Parathyroid cysts: report of a case with ultrastructural observations.

Parathyroid cysts are an uncommon cause of neck masses which are of uncertain origin. Electron microscopic observations reveal the cysts to be lined by a simple absorptive rather than secretory cell, which rests on a basement membrane. These are not cheif cells. Smooth muscle forms an integral part of the cyst wall. These findings of simple epithelial cells and mesenchymal tissue (smooth muscle) support the concept that these cysts represent persistent embryological remnants. A likely source is the third pharyngeal pouch.