Invasive explorations in children younger than 3 years.

Purpose: In children with drug-resistant focal epilepsy who are candidates for surgery, invasive exploration is sometimes required. However, this is being controversially discussed for children younger than 3 years. The question of its necessity, feasibility and its risks is often raised, since it concerns primarily lesional epilepsy and a lesionectomy might be proposed right away. However, this attitude does not take into account the specificities of epilepsy at this age, including poor specificity of electroclinical semiology and the ongoing myelination challenging the interpretation of magnetic resonance imaging (MRI).

Methods: We retrospectively studied the records of children with drug-resistant epilepsy who were younger than 3 years of age at the time of their invasive exploration at our institution from 2000 to 2009. We reviewed the clinical, imaging and electrophysiological data, and included post-operative outcome for those who underwent surgery.

Key Findings: 26 Children met the inclusion criteria. All had drug-resistant epilepsy that started at an average of 5.2 months (range 0-20 months) with multiple daily seizures in all and developmental delay in 16. The average age at the time of exploration was 21.8 months (range 5-35). In 20 children, subdural electrodes in combination with two or three depth electrodes were implanted, and in six children aged over 2 years a stereo-electro-encephalography (SEEG) was performed. SEEG was considered technically difficult to achieve before the age of 2 years. The tolerance of invasive exploration was good with a 3% morbidity consisting of one subdural hematoma during exploration by subdural electrodes, evacuated without any particular sequelae. In 25 patients, the exploration permitted to propose a focal resection. The surgical intervention was in the frontal lobe in 12 cases, the parietal lobe in six, the occipital lobe in two patients, and the temporal lobe in one child who underwent an additional resection. Four children had a resection of two or three lobes. Five underwent a second surgery, following a second invasive exploration. Histologically, the resected tissue revealed focal cortical dysplasia in 21 cases (including three patients with tuberous sclerosis), two post-ischemic lesions, one dysembryoplastic neuroepithelial tumor, and one gangliglioma associated with dysplasia. The mean postoperative follow-up period was 51 months (range 4-110). For the children operated on twice, follow-up was counted from the second surgery on. Seventeen children (68%) had an outcome of Engel class 1. In five (20%), seizure frequency was significantly improved (Engel class 3). In two of three patients without improvement in seizure frequency (Engel class 4), a new SEEG is planned and the third is presently a candidate for hemispherotomy.

Significance: Invasive exploration is feasible, well tolerated and carries a low morbidity in children under 3 years of age. At this age, it is indicated for drug-resistant lesional epilepsy associated with developmental delay. It permits delineating the lesion, which is not possible with MRI. The choice of the technique is in part age-dependent. The discussion of its indication arises in the same way as in the older child.