Validation of automatic MRI hippocampal subfield segmentation by histopathological evaluation in patients with temporal lobe epilepsy

OBJECTIVE

The present study validates the results of automated hippocampal subfield segmentation with histopathology in epilepsy patients undergoing epilepsy surgery.

METHODS

We performed an automated hippocampal subfield segmentation on presurgical three-dimensional, T1-weighted magnetization Prepared Rapid Acquisition of Gradient Echoes Magnetic Resonance Imaging (MRI) data of 25 patients with unilateral mesial temporal lobe epilepsy due to hippocampal sclerosis (HS), using Freesurfer Version 6.0. The resulting volumes of cornu ammonis (CA) subfields CA1, CA2/3, CA4 and the dentate gyrus (DG) were compared to the histopathological cell count.

RESULTS

We found a significant correlation between histopathology in subregion CA2 and automated segmentation of subregion CA1 (p = 0.0062), CA2/3 (p = 0.004), CA4 (p = 0.0062) and the DG (p = 0.0054), between histopathology in CA3 and automated segmentation of CA1 (p = 0.0132), CA2/3 (p = 0.0004), CA4 (p = 0.0032) and the DG (p = 0.0037), as well as between histopathology in the DG and automated segmentation of CA1 (p = 0.0115), CA2/3 (p < 0.0001), CA4 (p < 0.0001) and the DG (p = 0.0001). The histopathological finding of HS type 1 could correctly be classified in all cases on MRI.

SIGNIFICANCE

The present study shows significant correlations between histopathological evaluation and results of the automated segmentation of the hippocampus, thereby validating the automated segmentation method. As the differential involvement of different hippocampal subfields may be associated with clinical parameters and the outcome after epilepsy surgery, the automated segmentation is also promising for prognostic purposes.

Visual Deficit From Laser Interstitial Thermal Therapy for Temporal Lobe Epilepsy: Anatomical Considerations

BACKGROUND

Laser interstitial thermal therapy (LITT) is quickly emerging as an effective surgical therapy for temporal lobe epilepsy (TLE). One of the most frequent complications of the procedure is postoperative visual field cuts, but the physiopathology of these deficits is unknown.

OBJECTIVE

To evaluate potential causes of visual deficits after LITT for TLE in an attempt to minimize this complication.

METHODS

This retrospective chart review compares the case of a 24-year-old male who developed homonymous hemianopsia following LITT for TLE to 17 prior patients who underwent the procedure and suffered no visual deficit. We examined both features of the surgical approach (trajectory, laser energy, ablation size) and of preoperative surgical anatomy, derived from volumetric tracings of mesiotemporal structures.

RESULTS

For the patient with postoperative homonymous hemianopsia imaging suggested inadvertent ablation of the lateral geniculate nucleus, although the laser was positioned entirely within the hippocampus. This patient's laser trajectory, ablation number, energy delivered, and ablation size were not significantly different from the prior patients. However, the subject with the visual deficit did have significantly smaller choroidal fissure cerebrospinal fluid volume.

CONCLUSION

Visual deficits are the most common complication of LITT for mesiotemporal epilepsy and patients at most risk may have small cerebrospinal fluid volume in the choroidal fissure, allowing heat to spread from the hippocampal body to the lateral geniculate nucleus. When such anatomy is identified on preoperative magnetic resonance imaging, we recommend lowering laser trajectory, decreasing ablation power through the hippocampal body, and using temperature safety markers at the lower thalamic border.