LG-67: MIDBRAIN GLIOMAS: A LARGE SERIES OF CLINICALLY AND RADIOGRAPHICALLY HETEROGENEOUS TUMORS

Midbrain gliomas are a group of slow-growing, low-grade tumors that arise from the tectum and/or tegmentum of the midbrain. These have classically been considered indolent tumors that cause clinical symptoms primarily by causing obstructive hydrocephalus due to their location, and can thus be treated with an endoscopic third ventriculostomy alone. In the majority of patients, diagnosis is made based on imaging characteristics, and only a subset undergo biopsy or resection. As a result, little is known about the histopathological and molecular genetic spectrum of midbrain gliomas. We reviewed a series of 60 consecutive patients (age range birth-52 years) with midbrain gliomas treated at our institution over more than 30 years. Anatomically, these tumors appear to fall into two distinct radiographic categories: limited to the tectum and/or the periacqueductal gray matter of the tegmentum, and diffuse tumors that infiltrate the pons and/or thalamus. Twenty-eight of our patients had biopsies or surgical resection, providing tissue for histologic and molecular analyses. Most tumors with available tissue were found to be low-grade gliomas, primarily pilocytic astrocytomas (14 pilocytic astrocytomas, 5 low grade gliomas). In our series, we found that midbrain gliomas are a clinically heterogeneous group of tumors, a subset of which behave quite aggressively and require multiple treatment courses with different treatment modalities including surgery, chemotherapy, and/or radiation therapy. We will describe the clinical, radiographic, and histopathologic and molecular genetic characteristics of this large series of midbrain gliomas in order to identify features that may indicate a more aggressive course.