A pheochromocytoma is a tumor that usually arises in the adrenal medulla and the patient presents with signs and symptoms of excessive production of catecholamines. These symptoms are hypertension, a fast heart rate, palpitations, headache, sweating, flushing and anxiety. Sudden onset of hypertension (high blood pressure) in a young patient without any family history of hypertension should be investigated for the presence of endocrine tumors such as pheochromocytoma, Conn’s syndrome and abnormalities of the renal artery as a cause for their underlying hypertension.
Diagnosis of a pheochromocytomaThe diagnosis of pheochromocytoma is made by measuring for increased levels of catecholamines in the blood and in the urine. Catecholamines are broken down and excreted into the urine where some of the broken products such as VMA may be measured. The urinary measurements involve collection of the urine over a 24hour period for measurement of the breakdown products of catecholamines.
A diagnosis of a pheochromocytoma is made if the laboratory studies confirm elevated levels of catecholamines in the urine or blood. Once the diagnosis is confirmed on laboratory studies then further are aimed at localizing (finding) the tumor.
The following the studies are available to find the tumor:
CT ScanA CT scan is obtained to localize the tumor in the adrenal gland. Modern CT technology provides the diagnosis in more than 90% of patients with a pheochromocytoma in the adrenal gland. In about 10% of patients the tumor may occur outside the adrenal gland. These tumors are often much smaller and difficult to find on a CT scan and other studies such as an MIBG scan may be indicated.
MRI scans provide similar information to the CT scan. Adrenal tumors have a very rich blood supply and a pheochromocytoma light up very brightly on MRI scans providing the diagnosis.
Additional studies that are available for localizing a pheochromocytoma include the MIBG scan and octreotide scan. MIBG scans is used to detect adrenal pheochromocytoma. This test does not detect any other type of adrenal tumor. This is a radioisotope study in which a substance that is required by the adrenal gland to manufacture adrenaline is labeled with a radioactive isotope. Tumor tissue, which makes large amounts of catecholamines, will selectively take up the radioactive labeled substance. This is then identified as hot spot under a machine that detects the radioisotope.
Octreotide scans are useful in many neuroendocrine tumors. Many neuroendocrine tumors have receptors (tiny molecular holes) into which a hormone called somatostatin enters. In octreotide scan an antibody to this receptor is labeled with a radioisotope. Tumors that are rich with these receptors will have many of the antibodies bind to them. Many neuroendocrine tumors have much higher concentration of the somatostatin receptors compared to normal tissue. Injection of the antibody to the somatostatin receptor that is coupled with a radioisotope will selectively go to neuroendocrine tumors. Imaging the patient under a machine that recognizes the radioisotope produces a hot spot where the tumor is located. This is an important for study for localizing neuroendocrine tumors that are not visible on studies such as the CT scan and MRI scan.
Treatment of Pheochromocytoma
Prior to surgery adequate medical preparation of the patient is critically important to provide a good outcome from surgery. Patients require medications that block the excessive amounts of noradrenaline and adrenaline that is secreted by the tumor. A medication called phenoxybenzamine is used to block noradrenaline activity. This medication usually controls the hypertension and also allows an expansion of the blood volume. In patients with pheochromocytoma the blood volume is diminished because of the effects of the catecholamines. After some periods of treatment with phenoxybenzamine, a beta-blocker is added to control the effects of the excessive production of adrenaline from the tumor.
adrenalectomy is the treatment of choice for pheochromocytoma.
For the most favorable treatment outcome for this tumor,
careful planning prior to surgery amongst an experienced anesthesiologist,
endocrinologist and adrenal surgeon is very important. Adrenalectomy
for a pheochromocytoma should be performed only in centers that are experienced
in treatment of this disorder. Meticulous preparation described
above prior to surgery, is critical for good outcomes. The surgery should
be performed in a tertiary center equipped to do complex cases. Laparoscopic
adrenalectomy is the procedure of choice today. Close cooperation with
the anesthesiologist is critical during the surgery. Excessive manipulation
of the tumor should be avoided during the surgery to avoid life threatening
hypertension. The surgical procedure is safe and is associated with a
low complication rate in the hands of an experienced surgeon.
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