Spindle cell oncocytoma of the pituitary gland with follicle-like component: organotypic differentiation to support its origin from folliculo-stellate cells

Abstract

Spindle cell oncocytoma (SCO) is a rare, nonadenomatous tumor originating from the anterior pituitary gland. Composed of fusiform, mitochondrion-rich cells sharing several immunophenotypic and ultrastructural properties with folliculo-stellate cells (FSC), SCO has been proposed to represent a neoplastic counterpart of the latter. To date, however, SCO has failed to meet one criterion commonly used in histological-based taxonomy and diagnostics; that of recapitulating any of FSCs' morphologically defined developmental or physiological states. We describe a unique example of SCO wherein a conventional fascicular texture was seen coexisting with and organically merging into follicle-like arrangements. The sellar tumor of 2.7 9 2.6 9 2.5 cm was transphenoidally resected from a 55-year old female. Preoperative magnetic resonance imaging indicated an isointense, contrast enhancing mass with suprasellar extension. Histology showed multiple rudimentary to well-formed, follicle-like cavities on a classical spindle cell background; while all the participating cells exhibited an SCO immunophenotype, including positivity for S100 protein, vimentin, EMA, Bcl-2, and TTF-1, as well as staining with the antimitochondrial antibody 113-1. Conversely no expression of GFAP, follicular-epithelial cytokeratin, carcinoembryonic antigen, or anterior pituitary hormones was detected. Ultrastructurally, tumor cells facing follicular lumina displayed organelles of epithelial specialization, in particular surface microvilli and apical tight junctions. This constellation is felt to be reminiscent of FSCs' metaplastic transition to follicular epithelium, as observed during embryonic development and physiological renewal of the hormone-secreting parenchyma. Such finding is apt to being read as a supporting argument for SCO's descent from the FSC lineage.

An Unusual Oncocytic Sellar Neoplasm in a Patient with Birt-Hogg-Dubé Syndrome

“…Although typically described as positive in SCO, galectin-3 is generally not useful in the workup of primary sellar neoplasms, as pituicytoma, meningioma, nerve sheath tumors, granular cell tumor, and even metastases have consistently expressed galectin-3 (Rodriguez et al, 2008). The cases in which bcl2 immunohistochemistry has been performed on SCO have largely showed negative expression; however there are two previously reported cases besides our case with immunopositivity for bcl2 (Vajtai et al, 2006;Vajtai, Beck, Kappeler, & Hewer, 2011). …”

TTF-1-positive oncocytic sellar tumor with follicle formation/ependymal differentiation: non-adenomatous tumor capable of two different interpretations as a pituicytoma or a spindle cell oncocytoma

“…The tumor was diagnosed as a mixed ependymal and oncocytic pituicytoma. Vajtai et al [12] reported another interesting TTF-1 positive sellar tumor showing similar histological features. The tumor was composed of fusiform oncocytic cells with follicle-like cavities that were immunopositive for S100 protein, vimentin, and TTF-1 and negative for GFAP and CAM5.2.…”

“…GFAP is variably detected in all of these tumors, but preferentially in pituicytomas. Immunoreactivity for neuronal markers was reported in a few cases of SCO and pituicytoma [4,12,13].…”

“…Luminal structures, characterized by the presence of microvillous/cilia-like structures projecting into extracellular lumens, have been reported in a few cases of pituicytoma and SCO [10,12]. In pituicytomas, these structures are thought to result from ependymal differentiation of the tumor cells, which originally have glial features.…”

The “game” of glial fibrillary acidic and S100 proteins in pituitary adenomas: two players or several?

“…It appears that, besides their role as sustentacular cells of the adenohypophysis, folliculo-stellate cells are characterised by a great plasticity and possess the ability to modulate the hypothalamo-hypophyseal-adrenal axis in special conditions [11,12]. In spindle cell oncocytoma, a discussed pathologic entity, which seems to originate from folliculo-stellate cells, tumour cells are positive for S100 but, surprisingly, negative for GFAP [13][14][15]. Unlike spindle cell oncocytomas and adenomas of the anterior hypophysis, the adamantinomatous type of craniopharyngioma exhibits a positive GFAP reaction, while other tumour types appear to be negative for both S100 protein and GFAP but positive for TTF1 [16,17].…”