Pituitary Blastoma: Expanding the Spectrum of Histopathological Findings in a Young Adult With DICER1 Mutation.

Pituitary blastoma is a rare embryonal tumor of the pituitary gland, typically occurring in children under 2 years of age and strongly associated with germline DICER1 mutations. Only a limited number of cases have been reported, with very few occurring beyond early childhood. We present the case of a 27-year-old male who presented with severe headaches, vomiting, visual disturbances, and altered behavior. Magnetic resonance imaging revealed a large suprasellar mass with sellar extension, diffusion restriction, and hemorrhagic components. The radiological differential diagnoses included papillary craniopharyngioma, pilocytic astrocytoma, and high-grade glioma. Surgical decompression was performed, and histopathological examination revealed a highly cellular tumor with blastemal, glandular, and rosette-forming components, consistent with pituitary blastoma. Immunohistochemistry showed patchy positivity for OLIG2, synaptophysin, and LIN28A, along with a high Ki-67 proliferation index (~90%). Next-generation sequencing confirmed a pathogenic DICER1 mutation (p.Glu1813Asp, p.Pro817fs), supporting the diagnosis. Unlike most reported cases, which present with Cushing's syndrome or ophthalmoplegia, this patient had an elevated prolactin level, a feature not previously described in pituitary blastoma. The tumor followed an aggressive course, and the patient succumbed within a month post-surgery. This case expands the clinicopathologic spectrum of pituitary blastoma, emphasizing unusual age and known genetic associations, and highlights the need for a high index of suspicion in atypical cases.