Considered a neoplasm of pituicytes, pituicytoma is a rare and distinct type of glioma that arises in the suprasellar space and within the sells turcica. Only 12 previously reported cases of pituicytoma are documented in the literature. We report an intrasellar pituicytoma in a 66-- year-old man presenting with symptoms and radiologic appearance indistinguishable from a nonfunctional pituitary adenoma. The patient also had a medical history significant for parathyroid adenomas and follicular carcinoma of the thyroid. The intrasellar tumor had morphologic features of a pituicytoma, with interlacing fascicles and a storiform pattern much like a benign fibrous histiocytoma. Immunoreactivity for S100 was strong, but the tumor lacked intercellular collagen type IV. The differential diagnosis of a low-grade spindle cell lesion of the sellar space is discussed, and the literature is reviewed. A summary of the clinical and pathologic features of this case, as well as the 12 previously reported cases, is presented.
(Arch Pathol Lab Med. 2001;125:527-530)
The posterior lobe of the pituitary gland or neurohypophysis contains unique glial elements referred to as pituicytes. These cells play a supportive role for the axons of large vasopressin and oxytocin-producing neurons whose cell bodies reside in the hypothalamus.1 Among neoplasms that arise from the neurohypophysis, intrasellar granular cell tumors are best known and may originate from pituicytes.2 In addition, very rare lowgrade spindle cell tumors,3-6 claimed to represent pituicytomas and thought to arise from pituicytes, are encountered along the neurohypophysis. The morphologic features of these tumors are distinct, but their immunophenotype is somewhat variable. We report a case of pituicytoma and compare its immunophenotypic characteristics with those of normal neurohypophysis and other low-grade spindled lesions of the sellar compartment. We describe the first case of pituicytoma that is associated with other endocrine neoplasms. The relevant literature is reviewed and discussed.
REPORT OF A CASE
A 66-year-old man presented with lassitude, weakness, poor balance, impaired vision, and headache. This prompted a magnetic resonance image of the brain, which showed a 1.5 x 1.5-- cm mass in the pituitary fossa with mild effacement of the chiasm, most consistent with a pituitary adenoma. The pituitary mass was isointense on Tl-weighted noncontrast images, enhanced moderately with gadolinium (Figure 1), and had increased signal intensity on proton-density weighted images. A left temporal field deficit was noted on visual field examination. The results of neurological examination were otherwise unremarkable. Medical history was significant for parathyroid adenomas removed in 1975. During the neck exploration for his parathyroidectomies, he was found to have an incidental follicular carcinoma that was treated with total thyroidectomy and postoperative radioactive iodine. He experienced no recurrence of the thyroid carcinoma. Transsphenoidal surgery was performed for diagnosis, resection of the mass, and decompression of the optic chiasm. Visual deficits and other symptoms resolved. No recurrence of the neoplasm was present 26 months following surgery.
PATHOLOGIC FINDINGS
The transsphenoidal resection specimen consisted of a soft, yellow, well-circumscribed mass that measured 1.5 cm. Microscopic examination showed a benign, spindle cell neoplasm associated with a rich capillary network. The spindle cells were characterized by oval to elongated, mildly irregular nuclei, and syncytial fibrillary cytoplasm. A single mitotic figure was seen. The spindle cells often radiated around blood vessels (Figure 2). In some areas, spindle cells were arranged in short, curvilinear fascicles that focally formed a storiform-like pattern. Rare swirls were also present. No Verocay bodies, thick-walled blood vessels, Rosenthal fibers, granular bodies, calcifications, or psammoma bodies were present. An immunoperoxidase panel was performed, including glial fibrillary acid protein (GFAP), S100, MIB-1, factor XIIIa, epithelial membrane antigen, CD34, chromogranin, neurofilament, synaptophysin, type IV collagen, and progesterone receptor. S100 showed strong and diffuse cytoplasmic and nuclear positivity. Collagen type IV showed a perivascular staining pattern but was absent between tumor cells. All other immunostains were negative within the neoplastic cells. The MIB-1 proliferative rate was low, quantitated at 1.5%.
COMMENT
Pituicytomas are uncommon neoplasms of the neurohypophysis. A literature search reveals only 12 examples of this type of neoplasm.36 The pathologic and clinical features of these cases, including our case report, are summarized in the Table. Invariably, these tumors are composed of spindle cells with round-oval to elongated-irregular nuclei and syncytial, fibrillary cytoplasm. The tumors have a rich capillary network, with the vessels often surrounded by radiating spindle cells. Mitotic activity is either absent or very sparse. No features of malignancy are present. In our case, the tumor cells also form short, curvilinear fascicles that assume storiform patterns and swirls. Pituicytomas are histopathologically distinct from other tumors previously reported to occur within the sella turcica. The storiform architectural pattern is similar to that of a benign fibrous histiocytoma; however, in sharp contrast with benign fibrous histiocytomas, pituicytomas are typically strongly S100 positive (Table) and, in our case, are factor XIIIa negative. Although the morphologic features were consistent with pituicytoma, the differential diagnosis of a low-grade spindle cell lesion of the sella includes meningioma, schwannoma, spindle cell adenoma, and pilocytic astrocytoma. These tumors show none of the typical morphologic features of a schwannoma (ie, Antoni A and B areas, Verocay bodies, or thick-walled blood vessels). In addition, collagen type IV, reflecting basal lamina, is limited to perivascular regions in pituicytomas, whereas it is present between tumor cells in schwannomas. Unlike spindle cell adenomas, pituicytomas have cells with fibrillary cytoplasm often arranged in a storiform pattern and do not show immunoreactivity for synaptophysin or, in our case, chromogranin. In contrast with pilocytic astrocytomas, pituicytomas lack Rosenthal fibers, granular bodies, and biphasic morphologic structure. The immunohistochemical features of this tumor supported the diagnosis of pituicytoma over the other entities. Unfortunately, no tissue was procured for ultrastructural study.
Nonneoplastic pituicytes are reported to be positive with GFAP7-9; however, the staining patterns with the antibody have not been well characterized. Consequently, we stained the normal neurohypophysis from 2 surgical and 4 autopsy pituitary glands with GFAP The GFAP was focally positive in discrete branching processes in pituicytes without staining nuclei or most cell bodies (Figure 3). Many areas were negative for GFAP In summary, normal posterior pituitary gland shows variable positive staining with GFAP, results that are similar to the staining pattern observed in pituicytomas.
As the name suggests, pituicytomas most likely derive from pituicytes, the specialized glial population of the normal posterior lobe. The cytologic and architectural features of these tumors are reminiscent of those of the normal posterior pituitary lobe (Figure 3). Pituicytomas share some similar ultrastructural features with pituicytes, including numerous long intercellular junctions.3,4 Immunohistochemically, these tumors reportedly are positive with S100 and show variable immunoreactivity for GFAP and are nonreactive for epithelial membrane antigen and markers of neuronal differentiation. These results are similar to the staining pattern that we have observed for GFAP in normal posterior pituitary gland. The unreactivity for GFAP in the tumor cells is unusual but not unheard of in pituicytomas. In one series of 9 tumors, GFAP was focal and weak in 4 cases and negative in 1.
Several morphologically distinct tumors of the sella have been referred to in the literature as pituicytomas, including pilocytic astrocytoma and granular cell tumors. Although granular cell tumors (also referred to as choristomas and granular cell myoblastomas) and pituicytomas are low grade and may have a shared histogenesis, they represent 2 distinct lesions pathologically, and we prefer reserving the designation pituicytoma for low-grade spindled lesions. Although pilocytic astrocytomas are low-grade glial tumors, like pituicytomas, the former have their own characteristics, including Rosenthal fibers, well-developed fibrillarity, and a biphasic morphologic structure.
Clinically, pituicytomas present with features indistinguishable from nonfunctional pituitary adenomas. Our case, as well as 3 cases reported in the literature,3,4,6 demonstrated suprasellar extension, including one case that showed extensive involvement of surrounding structures.4 In addition, 5 reported cases presented as suprasellar masses.6 Magnetic resonance imaging scans are available for our case and 10 others.3,6 These pituicytomas appear as solid, uniformly contrast-enhancing masses. Only one had a cystic component.6 Although the tumors are thought to arise from the posterior pituitary glial cells, none of the patients experienced diabetes insipidus at presentation. Long-term follow-up (2 years or more) is available for 5 patients. Four patients experienced no recurrence 2 or more years after their operations.3,6 One patient experienced a recurrence 26 months after the initial subtotal resection; however, this patient is clinically stable 28 months after a second procedure. In addition to this patient, 2 other patients experienced recurrence following subtotal resections.6
Pituicytomas have not previously been reported to occur with other endocrine neoplasms. A report of a granular cell pituicytoma associated with multiple endocrine neoplasia type 2 is in the literature)10; however, this tumor is an example of a granular cell tumor or granular cell myoblastoma. Interestingly, our patient is the first documented case of pituicytoma that had other documented endocrine neoplasms, namely, multiple parathyroid adenomas and a follicular carcinoma of the thyroid. This finding suggests that pituicytomas may occur in the setting of a tumor syndrome, such as multiple endocrine neoplasia syndrome, but this possibility requires additional study.
In conclusion, pituicytomas are a rare and unique type of glioma derived from pituicytes and distinct from other intrasellar neoplasms, including granular cell tumors and pilocytic astrocytomas. A histologic hallmark of these tumors is the arrangement of spindle cells around blood vessels, a pattern that is very similar to the architecture of the normal neurohypophysis. Also like the normal neurohypophysis, immunostaining with GFAP is variable. Clinically, the tumors present very similarly to nonfunctional pituitary adenomas. Because of a paucity of reports on pituicytomas, little is known about the clinical behavior of these histologically benign tumors; however, subtotal resections seem to locally recur.
References
1. Hatton GI, Perimutter LS, Salm AK, Tweedle CD. Dynamic neuronal-glial interactions in hypothalamus and pituitary: implications for control of hormone synthesis and release. Peptides. 1984;5:121-138.
2. Liss L, Kahn EA. Pituicytoma: tumor of the sella turcica: a clinicopathological study. J Neurosurg. 1957;15:481-488.
3. Hurley TR, D'Angelo CM, Clasen RA, Wilkinson SB, Passavoy RD. Magnetic resonance imaging and pathological analysis of a pituicytoma: case report. Neurosurgery. 1994;35:314-317.
4. Rossi ML, Bevan JS, Esiri MM, Hughes JT, Adams CBT. Pituicytoma (pilocytic astrocytoma): case report. J Neurosurg. 1987;67:768-772.
5. Scothorne CM. A glioma of the posterior lobe of the pituitary gland. J Pathol Bacteriol. 1955;69:109-112.
6. Brat DJ, Scheithauer BW, Staugaitis SM, Holtzman RNN, Morgello S, Burger PC. Pituicytoma: a distinctive low-grade glioma of the neurohypophysis. Am J Surg Pathol. 2000;24:362-368.
7. Salm AK, Hatton GI, Nilaver G. Immunoreactive glial fibrillary acidic protein in pituicytes of the rat neurohypophysis. Brain Res. 1982;236:471-476.
8. Suess U, Pliska V. Identification of the pituicytes as astroglial cells by indirect immunofluorescence-staining for the glial fibrillary acidic protein. Brain Res. 1981;221:27-33.
9. Weinrauder H, Zareba-Kowalska A. Glial fibrillary acidic protein and differentiation of neonatal rat pituicytes in vitro. Cell Tissue Res. 1984;238:191-- 195.
10. Cussick JF, Ho KC, Hagen TC, Kun LE. Granular-cell pituicytoma associated with multiple endocrine neoplasia type 2. J Neurosurg. 1982;56:594-596.
Alice B. Schultz, MD; Daniel J. Brat, MD, PhD; Nelson M. Oyesiku, MD, PhD; Stephen B. Hunter, MD
Accepted for publication September 12, 2000.
From the Departments of Pathology (Drs Schultz, Brat, and Hunter) and Neurosurgery (Dr Oyesiku), Emory University School of Medicine, Atlanta, Ga.
Reprints: Daniel J. Brat, MD, PhD, Department of Pathology, H190 Emory University Hospital, 1364 Clifton Rd NE, Atlanta, GA 30322 (e-- mail: dbrat@emory.edu).
Copyright College of American Pathologists Apr 2001
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