Atypical granular cell tumor of the neurohypophysis.
"Granular cell tumor" (GCT) is a purely descriptive term for a histogenetically heterogeneous group of neoplasms. "Peripheral" GCTs are either congenital (congenital epulis) or, more frequently, develop during later life. Intracranial GCTs are usually found in the posterior hypophysis, and only rarely in the cerebral hemispheres or leptomeninges.
Symptomatic GCTs of the neurohypophysis are rare neoplasms. Only 42 reports were found by Schaller et al. (8). Additionally, we identified 5 further instances, including our own case (6, 9, 10). There is a wide range of age distribution. Most frequently the tumors are diagnosed between 30 and 60 years of age, with a 2:1 predominance of females.
GCTs of the neurohypophysis are usually regarded as slowly growing, well-circumscribed benign tumors. As a rule, uncharacteristic clinical symptoms of a hypophyseal neoplasm develop insidiously (1). To the best of our knowledge, only five cases with short duration of symptoms have been described previously (2, 3, 4, 8, 11). In our case, only four weeks elapsed between the onset of symptoms and surgery.
The tumor showed a number of peculiarities: First, it infiltrated the optic chiasm. Histologically, there was remarkable cellular and nuclear polymorphism, which to date has been mentioned in neurohypophyseal GCTs only by Shuangshoti et al. (10). As mitoses were very rare and necroses or vascular proliferations did not occur, there were no clear signs of malignancy. To obtain further insight into the biology of the tumor, we performed a number of immunohistochemical analyses. Positivity of tumor cells were for p53 and bcl-2 as well as negative results concerning bax may correlate with the relatively aggressive behavior of this GCT, and its rapid recurrence.
The biology of GCTs is poorly understood. At autopsy, small neoplasms of the posterior lobe of the pituitary gland are not uncommon as an incidental finding. In systematic postmortem histological studies, micronodules of granular cells (tumorettes) were registered in up to 17% of unselected adult autopsy cases (2). Evidently, these lesions grow very slowly for a long time, and the majority never produce clinical symptoms. In contrast to "peripheral" counterparts, overtly malignant GCTs of the posterior hypophysis have not been reported. Our observation, in the context of cases reported in the literature, shows that the natural course of GST of the neurohypophysis may not be as favorable as is generally believed today (8, 11). Whether histological atypia influences the outcome of the neoplastic disease needs further investigation.
Contributed by Silke Vogelgesang , Michael H. Junge, Jens Pahnke, Michael R. Gaab, Rolf W. Warzok