A rare case of mixed pineal melanocytoma and pilocytic astrocytoma: neuroimaging-based differential diagnosis and histopathologic correlation

Abstract

Case Presentation: An 11-year-old female patient presented with a one-year history of daily frontal headache, described as intense stabbing or lancinating pain, associated with nausea and blurred vision, worsened by physical activity and improved with dexamethasone. On neurological examination, the Glasgow Coma Scale was 15, pupils were equal and reactive to light, motor strength and sensation were intact, and no meningeal signs were present. Magnetic Resonance Imaging (MRI) demonstrated a 2.7 x 2.2 x 2.2cm lobulated mixed solid-cystic pineal region mass with a centrally enhancing solid nodule, no diffusion restriction on the ADC map, and intralesional T1 hyperintense foci. The lesion was hyperintense on T2/FLAIR images and demonstrated heterogeneous enhancement on T1-weighted images after contrast administration. T2-FLAIR weighted images also revealed a hyperintense area in the periventricular white matter, consistent with transependymal cerebrospinal fluid (CSF) transudation. Susceptibility Weighed Imaging (SWI) revealed hypointense areas consistent with proteinaceous or hemorrhagic content, as well as calcification or hemosiderin. The lesion caused mass effect on the tectal plate and the cerebral aqueduct, producing moderate obstructive supratentorial hydrocephalus with transependymal CSF edema. CSF analysis revealed normal protein and glucose levels and no neoplastic cells. Alpha-fetoprotein and β-hCG were normal. After the biopsy and histopathologic exam, the final diagnosis was of a mixed pineal region tumour with melanocytoma and pilocytic astrocytoma components, both low-grade. Discussion: Pineal melanocytomas are extremely rare, benign, slow-growing tumours that present as well-circumscribed, solid masses on MRI. To our knowledge, only two other cases have been reported in the literature, both in adults. Pilocytic astrocytomas are slow-growing, well-circumscribed glial tumours that can sometimes arise from astrocytic cells near the pineal gland; they typically present as well-demarcated cystic masses with an intensely enhancing mural nodule, T1-hypointense and T2-hyperintense solid components on MRI. Here, we report on the first case of a mixed tumour of the pineal region composed of melanocytoma and pilocytic astrocytoma. Our case presented with a mixed solid-cystic mass, with focal T1 hyperintense areas (which may suggest melanin deposits), intralesional SWI hypointensities and periventricular T2-FLAIR hyperintensities, consistent with a mixed tumour. This heterogeneous neuroimaging profile contrasts with findings in previously documented pure pineal melanocytomas, which exhibit solid masses with homogeneous T1-weighted hyperintensity and corresponding T2-weighted hypointensity. Therefore, histopathological confirmation is mandatory for final diagnosis. Final Comments: This is the first report of a mixed melanocytoma and pilocytic astrocytoma in the pineal region, underscoring the main MRI findings and the importance of histopathological evaluation for the final diagnosis.