Sella and Pituitary Overview

Sella

Bony anatomy : The sella turcica (“Turkish saddle”) is a concave, midline depression in the basisphenoid that contains the pituitary gland (also called the hypophysis). The anterior borders of the sella are formed by the anterior clinoid processes of the lesser sphenoid wing and the tuberculum sellae, whereas the posterior border is formed by the dorsum sellae. The top of the dorsum sellae expands to form the posterior clinoid processes, which in turn form the upper margin of the clivus. The floor of the sella is part of the sphenoid sinus roof, which is partially or completely aerated. The cavernous segments of the internal carotid artery lie in shallow grooves, called the carotid sulci, which are located inferolateral to the sella.

Meninges : The meninges in and around the sella turcica form important anatomic landmarks. Dura covers the bony floor of the sella itself. A thin dural reflection borders the pituitary fossa laterally and forms the medial cavernous sinus wall. A small circular dural shelf, the diaphragma sellae, forms a roof over the sella turcica that, in most cases, almost completely covers the pituitary gland. The diaphragma sella has a variably sized central opening that transmits the pituitary stalk. In some cases, this dural opening is large and gapes widely. In such cases, arachnoid with or without accompanying cerebrospinal fluid may protrude from the suprasellar cistern inferiorly through the diaphragma sellae opening into the sella turcica and cause the imaging appearance of an empty sella.

Pituitary Gland

Overview : The pituitary gland, also called the hypophysis cerebri, consists of 3 major parts: The adenohypophysis (AH), the neurohypophysis (NH), and the pars intermedia (PI) plus the infundibulum, which are generally considered together as a unit.

Adenohypophysis : The AH, also called the anterior lobe, wraps anterolaterally around the NH in a U-shaped configuration. The AH contains acidophil, basophil, and chromophobe cells, as well as other cells, such as tanycytes. Cells of the AH secrete trophic hormones (TSH, ACTH, LH, and FSH) as well as growth hormones. The AH forms 80% of the pituitary gland by volume.

Neurohypophysis : The NH, sometimes called the pars nervosa, consists of the posterior lobe of the pituitary gland, infundibular stem, and median eminence of the hypothalamus. The NH is formed from the embryonic diencephalon (forebrain) as a downward extension of the hypothalamus. Vasopressin and oxytocin are formed within the hypothalamus, pass inferiorly along the hypothalamohypophysial tract, and are stored in the NH. The NH comprises ~ 20% of the pituitary gland.

Pars intermedia : The PI is derived from the buccal ectoderm of the embryonic Rathke pouch. It is relatively small (< 5% of the pituitary volume). Axons from the hypothalamus carry granules of releasing hormones to the AH.