What are some clinical, CT and MRI features of paraganglioma?
Paraganglioma, also known as an extraadrenal pheochromocytoma, is a rare neurogenic tumor that most commonly occurs in the fourth to fifth decades of life. In the abdomen, it most commonly arises in the retroperitoneum in the paired organs of Zuckerkandl that overlie the distal abdominal aorta. Ten percent of paragangliomas are multicentric, 40% are malignant (vs. 10% of adrenal pheochromocytomas), and 60% are functional (i.e., secrete catecholamines). Paragangliomas occurring in conjunction with gastrointestinal stromal tumors and pulmonary chondromas comprise Carney’s triad and occur with increased incidence in multiple endocrine neoplasia (MEN) syndrome types IIA and IIB, NF-1, von Hippel Lindau syndrome, and hereditary paraganglioma- pheochromocytoma syndrome (HPPS) related to genetic mutations in succinate dehydrogenase (SDH). Detection of elevated urine catecholamine levels is suggestive of the diagnosis.
A retroperitoneal mass is typically visualized with soft tissue attenuation, low-intermediate signal intensity on T1-weighted images, and intermediate-high signal intensity on T2-weighted images relative to skeletal muscle, sometimes with areas of low T2-weighted signal intensity, and progressive enhancement. Heterogeneity due to cystic change, hemorrhage, or calcification is often seen. Functional tumors tends to be smaller in size than nonfunctional tumors, but otherwise the two cannot be distinguished from one another on CT or MR imaging. Similarly, the presence of metastatic disease is the only definitive imaging criterion of malignancy.