Primary papillary epithelial tumour of the sella: expanding the spectrum of TTF-1 positive sellar lesions

AIM: To describe fournovel primary epithelial tumours of the sella with papillary architecture and TTF-1 expression. METHODS: Paraffin embedded tissue from the four cases and recurrence of patient 1was investigated with haematoxylin-eosin, special histochemical stains, immunohistochemistry with a broad panel of antibodies,and next generation sequencing. The ultrastructure of one tumour was studied in tissue retrieved from paraffin. RESULTS: The lesions occurred in three females aged 20, 26 and 42 years and a male aged 49years. They presented with signs and symptoms secondary to pituitary stalk compression. Pre-operative neuroimaging documented mixed solid and cystic, enhancing sellar masses with suprasellar extension. Histologically, the tumours showed thin papillae lined by a single layer of cytokeratin and TTF-1 positive cuboidal and cylindrical cells with mildly atypical nucleus. Next generation sequencing performed in three cases did not identify any mutations. The main differential diagnosis included metastasis from lung or thyroid carcinoma,extra-ventricular choroid plexus papilloma,and sellar ependymoma. CONCLUSION: We suggest the descriptive term of primary papillary epithelial tumour of the sella (PPETS) for this entity and propose that it could represent the intracranial equivalent of thyroid-like low-grade nasopharyngeal papillary adenocarcinoma. The cell of origin of PPETS remains undetermined although the intense and ubiquitous expression of TTF-1 may suggest a derivation fromthe infundibulum or ventricular recess. Our study expands the spectrum of sellar TTF-1-positive tumour and challenges the view that they all derive from pituicytes.