Pituitary

Pituitary

Posterior Lobe:

• Large cells(magnocellular)
• Located in: supraoptic & paraventricular nuclei
• Hormones: ADH/Vasopressin, Oxytocin

Anterior Lobe:

• Known as; Master gland
• Parts: distalis, tuberalis, intermedia
• Cells: chromophobe(not secretory), chromophil
• 30-40%somatotropes,20%corticotropes,3-5% others

Pituitary

• The pituitary region harbors a confluence of neuroendocrine and ectodermal tissue, a portal circulation between two critical venous plexuses, and the osseous junction of the three cranial fossae.
• Because of the secretory capability of adeno hypophysial cells, many pituitary tumors liberate physiologic hormones to pathologic excess, generates a metabolic aberrations and some of the most classic syndromes .
• Pituitary tumors constitute a unique class of neoplasia
• The diagnostic and therapeutic imperatives that accompany pituitary tumors are necessarily unique.

EPIDEMIOLOGY

• 15% of all primary brain tumors and almost 25% of benign primary brain tumors.
• annual incidence of 3 to 94 cases per 100,000 people
• The third most common primary intracranial tumor,
• Autopsy and modern imaging studies suggest that 20% to 25% of the general population harbor pituitary microadenomas
• The incidence is highest between the fourth and seventh decades of life
• 2% of all primary pediatric brain tumors.
• Functioning pituitary tumors tend to be more common among younger adults, whereas Nonfunctioning adenomas become more prominent with increasing age
• More common among women, particularly premenopausal women

EMBRYOLOGY, MORPHOLOGY, AND ANATOMY OF THE NORMAL PITUITARY GLAND

• A bilobed, composite neuroendocrine structure
• It has three divisions:
• An anterior adenohypophysis,
• A posterior neurohypophysis (pars nervosa), and
• An intermediate lobe (pars intermedia), with distinct morphologic, embryologic, and functional roles.
• The wide collection of pathologic conditions that occur in the sellar region reflects the embryologic diversity within this compact space

“a ball held in a catcher’s mitt”

• Auguste Théodore Liégeois first identified the pituitary as a ductless gland in the 1860s and noted its ability to affect distant organs.

The anterior lobe is composed of five principal secretory cell types,

1. Somatotrophs (GH),

2. Lactotrophs (PRL),

3. Corticotrophs (ACTH),

4. Thyrotrophs (TSH), and

5. Gonadotrophs (luteinizing hormone [LH] and follicle-stimulating hormone [FSH])

On microscopic views;

• An awareness of this topologic organization is important to neurosurgeons, who must occasionally dissect through a seemingly normal pituitary gland in search of a microadenoma.
• A fully pneumatized sphenoid sinus, with aeration beneath the entire sella, is termed a sellar type sphenoid bone and is found in 80% of the population.
• A nonpneumatized sphenoid sinus is common in children and persists as the conchal type in 3% of adults.

• The cavernous sinuses flank the pituitary gland and are connected superiorly and inferiorly by intercavernous (circular) sinuses.
• Trabeculated venous spaces house the cavernous segment of the internal carotid artery, as well as cranial nerves III, IV, and VI and one to two branches of cranial nerve V (trigeminal )
• The abducens nerve enters the cavernous sinus after exiting Dorello’s canal and courses in a medial-to-lateral direction to the internal carotid artery