Elsevier

World Neurosurgery

Volume 84, Issue 5, November 2015, Pages 1494.e1-1494.e6
World Neurosurgery

Case Report
Evaluation of Posterior Hippocampal Epileptogenicity During Epilepsy Surgery For Temporal Lobe Cavernoma by the Occipital Approach

https://doi.org/10.1016/j.wneu.2015.04.047Get rights and content

Background

Cavernomas frequently are associated with intractable epilepsy. When cavernomas located in the temporal lobe are associated with intractable epilepsy, the hippocampus also may have an epileptic focus. The objective in the present study was to clarify the importance of evaluation of the posterior hippocampal epileptogenicity during epilepsy surgery for posteromedial temporal lobe cavernoma.

Case Descriptions

In this study, we describe 2 rare cases of medically intractable epilepsy in patients with posteromedial temporal lobe cavernomas who underwent surgery via the occipital approach. Using longitudinal insertion of depth electrodes into the hippocampus, we evaluated epileptogenicity in both patients from the cavernoma cavity and its surrounding hemosiderin, as well as from the posterior hippocampus near the cavernoma. We show that the transoccipital approach to the posteromedial temporal lobe is compatible with depth electrode insertion and subdural electrode placement on the temporal lobe, enabling an accurate evaluation of potential epileptogenic zones in the posterior part of the hippocampus. Both patients did not experience any seizures and had no postoperative neurologic deficits, and their cognitive functions were intact.

Conclusions

The transoccipital approach enables the optimization of the extent of posterior hippocampectomy while avoiding unnecessary resection for seizure control. We suggest resecting the posterior part of the hippocampus in addition to the cavernoma and surrounding areas in patients with medically refractory epilepsy due to a posteromedial temporal cavernoma. Tailored systematic resection guided by intraoperative electrocorticography and electroencephalography with a depth electrode was important and necessary in the present cases.

Introduction

Many pathologies are associated with epilepsy, including developmental anomalies, tumors, gliotic regions, and vascular malformations. Cavernomas frequently are associated with intractable epilepsy. When cavernomas located in the temporal lobe are associated with intractable epilepsy, the hippocampus also may have an epileptic focus. It remains unclear whether the hippocampus needs to be removed for effective seizure control in cases of intractable epilepsy associated with temporal cavernoma. Many reports suggest the necessity of resecting the cavernoma along with surrounding hemosiderin and a portion of the hippocampus for cavernomas in the anterior part of the temporal lobe. It also is necessary to choose a proper surgical approach: transcortical, transsylvian-transcisternal, or subtemporal 12, 23, 30, 32. To the best of our knowledge, no study has described the regional distribution of epileptogenicity in the posterior part of the hippocampus in patients with temporal lobe cavernomas (located in the posteromedial temporal lobe).

In this report, we describe 2 rare cases with cavernomas located in the posteromedial part of the temporal lobe. These patients underwent surgery via an occipital supratentorial approach that enabled intraoperative evaluation of epileptogenicity with subdural and depth electrodes.

Section snippets

Patients and Methods

This study was approved by the Sapporo Medical University Institutional Review Board (#25-103).

Case 1

Intraoperative ECoG from the base of the temporal lobe showed occasional epileptiform discharges in the area surrounding the former cavernoma even after resection of the cavernoma (Figure 3A). After resection of the surrounding hemosiderin area, ECoG from the temporal lobe showed comparatively few spikes per minute, and electroencephalography (EEG) from the depth electrode showed almost complete elimination of epileptiform discharges (Figure 3B). No further resection was performed.

Temporal Cavernoma Etiology

The prevalence rate of cavernomas according to several reports ranges from 0.3% to 0.6% of the total population 7, 14, 25. Within the brain, the cavernomas are located in the cerebral hemisphere (66%), the brainstem (18%), the basal ganglia (8%), and the cerebellum (6%) (10). An estimated 10%–20% of patients with cerebral cavernomas have temporal lobe lesions 2, 6, 8. Epilepsy occurs in 23%–50% of these patients and is refractory to medical treatment in 50%–90% of these cases. In case of

The Occipital Approach

The occipital approach facilitates both ECoG from the base of the posterior temporal lobe and depth electrode insertion into the hippocampus. These electrodes enable accurate localization of epileptogenic points and complete lesion removal. One report has described stereotactic insertion of a depth electrode through a burr hole into the hippocampal head and body to evaluate medial temporal lobe epilepsy (31). The occipital approach to the posteromedial part of the temporal lobe offers major

Conclusion

The posteromedial hippocampus can be approached via transoccipital or subtemporal routes. Treatment benefits of cavernoma resection for epilepsy might be disappointing in patients with longer follow-up times because epileptogenic lesions might not be limited to the area surrounding the cavernoma and may be present in the hippocampus as well. The transoccipital approach is useful for reaching the posterior hippocampus for depth electrode insertion to evaluate potential epileptogenic regions and

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  • Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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