Utility of diffusion tensor imaging studies linked to neuronavigation and other modalities in repeat hemispherotomy for intractable epilepsy

Abstract

<jats:sec> <jats:title>OBJECT</jats:title> <jats:p>Hemispherectomy for unilateral, medically refractory epilepsy is associated with excellent long-term seizure control. However, for patients with recurrent seizures following disconnection, workup and investigation can be challenging, and surgical options may be limited. Few studies have examined the role of repeat hemispherotomy in these patients. The authors hypothesized that residual fiber connections between the hemispheres could be the underlying cause of recurrent epilepsy in these patients. Diffusion tensor imaging (DTI) was used to test this hypothesis, and to target residual connections at reoperation using neuronavigation.</jats:p></jats:sec> <jats:sec> <jats:title>METHODS</jats:title> <jats:p>The authors identified 8 patients with recurrent seizures following hemispherectomy who underwent surgery between 1995 and 2012. Prolonged video electroencephalography recordings documented persistent seizures arising from the affected hemisphere. In all patients, DTI demonstrated residual white matter association fibers connecting the hemispheres. A repeat craniotomy and neuronavigation-guided targeted disconnection of these residual fibers was performed. Engel class was used to determine outcome after surgery at a minimum of 2 years of follow-up.</jats:p></jats:sec> <jats:sec> <jats:title>RESULTS</jats:title> <jats:p>Two patients underwent initial hemidecortication and 6 had periinsular hemispherotomy as their first procedures at a median age of 9.7 months. Initial pathologies included hemimegalencephaly (n = 4), multilobar cortical dysplasia (n = 3), and Rasmussen's encephalitis (n = 1). The mean duration of seizure freedom for the group after the initial procedure was 32.5 months (range 6–77 months). In all patients, DTI showed limited but definite residual connections between the 2 hemispheres, primarily across the rostrum/genu of the corpus callosum. The median age at reoperation was 6.8 years (range 1.3–14 years). The average time taken for reoperation was 3 hours (range 1.8–4.3 hours), with a mean blood loss of 150 ml (range 50–250 ml). One patient required a blood transfusion. Five patients are seizure free, and the remaining 3 patients are Engel Class II, with a minimum follow-up of 24 months for the group.</jats:p></jats:sec> <jats:sec> <jats:title>CONCLUSIONS</jats:title> <jats:p>Repeat hemispherotomy is an option for consideration in patients with recurrent intractable epilepsy following failed surgery for catastrophic epilepsy. In conjunction with other modalities to establish seizure onset zones, advanced MRI and DTI sequences may be of value in identifying patients with residual connectivity between the affected and unaffected hemispheres. Targeted disconnection of these residual areas of connectivity using neuronavigation may result in improved seizure outcomes, with minimal and acceptable morbidity.</jats:p></jats:sec>

Endoscope-assisted hemispherotomy: translation of technique from cadaveric anatomical feasibility study to clinical implementation

“…Previous studies have shown that patients in whom hemispherectomy has failed are likely to have remaining hemispheric connections, particularly anteriorly, and can benefit from reoperation to complete the disconnection. 11 This new technique may raise concerns that complete disconnection may be inadequately evaluated with the endoscopic view compared to the direct visualization provided by classic open procedures; therefore, we have high standards of close inspection and verification of every disconnection step. We also carefully reviewed the intraoperative endoscopic video of every surgery and verified disconnec-tions radiographically with postoperative tractography in our patients.…”

Risk factors and results of hemispherotomy reoperations in children

“…2,5,13 Thus, redo disconnective surgery becomes a good option and is often able to achieve satisfactory outcomes. 2,8 The exact point where disconnection is usually incomplete depends on the technique adopted for hemispheric disconnection and the personal experience of the surgeon. Once this point is identified, more attention must be taken in the initial surgery for this specific step and in the postoperative MRI when looking for reasons of seizure persistence.…”

“…Tractography is particularly helpful for this assessment. 8 From an anatomical point of view, the two hemispheres are connected by commissural fibers basically present in the corpus callosum, the anterior commissure, and the hippocampal commissure. The corpus callosum can be divided into anterior genu (connecting the frontal lobes), rostrum, body (connecting the posterior portions of the frontal lobes and the parietal lobes), and splenium (temporal and occipital connections).…”

Clinical application of advanced MR methods in children: points to consider

“…These detrimental effects are at least partly due to impairing previously unaffected regions of the brain (“kindling”), requiring a speedy decision‐making process . In these children with severe early epileptic encephalopathies of structural origins, both functional and diffusion MRI may play an important role in neurosurgical decision‐making, particularly for initial or repeat hemispherotomy …”