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Extrapial Hippocampal Resection in Anterior Temporal Lobectomy for Drug-Resistant Temporal Lobe Epilepsy

Key findings

  • This retrospective study of 62 patients investigated the safety of a previously undescribed surgical technique for hippocampal resection in anterior temporal lobectomy for treatment of drug-resistant temporal lobe epilepsy
  • Morbidity was lower than that reported from most case series, with three patients (4.8%) exhibiting MRI evidence of interruption of minor vascular supply to the thalamus, none of whom experienced a permanent deficit
  • 94% of patients were seizure-free 12 months after surgery and 63% remained seizure-free at 40 months
  • In every case, it was possible to obtain an en bloc specimen to send for clinical neuropathology evaluation

Randomized controlled trials have demonstrated the superiority of anterior temporal lobectomy over the medical treatment of drug-resistant temporal lobe epilepsy, as reported in JAMA and The New England Journal of Medicine. However, alternatives such as neurostimulation are being used increasingly often, resulting in a growing inability to collect intact hippocampal specimens and obtain the correct histopathologic diagnosis.

Mark Richardson, MD, PhD, director of the Functional Neurosurgery Program at Massachusetts General Hospital, developed a variation of the standard anterior temporal lobectomy, an extrapial approach via an opening of the crural and ambient cisterns using microvascular techniques. This facilitates complete resection of the hippocampus.

In Operative Neurosurgery, Dr. Richardson and colleagues describe and illustrate the technique in detail. They also report on a retrospective review in which the approach was safe and appeared to optimize seizure outcomes.

Study Methods

The researchers used aprospectively collected database to review 62 patients with drug-resistant temporal lobe epilepsy for whom Dr. Richardson performed anterior temporal lobectomy using the extrapial approach to hippocampectomy between October 2011 and February 2019.


  • Infection requiring reoperation: 1 patient
  • Posterior thalamic infarcts on postoperative MRI: 3 patients (2 experienced temporary contralateral upper extremity motor weakness and 1 was asymptomatic); the infarcts probably reflected vascular injury when performing microvascular detachment of the hippocampal arterial supply from the cisternal space
  • Postoperative quadrantanopia: 11 patients (not all underwent recommended postoperative visual field testing)

There were no deaths during the mean follow-up period of 24.6 months.


  • Seizure freedom (Engel class I): 94% of patients at 12 months, 89% at 24 months, 63% at 40 months (longest follow-up)
  • Favorable outcome (Engel class I/II): 95% at 12 months, 94% at 24 months, 86% at 40 months


The rates of infarct compare favorably with those reported in other studies of temporal lobectomy, and the rates of seizure freedom are at the high end of the range reported previously. Unlike subpial approaches, the extrapial approach allows no possibility of inadvertently leaving behind portions of the hippocampal body, which may facilitate favorable outcomes.

In every case, it was possible to obtain an en bloc specimen in which the subiculum and all hippocampal subfields were preserved. A portion was banked for further neuroscientific analysis. These specimens will allow research into how the results of noninvasive imaging relate to the cellular substrate.

of patients who underwent an extrapial approach to hippocampectomy in anterior temporal lobectomy were seizure-free at 12 months

of patients who underwent an extrapial approach to hippocampectomy in anterior temporal lobectomy were seizure-free at 40 months

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Jimmy C. Yang, MD, and Sydney S. Cash, MD, PhD, of the Department of Neurology, and colleagues made microelectrode recordings during neurosurgeries and identified cortex microdomains that seem to contribute to the seizure network—an important step toward understanding how to develop better treatments for epilepsy.


Neurologists at Massachusetts General Hospital have demonstrated that measuring different types of connectivity in the brain can have entirely different implications for the interpretation of brain function as well as for understanding connectivity relative to clinical diagnoses.