A proposed new classification system of hypothalamic hamartomas in the era of stereotactic ablation surgery

Objective: Since the recent development of stereotactic ablation surgery, which can provide good seizure outcomes without limitations in size or location, conventional classification systems have become unsuitable for surgical guidance. The present study aimed to evaluate the validity of a newly proposed classification system focusing on the attachment pattern.

Methods: This retrospective study investigated 218 patients with hypothalamic hamartomas who underwent MRI-guided stereotactic radiofrequency thermocoagulation and were followed for at least 1 year after their last surgery. Hypothalamic hamartomas were classified by their attachments into six subtypes: parahypothalamic-unilateral (PU), parahypothalamic-bilateral (PB), intrahypothalamic-unilateral (IU), intrahypothalamic-bilateral (IB), mixed-unilateral (MU), and mixed-bilateral (MB) types. Clinical features, surgical factors, scales of surgical procedures including numbers of trajectories and coagulations, requirement for a trans-third ventricular approach, reoperation rates, and complication rates were investigated. Seizure outcomes were evaluated separately for gelastic seizures (GSs) and non-GSs.

Results: In 218 patients (131 [60.1%] males, median age at surgery 7.2 [range 1.8-51] years), the hypothalamic hamartomas were classified as PU type in 10 (4.6%), PB type in 11 (5.0%), IU type in 41 (18.8%), IB type in 17 (7.8%), MU type in 40 (18.3%), and MB type in 99 (45.4%) patients. Patients with MB type were significantly younger at GS onset (p < 0.001) and surgery (p = 0.005). The numbers of trajectories and coagulations were significantly greater in MB type (p < 0.001) and the trans-third ventricular approach was more often required in the PB type (5/6, 83.3%, p < 0.001). Seizure outcomes were not different among subtypes. The rate of transient complications was not different among subtypes, but hyperthermia (p = 0.002) and hyponatremia (p < 0.001) were more frequently found in patients with PB and MB types. Prolonged or persistent neurological complications were also not different and were only found in bilateral subtypes.

Conclusions: The new classification predicts clinical features, as well as surgical complexity and complications. Although seizure outcomes were not different among subtypes because the authors' surgical strategy is consistently based on complete disconnection at the border, the new classification could improve seizure outcomes and would be helpful in the appropriate guidance for surgery of hypothalamic hamartomas to provide consistently good outcomes regardless of surgical procedures.