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.

Occipital calcified pseudoneoplasms of the neuraxis (CAPNON): understanding a rare pathology.

Calcifying pseudoneoplasms of the neuraxis (CAPNON) are rare and typically benign lesions that can occur anywhere within the central nervous system. Aetiology of this lesion is unclear and surgical removal is usually curative. We present a 24-year-old male patient with a history of occipital migraines who was admitted after sudden onset seizure and loss of vision. CT and MRI demonstrated a small calcifying lesion in the right temporo-occipital lobe. The patient underwent gross total resection of the tumour mass and pathological analysis revealed a CAPNON. The preoperative diagnosis of CAPNON remains difficult due to unspecific radiological findings, yet a clear understanding of characteristic pathological findings and prognosis of CAPNON remains paramount.