Pituitary disease
The pituitary gland lies within a bony depression called the sella turcica within the sphenoid bone at the base of the brain. Its small size belies its many important functions. The pituitary gland has a central role in body growth, metabolism, and reproduction functions.
Anatomy and Function
The pituitary gland consists of the anterior lobe (adenohypophysis), a pars intermedia, and the posterior lobe (neurohypophysis). The anterior lobe and pars intermedia are derived from Rathke's pouch. The anterior lobe is responsible for production and release of prolactin, adrenocorticotropin (ACTH), somatotropin (growth hormone), gonadotropin (GH), follicle stimulating hormone (FSH), luteinizing hormone (LH), and thyroid stimulating hormone (TSH). A portal-hypophysial system provides a direct vascular link between the median eminence of the hypothalamus and the anterior lobe. Releasing factors produced in the hypothalamus reach the pituitary through the portal system to direct release of the hormones.
The posterior lobe and infundibulum (pituitary stalk) are direct extensions of the hypothalamus. Vasopressin (ADH) and oxytocin are produced within neurons of the supraoptic and paraventricular nuclei and transported via axonal flow to the posterior lobe. The hormones are stored in secretory granules until their release into nearby capillaries.
The pituitary stalk transverses the suprasellar cisterns. The optic chiasm and nerves are located superior and anterior to the stalk and the supraclinoid carotid arteries are positioned laterally. The cavernous sinuses lie within the dura on either side of the pituitary gland and contain a meshwork of venous channels. The carotid arteries course through the middle of the sinuses. Cranial nerves 3 and 4 and the 1st (ophthalmic) and 2nd (maxillary) divisions of the 5th nerve are within the lateral walls of the cavernous sinuses. The 6th cranial nerve lies more medially within the sinus just below the cavernous carotid artery. The sphenoid sinus is immediately below the sella turcica.
The shape of the pituitary gland is variable but the gland height should not exceed 8 mm. The gland normally increases in size and upward convexity in adolescent females and during pregnancy.
The gland parenchyma is relatively homogeneous with standard spin-echo pulse sequences. However, very high resolution techniques will reveal a more heterogeneous texture. The anterior lobe is relatively isointense to gray matter on T1-weighted images except during the neonatal period when it is hyperintense. Endnote The normal posterior lobe is hyperintense due to T1 shortening by the phospholipid components of the neurosecretory vesicles Since the pituitary gland, stalk, and median eminence do not have a blood-brain barrier, they enhance routinely with gadolinium. The vascular plexus surrounding the stalk and the cavernous sinuses also enhance. The carotid arteries maintain a low-signal flow void.