurocognitive outcome.…”

Characteristics of cognitive impairment in adult asymptomatic moyamoya disease

“…The main function of the temporal lobe is not fully understood, but auditory perception is one of its main functions. Some visual skills and language, memory, and some motor functions may depend on the temporal lobe [30,31].…”

Odor identification predicts postoperative seizure control following magnetic resonance–guided laser interstitial thermal therapy

“…Although the study of olfactory performance in epilepsy is limited, previous studies have noted that profound interictal olfactory dysfunction is present in patients with temporal lobe epilepsy ipsilateral to the seizure focus. 13,[15][16][17][22][23][24][25]30 In their pioneering study, Savic et al tested odor discrimination ability in mTLE patients and found that odor discrimination performance was more impaired in the nostril that was ipsilateral to the epileptogenic region. 24 Patients with mTLE made more discrimination errors compared to patients with neocortical seizures and matched healthy controls.…”

“…Given emerging evidence that 40%‐60% of patients do not achieve seizure freedom with MRgLiTT, 10,11 identification of presurgical factors that predict postoperative seizure control is important to identify appropriate candidates for MRgLiTT. Previous studies have observed interictal olfactory dysfunction in TLE, with variable impairment on observed measures of odor detection threshold, odor identification, and odor discrimination 12–16 . A recent investigation by Espinosa‐Jovel et al found that patients with mTLE showed greater baseline olfactory dysfunction than patients with extrahippocampal focal epilepsy and healthy controls 17 .…”

“…Previous studies have observed interictal olfactory dysfunction in TLE, with variable impairment on observed measures of odor detection threshold, odor identification, and odor discrimination. [12][13][14][15][16] A recent investigation by Espinosa-Jovel et al found that patients with mTLE showed greater baseline olfactory dysfunction than patients with extrahippocampal focal epilepsy and healthy controls. 17 The clinical significance of interictal preoperative olfactory dysfunction in the presurgical paradigm for MRgLiTT is not known.…”