Pituitary adenoma

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Pituitary adenoma in a 9-year-old female dog[1]

Pituitary adenoma are a relatively common, usually benign, pituitary neoplasia of older dogs[2].

Pituitary tumors account for approximately 15% of intracranial tumors and are often benign monoclonal endocrine-producing adenomas of the neurohypophysis[3].

Pituitary adenomas are frequently associated with one of two common diseases in dogs; pituitary-dependent hyperadrenocorticism[4] and central diabetes insipidus. These tumors may be small (micradenomas) or sufficently large to cause a mass-effect (macroadenomas) with secondary thalamic disease such as Frohlich's adiposogenital syndrome[5].

Clinically affected dogs present with non-neurological symptoms of weight loss, polyuria, polydipsia and lethargy. Other, more specific symptoms, are referable to individual disease states. For example, symptoms associated with hyperadrenocroticism due to pituitary adenoma include polyphagia, polyuria, polydipsia, dermatopathy, distinctive 'potbelly' appearance and symmetrical alopecia[6].

Neurological signs due to cranial compression due to mass-effect are extremely rare and are usually associated with pituitary adenocarcinomas. However, pressure on the optic chiasma may induce ocular changes.

Diagnosis is difficult as imaging with CT or MRI may not reveal a mass within the sella turcica, requiring hypophyseal biopsy or exploratory craniotomy.

Definitive diagnosis usually requires intraoperative or postmortem biopsy, verifying adenomatous changes to the pituitary gland.

A differential diagnosis would include lymphoma, hypothalamic-pituitary trauma[7], dorsally expanding cysts, inflammatory granuloma, lymphocytic hypophysitis[8], congenital malformations such as empty sella syndrome and neoplasms such as infundibuloma, xanthogranuloma, craniopharyngioma, pituitary adenocarcinoma[9] and metastatic tumors such as metastatic mammary carcinoma, lymphoma[10], malignant melanoma and pancreatic carcinoma.

Treatment may be effective with corrective hormonal therapy (such as mitotane for hyperadrenocorticism, cabergoline for somatostain control[11], or hypophysectomy.

References

  1. Vet Path
  2. Goossens MM et al (1995) Central diabetes insipidus in a dog with a pro-opiomelanocortin-producing pituitary tumor not causing hyperadrenocorticism. J Vet Intern Med 9(5):361-365
  3. Melmed S (2003) Mechanisms for pituitary tumorigenesis: the plastic pituitary. J Clin Invest 112(11):1603–1618
  4. Ishino H et al (2011) Ki-67 and minichromosome maintenance-7 (MCM7) expression in canine pituitary corticotroph adenomas. Domest Anim Endocrinol 41(4):207-213
  5. Saunders, LZ & Rickard, CG (1952) Craniopharyngioma in a dog with apparent adiposogenital syndrome and diabetes insipidus. Cornell Vet 42(4):490-495
  6. Kemppainen RJ (1994) Animal models of Cushing’s disease. Trends Endocrinol Metab 5(1):21–28
  7. Foley C et al (2009) Hypothalamic-pituitary axis deficiency following traumatic brain injury in a dog. J Vet Emerg Crit Care (San Antonio) 19(3):269-274
  8. Meij BP et al (2012) Lymphocytic hypophysitis in a dog with diabetes insipidus. J Comp Pathol 147(4):503-507
  9. Goossens MM (1994) Diabetes insipidus in a dog with an αMSH-producing pituitary tumor. Vet Q 16(1):61
  10. Nielsen L et al (2008) Central diabetes insipidus associated with primary focal B cell lymphoma in a dog. Vet Rec 162(4):124-126
  11. Pivonello R et al (2009) The medical treatment of Cushing’s disease: effectiveness of chronic treatment with the dopamine agonist cabergoline in patients unsuccessfully treated by surgery. J Clin Endocrinol Metab 94(1):223–230