Adult deep midline pilocytic astrocytoma: A case report highlighting diagnostic and management challenges with brief literature review

Adult deep midline pilocytic astrocytoma (PA) is a rare, slow-growing World Health Organization (WHO) grade 1 central nervous system tumor arising in deep structures such as the brainstem, hypothalamus, or thalamus. Recognition of this entity is important because its deep location often precludes complete surgical resection. Adults may experience higher recurrence rates than children, and misdiagnosis can lead to inappropriate or overly aggressive treatment.
We report the case of a 34-year-old man with progressive headaches, nausea, and diplopia. Neuroimaging revealed a cystic hypothalamic mass with an avidly enhancing mural nodule extending toward the optic chiasm. Histopathologic examination demonstrated the classic biphasic pattern and Rosenthal fibers characteristic of PA. The tumor showed a low Ki-67 proliferation index. Molecular testing was negative for IDH1 mutations and the common BRAF-KIAA1549 fusion. Because of the tumor location, maximal subtotal resection was performed, resulting in improvement of hydrocephalus and visual symptoms.
At the 18-month follow-up, the patient remained clinically stable, and MRI showed a residual lesion with no significant change. However, at 26 months, imaging demonstrated slight enlargement of the residual nodule, consistent with tumor progression. To preserve neurological function, targeted therapy with a BRAF/MEK inhibitor was initiated. The patient was advised to undergo long-term surveillance with serial MRI, given the possibility of delayed recurrence following initial treatment.
This case underscores the diagnostic and therapeutic challenges of deep midline PA in adults. It highlights the value of multidisciplinary management and molecular profiling in guiding treatment when gross total resection is not feasible.