Pheochromocytoma in Horses (Equis) | Vetlexicon
equis - Articles


ISSN 2398-2977

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  • A pheochromocytoma is the most frequently diagnosed adrenomedullary neoplasm of equids although the disorder itself is extremely rare.
  • Cause: neoplasm of chromaffin cells or tissue.
  • Signs: profuse sweating, edema, cardiac problems, colic. May be asymptomatic.
  • Treatment: adrenalectomy
  • Prognosis: good to guarded.

Presenting signs

Acute presentation

  • Sudden death due to cardiovascular collapse, like rupture of a vessel wall due to hypertension.
  • Colic.
  • Sweating, tachycardia Heart: ventricular tachycardia.

Age predisposition

  • 0.5-31 years.

Special risks

  • Sudden death due to rupture of a vessel wall (in the neoplasm) following hypertension.



  • Neoplasm of chromaffin cells of either the left or the right adrenal gland.
  • Both adrenal glands may be involved.


  • The exact cause of the neoplasm is unknown.
  • The clinical signs are largely attributable to the increased production and release of catecholamines.


  • Unknown.
  • Some cases are asymptomatic.


Presenting problems

Client history

  • Profuse intermittent sweating Skin: perspiration - heavy.
  • Excitement.
  • Intermittent colic Abdomen: pain - adult.
  • Tachypnea.
  • Ventral edema Abdomen: ventral edema 01Abdomen: ventral edema 02.

Clinical signs

Diagnostic investigation


  • Hormone assay:
    • Measurement of circulating catecholamines and/or their urinary metabolites.
    • Most veterinary laboratories are not equipped to assay for equine plasma, urinary catecholamines or metabolites.


  • Hemoconcentration.


Abdominal ultrasound

  • Abdominal ultrasound may allow visualization of a large soft tissue mass adjacent to or within either (or both) kidneys
  • The tumor may obscure the view of the associated kidney and other normal adjacent structures

Confirmation of diagnosis

Discriminatory diagnostic features

  • Hormone assay: in the equine species it is not certain whether adrenaline Epinephrine or noradrenaline is predominantly produced by pheochromocytomas.

Definitive diagnostic features

  • Measurement of circulating catecholamines and/or their urinary metabolites.

Gross autopsy findings

  • Uni- or bilateral neoplasm involving the adrenomedullary chromaffin cells usually without metastasis.
  • Up to 20-30 l of blood within the abdominal cavity.

Histopathology findings

  • Well encapsulated circumscribed nodules of chromaffin cells.


Initial symptomatic treatment

  • Unilateral adrenalectomy.


  • Measurement of circulating catecholamines and/or their urinary metabolites.
  • Heart rate Heart: auscultation.
  • Pupillary diameter Pupil: normal.
  • Absence of excessive sweating.

Subsequent management





  • Complete regression of signs may be expected following successful adrenalectomy of the diseased gland.

Reasons for treatment failure

Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Johnson P J, Goetz T E, Foreman J H & Zachary J F (1995) Pheochromocytoma in two horses. JAVMA 206, 837-841 PubMed.
  • Yovich J V, Horney F D & Hardee G E (1984) Pheochromocytoma in the horse and measurement of norepinephrine levels in horses. Can Vet J 25, 21-25 PubMed.
  • Yovich J V & Ducharme N G (1983) Ruptured pheochromocytoma in a mare with colic. JAVMA 183, 462-464 PubMed.