The pheochromocytoma is the most common tumor of the adrenal gland medulla. The “rule of tens” applies to pheochromocytomas stating that bilateral affection is present in 10% of cases, malignant transformation occurs in 10% of cases, 10% are familial, and 10% of all pheochromocytomas may occur in the ganglions along the course of the sympathetic chain outside of the adrenal gland medulla.
In 5 to 10% of all cases, pheochromocytoma is associated with other neuroectodermal diseases such as neurofibromatosis, von Hippel-Lindau syndrome, tuberous sclerosis, and Sturge-Weber syndrome.
Three percent of all pheochromocytomas are associated with multiple endocrine neoplasms (MEN II). In patients suffering from MEN syndromes, pheochromocytomas are virtually always bilateral and almost never extra-adrenally located.
Malignant pheochromocytomas seem to be more often located extra-adrenally than in the adrenal medulla. They metastasize preferably into the lungs, the liver, and the skeleton.
At the time of diagnosis, pheochromocytomas are most often larger than 3 cm and measure on average 5 cm in diameter. Large tumors are irregularly bordered.
A typical characteristic of pheochromocytomas is the high SI on T2-weighted images. Even compared to the retroperitoneal fat tissue they are hyperintense. Large pheochromocytomas can reveal necrosis, hemorrhagic transformed areas, and cysts. From these features, inhomogeneous SI can result on T2-weighted images.
Calcifications of the tumor, which can be seen in up to 7% of the cases on CT images, are another source of inhomogeneous SI.
Malignant pheochromocytomas cannot be differentiated from benign pheochromocytomas based on imaging findings. The sole criterion for the definition of malignant disease is the invasive nature of the tumor growth and the detection of distant metastases.
After bolus injection of paramagnetic contrast agents, pheochromocytomas reveal a contrast pattern similar to that of metastases and carcinomas, with substantial signal increase and signal increase lasting as long as 50 min.