Cytomorphology of cystic parathyroid lesions: report of four cases evaluated preoperatively by fine-needle aspiration.

Cystic parathyroid lesions (CPL) account for 1-5% of neck cysts. They are seldom palpable; however, they may present as neck swellings that are mistaken both clinically and cytologically for thyroid nodules and subsequently referred for evaluation by fine-needle aspiration. We present 4 cases of histologically confirmed CPL (one simple cyst, one hyperplasia, and two adenomas), 2 of which were misdiagnosed as adenomatoid thyroid nodules by fine-needle aspiration. Aspirated fluid from one patient was clear and colorless, a classic finding for parathyroid cysts, and contained high levels of C-terminal/midmolecule parathyroid hormone (CMPH). Fluids obtained from the remaining 3 patients were bloody to brown, resembling thyroid cyst fluid. In only 1 of the 3 patients, the fluid was analyzed and contained high levels of CMPH. Though cytologic features of parathyroid epithelium overlap with those of thyroid epithelium, distinguishing features such as unusual cytoplasmic vacuolization and granularity, and the absence of colloid, should raise suspicions of a parathyroid lesion. Fluid from CPL may not possess the classic appearance; however, identification of the subtler cytologic features with knowledge of relevant clinical data should prompt analysis of cyst fluid for CMPH, thus confirming the diagnosis and avoiding inappropriate therapy.