Fig. 22.214.171.124. Pituitary adenomas are not tumors of nervous tissue. However, because of their intracranial location, they are a domain of neurosurgeons. This is why they are in our Atlas. Chromophobe pituitary adenoma (sometimes inactive, containing rare secretory granules only - "null cell adenoma", sometimes containing prolactin secretory granules 100-500 nm in diameter or ACTH granules 100-250 nm in diameter). N - nucleus of adenoma cell. Note marginal (subplasmalemmal) location of small endocrine granules (inset). Scale = 1 µm. (Human, pituitary adenoma.) Download the high resolution image.