What are some parathyroid gland pathologies that may occur?
Parathyroid adenomas cause the affected parathyroid gland to appear solid and homogeneously hypoechoic as a result of compact cellularity and usually measure between 1 to 2 cm in greatest dimension. They are usually oval or bean shaped, but larger adenomas can be multilobulated and have cystic areas, and rarely calcifications. Color and power Doppler US imaging commonly show a characteristic extrathyroidal feeding vessel (typically a branch of the inferior thyroidal artery), which enters at one of the poles and travels around the periphery of the gland, resulting in a characteristic arc or rim of vascularity, an important distinguishing feature from lymph nodes, which have a central vascular supply. The sensitivity and specificity of US in localizing a solitary parathyroid adenoma are quite variable, ranging from 70% to 90%. The wide range of sensitivities is likely due to a variety of factors including patient size, quality of probe used, size and location of adenoma, concomitant thyroid disease, and, perhaps most important, the skill and experience of the sonographer. The specificity of US in locating parathyroid adenomas, on the other hand, is much more consistent and ranges from 92% to 97%.
The appearance of both hyperplastic parathyroid glands and parathyroid carcinoma can overlap with a parathyroid adenoma. In general, hyperplastic parathyroid glands are only minimally enlarged. Some consider the visualization of a parathyroid gland by neck US to be abnormal, reflecting a change from the high adipose content in a normal gland which blends in with the fibrofatty connective tissue of the neck and is difficult to visualize to a gland with hypercellular composition and visible hypoechogenicity. The patient is often not yet hypercalcemic at this stage but may become so in the future. Parathyroid cancers are relatively uncommon but should be suspected when a lesion demonstrates irregular margins or size over 2 cm. Parathyroid cysts may also be seen as anechoic lesions with posterior acoustic enhancement in the expected location of the parathyroid gland