What brain structures are resected in an interhemispheric (vertical) hemispherotomy?

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Interhemispheric (Vertical) Hemispherotomy: Resected Brain Structures

In interhemispheric vertical hemispherotomy, the resected brain structures are minimal and limited to: the corpus callosum (complete resection), portions of the cingulate gyrus, the inferior part of the amygdala, the uncal gyrus, and the posterior column of the fornix at the trigone. 1, 2

Primary Surgical Goal: Disconnection Over Resection

The fundamental principle of vertical hemispherotomy is functional disconnection rather than anatomical resection, distinguishing it from older anatomical hemispherectomy techniques. 1, 3

  • The procedure aims to disconnect commissural fibers, projecting fibers, and the limbic system from the affected hemisphere while minimizing parenchymal removal. 1
  • This disconnective approach reduces surgical morbidity, blood loss, and complications compared to traditional resective techniques. 4

Specific Structures Resected (Not Just Disconnected)

Corpus Callosum

  • Complete interhemispheric total corpus callosotomy is performed to disconnect commissural fibers between hemispheres. 1, 2
  • The interhemispheric approach provides direct visualization and anatomic control of the corpus callosum, which is a frequent site of incomplete disconnection in other techniques. 2

Cingulate Gyrus

  • Corticotomy on the cingulate gyrus is performed to access the lateral ventricle after corpus callosum section. 1
  • Part of the cingulate gyrus is removed to create the surgical corridor for deeper disconnection. 4

Amygdala and Uncal Gyrus

  • The inferior part of the amygdala and uncal gyrus are removed at the anteromedial side of the hippocampus. 1
  • This resection exposes the basal cistern and disconnects the hippocampus and amygdala from the limbic system. 1

Posterior Column of Fornix

  • The posterior column of the fornix at the trigone of the lateral ventricle is resected to complete limbic system disconnection. 1

Structures Disconnected But NOT Resected

Hippocampus

  • The hippocampus is disconnected at the amygdala and atrial segment of the fornix but is NOT resected in modern vertical hemispherotomy. 5
  • Recent evidence demonstrates that hippocampal resection (as part of anterior temporal lobectomy) provides no additional benefit for seizure control compared to disconnection alone. 5
  • Both hippocampal resection and disconnection groups achieved similar Engel outcome scores (p = 0.53) in a large bicentric study. 5

Thalamus and Projecting Fibers

  • The lateral border of the thalamus is cut from posterior to anterior until exposing the inferior horn of the lateral ventricle and hippocampal head, but the thalamus itself is not resected. 1
  • This maneuver disconnects projecting fibers without removing thalamic tissue. 1

Insula

  • The insula is NOT resected in vertical hemispherotomy, which is a major advantage over lateral peri-insular approaches. 3
  • Complete hemispheric disconnection in patients with significant insular involvement is possible without the complications usually reported with insular resection techniques. 3

Technical Advantages of Minimal Resection

  • The interhemispheric approach minimizes cortical resection and blood loss compared to lateral approaches. 4
  • Intraoperative blood transfusion requirements are significantly lower with vertical hemispherotomy (only 5% of patients required blood replacement in one series). 3
  • The procedure avoids opening and dissecting the subarachnoid space of the Sylvian fissure, reducing surgical trauma. 3

Common Pitfall to Avoid

  • Incomplete disconnection of the corpus callosum is the most frequent cause of seizure relapse, occurring in approximately 10-15% of cases. 2
  • The interhemispheric vertical approach provides superior anatomic control to ensure complete callosal section compared to lateral approaches. 2
  • Postoperative MRI should confirm complete disconnection; incomplete disconnection on imaging warrants reoperation even in seizure-free patients. 2

References

5
Research

Hippocampal resection during hemispherotomy: is it needed?

Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery, 2024

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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