A Functional Parathyroid Cyst from the Hemorrhagic Degeneration of a Parathyroid Adenoma

Abstract

A 77-year-old man with a history of hypertension, prostate hyperplasia, and urolithiasis was admitted for acute kidney injury caused by hypercalcemia. Neck ultrasonography showed a large cyst adjacent to the right lower thyroid lobe. Although a ^99mtechnetium sestamibi scan was negative, an extremely high intracystic intact parathyroid hormone level suggested that the cyst had a parathyroid origin and that a functional parathyroid cyst was present. Immunohistochemical staining for the calcium-sensing receptor (CaSR) after right lower parathyroidectomy revealed CaSR-positive cells lining the cyst, indicating that the functional parathyroid cyst had originated from the hemorrhagic degeneration of a parathyroid adenoma.

Keywords: acute kidney injury; functional parathyroid cyst; hypercalcemia; primary hyperparathyroidism.

Figure 1.

(A) Ultrasonography showing a large cyst with low echogenicity adjacent to the right lower thyroid gland. (B) Computed tomography showing a large cyst (arrow) compressing the trachea.

Figure 2.

The serum calcium, serum creatinine, intact parathyroid hormone levels, and cinacalcet dose administered after the patient was admitted to our hospital for the first time. When the patient’s serum albumin level was <4.0 g/dL, the albumin-corrected calcium level was calculated as total calcium (mg/dL)+0.8×[4.0-serum albumin (g/dL)]. The serum calcium level was stable for eight months following cinacalcet initiation, after which it began to increase, requiring frequent admissions.

Figure 3.

(A) Hematoxylin and Eosin staining showing a parathyroid adenoma (thick arrows) with adjacent atrophic parathyroid tissue (open arrows), cyst formation (asterisk), and hemorrhaging inside both the adenoma and cyst (thin arrows). (B) Immunohistochemical staining for the calcium-sensing receptor (CaSR) revealed that the cyst was lined with one layer of CaSR-positive cells, suggesting a functional parathyroid cyst.