JAFES, Vol. 27 No. 2 November 2012
Here we describe 4 cases with cystic lesions of the parathyroid gland. Three of these (Cases 1,2 and 3) had parathyroid adenomas with cystic degeneration whereas Case 4 had a true parathyroid cyst. Cystic lesions of the parathyroid gland are rare (0.5%–1% of all parathyroid pathologies). Macroscopic cysts larger than 1 cm in diameter are referred to as parathyroid cysts and necessitate further investigation. Some investigators have suggested that the true prevalence of parathyroid cysts remains uncertain and that these lesions may occur more frequently than is generally appreciated.Cystic lesions of the parathyroid gland can be either due to true parathyroid cyst as seen in Case 4, or due to cystic degeneration of parathyroid adenoma as seen in Cases 1, 2 and 3. Most of the parathyroid gland adenomas are solid while cystic degeneration is seen in 1-2% of patients with primary hyperparathyroidism.
Approximately 90% of true parathyroid cysts are classified as nonfunctioning cysts with normal calcium concentrations and 10% are functioning cysts with elevated calcium concentration. However, in one study, functioning parathyroid cysts were more common. A true parathyroid cyst needs to be differentiated from a parathyroid adenoma with cystic degeneration. Parathyroid cysts are more frequent in females between 20 to 60 years of age, whereas parathyroid adenomas are more common after 50 years of age.
Patients with true nonfunctional parathyroid cysts present with compressive symptoms. On the other hand, patients with true functional parathyroid cysts and patients with cystic parathyroid adenoma present with signs and symptoms of hypercalcemia.
Parathyroid cysts are of variable sizes, ranging from 1 to 10 cm in greatest dimension, with the average cyst measuring approximately 3 to 5 cm. In 85 - 90% of cases, they are located in the neck and often involve the inferior parathyroid glands. In 5 - 10% of cases they have been detected at ectopic sites anywhere from the angle of the mandible to the mediastinum. The mediastinal location of the parathyroid cyst can be ascribed to two factors. First, the cyst may descend into the mediastinum because of its weight and negative intrathoracic pressure. Second, an aberrant mediastinal parathyroid gland may give rise to the cyst.
Degeneration of an existing parathyroid adenoma secondary to hemorrhage into the adenoma, also results in cyst formation. The other different theories proposed are: (1) retention of glandular secretions, (2) persistence of vestigial pharyngobranchial ducts, (3) persistence of Kursteiner's canals, (4) enlargement of a microcyst, or (5) coalescence of the microcysts. None of these theories are
universally applicable, and the processes leading to cyst formation may well differ from one person to the next.
Ultrasonography may reveal a nonspecific cystic structure. Analysis of the aspirate generally reveals elevated PTH level, diagnostic of parathyroid cyst.Nonfunctional parathyroid cysts have high fluid PTH
concentrations, in conjunction with normal serum PTH concentrations.
In functional parathyroid cysts, cystic fluid PTH levels can reach several million pg/ml.PTH levels in the cystic fluid were measured only in the fourth patient.
The histologic distinction between a cystic parathyroid adenoma and the rare functional parathyroid cyst is made by the former having a preponderance of chief cells with multilocular degenerative thick-walled cysts and the latter usually consisting of a unilocular thin-walled cyst.
Treatment strategies for parathyroid cysts include surgical excision or aspiration or injection of sclerosing agents.Surgical treatment seems to be the preferred intervention for functional and symptomatic parathyroid cysts as in our patient. Fine-needle aspiration yields the diagnosis and may be considered the treatment of choice for nonfunctional parathyroid cysts. It leads to cystic regression without recurrence.
Several reports in the literature support fine-needle aspiration as a therapeutic modality. For recurrent nonfunctional parathyroid cysts, sclerotherapy with use of tetracycline and alcohol has also been described. It has been effective but is associated with the risk of subsequent fibrosis and recurrent laryngeal nerve palsy.If aspiration cannot be done safely or the cyst recurs after successful aspiration, surgical excision should be done.