Pituitary Gland - Pathology

Anatomy and Physiology

Anatomy and Physiology of the pituitary gland can be found here.

General Pathological Principles

Two major changes can occur in an endocrine gland:

• Failure of hormone production:
  • Destruction or lack of cells.
  • Lack of trophic drive.
• Overproduction of hormone:
  • Hyperplasia or neoplasia.
  • Excessive trophic drive.

Pituitary Hypofunction

Pituitary Neoplasia

Tumours within the pituitary fossa may be functional and sectrete trophic factors. However, more commonly they are non-functional and are space-occupying lesions. Pressure on neighbouring structures causes clinical signs, for example:

• Pressure on the optic chiasma produces ocular signs.
• Pressure on the hypothalamus may lead to Frohlich's adiposogenital syndrome.
• Pressure on the neurohyposphysis may lead to failure of ADH secretion. This will allow large volumes of water to be lost form the kidney; Diabetes Insipidus.

Pituitary neoplasia. Courtesy of A. Jefferies

Neoplasia may be derived from:

• Pituitary itself.
• Surrounding brain tissue.
• Ependyma.

Pituitary neoplasia in the horse

Neoplasia usually occurs in the pars intermedia of the anterior pituitary and compresses the hypothalamus.

Clinical signs:

• Polyuria and polydipsia.
• Increased appetite reulting in increased food intake and downregulation of insulin receptors. This leads to a hyperglycaemia.
• Somnolence.
• Muscle wekaness.
• Hirsutism.
• Hyperhidrosis.

Pituitary Hyperfunction

Gigantism