Adult brainstem glioma classification
Adult brainstem gliomas are relatively rare compared to pediatric cases and can be classified based on several criteria, including their location, histology, and molecular features. Here’s an overview of the classification:
1. Location-Based Classification
Midbrain Gliomas: Tumors located in the upper portion of the brainstem.
Pons Gliomas: Tumors situated in the middle part of the brainstem, which are more common in adults compared to midbrain or medullary tumors.
Medullary Gliomas: Tumors found in the lower part of the brainstem.
2. Histological Classification Astrocytomas: The most common type of brainstem glioma in adults, categorized into: Pilocytic Astrocytoma: Typically a low-grade tumor, though it is rare in adults. Fibrillary Astrocytoma: Generally classified as a grade II tumor, often infiltrative. Anaplastic Astrocytoma: A higher-grade (grade III) tumor that is more aggressive and can occur in the brainstem. Glioblastoma Multiforme (GBM): The most aggressive form (grade IV), which can occur in the brainstem but is more common in the cerebral hemispheres. Ependymomas: These tumors can arise from the ependymal cells in the brainstem and are classified as grade II (ependymoma) or grade III (anaplastic ependymoma). 3. Molecular Classification Advances in molecular profiling have identified specific genetic alterations that can help classify and stratify gliomas: IDH Mutant Gliomas: Often associated with lower-grade astrocytomas and secondary GBMs. H3 K27M Mutant Gliomas: More common in pediatric tumors but can occur in adults and are associated with aggressive behavior. Chromosome 1p/19q Codeletion: Associated with oligodendrogliomas, though less common in the brainstem. 4. Age-Based Considerations Pediatric vs. Adult: While many brainstem gliomas are seen in children, adults tend to present with higher-grade tumors like GBM or anaplastic astrocytomas.
Because biopsies are rarely performed, classifications based on the radiological aspect of magnetic resonance imaging results have been proposed to establish treatment strategies and to determine outcomes:
A.- diffuse intrinsic low-grade,
B.- enhancing malignant glioma,
C.- focal tectal gliomas
D.- exophytic gliomas.
Despite significant advances in neuroradiology techniques, a purely radiological classification remains imperfect in the absence of a histological diagnosis. Whereas a biopsy may often be reasonably avoided in the diffuse nonenhancing forms, obtaining histological proof seems necessary in many contrast-enhanced brainstem lesions because of the wide variety of differential diagnoses in adults.
Adult brainstem gliomas are characterized into subtypes depending on clinicopathologic and radiographic characteristics. Among them, brainstem glioblastoma is the most malignant and has the poorest prognosis, with surgical resection for this condition posing a great challenge and risk. Postoperative synchronous radiotherapy and temozolomide (TMZ) chemotherapy, or “Stupp protocol”, is the standard of care for glioblastomas. However, antiangiogenic therapy, which is widely used for different cancers, is now an alternative treatment for malignant tumors. Angiogenesis is one of the pathological features of glioblastoma and is involved in tumor progression and metastases. Besides, previous studies suggested a better response to antiangiogenic therapy in some solid tumors with TP53 mutation than TP53 wide-type. Apatinib is a novel, oral, small-molecule tyrosine kinase inhibitor that mainly targets vascular endothelial growth factor receptor-2 (VEGFR-2) to inhibit angiogenesis. In addition, apatinib can cross the blood-brain barrier and improve encephaledema. A report by Zhu et al. describes the use of concurrent apatinib and dose-dense TMZ in a clinically inoperable patient who had a refractory brainstem glioblastoma with a TP53 germline mutation. He obtained an ongoing progression-free survival (PFS) of nearly 16.0 months after resistance to TMZ maintenance. Due to the patient's circumstances, apatinib and TMZ was considered an effective and safe treatment method 1)