Newer Operative and Stereotactic Techniques and Their Application to Hypothalamic Hamartoma

A. Simon Harvey

Jeremy L. Freeman

Hypothalamic hamartomas (HHs), or hamartomata, are congenital, tumor-like malformations of the tuber cinereum that are associated with precocious puberty, epilepsy, intellectual disability, and behavioral disturbances. The common seizure type seen in individuals with HH is the gelastic seizure in which patients have uncontrollable laughter. Such seizures often present from the first year of life. In many patients with HH, there is evolution of the epilepsy overtime, with appearance of complex partial, focal motor, atonic and convulsive seizures (1). Such epileptic progression is usually associated with behavioral deterioration, cognitive arrest or decline, and the appearance of generalized spike-waves on scalp electroencephalogram (EEG) (2, 3, 4). Epileptic seizures associated with HH are typically refractory to treatment (1, 2, 3), although some patients experience only minor gelastic attacks without the aforementioned progression (5,6). Patients undergoing surgical evaluation have usually failed treatment with antiepileptic drugs, vagal nerve stimulation, and the ketogenic diet.

HHs are unique epileptogenic lesions that pose challenges for the epileptologist in the course of presurgical evaluation. Because of the deep location, amorphous structure, and complex connectivity of HHs, it is not possible to record interictal or ictal epileptiform activity using scalp electroencephalography. Ictal single-photon-emission computed tomography (SPECT) may show HH hyperperfusion in some patients (7,8), but if seizures are brief or the HH is small, this may not be present. Clinical seizure characteristics and scalp electroencephalography during partial seizures may suggest focal frontal or temporal involvement (1,9), often lateralized in patients with asymmetrically attached HH. Similarly, generalized seizures and spike-wave EEG patterns may suggest a widespread epileptic disturbance of the cerebrum (1,9). Depth EEG recordings may reveal interictal epileptiform activity in the HH, and ictal activity arising in the HH during gelastic seizures has been reported (3,7,10, 11, 12). However, depth EEG recordings do not reveal ictal origin of tonic seizures in the HH (10), nor do they show HH origin of generalized slow spike-waves in patients with SGE (4). Thus, demonstration of seizure origin from the HH may be difficult or impossible, and associated focal or generalized electroclinical features may suggest localized or diffuse cortical origin of seizures.

In recent surgical series, seizure origin in the HH was generally assumed, without confirmation from depth recordings, and focal or lateralized clinical or EEG findings were ignored (3,13, 14, 15, 16). The key elements in the presurgical evaluation of patients with HH and intractable epilepsy should be to (a) determine the type of seizures, the presence of SGE, and the impact of epilepsy on the patient; (b) demonstrate
the anatomy of the HH and exclude any associated cortical malformation; (c) characterize the patient’s cognitive, behavioral, and psychiatric profile; and (d) assess the patient’s preoperative endocrine and visual status (17, 18, 19).

HHs also pose considerable challenges for the epilepsy surgeon, requiring expertise with third ventricular microsurgical, endoscopic, or stereotactic techniques. The postoperative course of patients with HH is different from that of other epilepsy surgery patients, in that many have transient diabetes insipidus and require close attention to fluid management (14,16,17,20); nocturnal tonic seizures may persist for weeks after surgery before gradually “running down” (4,16,21,22); and transient or permanent short-term memory impairment (12,16,23), appetite stimulation (4,12,14,16), hemiparesis (3,12,14,16), and ocular palsy (3,12,14,20) are not uncommon complications of surgery.

The disappointing early results from cortical resection (9), corpus callosotomy (9,24), and attempted hamartoma removal (25, 26, 27, 28), as well as concern about widespread cerebral dysgenesis (29) or epileptogenesis (1,9), dissuaded many clinicians from surgery in patients with HH, despite the disabling and often progressive nature of the seizure disorder. It was not until data was amassed from depth electroencephalography (7,10,11) and ictal SPECT (7,8) supporting the HH origin of at least gelastic seizures, and reports emerged of successful surgical amelioration of seizures with minimal morbidity (7,8,15,21,30, 31, 32), that surgical treatment of HH became more widely adopted (2,33). Currently, several operative techniques are described using open craniotomy (pterional, frontotemporal, frontal, or paramedian) and either microsurgical or endoscopic resection, disconnection, or ablation of the HH. Minimally invasive stereotactic approaches with image-guided endoscopy, radiofrequency thermocoagulation, and radiosurgery are also reported. In 2003, approximately 120 patients with HH undergoing more than 150 operations for epilepsy were reported in the literature, with surgery performed from early infancy (14,23) to young adulthood (mean age at surgery, 11 years). The following is a review of surgical approaches for the treatment of intractable epilepsy associated with HH; some of these novel approaches also have been applied to other epileptogenic lesions.

PTERIONAL AND FRONTOTEMPORAL OPERATIVE APPROACHES

Early approaches to the resection of HH associated with epilepsy (26,27,34, 35, 36) drew on neurosurgical experience with resection of craniopharyngiomas, other suprasellar tumors, and HH associated with precocious puberty. These lateral approaches from below are performed with a pterional or large frontotemporal craniotomy, accessing the HH via a transsylvian, transfrontal, subtemporal, or subfrontal approach (3,14,21,23,30,31), in some cases following removal of the temporal pole and/or orbital cortex. HHs associated with precocious puberty are treatable in this fashion (23,37), as these lesions tend to be pedunculated and lack much of an intraventricular attachment (4,31,38). However, such approaches to epileptogenic HH may be ineffective, as only the subventricular component of the HH can be removed, leaving the intraventricular component attached to the mammillary bodies—a connection that seems to be important for epileptogenesis (2, 3, 4,33). Furthermore, the neurosurgeon encounters pituitary and neurovascular structures, which significantly increase the risk for endocrine complications, stroke, and oculomotor paresis (3,14). In the multicenter series reported by Palmini and colleagues (3), of 12 patients with HH ages 3 to 33 years (mean age, 8 years) undergoing surgery using a pterional or frontotemporal approach, complete resection was achieved in only 2, thalamocapsular stroke occurred in 4, and third nerve palsy was reported in 4, with the neurologic deficits improving or resolving in all patients. Three patients were seizure free, six had a greater than 90% reduction in seizures, and four had a 50% or less reduction in seizures (mean follow-up, 3.3 years). Improvements in behavior, cognition, and development were reported in all patients, regardless of seizure outcome.

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