Is spindle cell oncocytoma a true entity or a variant of pituicytoma? A case report with review of literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.241353
Source of Support: None, Conflict of Interest: None
Keywords: Folliculo-stellate cell, pituicyte, pituitary, spindle cell oncocytoma, TTF-1
Spindle cell oncocytoma (SCO) of the adenohypophysis is a rare, relatively newly recognized tumor, first reported by Roncaroli et al., in 2002. It is a benign nonendocrinal neoplasm of the anterior pituitary gland and is believed to arise from the folliculostellate cells of the adenohypophysis. It was included as a distinct entity in the 2007 World Health Organization's (WHO) classification of tumors of the central nervous system. SCO occurs in adults and corresponds to WHO grade I tumors. The clinical presentation and radiological features are nonspecific and are indistinguishable from nonfunctioning pituitary adenomas. However, these tumors do not show immunoreactivity for neuroendocrine markers (chromogranin, synaptophysin) and pituitary hormones, but coexpress vimentin, S-100 protein, and epithelial membrane antigen (EMA). They are highly vascular tumors when compared to pituitary adenomas, and their surgical excision poses a great challenge. Till date, only 39 cases have been reported in the literature [Table 1].,,,,,,,,, We describe herein a case of a thyroid transcription factor (TTF)-1-positive SCO in a young lady with a detailed review of literature.
A 28-year old young female patient was referred to the Neurosurgery outpatient department (OPD) with the chief complaints of amenorrhea and galactorrhea for the past three years and painless loss of vision in both the eyes (more on the right side) since one year. She also complained of on-and-off headache for the past 3 months. Contrast-enhanced computed tomographic imaging (CECT) showed a large, well-defined, round, enhancing soft tissue density mass in the sellar/suprasellar region measuring 25 × 23 mm. It showed erosion of the sellar floor with widening of the pituitary fossa and indentation of the floor of third ventricle suggestive of a pituitary macroadenoma or a meningioma [Figure 1]. Serum hormonal levels were evaluated to look for the functional status of the pituitary, which revealed markedly raised prolactin (1265 ng/ml) levels and a normal range of other hormones. A transnasal transsphenoidal tumor decompression was planned after a course of cabergoline (0.2 mg/day) for 2 weeks. Postoperatively, the patient's prolactin levels reduced drastically and her symptoms also improved, following which she was discharged on day 5. At a follow-up of 7 months, she was free of headache and galactorrhea and had a normal vision; however, her menstrual cycle had still not resumed.
An intraoperative frozen section was received which on haematoxylin and eosin (H and E) staining showed a spindle cell tumor comprising of bland spindle cells arranged in sheets with abundant eosinophilic cytoplasm [Figure 2]a. No pleomorphism, mitosis, or necrosis was seen. A provisional diagnosis of a low grade spindle cell tumor was offered.
The main tumor tissue revealed a spindle cell tumor arranged in nests and short fascicles. The individual tumor cells displayed vesicular chromatin, prominent nucleoli, indistinct cell borders, and abundant eosinophilic cytoplasm [Figures 2b-d]. Focal areas of inflammatory cell infiltrate comprising of mature lymphocytes and plasma cells were noted. No significant pleomorphism, mitosis, microvascular proliferation, or necrosis was seen. Immunohistochemistry (IHC) showed diffuse positivity for epithelial membrane antigen [EMA] (Thermo-scientific), vimentin (Thermo-scientific), S-100 (Thermo-scientific), and TTF-1 (Dako), while being negative for glial fibrillary acidic protein [GFAP] (Thermo-scientific), Smooth muscle actin [SMA] (Thermo-scientific), synaptophysin (Thermo-scientific), chromogranin-A (Thermo-scientific), cytokeratin (Thermo-scientific), and pituitary hormones prolactin (Thermo-scientific), growth hormone (Thermo-scientific), and follicular stimulating hormone (Thermo-scientific) [Figure 3]. The MIB-1 labeling index was approximately 1–2%.
Ultrastructural examination showed spindle-shaped cells with the cytoplasm containing numerous mitochondria with interspersed intermediate filaments and having an oval nucleus and a prominent nucleolus [Figure 4]. Occasional electron dense neurosecretory granules were also seen. Based on the histomorphology, IHC, and ultrastructural findings, a final diagnosis of SCO was made.
SCO is a recently described distinct pituitary benign neoplasm which usually occurs in adults and accounts for 0.1–0.4% of all sellar region tumors. On extensive literature search, 39 cases of SCO were found published between 2002 and 2015. Only two small series were published including studies by Cote et al. and Mete et al., describing 4 and 7 cases of SCOs, respectively.
Clinically and radiologically, they are indistinguishable from nonfunctioning pituitary adenomas and are often misdiagnosed initially. SCO often leads to pituitary hormone disorders due to the compression phenomenon called the ‘stalk effect'. The most common clinical manifestations of SCO are visual impairment and panhypopituitarism. Additional features of oligomenorrhea/amenorrhea and galactorrhea, as present in this case, have also been described.,, SCOs may be associated with the development of postoperative complications such as diabetes insipidus.
Most of the SCOs described are usually located within the sella, often with a suprasellar extension. However, local invasion has been sometimes reported, with 3 known cases invading into the cavernous sinus or extending into the sphenoid sinus.,, Due to their rich vascularity, a SCO usually shows enhancement in the CECT as well as magnetic resonance imaging (MRI) scans. Fujisawa et al., demonstrated numerous intratumoral vessels originating from bilateral internal carotid arteries on magnetic resonance angiogram. Therefore, a preoperative angiograph is advised in all suspected cases of SCO to minimize an intraoperative bleeding catastrophe, which is always an imminent risk.
SCOs possess characteristic histological, immunohistochemical, and ultrastructural features, which help to distinguish it from other tumors occurring in this area such as pituitary adenoma with oncocytic change, schwannoma, pituicytoma, granular cell tumor, paraganglioma, meningioma with oncocytic change, and solitary fibrous tumor. SCOs are immunopositive for vimentin, EMA, S-100, and galectin-3; however, they are negative for pituitary hormones, synaptophysin, and chromogranin. This helps to especially exclude them from pituitary adenomas with oncocytic change. Schwannomas show a classical histology with Verocay bodies but do not show oncocytic change. They are also negative for EMA.
Intrasellar meningiomas with oncocytic change usually demonstrate a dural attachment on radiology. Solitary fibrous tumor shows positivity for cluster of differentiation (CD) 34 and B cell lymphoma-2 (Bcl-2), which helps to differentiate it from SCO.
Granular cell tumors and pituicytomas tend to develop in the posterior pituitary gland rather than in the adenohypophysis and are thought to originate from pituicytes. Granular cell tumors often lack the typical spindle cell morphology of SCO and are composed of plump or polygonal cells with eosinophilic, granular, and periodic acid Schiff-positive cytoplasm. In addition, in contrast to SCO, granular cell tumors show a strong expression of CD68 but are not strongly positive for S-100 protein. Furthermore, the cytoplasm of the granular cells is filled with phagolysosomes, and there are no mitochondria. Pituicytomas are vimentin, S-100, and GFAP positive but usually lack EMA reactivity. They also show only a few mitochondria on ultrastructural examination. SCOs, on the other hand, show numerous mitochondria with interspersed intermediate filaments. In addition, this particular case showed occasional neurosecretory granules, which have also been described in a few case reports published earlier.,,
Based on similar immunohistochemistry and ultrastructural features, an origin from folliculostellate cells (FSC) has been suggested. FSCs are thought to act as adult stem cells of pituitary, capable of divergent differentiation. Expression of TTF-1 is a characteristic marker for pituicytes and is also expressed in fetal neurohypophysis. Interestingly, Mete et al., reported TTF-1 expression in SCO, pituicytomas, and granular cell tumors; however, all were negative for markers of FSCs. They hypothesized that all three tumors may have an origin in the pituicyte, and that SCO and granular cell tumors may be variants of pituicytoma. They, therefore, proposed the terms “oncocytic pituicytoma” and “granular cell pituicytoma” to refine the classification of these lesions.
The most important factor determining the prognosis of these tumors is the presence of frequent recurrences; 10 out of the 25 reported cases showed a recurrence during the course of their follow-up. The significance of MIB-1 labelling is questionable because most of these patients show a low MIB-1 labelling index. Incomplete resection is identified as the one single most important factor leading to recurrence. Moreover, a few cases showed a large invasive growth at the initial examination and recurrences were noted beyond a long follow-up, even with complete surgical resection. Therefore, classifying SCO under WHO grade I category is questionable.
To conclude, SCO is a rare, recently described entity, with clinicoradiological presentation similar to that of nonfunctioning pituitary adenomas, but they are relatively more vascular and have a marked variation in outcome.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]