5th April 2024

Phaeochromocytoma

Pathophysiology

A phaeochromocytoma is a rare tumour of the chromaffin cells within the adrenal medulla that produces excessive secretions of catecholamines e.g., adrenaline and noradrenaline. The 10% rule is used to describe the aetiology: 10% are malignant, 10% are extra-adrenal, 10% are bilateral and 10% are familial. From this, we can understand that most phaeochromocytomas are benign, sporadic tumours within one adrenal gland.

Clinical manifestations

The symptoms of a phaeochromocytoma occur due to the excess catecholamine levels and include headaches, diaphoresis, palpitations and hypertension. These symptoms generally occur in distinct episodes coinciding with the pulsatile release of catecholamines from the tumour.

Diagnosis

There is no definitive test for phaeochromocytomas but the initial approach in a patient with symptoms suggestive of it should be to measure catecholamine levels. This can be done through a blood test but catecholamine levels in the blood can be raised for a variety of reasons e.g., stress, and aren’t very specific for pheochromocytomas. Testing 24-hour urine collections for catecholamine levels is a much more specific test.

In a minority of patients, plasma or urine catecholamine levels may yield false-positive results. This may be because catecholamine levels in these individuals are always raised e.g., poor renal excretory function. In this cohort of patients, a clonidine suppression test can be used. Clonidine acts on adrenoreceptors at nerve terminals to decrease adrenaline release. However, a phaeochromocytoma will release adrenaline independently of this system and so adrenaline levels remain raised despite the administration of clonidine.

If there is biochemical evidence of a phaeochromocytoma, or if suspicion remains high despite negative tests, imaging such as CT or MRI of the adrenal glands are needed to confirm the diagnosis.

Management

Management is based around medically treating the effects of the tumour, particularly hypertension, followed by surgical resection. Some patients may present in hypertensive crises (SBP >250 mmHg) and will require urgent admission and medical management to reduce their blood pressure. This is usually achieved using phentolamine or nitroprusside.

Prior to surgery, steps must be taken to suppress the sympathetic system and stop the patient going into a hypertensive crisis. This is achieved through alpha blockers e.g., phenoxybenzamine or doxazosin, and then beta blockers if needed. Surgical excision of the affected adrenal gland is the main approach and is curative in 85% of cases. In the rare cases of malignant phaeochromocytoma, treatment is based around surgery followed by chemotherapy.

References

• Phaeochromocytoma. BMJ Best Practice. Last reviewed 24 Jan 2022
• Phaeochromocytoma. Oxford Clinical Handbook. 9ᵗʰ edition
• Medullary thyroid cancer. National Cancer Institute. Available at: https://www.cancer.gov/pediatric-adult-rare-tumor/rare-tumors/rare-endocrine-tumor/medullary-thyroid-cancer