Complete hemispherotomy leads to lateralized functional organization and lower level of consciousness in the isolated hemisphere

Interhemispheric Vertical Hemispherotomy: Technique, Outcome, and Pitfalls-A Bicentric Retrospective Case Series of 39 Cases

BACKGROUND AND OBJECTIVES

When seizure onset affects a whole hemisphere, hemispheric disconnections are efficient and safe procedures. However, both lateral peri-insular hemispherotomy and vertical paramedian hemispherotomy approaches report a failure rate around 20%, which can be explained by residual connections giving rise to persistent seizures. In this study, we present the interhemispheric vertical hemispherotomy (IVH), a technical variation of the vertical paramedian hemispherotomy approach, that aims to increase seizure control avoiding residual connections while exposing the corpus callosum.

METHODS

This is a retrospective study of IVH in two centers, with analysis of clinical and MRI data and outcomes. A detailed description of the technique is provided with a video.

RESULTS

IVH was performed in 39 children. The mean age at surgery was 7.2 years, and etiologies were as follows: malformations of cortical development (n = 14), Rasmussen's encephalitis (n = 10), stroke (n = 10), post-traumatic (3), and Sturge-Weber Syndrome (2). Hemispheric disconnection was complete on postoperative MRI in 34 cases. There was no mortality, hydrocephalus occurred in one case, and subdural collection occurred in four cases. A second surgery was performed in four cases because of seizure relapse (n = 3) and/or incomplete disconnection on MRI (n = 4). With a mean follow-up of 3.2 years, International League Against Epilepsy class I epilepsy outcome was obtained for 37/39 patients.

CONCLUSION

IVH is a safe and effective variation of the vertical approaches for hemispheric disconnection. It allows a good exposure and anatomic control of the corpus callosum, which is a frequent site of incomplete disconnection. IVH may be limited by the thalamic volume and the ventricular size, notably in hemimegalencephaly cases.

Case Report: Resting-State Brain-Networks After Near-Complete Hemispherectomy in Adulthood

Objectives

Understanding the dynamics of reorganized network-level brain functions after hemispherectomy is important for treatment, prognostication, and rehabilitation of brain injury, but also for investigating questions of fundamental neurobehavioral interest: How does the brain promote consciousness despite loss of one hemisphere?

Methods

We studied resting-state functional connectivity (RSFC) in a high-functioning middle-aged man 6 years after functional hemispherectomy following malignant middle cerebral artery infarction, and we compared results to RSFC in 20 healthy controls.

Results

Our analysis indicates increased between-network connectivity for all seven networks examined in the patient's preserved hemisphere, compared to healthy controls, suggesting a shift toward increased between-network connectivity following near-complete loss of one hemisphere during adulthood.

Conclusions

These data corroborate and extend recent findings of increased between-network connectivity in the remaining hemisphere after surgical hemispherectomy for intractable epilepsy during childhood. Our results support a neuroplasticity model with reorganization of distributed brain connectivity within the preserved hemisphere as part of the road to recovery after brain injury, as well as recovery of consciousness and cognitive functions, after hemispherectomy.

Hard but so valuable to define hard criteria for empirical theories of consciousness

I congratulate Doerig, Schurger, and Herzog for their stimulating contribution for an empirical approach to theories of consciousness. I must also admit that the excellent way Global Neuronal Workspace Theory (GNWT) I've contributed to since 2001 passes the test they designed may contribute to my enthusiasm (see Table 1 of their article). In this Comment, I focus on two points: highlighting a potential epistemological weakness of their approach, and proposing how GNWT can solve the 'small network argument.'