A lingual thyroid is relatively rare and is estimated to occur in 1 in 3000 cases of thyroid disease. However, it represents the most common location for functioning ectopic thyroid tissue. Lingual thyroid tissue is associated with an absence of the normal cervical thyroid in 70% of cases. It occurs much more commonly in women than in men.

The diagnosis is usually made by the discovery of an incidental mass on the back of the tongue in an asymptomatic patient (Fig. 18 b). The mass may enlarge and cause dysphagia, dysphonia, dyspnea, or a sensation of choking (75). Hypothyroidism is often present and may cause the mass to enlarge and become symptomatic, but hyperthyroidism is very unusual. In women, symptomatic lingual thyroid glands develop during puberty or early adulthood in most cases. Buckman, in his review of 140 cases of symptomatic lingual thyroids in females, reported that 30% occurred in puberty, 55% between the ages of 18 and 40 years, 10% at menopause, and 5% in old age (76). He attributed this distribution to hormonal disturbances, which are more apparent in female subjects during puberty and may be precipitated by pregnancy. The incidence of malignancy in lingual thyroid glands is low (77). The diagnosis of a lingual thyroid should be suspected when a mass is detected in the region of the foramen cecum of the tongue, and it is definitively established by radioisotope scanning (Fig. 18a).

The usual treatment of this condition is thyroid hormone therapy to suppress the lingual thyroid and reduce its size. Only rarely is surgical excision necessary. Indications for extirpation include failure of suppressive therapy to reduce the size, ulceration, hemorrhage, and suspicion of malignancy (78). Autotransplantation of thyroid tissue has been tried on rare occasions when no other thyroid tissue is present, and it has apparently been successful. A lingual thyroid was reported in two brothers, which suggests that this condition may be inherited (79).

Both cysts and fistulas can develop along the course of the thyroglossal duct (80) (Fig. 19). These cysts are the most common anomaly in thyroid development seen in clinical practice. Normally, the thyroglossal duct becomes obliterated early in embryonic life, but occasionally it persists as a cyst. Such lesions occur equally in males and females. They are seen at birth in about 25% of cases; most appear in early childhood; and the rest, about one-third, become apparent only after age 30 years (82). Cysts usually appear in the midline or just off the midline between the isthmus of the thyroid and the hyoid bone. They commonly become repeatedly infected and may rupture spontaneously. When this complication occurs, a sinus tract or fistula persists. Removal of a thyroglossal cyst or fistula requires excision of the central part of the hyoid bone and dissection of the thyroglossal tract to the base of the tongue (the Sistrunk procedure) if recurrence is to be minimized. This procedure is necessary because the thyroglossal duct is intimately associated with the central part of the hyoid bone (Fig. 20). Recurrent cysts are very common if this operative procedure is not followed.

At least 115 cases of thyroid carcinoma have been reported to originate from the thyroglossal duct (81). Often, in such cases an association is noted with low-dose external irradiation of the head and neck in infancy or childhood. Almost all carcinomas have been papillary, and their prognosis is excellent. If a carcinoma is recognized, at the time of surgery the thyroid gland should be inspected for evidence of other tumor nodules, and the lateral lymph nodes should be sampled. Our practice and that of many others is to perform near-total or total thyroidectomy with appropriate nodal resection when a thyroglossal duct carcinoma is found and resected. In one series of 35 patients with papillary carcinoma arising in a thyroglossal duct cyst, the thyroid gland of 4 patients (11.4%) also contained papillary cancer (81). This operative procedure permits later radioiodine therapy as well.

In addition to papillary cancer, about 5% of all carcinomas arising from a thyroglossal duct cyst are squamous; rare cases of Hurthle cell and anaplastic cancer have also been reported. Finally, three families have been reported in which a total of 11 members had a thyroglossal duct cyst (83).

In these cases, thyroid tissue is present in a midline position above or below the hyoid bone. Hypothyroidism with elevation of thyrotropin (TSH) secretion is commonly present because of the absence of a normal thyroid gland in most instances. An enlarging mass commonly occurs during infancy, childhood, or later life. Often, this mass is mistaken for a thyroglossal duct cyst because it is usually located in the same anatomic position (84). If it is removed, all thyroid tissue may be ablated, a consequence that has definite physiologic as well as possible medicolegal implications. To prevent total thyroid ablation, many recommend that a thyroid scan or ultrasound examination be performed in all cases of thyroglossal duct cyst before its removal to be certain that a normal thyroid gland is present. Furthermore, before removing what appears to be thyroglossal duct cyst, a prudent surgeon should be certain that no solid areas are present. If any doubt exists, the normal thyroid gland should be explored and palpated. Finally, if ectopic thyroid tissue rather than a thyroglossal duct cyst is encountered at surgery, its blood supply should be preserved; the ectopic gland divided vertically; and each half translocated laterally, deep to the strap muscles, where it is no longer manifested as a mass. If normal thyroid tissue is demonstrated to be present elsewhere, it may be better to remove the ectopic tissue rather than transplant it, because carcinoma arising from these developmental abnormalities, although rare, has been reported.

Small amounts of histologically normal thyroid tissue are occasionally found separate from the thyroid. If these tissue elements are near the thyroid, not in lymph nodes, and entirely normal histologically, it is possible that they represent developmental abnormalities. True lateral aberrant thyroid tissue or embryonic rests of thyroid tissue in the lymph nodes of the lateral neck region are very rare. Most agree that the overwhelming number of cases of what in the past was called “lateral aberrant thyroid” actually represented well-differentiated, metastatic thyroid cancer within cervical lymph nodes or replacing them rather than an embryonic rest. In such cases, we favor near-total or total thyroidectomy with a modified radical neck dissection on the side of the lymph node, probably followed by radioiodine therapy.

Several lateral thyroid masses have been reported that are said to be benign adenomas in lateral ectopic sites (85,86). The authors of these studies suggest that they may develop ectopically because of failure of fusion of the lateral thyroid component with the median thyroid. However, before accepting this explanation, it is important to be certain that each of these lesions does not represent a well-differentiated metastasis that has totally replaced a lymph node and in which the primary thyroid carcinoma is small or even microscopic and was not recognized.

Developmental abnormalities may lead to the finding of thyroid tissue in the mediastinum or, rarely, even within the tracheal or esophageal wall. However, most substernal goiters undoubtedly originate in the neck and then “fall” or are “swallowed” into the mediastinum and are not embryologically determined at all.

Intrathoracic goiters have been reported to occur in 0.1% to 21% of patients in whom thyroidectomies were performed. This large variability is undoubtedly caused partly by a difference in classification among the authors, but it may also be caused by the incidence of endemic goiter. More recent series report an incidence of 2% or less (87).

Many substernal goiters are found on routine chest radiography in patients who are completely asymptomatic. Other patients may have dyspnea or dysphagia from tracheal or esophageal compression or displacement. Superior vena caval obstruction can occasionally occur with edema and cyanosis of the face (88) and venous engorgement of the arms and face is present (Fig. 21). Most individuals with substernal goiters are euthyroid or hypothyroid; however, hyperthyroidism occurs as well. Although the goiters of Graves’ disease are rarely intrathoracic, single or multiple “hot” nodules may occur within an intrathoracic goiter and result in hyperthyroidism as part of a toxic nodular goiter.

Intrathoracic goiters are usually found in the anterior mediastinum and, less commonly, in the posterior mediastinum. In either instance the diagnosis is suggested if a goiter can be palpated in the neck and if it appears to continue below the sternum. Rarely, however, no thyroid enlargement in the cervical area is present, and instead of being in continuity, the intrathoracic component may be attached to the cervical thyroid only by a narrow bridge of thyroid or fibrous tissue. The diagnosis of an intrathoracic thyroid mass can be made with certainty by the use of a thyroid isotope scan; however, CT or MRI may be more helpful.

Regarding therapy, we generally agree with the recommendation made by Lahey and Swinton more than 70 years ago that goiters that are definitely intrathoracic should usually be removed if the patient is a good operative risk (89). Because of the cone-shaped anatomy of the upper thoracic outlet, once part of a thyroid goiter has passed into the superior mediastinum, it can increase its size only by descending further into the chest. Thus, delay in surgical management may lead to increased size of the lesion, a greater degree of symptoms, and perhaps a more difficult or hazardous operative procedure.

Substernal goiters should be operated on initially through a cervical incision, because the blood supply to the substernal thyroid almost always originates in the neck and can be readily controlled in this area. Only rarely does an intrathoracic goiter receive its blood supply from mediastinal vessels; however, such a finding favors a developmental cause. Thus, in most instances, good hemostasis can be obtained by control of the superior and inferior thyroid arteries in the neck.

The authors like to divide the isthmus and the upper pole vessels early in the dissection. The affected thyroid lobe is then carefully dissected along its capsule by blunt dissection into the superior mediastinum. While gentle traction is exerted from above, the mass is elevated by the surgeon’s fingers or blunt, curved clamps (Fig. 22). Often these maneuvers suffice to permit extraction of a mass from the mediastinum and into the neck area. Any fluid-filled cysts may be aspirated to reduce the size of the mass and permit its egress through the thoracic outlet. Piecemeal morcellation of the thyroid gland should not be practiced, because this occasionally has led to severe bleeding. Furthermore, several substernal goiters have been found to contain carcinoma, and this technique violates all principles of cancer surgery.

With the use of this method, the great majority of substernal thyroid glands can be removed transcervically. If the thyroid gland cannot be easily extracted from the mediastinum, however, a partial or complete sternotomy should be performed. This procedure affords direct control of any mediastinal vessels and permits resection of the thyroid gland to be carried out safely.

As in all thyroid surgery, the recurrent laryngeal nerves must be preserved and treated with care. The parathyroid glands should be identified and preserved, and the inferior thyroid artery’s branches should be ligated close to the thyroid capsule to prevent ischemia of the parathyroid glands, which might result in hypoparathyroidism.

Ectopic development of thyroid tissue far from the neck area can also lead to difficulties in rare instances. Dermoid cysts or teratomas, which are uncommon ovarian germ cell tumors, occur in female subjects of all age groups. About 3% can be classified as an ovarian struma, because they contain functionally significant thyroid tissue or thyroid tissue occupying more than 50% of the volume of the tumor. Many more such tumors contain small amounts of thyroid tissue. Some strumae ovarii are associated with carcinoid-appearing tissue. These strumal-carcinoid tumors secrete or contain thyroid hormones as well as somatostatin, chromogranin, serotonin, glucagon, insulin, gastrin, or calcitonin (90). Some are associated with carcinoid syndromes.

Struma ovarii is sometimes manifested as an abdominal mass lesion, often with peritoneal or pleural effusion that may be bloody. Most of these lesions synthesize and iodinate thyroglobulin poorly, and thus, despite growth of the mass, thyrotoxicosis does not develop. However, perhaps one-fourth to one-third of ovarian strumae are associated with thyrotoxicosis (91,92). Many of these lesions may be contributing to autoimmune hyperthyroidism in response to a common stimulator such as thyroid-stimulating immunoglobulins. In other instances, the struma alone is clearly responsible for the thyrotoxicity. An elevated free thyroxine index, a suppressed TSH value, and uptake of radioiodine in a mass in the pelvis are the obvious prerequisites for making the diagnosis (93). Often, in ovarian struma, symptoms and findings of thyrotoxicosis are present in patients who have low uptake of radioiodine in their thyroid glands. Thus, a “high index of suspicion” is most important. Usually, operative resection of an ovarian tumor is indicated. After surgery, transient postoperative hypothyroidism and “thyroid storm” have occasionally been reported.

Benign thyroid adenomas in strumae are common, and about 5% manifest evidence of carcinoma (94). Usually these lesions are resectable, but external radiation therapy and/or 131I ablation has been advised after resection of the malignant tumors to avoid the tendency for late recurrence or metastatic disease, which has sometimes been fatal. Metastatic disease occurs in about 5% of these malignant tumors. It is best treated with 131I therapy, and TSH suppression should be given as for thyroid cancer originating in the usual location.

Functioning apparently normal intracardiac thyroid tissue has been reported a few times and has been visualized by radioiodine imaging (95). The clinical finding is usually a right ventricular mass, and the diagnosis has typically been made after operative removal.

Finally, ectopic thyroid tissue has been reported rarely in the submandibular (96) an parotid (97) salivary glands, in the duodenum (98), the adrenal (99), the gallbladder (100), and the iris of the eye (101). Of course, great care must be exercised to be certain that these are not metastases from a well differentiated thyroid cancer.

Acknowledgements: The authors wish to thank Mrs. Patricia Schaddelee for her assistance in the preparation of this chapter.