"Epilepsy surgery" versus lesionectomy in patients with seizures secondary to cavernous malformations.

Cerebral cavernous malformations (CCMs) are angiographically occult and consist of a honeycomb-like, low-pressure bed of ectatic vasculature with no intervening neural tissue. Although most cases are sporadic, there are several familial forms. A hemosiderin rim frequently exists from repeated microhemorrhage, leading to reactive cortical gliosis. Because there are no neurons within a cavernous malformation, seizures arise from the complex interactions among neurons, astrocytes, and microvasculature at the margin of CCMs. These lesions are highly epileptogenic: seizures are the most common presentation of CCM, occurring in up to 39% of cases.17 When seizures resulting from a CCM are refractory to anti-epileptic medication, resection of the CCM and the surrounding epileptogenic zone is indicated. The most appropriate surgical treatment of epilepsy secondary to cavernous malformation remains controversial. Certain patients benefit from isolated lesionectomy alone, whereas others need more extensive epilepsy evaluation and resection to achieve seizure freedom. As a result, there have been numerous retrospective series attempting to determine the optimal management paradigm for this condition as related to lesion number, location, seizure type, and duration of epilepsy. Despite these efforts, no clear consensus has been reached. We review the literature regarding the role of comprehensive epilepsy surgery versus isolated lesionectomy in patients with seizures secondary to cavernous malformations and present representative cases. Based on our interpretation of the literature and experience managing these lesions, we speculate on the mechanisms involved in the development and maintenance of epilepsy in these patients as well as synthesize a series of management guidelines. These recommendations are founded in proper patient selection and the integration of microsurgical and neuromonitoring techniques. Critical to our guidelines is collaboration by a highly experienced team of neurosurgeons and neurologists working at a tertiary medical center with a high case volume and using a decision-making paradigm designed to minimize treatment risks. MEDICAL INTRACTABILITY As discussed subsequently, seizure intractability with anti-epileptic medication refractoriness is a risk factor for continued epilepsy despite CCM resection. However, what exactly defines “medical intractability” remains imprecise. Conceptually, it is the inability to achieve satisfactory seizure control despite adequate trials with a sufficient number of anti-epileptic medications at doses that are associated with acceptable side effects. Although seemingly straightforward, several questions regarding “medical intractability” remain disputed in the medical literature: 1. What degree of seizure control is “satisfactory”? Are rare simple partial seizures that do not secondarily generalize on medications acceptable? 2. What is an adequate number of anti-epileptic trials? In the landmark study of Kwan and Brodie,14 nearly 90% of seizure freedom was achieved with the first medication tried if the drug was not stopped for side effects. Only 11% of patients who failed to respond to a first anti-epileptic drug at therapeutic dosage achieved seizure freedom on a second drug. In their discussion, the authors suggest that patients who fail two first-line drugs, who have a correctable epileptogenic structural abnormality, should be referred for surgery. Although many neurologists have historically been hesitant to refer patients with epilepsy to neurosurgeons for evaluation, the strong likelihood of seizure freedom after surgery weighs in favor of surgery over continued medication trials. 3. What are acceptable side effects of anti-epileptic medications? Another important issue that must be considered in evaluating both medical intractability and different outcomes of epilepsy surgery for cavernous malformations is the inability of patients to recognize their own seizures reliably. Well recognized in the epilepsy community, poor self-recognition of seizures confounds success rates reported in surgical series. In one study of patients evaluated in the epilepsy monitoring unit with video encephalography, 30% of patients denied all seizures, and only 23% of patients were aware of all of their recorded seizures.5 In addition, patients with the Copyright © 2008 by The Congress of Neurological Surgeons 0148-703/08/5501-0101