ACR Codes: 8.5
Pheochromocytoma is a paraganglioma, a functional adrenergic tumor. Other functional adrenergic tumors include neuroblastomas, ganglioneuroblastomas and ganglioneuromas. Pheochromocytoma is a rare tumor that causes symptoms including hypertension, headache, tremors, palpitations, sweating, flushing and anxiety. The symptoms are produced by excessive secretion of catecholamines by the tumor. Paroxysmal symptoms are characteristic but not always present. These paroxysms may be precipitated by emotional stress, exercise, abdominal pressure, anesthesia or intake of tyramine-containing foods. Hypertension associated with pheochromocytoma does not respond to standard antihypertensive medications.
Pheochromocytomas are said to follow the 'rule of tens':
10% are bilateral*
10% are extraadrenal
- They can occur in any sympathetic ganglion in the body.
- Extraadrenal sites include the paraaortic sympathetic chain, the organ of Zuckerkandl, and even the bladder.
10% are malignant
10% are familial
- MEN IIA aka Sipple Syndrome (medullary thyroid cancer and pheochromocytoma + parathyroid adenoma) and IIB (+ mucosal neuromas), other neuroectodermal disorders (ie von Hippel-Lindau, Neurofibromatosis, and Tuberous Sclerosis)**
* our patient
** chances are small in our patient given her age
The diagnosis is made by demonstrating elevated urinary excretion of catecholamines or their metabolites, the metanephrines, and VMA (Vanillylmandelic acid) during a period of hypertension. The single best test is urinary metanephrines but usually the panel obtained is urinary metanephrine levels, urinary total catecholamines, and VMA. Once the clinical diagnosis is made, a CT of the adrenals is performed. Extraadrenal pheochromocytoma can be excluded by an 131-I or I-123 MIBG scan or an abdominal MRI.
On CT, the tumor size is typically greater than 2 cm in diameter. The tumors vary in appearance from purely solid to predominantly cystic. Calcifications are rare, but, if present, are eggshell type. Consistent with non-adenomatous lesions, they are greater than 10 HU on noncontrast images and densely enhance after contrast with HU > 37. On delayed images, there is delayed wash-out with HU > 60% pre-washout values.
On MRI, the tumor has an extremely bright signal intensity ("light bulb bright") on T2WI that makes it stand out from surrounding structures.
Regarding I-131 or I-123 labeled MIBG scans: MIBG or metaiodobenzylguanidine is an analog of guanethidine. This agent is taken up by the active amine transport system in adrenergic nerves. This agent can be radiolabeled with both I-131 and I-123. I-123 has the advantage of a lower radiation dose to the patient and I-131 facilitates delayed imaging. To achieve sufficient target to background ratios, imaging is typically delayed 24 hours after tracer administration and may be repeated at Day 2 or Day 3. (Other tissues which demonstrate uptake include organs rich in adrenergic innervation including the heart, salivary glands, spleen and even liver. Bladder activity is seen if there is free radioiodine). With time, visualization increases in the adrenal medulla as the other organs clear. For pheochromocytoma, the posterior view of the midabdomen with the region of the adrenals is key. Additional images from the pelvis to the base of the skull are indicated to detect extraadrenal foci. Sensitivity for the detection of pheochromocytoma is 90% or better with specificity 95% or better.
In this patient, MIBG was labeled with I-123 and images obtained at 2-3 hours with delayed imaging at 24 and 48 hours using SPECT.
The treatment of pheochromocytoma is surgical. Therapy with I-131 MIBG is experimental.
Reference(s): 1) Andreoli, TE, et al. Cecil Essentials of Medicine. 4th ed. WB Saunders, 1997. 507-508.
2) Slone, RM, et al. Body CT A Practical Approach. McGraw-Hill, 2000. 183-184.
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