Surgical and medical management of midline ectopic thyroid

Hickman in 18691 is credited for the first report on lingual thyroid, which is the most common thyroid ectopia and accounts for 90 percent of reported cases.2 Ectopic thyroid is defined as thyroid cells that are located at sites other than anterior or lateral to the second, third, and fourth tracheal rings. Rare locations include the mediastinum,3 trachea,4 esophagus,5 aorta,6 heart,7 and abdomen (Fig 1).8 An ectopic thyoid has a prevalence of approximately 1 per 100,000 to 300,000 persons and is reported to occur in 1 in 4000 to 8000 patients with thyroid disease.9 Locations of ectopic thyroid: linguinal (1), intralingual (2), thyroglossal duct cyst (3), low neck ectopia (4), normal position (5), intratracheal (6), esophageal (7), mediastinal (8), aortic (9), intracardiac (10), abdominal (11). Anterior midline masses that appear suddenly are most commonly due to thyroglossal duct remnants. The differential diagnosis warrants that epidermal cyst, lymphadenopathy, lipoma, lymphangioma, neoplasms sebaceous cyst, cystic hygroma, dermoid cyst, and midline branchial cyst all be considered possibilities. Patients with the mentioned anomalies are typically euthyroid, and thyroid function remains normal after surgical excision of the midline mass, because the developed thyroid is usually in its correct anatomical location. Less frequently, such a quickly arising mass may be the result of an undescended thyroid that migrated incompletely during embryological development. Such glands may be located in any position from the foramen cecum all the way down to the mediastinum. If an ectopic thyroid gland is suspected, then an ultrasound of the normal thyroid or a radionuclide scan may be done to confirm clinical suspicion. Because 70 percent of patients with displaced thyroid lack thyroid tissue at its normal anatomical location, it is important to consider ectopia in the clinical differential diagnosis of midline neck masses.10 This ectopic tissue is prone to functional insufficiency and may come to attention only after compensatory enlargement. Because most of the time there is no other functioning thyroid tissue, the removal of thyroid ectopia frequently is followed by severe hypothyroidism.11 Thyroglossal duct cysts are common congenital lesions that typically present in the childhood years, but such lesions may include the entire thyroid in an atypical undescended location. These lesions can appear at almost any age, but most are apparent by the second decade of life. Sudden increases in size occur in concurrence with upper respiratory infections due to association of involved lymphoid tissue. When inflamed, thyroglossal duct cysts move with the hyoid bone during swallowing and are always within 2 cm of the midline. There have been a number of reports of the inadvertent surgical removal of an ectopic thyroid gland that was thought to be a thyroglossal duct cyst,12 which, as mentioned, can lead to profound hypothyroidism. A lingual thyroid may be discovered on routine oropharyngeal examination as a midline lingual mass originating in the area of the foramen cecum. Prominent veins are usually seen as well as a texture that noticeably differs from surrounding tongue tissue. During puberty or pregnancy, the lesion may become enlarged and cause dysphagia, dysphonia, or dyspnea.13 In rare instances, a patient is referred for a routine thyroidectomy during which the thyroid gland cannot be found. First and foremost, the relationship between the cricoid cartilage and the thyroid isthmus should be remembered. The isthmus is typically found 1 cm caudal to the cricoid cartilage. Second, the use of preoperative or intra-operative ultrasound should allow identification of thyroid tissue in almost all patients. Third, a lateral approach should be considered in performing any revisional thyroid surgery that involves extensive scarring. It also should be noted that cervical incisions that are too low often make it difficult to visualize the thyroid. The thyroid gland is the first endocrine gland to develop in the embryo. The thyroid gland appears in the 3rd to 4th week of development as an epithelial proliferation in the pharyngeal floor between the tuberculum impar (which becomes the anterior two thirds of the tongue) and the hypo-branchial eminence (which becomes the posterior one third). This site of origin of the thyroid then becomes the site at which the foramen cecum develops. This thickening soon forms a small outpouching that becomes the thyroid diverticulum. The thyroid then descends in front of the pharyngeal gut as a bilobed diverticulum. While the thyroid is migrating caudally, the thyroglossal duct maintains a connection between the thyroid and the tongue. This duct later regresses between the 5th and 10th embryonic weeks. Continuing on its path, the thyroid gland descends anterior to the hyoid bone and the laryngeal cartilages. In the seventh week of embryonic development, the thyroid reaches its final position in front of the trachea anterior to the developing second and third tracheal rings. Functional thyroid tissue appears at the end of the third month, at which time follicles containing colloid become visible.14 If the thyroid varies from this normal path, it is considered to be ectopic. The three diagnostic aids in evaluating a midline mass are radionuclide thyroid scanning, ultrasound, and computed tomographic (CT) scanning. The use of radioactive iodide and pertechnetate to determine the size, distribution, and activity of thyroid tissue is well-established. The use of technetium-99m pertechnetate is generally preferred to iodine-131, because the radiation dose is lower. There has been a great deal of controvery over whether to order radionuclide scanning or other studies in patients with midline neck masses. A 1992 survey revealed that 28 percent of pediatric surgeons versus 65 percent of pediatric otolaryngologists routinely order scans.15 Several reports in the literature suggest that ultrasound can be used to accurately determine the presence of a normal thyroid, thereby excluding the possibility of a lone ectopic thyroid gland masquerading as a thyroglossal duct cyst.16 However, it has been established that a pitfall in this study shows that an altered configuation of the infrahyoid muscles may produce a "pseudothyroid" gland appearance in cross-section. This anomaly has caused isolated ectopic thyroid to be inadvertantly excised.17 Although ectopic thyroid gland simulating a thyroglossal duct cyst is a very rare condition, it still warrants clinical suspicion, because it can lead to severe hypothyroidism. Aberrant thyroid tissue can be observed with a CT scan, but this diagnostic medium is usually avoided because of cost and the provision of similar results by ultrasound and radionuclide scanning. Small thyroglossal duct cysts that escape infection need not be excised. Recurrence after simple excision of the cyst reached as high as 50 percent before Schlange introduced in 1893 a procedure involving removal of the central portion of the body of the hyoid bone. This procedure reduced the recurrence to 20 percent until Sistrunk proposed in 1920 concomitant removal of the proximal duct, thus lowering recurrence to 3 percent. Sistrunk's procedure is the mainstay of therapy to this day.18 No treatment is required for a patient with a lingual thyroid or parathyroid gland. A hypothyroid patient with obstructive symptoms is best managed with hormone replacement therapy, which induces glandular shrinkage. If obstructive symptoms cannot be relieved, then excision is required and, if it is the only thyroid tissue, the patient will require lifelong hormone replacement therapy. Techniques of thyroid transplant that have become more promising include autotransplantation of the thyroid tissue to the lateral pharyngeal wall involving a vascular pedicle.19, 20