Pituitary gland protective bony enclosure called the sella turcica. It is composed of three lobes: anterior, intermediate, and posterior. In many animals, these three lobes are distinct.The intermediate is avascular and almost absent in human beings. The intermediate lobe is present in many lower animal species, in particular in rodents, mice and rats, that have been used extensively to study pituitary development and function. In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary, which is an extension of the hypothalamus. The anterior pituitary arises from an invagination of the oral ectoderm and forms
Pituitary adenoma shown there are to date scant studies – of poor quality – to either support or refute this assumption. Adenomas which exceed in size are defined as "macroadenomas", with those smaller than 10 mm referred to as "microadenomas". Most pituitary adenomas are microadenomas, and have an estimated prevalence of 16.7% (14.4% in autopsy studies and 22.5% in radiologic studies). A majority of pituitary microadenomas often remain undiagnosed and those that are diagnosed are often found as an "incidental finding", and are referred to as "incidentalomas". Pituitary macroadenomas are the most common cause of hypopituitarism, and in the majority of cases