• Physiological Consequences of Pituitary Tumors

  • Hormonal over production/under production

  • Pituitary tumors: most common syndromes due to:

    • Growth hormone excess

      • Gigantism, acromegaly

    • Prolactin excess

      • Galactorrhea and/or hypogonadism

  • ACTH-secreting tumors: Cushing's disease

  • TSH-secreting tumors: hyperthyroidism (rare)

  • Gonadotropin-secreting tumors: hypogonadism (paradoxical)

  • Large pituitary tumors:

    • Hypopituitarism (due to gland compression; or pituitary stalk compression) ® visual field disturbances {optic chiasm compression}

• Hypothalamic disease

  • Hypopituitarism

  • Prolactin secretion increased

  • Significant Diagnostic Indication:

    • Diabetes insipidus ,due to vasopressin (AVP) deficiency.

• Anatomy: Pituitary

  • Pituitary gland (hypophysis) resides within sella turcica of the sphenoid bone at the skull base (weight = between 0.4 and 0.8 grams)

  • Midsagittal section through human pituitary (above)

  • Sagittal section of a human pituitary, showing the relationship of its blood supply to the hypothalamic neurosecretory cells in the adenohypophysis (above)

  • Sagittal section of a human pituitary, showing the relationship of its blood supply to the neurosecretory cells of the supraoptic and paraventricular nuclei of the hypothalamus (above)

  • Pituitary gland components:

    • Anterior lobe (adenohypophysis)

    • Posterior lobe (neurohypophysis)

  • Separated from brain by diaphragma sella (dura mater extension) and by thin bone layers from the sphenoid sinus anteriorly and inferiorly

  • Sella lateral walls abut on the cavernous sinuses (containing internal carotid arteries and cranial nerves III, IV, V, and VI. Recurrent

  •  Optic chiasm located slightly anterior to pituitary stalk -- just above diaphragma sella.

    • Reason why pituitary tumors result in visual field effects, cranial nerves palsies, sphenoid sinus invasion

Anatomy: Hypothalamus

Image source attribution:  University of Manitoba Anatomy

• Hypothalamus:

  • Anterior extension to optic chiasm margin

  • Posterior extension including mammillary bodies

  • Separated from pituitary by the hypothalamic sulcus of the third ventricle.

  • Rounded inferior hypothalamic base: tuber cinereum

    • Base central portion (median eminence or infundibulum) formed by third ventricle floor, continuing inferiorly to form the pituitary stalk.

      • Hypothalamic releasing factors synthesized in neurons located along third ventricular margins.

        • Fibers from these neurons terminate in the median eminence adjacent to portal capillaries.

  • Neuronal cell bodies of supraoptic and periventricular hypothalamic nuclei produce vasopressin and oxytocin which are transported  along nerve axons (supraopticohypophyseal and paraventriculohypophyseal tracts) to the posterior lobe.

  • Hypothalamic-anterior pituitary communication is chemically mediated:

    •  Hypothalamic neuronal releasing factors flow through the portal system to stimulate or inhibit anterior pituitary hormone production

    •  Anterior pituitary blood supply: (highest blood flow of any tissue, about 0.8mL/g/min.

      • Blood supplied by way of the hypothalamus:

        • Two derivatives of the internal carotid arteries, the superior hypophyseal arteries (SHA) terminate in median eminence,which resides outside the blood-brain barrier capillary network.

        • These capillaries exhibit a fenestrated endothelium which results in easy access to hypothalamic releasing hormones with the system regulated by vasoactive intestinal peptide, VIP.

        • Capillaries form 6-10 straight veins, the hypothalamic pituitary portal circulation, with the main blood supply to anterior lobe, supplying nutrients and hypothalamic factors.

 

Reference: Fitzgerald, P.A. and Klonoff, D.C. Hypothalamic and Pituitary Hormones, in Basic and Clinical Pharmacology, (Katzung, B. G., ed) Appleton-Lange, 1998, pp 603-618.

Reference: Biller, Beverly M. K. and Daniels, Gilbert, H. Neuroendocrine Regulation and Diseases of the Anterior Pituitary and Hypothalamus, In Harrison's Principles of Internal Medicine 14th edition, (Isselbacher, K.J., Braunwald, E., Wilson, J.D., Martin, J.B., Fauci, A.S. and Kasper, D.L., eds) McGraw-Hill, Inc (Health Professions Division), 1998, pp 1972-1998