Anatomically pituitary tumors are classified by their size based on radiological findings; either microadenomas (less than <10 mm) or macroadenomas (equal or greater than ≥10 mm).Classification based on radioanatomical findings places adenomas into 1 of 4 grades (I–IV):Stage I: microadenomas (<1 cm) without sella expansion.Stage II:  macroadenomas (≥1 cm) and may extend above the sella.Stage III:  macroadenomas with enlargement and invasion of the floor or suprasellar extension.Stage IV: destruction of the sella.Histological classification utilizes an immunohistological characterization of the tumors in terms of their hormone production. Historically they were classed as either basophilic, acidophilic, or chromophobic on the basis of whether or not they took up the tinctorial stains hematoxylin and eosin. This classification has fallen into disuse, in favor of a classification based on what type of hormone is secreted by the tumor. Approximately 20–25% of adenomas do not secrete any readily identifiable active hormones (non-functioning tumors) yet they are still sometimes referred to as chromophobic. Functional classification is based upon the tumors endocrine activity as determined by serum hormone levels and pituitary tissue cellular hormone secretion detected via immunohistochemical staining. The "Percentage of hormone production cases" values are the fractions of adenomas producing each related hormone of each tumor type as compared to all cases of pituitary tumors, and does not directly correlate to the percentages of each tumor type because of smaller or greater incidences of absence of secretion of the expected hormone.
The tallest historical individual with a known genetic cause was Julius Koch (Geant Constantin) who was found to have X-LAG on genetic study of his skeleton. X-LAG has 100% penetrance so far (all affected with the Xq26.3 duplication have the disease and it affects predominantly females. Isolated non familial cases of X-LAG can either have a constitutional duplication of a chromosome Xq26.3 including GPR101, or mosaicism for the duplication (present in a minority of cells) in the case of isolated male patients. X-LAG causes about 10% of cases of pituitary gigantism. Mechanism
The pituitary gland or hypophysis is often referred to as the "master gland" of the human body. Part of the hypothalamic-pituitary axis, it controls most of the bodys endocrine functions via the secretion of various hormones into the circulatory system. The pituitary gland is located below the brain in a depression (fossa) of the sphenoid bone known as the sella turcica. Although anatomically and functionally connected to the brain, the pituitary gland sits outside the blood–brain barrier. It is separated from the subarachnoid space by the diaphragma sella, therefore the arachnoid mater and thus cerebral spinal fluid cannot enter the sella turcica.The pituitary gland is divided into two lobes, the anterior lobe (which accounts for two thirds of the volume of the gland), and the posterior lobe (one third of the volume) separated by the pars intermedia.The posterior lobe (the neural lobe or neurohypophysis) of the pituitary gland is not, despite its name, a true gland.