Rare Collision Tumors: ACTH-Secreting Pituitary Adenoma and Pituicytoma: Histopathological and Ultrastructural Analyses- case report

Background Collision tumors are rare conditions characterized by the coexistence of two histologically distinct neoplasms in the same region without histological admixture or an intermediate cell population zone. Case presentation Our report represents one of the few studies on a collision tumor composed of an ACTH-secreting pituitary adenoma and a sellar pituicytoma. Here, we describe the clinical presentation, radiological findings, immunohistochemical/histopathological analysis and ultrastructural examination of a 21-year-old woman with two different intracranial primary tumors at adjacent sites. Magnetic resonance imaging (MRI) of the sellar region revealed a focal nodular, 4 mm lesion located in the left lateral recess that was hypointense at T2 and compatible with a pituitary microadenoma. Transnasal transsphenoidal resection was performed. Histopathological analysis revealed patterns consistent with a corticotroph PitNET, with diffuse, cytoplasmic ACTH positivity by immunostaining and a Ki-67 index of 4%. Furthermore, the specimens included scattered adenohypophyseal and neural tissue. The latter was characterized by increased neoplastic proliferation consistent with a pituicytoma, confirmed by nuclear positivity for TTF-1 and a Ki-67 index of 3%. Ultrastructural analysis confirmed the coexistence of two morphologically distinct lesions. Postoperatively, the patient developed diabetes insipidus and remained in clinical and biochemical remission with no remaining tumor at nine months postsurgery. Conclusions Pituitary collision tumors are sporadically reported and rare. Specifically, pituicytomas associated with pituitary hyperfunction are notably infrequent, and those linked to Cushing’s disease are extremely uncommon. Pituicytomas exhibit unique histological and ultrastructural characteristics that distinguish them from other pituitary tumors. A deeper understanding of pituicytomas will enable the development of more specific and effective treatments tailored to the molecular characteristics of individual patients in the future.