There are usually two pairs of parathyroid glands located in the neck. The superior parathyroid glands develop from the fourth pharyngeal pouch and the inferior glands develop from the third pharyngeal pouch. Anatomically these glands descend down into the neck, with the superior glands usually located near the cricothyroid junction, the dorsum of the upper pole of the thyroid or the retropharyngeal space and the inferior glands located close to the lower pole of thyroid or thymus. Rarely the inferior parathyroids may be at an ectopic location in the upper or lateral neck and mediastinum.
Hyperplasia of these glands or an adenoma occurring in anyone of these glands results in primary hyperparathyroidism. This results in increased production of the parathyroid hormone subsequently causing hypercalcemia and hypophosphatemia. These patients may be asymptomatic or have varied symptoms including peptic ulcerations, osseous brown tumors, nephrolithiasis and altered sensorium. Preoperative localization of these tumors has become important in the era of minimally invasive parathyroid surgery, which is the definitive treatment for these tumors.
The normal parathyroids are not commonly visualized on ultrasound. High-resolution gray scale and color Doppler ultrasound has been increasingly used to localize the parathyroid adenomas in the neck. They are usually visualized as soft tissue hypoechoic masses situated in close proximity to the thyroid gland. This preoperative localization has been reported to aid in reducing the operative exploration time, and may even obviate the need for contralateral neck exploration. Color and Power Doppler studies may additionally reveal feeding vessels to the adenoma making it more conspicuous. This feature also aids in differentiating it from an enlarged lymph node. Studies by Wolf, et al have reported the presence of a vascular arc formed by the branches of inferior thyroidal artery [90 to 270 degrees] around an adenoma, which is distinct from the central hilar flow that is characteristically seen in a lymph node. Demonstration of an extrathyroidal artery leading to the adenoma and increases in peak systolic velocities in the inferior and superior thyroid arteries ipsilateral to the adenoma aiding in more accurate localization of the adenoma have all been reported.
The other imaging modalities that can be used include scintigraphy, CT and MRI. Parathyroid scintigraphy with (99m) Tc-sestamibi is based on longer retention of the tracer in parathyroid than in thyroid tissue. Mariani, et al recently concluded that because of the frequent association of parathyroid adenomas with nodular goiter, the optimal imaging combination is (99m) Tc-sestamibi scintigraphy and ultrasonography. This enables the surgeon to perform minimally invasive parathyroid surgery versus bilateral neck exploration which was routinely required in the past.
The case demonstrated here also showed the presence of multiple nodules within the thyroid. Simultaneous occurrence of parathyroid adenomas and thyroid nodules are frequently noted and ultrasound in such cases accurately identifies both the entities, making simultaneous treatment, if required possible.