Somatostatin-producing atypical null cell adenoma manifesting as severe hypopituitarism and rapid deterioration--case report.

Atypical adenoma has an aggressive biological character, invades the surrounding structures, and grows rapidly. Morphological malignant findings such as increasing cellularity and nuclear atypism are not involved in this entity, but some cases with overt malignant features such as significant nuclear atypism and/or necrosis are known. Null cell adenoma generally grows slowly, but hormone secretion is little understood. Atypical null cell adenoma is rare, and hormone production is unknown. A 55-year-old woman presented with severe hypopituitarism and diabetes insipidus and bilateral upper temporal quadrantanopsia. Head magnetic resonance imaging revealed a large sellar tumor compressing the optic chiasm. Transsphenoidal surgery was performed, but the tumor was partially removed because of invasion into the neuronal structures. Histological examination showed atypical null cell adenoma with significant nuclear atypism and extensive necrosis. Immunohistochemistry showed positive reaction to somatostatin. Adjuvant treatment was planned, but the tumor regrew within 3 months. Conventional irradiation resulted in slight decrease in tumor size, but she required assistance for every type of daily activity. Atypical null cell adenoma has an aggressive biological character, and immediate adjuvant treatment is essential. Somatostatin secretion was proven in this tumor type.