A benign or malignant neuroendocrine neoplasm of the sympathetic nervous system that secretes catecholamines. It arises from the chromaffin cells of the adrenal medulla. Clinical presentation includes headaches, palpitations, chest and abdominal pain, hypertension, fever, and tremor. Microscopically, a characteristic nesting (zellballen) growth pattern is usually seen. Other growth patterns including trabecular pattern may also be present.