“An Unexpected Pit” - Ectopic Pituitary Adenoma

Background: Ectopic pituitary adenomas (EPAs) are exceedingly rare neoplasms, comprising about 0.5% of all pituitary adenomas. These are often misdiagnosed radiologically, while the correct diagnosis requires high index of suspicion on pathology and immunohistochemistry analysis. Clinical Case: 62-year-old female presented to the ED with transient unilateral visual loss. She denied orbital pain, headache, or motor or sensory deficit. Following unremarkable ophthalmology evaluation, initial MRI brain was suggestive of pituitary adenoma. MRI of the pituitary with gadolinium contrast showed nonenhancing focus of about 1.5 cm within the posterior sphenoid sinus adjacent to a normal-appearing pituitary gland. Lab assessment showed no pituitary hormone excess or insufficiency. ENT evaluation with repeat MRI brain with contrast showed a T2 heterogeneously enhancing hyperintense lesion in the clivus measuring 2.1 x 1.9 x 1.3 cm (transverse, AP and CC, respectively) with bony thinning/erosion of the sellar floor, the posterior wall of sphenoid sinus and dorsal clivus. Patient underwent transnasal transsphenoidal resection of the tumor with sample submitted as clival chordoma. Pathology report showed a 3.3 x 2.7 x 0.9 cm tumor with immunohistochemistry positive for ACTH, FSH, synaptophysin, chromogranin, S100 and cytokeratin while staining negative for GH, LH, TSH, prolactin and epithelial membrane antigen (EMA). Reticulin stain showed loss of reticulin network and Ki-67 labeling index was 1%. Neurosurgery and ENT teams confirmed no gross manipulation of the pituitary gland had been performed and findings supported a diagnosis of ectopic pituitary adenoma. On 6-month follow-up patient continued to do well clinically and MRI showed normal-appearing pituitary gland with no residual or recurrent tumor. Conclusion: EPA is a rare entity with about 133 cases described in literature. EPAs are generally benign, however up to 79% are functionally active and more likely than their sellar counterparts to secrete multiple pituitary hormones. EPAs arise from remnants of embryonic pituitary tissue in the migratory part of the Rathke’s pouch during early fetal development. The most common locations for EPA are in the sphenoid sinus, clivus, nasopharynx, cavernous sinus and suprasellar space and these are often misdiagnosed on initial radiology as neuroendocrine tumors, sino-nasal carcinomas, clival chordomas or even fungal infections. It is vital to consider EPA in the differential diagnosis of tumors removed from the mentioned anatomic locations as establishing the correct diagnosis helps to avoid the significant morbidity associated with treatments employed for other tumors. Reference: Riccio, L., Donofrio, C.A., Tomacelli, G. et al. Ectopic GH-secreting pituitary adenoma of the clivus: systematic literature review of a challenging tumour. Pituitary 23, 457-466 (2020)