Pituicytoma (WHO Grade 1)
Pituicytoma is a rare, poorly understood entity with confusing nomenclature. The 2007 WHO Classification of Tumors of the Central Nervous System clarified and redefined criteria for pituicytoma, codifying it as a separate diagnostic entity distinct from granular cell tumor of the neurohypophysis(5). The tumor is solid, benign and composed of bipolar spindle cells. Clinical signs and symptoms include visual disturbance, headache and features of hypopituitarism. Some patient have the symptoms of hyperprolactinemia, probably due to abnormal of dopamine resulting from the from the compression of infundibulum(9). In this report, the tumor is large enough to suppress the optic chiasm and infundibulum, thus leading to bitemporal hemianopsia and hyperprolactinemia. The neuroimaging features of pituicytoma are nonspecific, MRI imaging usually reveals a well-circumscribed mass in the sellar or suprasellar region, with intermediate signal intensity on T1-weighted images, intermediate to slightly increased signal intensity on T2-weighted images, and homogeneous enhancement with gadolinium administration(3, 6). Most pituicytoma has been reported to be located exclusively in the suprasellar (42.5%) or the sellar region (22.5%), and the rest 35% are located in suprasellar with sellar extension(8) . It's difficult to distinguish it from other tumors located in sellar or suprasellar region according to clinical symptoms, such as meningioma, pituitary adenoma, pilocytic astrocytoma and granular cell tumors. But they can be distinguished by pathological examination, wherein the pituicytoma is composed of elongate, bipolar spindle cells arranged in interlacing fascicles or in storiform pattern, with rich cytoplasm. The pituicytoma cells are usually positive for S-100, vim, GFAP, while they are negative for EMA and have a low labeling index of Ki-67(1, 5, 7). In this report, our immunohistochemistry results show that the tumor cells are positive in S-100, vim, GFAP, and 5% of them are positive for Ki-67. Different from previous report, we found that the tumor cells are positive for EMA.
Pituicytoma is a benign lesion, and surgical resection is the primary treatment. There is no recurrence after total resection and varying degrees recurrence of subtotal resection(2). A recent report demonstrated that the doubling time of tumor volume is about 7 years(4). The main reason for incomplete resection is due to intraoperative bleeding, which was exactly the case for our first surgery. Radiation therapy has been recommended for subtotal resection(8), however, the effect is still data question of debate.
Pituicytoma is a rare tumor, it's difficult to distinguish it from other tumors located in sellar or suprasellar region according to clinical symptoms, pathological examination is needed to have a clear diagnosis. This case demonstrated pituicytoma not only positive for S-100, GFAP, vim, but also can be positive for EMA, and proliferation index Ki-67 may be as high as 5%.
Contributed by Zhang Xie-jun, MD, Huang Guo-dong, MD, PhD, Ji Tao, MD, Zhang Xiao-biao, MD, Liu Wen-lan, MD, PhD, and Li Wei-ping, MD