Immature pituitary-specific transcription factor 1 (PIT1)-lineage pituitary neuroendocrine tumors are composed of PIT1-lineage cells with cytological atypia and limited differentiation. These tumors are rare and no cytological features of this neoplasm have been reported. This study is the first to report the cytological features of an immature PIT1-lineage tumor. A 15-year-old boy with mild and asymptomatic hyperprolactinemia underwent endoscopic endonasal transsphenoidal resection of a sellar tumor mass associated with areas of calcification. Intraoperative smear cytology revealed high cellularity and discohesive cells. Large, bizarre nuclei, nuclear irregularities, and pseudonuclear inclusions were present. Histological examination also revealed large nuclei and nuclear irregularities. Immunohistochemically, the tumor cells were diffusely positive for PIT1 and focally positive for thyroid-stimulating hormone, growth hormone, and prolactin. Ultrastructural examination of the tumor specimen revealed large cells with pseudonuclear inclusions and nuclear irregularities. These findings are consistent with those of immature PIT1-lineage tumors. Smear cytology findings, including large cells, pseudonuclear inclusion bodies, prominent nucleoli, epithelial clusters, and mitotic activity, are useful for the rapid intraoperative diagnosis of immature PIT1-lineage tumors.
Keywords: cytology; immature pit1-lineage tumor; pituitary; pseudonuclear inclusion; ultrastructural study.
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