Collision Tumor Composed of Nonfunctioning Pituitary Adenoma and Meningioma in the Sellar Region: Report of a Case and Literature Review.

The coexistence of two histologically distinct neoplasms in the same area without histological admixture or an intermediate cell population zone represents a rare tumor type called collision tumor. Collision tumor of pituitary adenoma and meningioma has been reported years later following irradiation to pituitary adenoma. However, collision tumor of pituitary adenoma and meningioma in absence of irradiation therapy is extremely uncommon.  We report an unusual case of collision tumor involving diaphragma sella meningioma and pituitary adenoma in a 50-year-old lady without prior radiation therapy. She presented with visual blurring and impaired field of vision. Her preoperative magnetic resonance imaging (MRI) was suggestive of pituitary adenoma. Total excision of the lesion was performed through endoscopic transsphenoidal route. Histological diagnosis was consistent with collision tumor of pituitary adenoma and meningioma.  Collision tumor comprising of nonfunctioning pituitary adenoma and meningioma is extremely rare. Preoperative MRI may not always be able to distinguish these histologically distinct neoplasms. Hence, histopathological examination is necessary to establish the diagnosis. Endoscopic transsphenoidal approach may suffice in excision of these collision tumors. Close follow-up is necessary to detect tumor recurrence. Though the association of these tumors can be coincidental, casual relationship between the occurrence of collision tumors cannot be totally excluded.