Ectopic Parathyroid Glands and their Anatomical, Clinical and Surgical Implications

Abstract

Ectopic parathyroid glands result from aberrant migration during early stages of development and lack of successful identification may lead to lack of success in parathyroid surgery. They constitute a common etiology of persistent or recurrent hyperparathyroidism, when they are missed at initial diagnosis. Their prevalence is about 2-43% in anatomical series and up to 16% and 14% in patients with primary and secondary hyperparathyroidism, respectively. Ectopic inferior parathyroids are most frequently found in the anterior mediastinum, in association with the thymus or the thyroid gland, while the most common position for ectopic superior parathyroids is the tracheoesophageal groove and retroesophageal region. Neck ultrasound and 99mTc Sestamibi scan are first-line imaging modalities, although with low sensitivity and specificity. However, their combination with modern techniques, such as single photon emission computed tomography (SPECT) alone or in combination with CT (SPECT/CT) increases their diagnostic accuracy. Fine needle-aspiration cytology of a lesion suspicious for parathyroid tissue and measurement of parathyroid hormone (PTH) in the aspired material further assist to the successful preoperative localization of ectopic glands. Common sites for surgical investigation are the upper thyroid pole and the upper vascular thyroid stalk behind the hypopharynx and cervical esophagus for the superior parathyroids, and the carotid artery bifurcation and the thymic tongue, for the inferior parathyroids. Radioguided minimally invasive parathyroidectomy after successful localization, assisted by rapid PTH measurement postoperatively, significantly improves surgical outcomes in patients with ectopic parathyroid adenomas.

Mediastinal parathyroid adenomas and their surgical implications

“…4 Imaging studies have reported low incidence (1.4%) of ectopic parathyroid adenomas in patients who underwent investigation for primary hyperparathyroidism. The actual prevalence of MPA is unknown but has been reported to be 6-30%.…”

Hypercalcemic Crisis Secondary to A Parathyroid Hormone-Secreting, Intrathymic, Cystic, Parathyroid Adenoma

“…The superior and inferior parathyroid glands develop from the dorsal wing of the fourth and third pharyngeal pouches, respectively, along with the thymus. The inferior glands can migrate with the thymus; hence they are more likely to be found in ectopic locations (2,5). Previous cases of functional, Fig.…”

“…The majority of PHPT cases are asymptomatic and are detected incidentally with hypercalcaemia on bloodwork. PHPT results from the intrinsic abnormal change in 1 or more of the 4 parathyroid glands, in which excess parathyroid hormone (PTH) is secreted autonomously (1,2). PHPT is commonly caused by a single parathyroid adenoma (75 to 85%), parathyroid gland hyperplasia (10 to 20%), multiple adenomas (4 to 5%), and rarely carcinoma (1%) (1,3).…”

“…Ectopic adenomas can be located anywhere from the base of the tongue to the mediastinum (7). Intrathymic parathyroid gland comprises 30% of ectopic cases, followed by the anterior-superior mediastinum (22%), within the thyroid gland (15 to 22%), in the thyrothymic ligament (17%), and in the submandibular region (9%) (2,5,8).…”

Primary hyperparathyroidism caused by mediastinal ectopic parathyroid adenoma

“…It is well known that parathyroid glands can be found in aberrant locations, mainly in the thyroid parenchyma or in the mediastinum. 3 The high incidence of ectopic inferior parathyroid glands has been attributed to abnormal migration during embryogenesis. Since parathyroid glands lack capsular fixation, an ectopic parathyroid gland may also develop from a gland that is initially present in a normal anatomic position but which enlarges and is displaced to an ectopic location where there is little resistance.…”