Spindle Cell Oncocytoma of Adenohypophysis.
Spindle cell oncocytoma of adenohypophysis (SCO) is a rare tumor of the pituitary gland first described by Roncaroli et al. in 2002 , and has been included in the WHO classification of tumors of the central nervous system since 2007. SCO occurs in adults without a sex predilection. The clinical presentations and neuroimage findings of SCO are usually similar and indistinguishable from those of a non-functioning pituitary adenoma. The patients often present with panhypopituitarism or exhibit visual defects and other non-specific symptoms, such as headache, nausea and vomiting. On radiologic examination, SCO usually appears as a well-demarcated, solid mass located over the intrasellar or suprasellar region. Skull base destruction or extension to the sphenoid sinus is rare.
Microscopically, SCO is typically composed of elongated or polygonal spindle cells arranged in interlacing fascicle patterns. These spindle cells show abundant eosinophilic cytoplasm with coarse granularity. Typically, the tumor cells show diffuse immunoreactivity to vimentin, galectin-3, S-100 protein, and frequently EMA. These tumor cells do not express GFAP, cytokeratins, CD34, synaptophysin, chromogranin and BCL-2. Cellular atypia is variable, ranging from absent to moderate; mitotic count and Ki-67 labeling index are generally low. Some tumors, including pituitary adenoma with oncocytic change (null cell adenoma) and granular cell tumor, could be excluded by evaluation of immunohistochemistry panels. However, overlapping immunoprofiles (immunoreactivity to S-100 protein, vimentin, focally to EMA) of SCO, meningioma with oncocytic change and pituicytoma are commonly observed and often lead to diagnostic confusion, especially when the immunostaining on GFAP is faint or equivocal. Thus, ultrastructural examination is crucial to a definite diagnosis of SCO. The typical neoplastic cells are spindle-like with abundant mitochondria in the cytoplasm but lack secretory granules, lysosomes and numerous intercellular processes, and lead to further differentiating SCO from pituicytoma, granular cell tumor or meningioma with oncocytic change.
The histogenesis of SCO is still a matter of debate. The cellular origin of SCO is initially proposed to be folliculostellate cells, which are supporting cells in the anterior pituitary gland with diverse functions, on the basis of similarities of their ultra-structural and immunohistochemical character. Roncaroli et al. and some other authors proposed that SCO should be termed "folliculostellate cell tumor of the pituitary gland" [6,7,8]. However, several recent studies showed that thyroid transcription factor 1 (TTF-1) antigen is diffusely expressed in SCOs, pituicytomas and granular cell tumors of the neurohypophysis[1.3.4]. They also found that TTF-1 is not only critical for the development of lungs and thyroid, but also expressed in the ventral neuroectoderm while not in the adenohypophysis or the intermediate lobe derived from the oral ectoderm. Thus, Mete et al. proposed that the pituicytomas, SCOs, and granular cell tumors are all derived from the pituicyte lineage based on the TTF-1 expression and their similar ultra-structure. In our case, diffuse TTF-1 expression of tumor cells was observed, which may support this hypothesis.
Generally, SCO is considered to be a WHO grade I tumor with a benign course and with the longest follow-up of 16 years without recurrence. However, recurrence and locally aggressive behavior were also described in about half of the reported cases. No well-known prognostic factors have been identified based on the limited reported case. Complete surgical resection with or without radiotherapy is the first choice of treatment. Recently, however, the effect of radiotherapy is still under debated [2,7].
In conclusion, an integration of histomorphology, immunohistochemical studies, and ultra-structural examination is necessary in order to make a definite diagnosis of SCO. Further research and more case studies are needed to identify the cell origin and determine the prognostic factors of SCO.
Contributed by Chih-Ying Wu, John Wang, Chii-Shuenn Yang, Fang-Yi Lee, Yee-Jee Jan