Spindle cell oncocytoma of the adenohypophysis (WHO Grade I)
Spindle cell oncocytoma is a recently described entity and recognized by the actual WHO classification (9,12). The clinical presentation is not specific and depends on the tumor mass syndrome or pituitary insufficiency since this tumor has no hormonal secretion. In one case epistaxis was the revealing symptom (8). The distinction of spindle cell oncoytoma of the adenohypophysis from other pituitary solid tumors on clinical and imaging is difficult because the imaging features are not specific (12,11,7). Intratumoral hemorrhage of varying ages can be encountered and the imaging aspect be more difficult to interpret (1).The diagnosis is histological and often relies on transphenoidal resection samples (7). Neuropathological examination is shows spindle cells, with sometimes pleomorphic nuclei. Rare nuclear pseudo-inclusions, like in our case and similar to those encountered in meningiomas can be seen (15). Such as other rare lesions of the central nervous system, spindle cell oncocytoma can be misdiagnosed as schwannoma (7,6). Pituitary spindle cell oncocytoma is highly vascular, which like in our case can lead to incomplete resection (11,7,3,4). Since the quality of the resection seems to be an important parameter for recurrence-free survival, although an allowed grade I, the prognosis of these tumors could be worsened (11). Immunohistochemical study shows a labeling of tumor cells by anti-Vimentin, EMA, S-100 protein, galectin3 and TTF-1 (13). There is no GFAP, chromogranin A, cytokeratin or pituitary hormone expression (13). Proliferation index is usually low, but in one report it is reported up to 20% and associated with necrosis raising the possibility of a more aggressive feature (8). No recurring mutations or characteristic molecular hallmark has yet been described in these tumors (10). The main differential diagnoses are pituicytoma, granular cell tumor of the neurohypophysis, oncocytic meningioma, oncocytic adenoma, solitary fibrous tumor, schwannoma and paraganglioma. Spindle cell oncocytoma, pituicytoma and granular cell tumor of the neurohypophysis differential diagnoses remain difficult (2). Although defined as separate entities in the actual WHO classification of tumors, some authors raise the possibility that spindle cell oncoytoma, pituicytoma and granular cell tumors could represent the same spectrum of tumor (10).
The treatment relies on complete surgical excision. Radiotherapy efficiency is debated and requires further study to assess its role in spindle cell oncocytoma treatment (3,5). It was first though that spindle cell oncocytoma could derivate from folliculostellate cells based on immunohistochemical (Galectin 3 expression) and ultrastructural features (12,14). Recently, it has been suggested that spindle cell oncocytoma and granular cell tumor of pituitary may be variants of pituicytoma based on ultrastructural features and immunohistochemical staining (diffuse TTF1 staining) (10). Because TTF-1 is not expressed by folliculostellate cells but is expressed by pituicytes, Mete et al. suggest that these tumors could indicate a common pituicyte lineage (10). The authors propose the terminology "oncocytic pituicytomas" and "granular cell pituicytomas" for spindle cell oncocytoma of the adenohypophysis, granular cell tumors of the neurohypophysis and pituicytoma (10).
This presentation must be known from neurosurgeons and pathologists since massive intraoperative bleeding can occur. Extensive bleeding can lead to incomplete resection. Because complete resection seems to be a major prognosis factor although an allowed WHO grade I, this should be integrated in the managing of this rare tumor.
The authors would like to thank Mrs Nathalie Chazalmartin, Mr Christophe Forest, Dr Lionel Chabanol, Dr Cyril Richard, Mrs Martine Laval and Centre de Microscopie Electronique Stéphanois for their help in the preparation of this manuscrip
Contributed by Fabien Forest, MD, François Casteillo, MD, Romain Manet, MD, Claire Boutet, MD, PhD, Cyril Habougit, MD, Violaine Yvorel, MD, Robert Duthel, MD, Michel Péoc’h, MD, PhD