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PREOPERATIVE DIAGNOSIS OF PARATHYROID CARCINOMA

Parathyroid carcinoma (PC) is one of the most rare known malignancies and accounts for less than 1 % of primary hyperparathyroidism (PHTP). However, there are reports from the United States, Australia and Finland indicating increasing incidences. PC is rather aggressive malignancy with a high recurrence rate ( > 50 %) and 5-year survival rate in metastatic disease < 50 %. Patients with PC should have primary radical en bloc surgery, performed by an experienced endocrine surgeon, as this is the only treatment that can ensure cure. Therefore, preoperative diagnosis of PC is extremely important. PC is a very rare disease and may be overlooked.

In the majority of cases PC is diagnosed postoperatively by histological examination, which may be demanding, especially in patients with atypical parathyroid adenoma. Some patients are correctly diagnosed only because of persistent disease after surgery or later recurrent or metastatic disease. Preoperative diagnosis is not easy, since PC cannot always be distinguished from benign causes of primary hyperparathyroidism (PHPT), as no disease-specific markers are available. However, there are some findings from the preoperative evaluation that may be useful for the preoperative diagnosis of PC, such as:

1.Local invasion of adjacent anatomic structures (trachea, inferior laryngeal nerve, strap muscles)

2.Occurence of distant or lymph node metastases

3.Palpable mass

4.Serum calcium levels > 3.5 mmol/L (*)

5.Markedly elevated PTH levels (*)

6.Severe renal and/or bone disease

7.Large (> 3 cm), hypoechoic/heterogeneous parathyroid gland on ultrasonography, with irregular borders, thick capsule, suspicious vascularity and calcifications (these ultrasonographic features may also be seen in parathyroid adenomas).

Preoperative fine-needle parathyroid biopsy is not recommended since it cannot distinguish a benign from a malignant lesion and has a risk of tumoral rupture and seeding.

(*) Very rarely PC is nonfunctioning  and these patients have normal levels of plasma calcium and PTH

(**) Sensitivity of preoperative imaging increases when the three diagnostic methods (ultrasonography, computed tomography and sestamibi-scan) are used together (combined preoperative imaging studies)