A 49-year-old woman presented with left visual disturbance. No signs of
Cushing's disease were evident. Basal levels of serum
cortisol and plasma
adrenocorticotropic hormone (
ACTH) were 16.8 microg/dL and 66.0 pg/mL, respectively. MRI demonstrated an irregularly shaped large
pituitary tumor, and the patient then underwent transsphenoidal surgery. By light microscopy the
tumor represented a chromophobic
adenoma with a few of the
adenoma cells showing immunoreactivity for
ACTH. On the basis of clinical and light microscopic examinations, the diagnosis of silent
corticotroph adenoma was made. Electron microscopy, however, demonstrated the honeycomb Golgi complex that has been reported as a typical finding of gonadotroph
adenomas. MRI taken 7 months after the first operation revealed
adenoma regrowth. Transcranial surgery was performed, and histology demonstrated a chromophobic
pituitary adenoma with most cells immunopositive for
ACTH. She was treated with gamma knife postoperatively. Three months later, MRI revealed remarkable shrinkage of the
adenoma, but she developed typical signs and symptoms of
Cushing's disease. Thus, the
hormone immunostaining and biological activity of
pituitary adenomas may change with time.