Parathyroid ultrasonography is an easy, accessible, and inexpensive non-invasive test. It can localize the enlarged parathyroids, and evaluate thyroid gland to roll out any synchronous thyroid disease which can be found in around 18-20% of the patients with PHPT, with an overall malignancy rate of 2% (29). Linear ultrasound transducer with a frequency of 7.5-10 MHz is the stander. Normal parathyroids cannot be visualized by ultrasonography, but parathyroid adenomas appear on grayscale images as hypoechoic or anechoic, discrete, and oval homogenous hypervascular solid masses. Larger adenomas may show some cystic changes, lobulations, occasional calcifications, and increased echogenicity due to fatty deposition. A small branch of the inferior thyroid artery can be identified at its entrance to the parathyroid gland.
However, the sensitivity of ultrasonography fluctuates from 22% to 80%, because it is a hand and experience dependent. Furthermore, it is difficult to locate retroesophageal, retrotracheal, retrosternal, intrathyroidal, mediastinal, small glands, and deep cervical glands using ultrasonography. In some cases, it is difficult to differentiate the parathyroid adenoma from thyroid nodules, and cervical lymphadenopathy based on ultrasonography image only, so a biopsy is required.
Computed tomography (CT) scanning and Magnetic resonance imaging (MRI)
Traditional CT has had limited utility in imaging parathyroid adenomas. However, 4D CT includes CT angiography of the neck can calculate the parathyroid gland perfusion over time. Thus, 4D CT provides detailed information about parathyroid gland location and function. Typically, parathyroid adenomas present as enlarged, enhancing, soft-tissue masses in the expected location of the parathyroids. CT can detect parathyroid adenomas is around 90% of the cases. While, false-positive findings can be seen in present of thyroid nodule, tortuous vessel, or laterally displaced esophagus, false-negative result can be seen in the case of small or ectopic adenomas, distorted neck anatomy due to prior surgery. However, the CT has its own risk due to the use of the ionizing radiation and...