Rationale: Classical classifications of hypothalamic hamartoma (HH) aimed to be indicators for treatment options because traditional neurosurgical treatments have limitations by location or size of HH. As recent trend of ablation surgeries, i.e., laser interstitial thermal therapy or radiofrequency thermocoagulation, become the first line treatment, disconnection at the border between HH and the hypothalamus has a significance for elimination of gelastic seizures (GSs). The present study aims to propose a new classification system focusing on patterns of attachment to the hypothalamus and to validate its usefulness by clinical characteristics and surgical strategies.
Methods: The new classification system is based on the reference line through the floor of third ventricle and the base of hypothalamus (R) as well as the midline between the bilateral mamillary bodies. HH below the line-R is classified into the parahypothalamic type (P) and that above the line-R as the intrahypothalamic type (I). HH located both above and below the line-R is classified as mixed type (M). The midline is the reference for which HH attached to the bilateral hypothalamus. According to this system, epileptic HHs are classified into six categories; parahypothalamic-unilateral (PU), parahypothalamic-bilateral (PB), intrahypothalamic-unilateral (IU), intrahypothalamic-bilateral (IB), mixed-unilateral (MU), and mixed-bilateral (MB) types. In 208 patients with HH who underwent stereotactic radiofrequency thermocoagulation (SRT), clinical features, surgical procedures, and seizure outcomes were investigated by subtypes.
Results: The population in each subtype was 10 (4.8%) in PU, 11 (5.3%) in PB, 42 (20.2%) in IU, 16 (7.7%) in IB, 38 (8.3%) in MU, and 91 (43.8%) in MB, respectively. MB type showed youngest ages at surgery (median, 5 y), GS onset (0.3 y), and other types of seizure (nonGS) onset (2.7 y) among subtypes. Maximum diameter is largest in MB type (22 mm). Behavioral problems and intellectual disabilities were more found in MU (63.2% and 52.6%) and MB (68.1% and 59.3%). Precocious puberty accompanied more in PU (70.0%), PB (63.6%), and MB (49.5%) subtypes. MB type required significantly large scale of surgery; most trajectories (6) and coagulations (13) (P< 0.001). MB and PB subtypes had significantly higher rates of requirement of bilateral or trans-third ventricular approach (47.3% and 54.6%, respectively) (P< 0.001). However, reoperation rates were not different among subtypes (10.0-35.7%). Furthermore, seizure outcomes were also not different among subtypes: GS freedoms; PU, 90.0%
; PB, 90.9%; IU, 95.2%; IB, 93.8%; MU, 89.5%; MB, 86.8%. NonGS freedom; PU, 85.7%; PB, 66.7%; IU, 77.4%; IB, 83.3%; MU, 81.1%; MB, 77.8%.
Conclusions: The new classification system correlates to clinical features and surgical procedures, especially MB and PB types requires special consideration in procedures. Surgical outcomes are not different because the surgical concept to disconnect at the border is consistent and SRT is appliable to every type or size of HH.
Funding: MHLW Research program on rare and intractable diseases, grant number JPMH20FC1039