The Dark Corner of the Pituitary Gland: A Case Report and Literature Review of Primary Melanocytoma.

Background: Primary pituitary melanocytoma, an exceedingly rare tumor, may resemble pituitary adenoma with apoplexy owing to its heterogeneous melanin concentration and possible hemorrhagic events. An accurate diagnosis of melanocytoma is, therefore, essential.

Case presentation: We present a case of a 31-year-old female patient who exhibited a progressively worsening headache that commenced one month prior. MRI showed a significantly enlarged sella turcica with a gourd-shaped lesion that had a mixture of short T1 and T2 signals. In conjunction with the MRI findings, CT scans, both non-contrast and contrast-enhanced, revealed a circular, dense region in the sellar area, exhibiting heightened enhancement post-contrast administration. Subsequently, this patient was scheduled for endoscopic transnasal skull base tumor resection and skull base reconstruction. Later, histopathological assessment showed red-S-100 (+), red-melanin A (+), red-KI-67 (+5%), red-melanoma (+), P53 (+), red-P53 (+) and Ki-67 (+) and suggested an intermediate-grade melanocytoma, positioning this lesion between benign and malignant on the spectrum of melanocytic neoplasms.

Conclusion: This case report evaluated the presentation, key imaging findings, and histopathological features that help differentiate primary melanocytoma from other tumors and discussed key management and prognostic considerations following diagnosis.