Core Topics in Endocrinology in Anesthesia and Critical Care provides a comprehensive, practical overview of the perioperative management of patients with endocrine disorders
The human neuroendocrine system has two components – hormonal secretion that is controlled by the hypothalamo-pituitary axis and the extra-hypothalamic neurohormones, such as somatostatin, atrial natriuretic peptide and the peptide hormones of the gastrointestinal tract. This chapter principally concentrates on the clinically significant disorders of the hypothalamo-pituitary axis, which through their anatomical and physiological complexity can present the anaesthetist with a wide variety of challenging perioperative problems. The most common lesions of this axis are benign adenomas of the anterior lobe of the pituitary gland. While principal attention focuses on the resulting endocrine hypersecretion that may be associated with such disorders, due regard should also be given to the potential ‘mass effect’ that such lesions may be exerting on neighbouring brain tissue as well as any consequences of the treatment that a patient may have received for their condition.
Clinical anatomy and physiology of the hypothalamo-pituitaryneuroendocrine axis
The hypothalamus is responsible for the maintenance of homeostasis and the integration of nervous and endocrine control mechanisms. It regulates many of the body’s autonomic functions, such as temperature, thirst and hunger, blood pressure and volume, sleep and sexual function, and is intimately related, both anatomically and functionally, to the pituitary gland . Anatomically it is regarded as a component of the diencephalon, the most rostral part of the brainstem, and lies within the walls and floor of the third ventricle of the brain. It is a complex collection of nervous and endocrine tissue, and contains a number of nuclei that have either a direct (neuronal) or indirect (vascular) communication with the pituitary gland.
The pituitary gland is similarly a composite of endocrine and nervous tissue that is located at the base of the brain and connected to the hypothalamus by the pituitary stalk. It weighs less than 1 g under normal circumstances, and lies within the sella turcica, a bony fossa of the skull base. The roof of the pituitary fossa is created by an incomplete fold of dura, the diaphragma sella, through which passes the pituitary stalk. The fossa is limited posteriorly by the clivus and both anteriorly and inferiorly by the bony air sinuses of the sphenoid bone. Important anatomical relationships of the pituitary gland are shown in Figure 1.1 . Laterally on either side lie the cavernous sinuses, various cranial nerves and beyond them the temporal lobes. Superiorly are found the pituitary stalk, the diaphragma sella and the optic nerves/chiasm, and beyond them the hypothalamus and third ventricle.
The gland itself is organised embryologically, anatomically and functionally into two parts (Figure 1.2). The anterior lobe (adenohypophysis) is derived embryologically from Rathke’s pouch, an upgrowth from the roof of the pharynx, and consists of cords of endocrine secretory tissue organised around an extensive network of sinusoids which arise from a local vascular network that extends from the hypothalamus to the anterior lobe along the pituitary stalk.