Scintigraphic parathyroid imaging: concepts and new developments

Abstract

Hyperparathyroidism is a condition caused by increased secretion of the parathyroid hormone, which plays an important role in calcium homeostasis. This condition has been diagnosed more frequently recently and can affect multiple organ systems resulting in a variety of signs and symptoms. Hyperparathyroidism can be classified as primary, secondary, or tertiary disease and can result from eutopic or ectopic parathyroid lesions. Parathyroid adenoma is the most common cause of primary hyperparathyroidism, accounting for more than 80% of cases. Parathyroid hyperplasia is the cause in about 20% of patients, while parathyroid carcinoma is rare and accounts for less than 1% of cases. Surgical removal of the abnormal gland(s) is the definite treatment for hyperparathyroidism. Bilateral neck exploration is the classical approach for parathyroidectomy. In recent years, minimally invasive parathyroidectomy is becoming more popular due to the fewer complications and shorter hospital stay. This new approach has placed a greater emphasis on the preoperative localization techniques. Multiple localization techniques have been used, including invasive techniques, anatomical, and scintigraphic imaging modalities. Thallium/pertechnetate subtraction method was introduced in 1980 and was the first method to gain widespread acceptance. It is not widely used now due to the suboptimal characteristics of thallium and the technical difficulties associated with subtraction and registration. The dual-phase method using Tc-99m sestamibi is currently the method of choice for parathyroid localization. It is based on the differential washout rate of sestamibi from the thyroid and abnormal parathyroid glands. The reported sensitivity of this method ranges from 80% to 90%. The addition of single-photon emission computed tomography (SPECT) and more recently SPECT/CT improves the anatomical localization and helps in the differentiation of the parathyroid from the thyroid lesions. Multiple factors can affect the sensitivity of the scan including the lesion size, cellularity, and the presence of P-glycoprotein. Modification of the imaging protocol may help to avoid false positive or false negative results in certain cases. Positron emission tomography has been recently investigated for possible role in parathyroid imaging and showed promising results with 11 C-methionine.