Detection challenges of temporal encephaloceles in epilepsy: A retrospective analysis

Abstract

Temporal encephaloceles (TEs) are herniations of cerebral parenchyma through structural defects in the floor of the middle cranial fossa. They are a relatively common, but only relatively recently identified potential cause of drug-resistant epilepsy. Uncontrolled epilepsy is associated with many negative long term health consequences including a heightened risk of death. The most effective treatment for drug-resistant epilepsy is surgery. One of the most predictive factors associated with successful surgery is identification of an abnormality on imaging. However, TEs can be difficult to detect and are often overlooked on neuroimaging studies. Improving our ability to accurately detect TEs by MRI is an important step in improving surgical outcomes in patients with drug-resistant epilepsy. We performed a review on existing imaging modalities for detecting TEs and report on our attempt to use a voxel-based morphometry (VBM) algorithm to detect TEs in T1-weighted MRIs of 81 patients from a database comprised of 25 patients with confirmed encephaloceles and 56 controls. Our program's sensitivity and specificity were compared to those of two neuroradiologists and two epileptologists using visualization during surgery as the gold standard. On average, the neuroradiologists and epileptologists had sensitivities of 41 % and 58 % and specificities of 81 % and 60 % while our VBM-based approach had sensitivities and specificities ranging from 11 % to 50 % and 0.2 % to 17 %, respectively. This work provides an overview of the different imaging modalities utilized in the detection of TEs and highlights the difficulties associated with their detection for both experienced physicians and cutting-edge computational methods. Our findings suggest that VBM-based methods could potentially be used to enhance clinicians' ability to detect TEs thereby facilitating surgical planning, improving surgical outcomes by allowing for more specific targeting, and bettering the long-term health and well-being of patients with drug-resistant epilepsy secondary to TEs.

Keywords: Encephalocele; Epilepsy; Morphometry; Refractory epilepsy; Temporal encephalocele; Voxel-based.

Figure 1:. TE Neuroimaging Example

(A) T1-weighted MRI showing left-sided TE (red circle) (B) Head CT highlighting defect in temporal bone which represents the same TE (red circle) (C) FDG-PET scan of the same patient which may show subtle area of hypometabolism in the left temporal lobe corresponding to the TE (red circle).

Figure 2:. VBM TE Detection Examples

(A) Example of normalized/corrected T1-weighted image with VBM extension image overlay from 1.5 – 4 SDs (left panel) and without VBM overlay (right panel) highlighting the locations of two TEs in a patient with bilateral TEs. No FP detections are present. (B) Patient with a right-sided TE with VBM overlay. There are two small FP detections in the right temporal lobe superior and lateral to the TE. (C) An additional example of a right TE with VBM overlay. There is a prominent FP detection just lateral to the sphenoid sinus on the right and a few small FP detections in the temporal lobes bilaterally. (Red arrows indicate TP detections, yellow arrows indicate FP detections).