Pheochromocytoma

Basics

Pheochromocytoma (pheo) is a catecholamine-producing tumor arising from the chromaffin tissues of the sympathetic nervous system
Origin from the adrenal medulla or sympathetic ganglia:
- 80% solitary adrenal (usually the right side)
- 10% bilateral
- 10% extra-adrenal in location:
  - Abdominal, within mesenteric ganglia (86%)
  - Thorax (10%), neck (3%), bladder (1%)
- 10% malignant
Incidence:
- 0.2–0.4% of hypertensive patients, but higher proportion of patients with severe hypertension
- 2–8/million population per year
- Peaks in decades 3–5, 10% in children
- Male = female, average age 40–50 yr
- In about 1/2 of the cases, the diagnosis is made postmortem
- 10% asymptomatic, incidental on CT
Genetics:
- Inherited form 10–20%, autosomal dominant
- More likely to be bilateral, extra-adrenal and malignant
- Usually associated with multiple endocrine neoplasia (MEN) 2A, less so with MEN 2B or von Hippel–Lindau (VHL) disease:
  - MEN 2A (medullary thyroid carcinoma [CA], pheo, and hyperparathyroidism)
  - MEN 2B (medullary thyroid CA, pheo, oral mucosal neuromas, skeletal and bony abnormalities)
  - VHL (hemangioblastomas of retina and CNS, pancreas and renal cysts, and pheo)
- Other associated diseases: Neurofibromatosis, tuberous sclerosis, Sturge–Weber syndrome, paragangliomas of the neck

The tumor synthesizes and stores catecholamines in the same manner as the normal adrenal medulla
Tumors predominantly secrete norepinephrine, and to a lesser extent epinephrine (some tumors are epinephrine predominant, in which hypotensive episodes are characteristic) and dopamine
Paroxysmal release of catecholamines:
- Spontaneously due to changes in blood flow or tumor necrosis
- Direct pressure on the gland from external forces (trauma, exercise)
- Precipitation of release (opiates, glucagon, metoclopramide, steroids, foods with tyramine, iodinated contrast media)
- Augmentation of catecholamine effect (tricyclic antidepressants [TCAs], β-blockers, sympathomimetics)

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