Transsylvian, Carotid-Oculomotor Triangle Approach for Resection of a Rapidly Enlarging Midbrain-Pontine Cavernous Malformation: 3-Dimensional Operative Video.

Cavernous malformations (CM) of the anterior midbrain are best reached through an orbitozygomatic (OZ) approach with removal of the orbital rim and wide Sylvian fissure dissection. Our surgical video demonstrates this approach to resect a ruptured CM in a 36-yr-old woman who presented with headaches, left face and left arm paresthesias/weakness, and right-sided partial oculomotor nerve (CN III) palsy. Initial magnetic resonance imaging (MRI) showed a midbrain CM, and the patient was managed conservatively. However, 1 wk later, she presented again with worsened left arm and leg weakness and complete CN III palsy. Seven Tesla MRI demonstrated a larger hematoma, and the CM with new mass effect and upper pons extension. The patient underwent a right modified OZ craniotomy and Sylvian fissure split under guidance of intraoperative neuronavigation and with neuromonitoring. The carotid-oculomotor triangle and the Liliequist membrane were dissected to access the midbrain, and CN III was identified and followed posteriorly to the midbrain. Confirmed with neuronavigation, a longitudinal incision of the midbrain was performed, and the CM was encountered. The hematoma and CM were debulked and removed in a piece-meal fashion, leaving hemosiderin-stained brain intact to prevent unnecessary additional damage to the midbrain. Postoperative MRI confirmed gross-total resection, and the patient's weakness recovered substantially. In this video, we demonstrate that the brainstem is no longer forbidden surgical territory, and show how the use of neuronavigation for surgical planning, positioning, and approach, in addition to the understanding of safe entry zones and meticulous microsurgical technique have made safe and effective surgery on the brainstem possible.