Granular cell tumor of the pituitary: a rare sellar tumor

Stephanie L. Lee

A 44-year-old woman was referred to the endocrine clinic with the history of pituitary macroadenoma and panhypopituitarism after a prior resection. She noted a stable visual field loss since her initial surgery and denied headache, polydipsia, polyuria, fatigue, palpations, tremor, heat/cold intolerance, diarrhea or constipation.

Her past medical history is significant for amenorrhea, galactorrhea and right eye visual field deficits, and a non-secreting pituitary tumor resection 20 years prior to presentation, which resulted in panhypopituitarism. She denied any drug allergies and her current medications included levothyroxine, bromocriptine, prednisone and ethinyl estradiol/norethindrone acetate. Her physical exam was significant for bilateral temporal visual field defect, more severe in the right than left eye. Fundus exam revealed optic atrophy in the left eye more so than the right.

Laboratory studies revealed a prolactin <0.3 ng/mL, luteinizing hormone 0.1 mIU/mL, follicle-stimulating hormone <0.3 mIU/mL, estradiol 88 pg/mL, free T4 1.43 ng/dL. MRI of the pituitary revealed a well-defined sellar and suprasellar mass measuring 2.5x1.7x1.6 cm with significant mass-effect on the optic chasm but no evidence of cavernous sinus invasion (Figures 1 and 2).

Without contrast, the mass was heterogeneously isointense to the brain parenchyma on T1- (Figures 1A and 2A) and T2- (Figure 3) weighted images, and vigorously enhanced after gadolinium contrast administration (Figures 1B and 2B). The clinical diagnosis was a recurrent non-secreting pituitary adenoma.

The patient had a second transsphenoidal resection of the tumor in an attempt to reduce the size and relieve the mass effect on the optic chiasm. Intraoperatively, the surgeon noted that the tumor was very firm and vascular and could not be removed by suction, which is typical of pituitary adenomas. Pathology indicated the tumor was composed of large polygonal cells with abundant cytoplasm with eccentric and small nucleoli. The cells were PAS-positive, immunoreactive for S-100, and contained abundant heterolysosomes by electron microscopy. The pathological diagnosis was a granular cell tumor of the pituitary.

Due to the large size and firm nature of the tumor, the resection was only partial, and it was recommended that she have a more complete resection by transfrontal craniotomy followed by stereotactic radiosurgery, which she declined. She also declined stopping the bromocriptine because her original doctors told her to never stop the medication.

To determine the etiology of a pituitary mass, it is important to order a MRI of the sella that provides fine-cut and enlarged images through the sella and hypothalamus with dynamic gadolinium contrast infusion. The appearance of granular cell tumor of the pituitary on MRI is rather non-specific but different than a typical pituitary macroadenoma (see Table). This mass had the typical MRI characteristics that suggest a granular cell tumor: a well-defined sellar mass often with suprasellar extension located posterior within the sella, loss of the posterior lobe hyper intensity and the mass is isointense with the brain on both T1- and T2- weighted sequences with vigorous enhancement after gadolinium contrast administration. Histological analysis of the tumor is necessary to diagnose granular cell tumor as it stains positive for PAS and S-100. It also may be positive for neuron-specific enolase, but negative for glial fibrillary acidic protein. These are benign, slow-growing tumors that are also known as pituicytomas and thought to arise within the neurohypophysis, but the cell of origin is uncertain. They generally are clinically silent and found incidentally during autopsy. These tumors rarely present as large sellar and suprasellar masses with visual field cuts, headaches and endocrine deficits. Most tumors cannot be completely removed because of the firm, vascular nature of the lesion, and there are no large clinical series demonstrating that radiotherapy is beneficial for these tumors. To provide the best care of patients with pituitary disease, the endocrinologist must order the appropriate imaging study, know the typical appearance of sellar masses and personally examine the studies prior to making management decisions.

For more information:

• Buhl R, Hugo HH, Hempelmann RG, et al. Granular-cell tumour: a rare suprasella mass. Neuroradiology.2001;43:309-312.
• Cohen-Gadol AA, Pichelmann MA, Link MJ, et al. Granular cell tumor of the sellar and suprasella region: clinicopathologica study of 11 cases and literature review. May Clin Proc. 2003;78:567-573.
• Iglesias A, Arias M, Brasa J, et al. MR imaging finds in granular cell tumor of the neurohypophysis: a difficult preoperative diagnosis. Eur Radiol. 2000;10:1871-1873.
• Rennert J and Doerfler A. Imaging of sellar and parasellar lesions. Clin Neurol and Neurosurg. 2007;109:111-124.

Stephanie L. Lee, MD, PhD, is an Associate Chief in the Section of Endocrinology, Diabetes and Nutrition and an Associate Professor of Medicine at Boston Medical Center.

Geunwon Kim, MD, PhD, is a Graduate Student in the MD/PhD Program, Division of Graduate Medical Sciences at Boston University School of Medicine.