What is an adrenal pheochromocytoma, and what are its CT and MRI features?
Adrenal pheochromocytoma is a relatively rare neuroendocrine tumor that is derived from the adrenal medulla, which may be benign or malignant in its biologic behavior. It affects women slightly more commonly than men, and it is most commonly seen in the third through fifth decades of life. Symptoms and signs, including headache, palpitations, diaphoresis, and hypertension, commonly occur secondary to catecholamine secretion, and detection of increased levels of catecholamines or metanephrines in the urine is essentially diagnostic. The “10% rule” is a useful mnemonic, because ≈10% of pheochromocytomas are malignant in their behavior, ≈10% occur bilaterally, ≈10% are extraadrenal in location (also known as paragangliomas), ≈10% are nonhyperfunctional, and ≈10% are associated with hereditary conditions.
On CT and MRI, an adrenal soft tissue nodule or mass is seen, which tends to be homogeneous in attenuation and signal intensity and avidly enhancing when small in size and heterogeneous when large in size secondary to hemorrhage, cystic change, and/or necrosis. Calcification is seen in ≈15% of cases. Occasionally, the lesion may be predominantly cystic in nature, potentially mimicking adrenal adenomas or cysts. Pheochromocytomas may also sometimes have an APW >60% or an RPW >40%, again potentially mimicking adrenal adenomas. A malignant behavior is suspected when invasion of adjacent organs, regional lymphadenopathy, or distant metastatic lesions are seen. Metastatic lesions from adrenal pheochromocytoma tend to avidly enhance during the arterial phase of enhancement.