The pituitary gland is a pea-sized endocrine gland directly attached to the diencephalon, the part of the brain that contains the hypothalamus. It sits in a concavity of the sphenoid sinus called the sella turcica. It is the master gland of the endocrine system, in the sense that it controls different endocrine systems through the stimulatory hormones it releases. A sellar mass is any type of tumor located in the sella turcica. The most common of these is the pituitary adenoma, a benign tumor of the hormone-producing cells of the anterior pituitary.
Because the gland sits in a confined bony space while controlling other endocrine organs, a sellar mass causes harm in two ways: by secreting hormones on its own, and by compressing the gland, its stalk and the structures around it. Which of the two dominates, together with the cell type the tumor came from, decides how it presents and how it is treated. The route below follows that reasoning: the normal gland, the masses that arise around it, how they present, are investigated and treated, and two groups that need their own explanation.
Choose a route through the topic
The normal gland comes first. Begin there if its anatomy and the hormones it controls are new:
- The pituitary gland and its hormones: the gland’s two embryological parts, how the hypothalamus controls them, the anterior and posterior hormones, and how gland height changes with age.
Next comes what a sellar mass is, what else grows in the region, and how adenomas are typed and how they form:
- Sellar masses and pituitary adenomas: the disorders of the sellar region, what a pituitary adenoma is, and how adenomas are classified by size and invasion and by sporadic or familial origin.
- Other sellar masses: craniopharyngiomas, Rathke’s cyst, meningiomas, pituitary metastases and the hypothalamic tumors that grow in the same region.
- Pituitary adenoma types and frequency: the five anterior pituitary cell types, the adenoma each gives rise to, the classification by transcription factor and hormone, and how common these tumors are.
- Molecular pathogenesis of pituitary adenomas: the primary and promoting changes that start an adenoma, and the genes, from GNAS and GPR101 to AIP, that carry them.
With the tumors defined, the clinical approach follows: how a mass presents, how it is investigated, and how it is treated:
- Clinical manifestations of sellar masses: how a mass presents through headache, visual loss, stalk compression, cranial nerve involvement and pituitary apoplexy.
- Investigating a sellar mass: MRI and the management of incidentalomas, ophthalmologic assessment, the laboratory panel, and when histology is needed.
- Treatment of pituitary adenomas: why prolactinomas are treated with drugs while other adenomas are operated on, and the options for acromegaly, Cushing’s disease, TSH and non-functioning tumours.
Two particular groups of tumors complete the picture, one defined by inheritance and one by the absence of a hormone syndrome:
- Genetic syndromes associated with pituitary tumours: MEN, Carney complex, McCune-Albright syndrome and familial acromegaly, and the gene behind each.
- Non-functioning and gonadotropin-producing adenomas: why these tumors present late through compression, and how stalk compression can mimic a prolactinoma.