Transanterior perforating substance approach to the thalamomesencephalic junction

Lesions in the thalamomesencephalic junction can be reached via an anterolateral approach, interhemispheric approach, transcortical (parieto-occipital lobule) approach, subtemporal approach, supracerebellar approaches, or transsylvian-insular approach. We now describe a new approach, a transanterior perforating substance approach, to this territory.

A 33-year-old man with progressive right arm tremors, mild hemiparesis, and a cavernous malformation of the thalamomesencephalic junction was followed for 5 years. Because of clinical progression, he underwent a left orbitozygomatic approach to the cavernous malformation, which could not be accessed because of a high-riding basilar artery. Hence, a new transsylvian corridor of exposure was developed using frameless neuronavigation. The trajectory, which was dorsal to M1, led through the perforating branches of M1. Care was taken to avoid violating any arterial perforators. To reach the lesion, a small opening into the brain was created near the optic tract.

The cavernous malformation was resected totally. Postoperatively, the patient's tremors were cured. No visual deficits were encountered. Imaging showed a small ischemic stroke in the basal ganglia likely related to manipulation of a perforator. Initially, his hemiparesis worsened, but it improved significantly within 10 months with only a moderate decrease in strength.

The transanterior perforating substance approach effectively allowed access to the thalamomesencephalic junction and was associated with significant morbidity. However, the safety of the approach needs further validation. Neuronavigation is indicated to choose the most direct trajectory through the M1 perforators. Tractography may help protect the optic tract.