Thanks to sophisticated imaging technology, such as magnetic resonance imaging, many children with drug resistant epilepsy who previously did not have a known cause are now discovered to have small structural abnormalities, or lesions, that cause their epilepsy. A lesion is a damaged or abnormally functioning area of the brain. Lesions can include scars from head injury or infection, as well as brain tumors, abnormal blood vessels, or swollen areas of blood called hematomas.
What is lesionectomy surgery?
A lesionectomy is a surgical procedure that removes a relatively small brain abnormality that causes seizures. The traditional surgical method is to open part of the skull (known as a craniotomy) and then remove the lesion using surgical tools.
Less invasive methods (known as minimally invasive epilepsy surgery) are now in use. In these procedures, access to the brain is made by using thin probes guided by MRI, with smaller craniotomies called “keyhole” craniotomies, or through small burr holes in the skull. Then an endoscope and laser are used to burn or remove the lesion.
What are the different types of lesions?
Lesions are classified as either congenital or acquired.
Congenital lesions include brain malformations that the child develops before birth, such as:
- cortical dysplasia (caused by abnormal brain folding or cellular migration during fetal brain development)
- vascular malformations (angiomas, cavernous malformations, and arteriovenous malformation (AVM)).
Acquired lesions include brain malformations that the child develops after birth, such as:
- brain tumors (astrocytomas, gangliogliomas, and dysembryoplastic neuroepithelial tumor (DNET))
- strokes (strokes can occur before or after the baby is born); and
- brain injuries.
Who benefits from lesionectomy surgery?
Lesionectomy may be an option for children whose epilepsy is linked to a defined lesion and whose seizures are drug resistant. In addition, it must be possible to remove the lesion and surrounding tissue without causing damage to areas of the brain responsible for vital functions, such as movement, sensation, language, and memory. Overall, lesionectomy is associated with excellent results with success rates that are generally better than with surgery performed in patients without discrete lesions.
Lesionectomy vs. lobectomy: How much should be removed?
There is some controversy regarding how much tissue should be removed during lesionectomy surgery. The surgeon will want to remove as much as necessary to stop the seizures (and prevent worsening of any additional conditions, as is the case with tumors or vascular malformations). At the same time, the surgeon will want to do as little as possible to prevent additional damage to the rest of the brain or do anything to harm the child’s functioning.
Often, removing the lesion and some of the surrounding tissue is enough to control the seizures. Sometimes, removal of a significant amount of the tissue surrounding the lesion, including an entire lobe, may be necessary to gain seizure control.
Goals of lesionectomy
Epilepsy surgery causes seizure freedom in about two thirds of patients with mesial temporal lobe epilepsy and in approximately one half of individuals with other causes of focal epilepsy. Seizure freedom is reported more often for some types of lesions such as vascular malformation and glioneuronal tumor than others such as glioma; however, this is in part because there do not exist well-designed studies for every etiology, and because, depending on the cause, the primary goal of surgery might be something other than seizure freedom. For instance, while seizure freedom might be the primary goal in surgery for cortical dysplasia, seizure freedom might be secondary to cancer treatment or hemorrhage prevention in glioma or arteriovenous malformation surgeries, respectively.
In general, seizure freedom is more likely among children with a lesion on MRI (81%) or in histopathologic (73%) findings (looking at the tissue removed surgically under a microscope) compared to children with epilepsy that is not associated with a lesion (45%-46%).
What if they don’t take enough?
While it is tempting to push for the neurosurgeon to take the least amount of tissue possible, not taking out the entire lesion reduces the chances that your child will be seizure free, and potentially increases other risks in the case of vascular malformation or brain tumor. Not getting it all increases the risk of ongoing seizures, cancer progression, or intracranial hemorrhage, depending on the underlying cause.
There is a long-standing debate in cases of cavernous malformation (CM) over lesionectomy alone versus lesionectomy plus corticectomy (taking a specific portion of the cerebral cortex, such as the entire lobe surrounding the lesion) which started when many surgeons observed that many patients become seizure free or close to seizure free without taking the entire lobe. The seizure reduction remained even though the scalp EEG continued to show abnormalities.
On the other hand, there are also cases where removing the CM lesion alone did not result in significant seizure reduction or seizure freedom. This could be due to many things: the presence of an area called the epileptogenic cortex separate from the lesion that is causing seizures, postoperative scar tissue, or inadequate removal of the lesion the first time. The epileptogenic cortex is an area of normal tissue separate from the original lesion that becomes prone to seizures due to being near the seizures caused by the lesion. This concept is also called “kindling”, and is not as well understood in humans as it is in animal models. In order to be certain about how much of the tissue surrounding a lesion to remove, many centers use subdural grids, or invasive EEG techniques, to guide their decision.
Given the high chance of seizure freedom for CM patients from lesionectomy alone, some centers advocate a compromise by starting with a simple lesionectomy and then only performing invasive monitoring before a second surgery if the seizures return.
For all types of lesions, gross total resection (which means removing the entire lesion) may prove to be difficult with a lesion involving eloquent brain (parts of the brain that control speech, motor functions, and senses) or located in a region that is difficult to access. There are tools such as direct cortical stimulation for invasive mapping of eloquent brain that can improve the chances of safely removing the entire seizure-causing lesion.
Questions for the surgeon
What are the advantages/disadvantages of taking only the lesion versus lesion plus surrounding tissue and/or lobe?
Are there additional goals, such as preventing the spread of a tumor, that we should weigh as a way to measure the success of our surgery?
Synopsis of Guidelines for the Clinical Management of Cerebral Cavernous Malformations: Consensus Recommendations Based on Systematic Literature Review by the Angioma Alliance Scientific Advisory Board Clinical Experts Panel
Chang EF, Clark A, Smith JS, Polley MY, Chang SM, Barbaro NM, Parsa AT, McDermott MW, Berger MS. Functional mapping-guided resection of low-grade gliomas in eloquent areas of the brain: improvement of long-term survival. Clinical article. J Neurosurg. 2011;114(3):566–573
Englot DJ, Han SJ, Berger MS, Barbaro NM, Chang EF. Extent of surgical resection predicts seizure freedom in low-grade temporal lobe brain tumors. Neurosurgery. 2012;70(4):921–928.
Englot DJ, Young WL, Han SJ, McCulloch CE, Chang EF, Lawton MT. Seizure predictors and control after microsurgical resection of supratentorial arteriovenous malformations in 440 patients. Neurosurgery. 2012;71(3):572–580.
Englot, D. J., & Chang, E. F. (2014). Rates and predictors of seizure freedom in resective epilepsy surgery: an update. Neurosurgical Review, 37(3), 389–405.
Falconer MA, Serafetinides EA: A follow-up study of surgery in temporal lobe epilepsy. J Neurol Neurosurg Psychiatry 1963;26:154-161.
Morrell F: Secondary epileptogenesis in man. Arch Neurol 1985;42:318-325.
Sanai N, Mirzadeh Z, Berger MS. Functional outcome after language mapping for glioma resection. N Engl J Med. 2008;358(1):18–27.
Te´llez-Zenteno JF, Herna´ndez Ronquillo L, Moien-Afshari F, Wiebe S. Surgical outcomes in lesional and non-lesional epilepsy: a systematic review and meta-analysis. Epilepsy Res. 2010;89(2-3):310-318.
Thapa A, Chandra PS, Sinha S, Gupta A, Singh M, Suri A, Sharma BS. Surgical interventions in intracranial arteriovenous malformations: indications and outcome analysis in a changing scenario. Neurol India. 2009;57(6):749–755.