Performing Hemispherectomy in Adulthood Doesn’t Compromise Seizure Freedom Rates

Long-term freedom from seizures and functional outcomes for adults following hemispherectomy are similar to those reported in patients undergoing the surgery during infancy or childhood. So finds a newly reported review of Cleveland Clinic experience with the procedure in adults, which also revealed prognostic indicators of postoperative outcomes.

“Hemispherectomy is rarely performed after childhood for refractory epilepsy, when it is feared that risks to language, cognition and motor skills may be too high,” says Cleveland Clinic epileptologist Ahsan N. V. Moosa, MD, primary investigator of the study, which was published in Epilepsia (2019 Nov 2 [Epub ahead of print]) and presented on December 7 at the American Epilepsy Society’s 2019 annual meeting. “But we found that this surgery is also safe and effective after age 16, and we identified factors that can inform preoperative counseling.”

A dearth of adult outcomes data

When indicated for refractory epilepsy secondary to a large, unilateral hemispheric lesion, hemispherectomy is usually performed in infancy or childhood to take advantage of the time of optimal neural plasticity. Long-term seizure freedom rates following hemispherectomy in childhood are reported to be about 66% to 80%. Because the procedure is so uncommonly performed in older age groups, less is known about immediate outcomes in this setting, and no longitudinal data were available.

Study population

This study reviewed 47 consecutive patients who were at least 16 years old when they underwent hemispherectomy between 1996 and 2016 at Cleveland Clinic’s Epilepsy Center. Preoperatively, 93% of patients had seizures either daily or weekly.

The mean age at surgery was 26.4 years, with age cohorts breaking down as follows:

• 11 patients (23%) were 16 to 18 years old
• 16 patients (34%) were 18 to 24
• 20 patients (43%) were 25 or older

Most patients acquired their epileptogenic lesion well before the surgery, as follows:

• 76% before age 2 years (including pre- and perinatally)
• 11% between 2 and 10 years
• 9% between 11 and 16 years
• 4% after age 16

Nearly half of etiologies (47%) were attributed to perinatal stroke. Other causes included malformations of cortical development (15%) and other acquired conditions (30%), including Rasmussen encephalitis, trauma and encephalitis.

Favorable outcomes overall

The following outcomes were found over mean postsurgical follow-up of 5.4 years (median, 2.9 years):

• Seizures improved in the vast majority. At five years post-surgery and beyond, 77% of patients (36 of 47) were classified as Engel I (free of disabling seizures), with outcomes remaining stable for up to 12 years. Of these, 27 remained seizure-free, with four off antiepileptic drugs. The others in this group were taking an average of 1.2 antiepileptic medications, down from 3.2 preoperatively. Five patients (10%) were classified as Engel II or III (some seizure improvement), and six (13%) had no worthwhile improvement (Engel IV).
• Motor function was typically unchanged. Hemiparesis, fine finger movements and ambulatory status were unchanged after surgery in 60% to 75% of patients. A few patients improved, and the others worsened.
• Language function was stable in all but one case. This patient had unexpected expressive aphasia postoperatively. His preoperative Wada testing showed a misleading result of language function in the opposite hemisphere (functional MRI was not in practice at the time).
• Cognitive measures mostly remained stable. Of the 19 patients who completed neuropsychological testing, 17 either stayed the same or improved postoperatively.

Predicting seizure recurrence

Multivariate analysis revealed two factors associated with seizure recurrence after hemispherectomy:

• Acute postoperative seizures
• Contralateral interictal spikes on six-month follow-up EEG

Although acute postoperative seizures are often regarded as transient and attributable to perioperative stresses, Dr. Moosa notes that they may be a predictor of poorer prognosis, especially in patients with severe epilepsy preoperatively. None of the patients who had Engel class I outcomes showed epileptic activity in the contralateral hemisphere postoperatively.

Nevertheless, Dr. Moosa emphasizes, bilateral or generalized epileptiform discharges seen on preoperative EEG should not disqualify a patient from consideration for hemispherectomy; such features were found in one-third of the patients who became seizure-free postoperatively.

Predicting postoperative motor function

In general, better preoperative motor function — and lack of cerebral peduncle atrophy on preoperative MRI (which was usually associated with it) — correlated with worsened motor function postoperatively. This was true for both ambulatory status and hand function.

What’s the role of neural plasticity?

According to Dr. Moosa, it is perhaps not surprising that outcomes of adult hemispherectomy were similar to those of hemispherectomy performed in childhood because most of the adult patients in this cohort experienced their brain injury in childhood.

“One might regard most of these patients as pediatric hemispherectomy candidates who had their surgery in adulthood,” he explains. “Our results suggest that neural plasticity and language transfer across hemispheres are determined by the age at brain injury, not by when surgery is performed.”