Ectopic thyroid is an atypical location of thyroid tissue in neighboring or distant anatomical structures. In most cases, it is accompanied by hypothyroidism, rarely by thyrotoxicosis. With compression of the neck organs, cough, dysphonia, shortness of breath, dysphagia may occur. Disease can become a source of tumor development. Diagnosis is based on the data of echography, scintigraphy, CT, endoscopy, biopsy, thyroid hormone studies. Asymptomatic ectopias do not require treatment, if necessary, hormone therapy is prescribed, thyroidectomy, radiofrequency ablation, radioiodotherapy, thyroid autotransplantation is performed.
Ectopic thyroid is an anomaly of the location of the organ, in which glandular tissue is formed not in a typical place, but in other localizations (organs of the head, neck, gastrointestinal tract, cardiovascular, genitourinary system). The anomaly occurs with a population frequency of 1:100-300 000 people. Among all variants of thyroid dysgenesis, ectopia accounts for 48-61%. The most common form is lingual ectopic thyroid – it is detected in 70-90% of observations. The anomaly is diagnosed in a wide age range ‒ from infancy to adulthood, it is more common in women (65-80%).
Congenital ectopic thyroid occurs due to a violation of the migration of thyrocyte precursors along the thyroid-lingual duct during organogenesis. This process may be associated with mutations of regulatory genes (TITF1, TITF2, PAX8). Most often, gene aberrations occur sporadically under the influence of negative exogenous and endogenous factors acting in early pregnancy:
- uncontrolled intake of medications by a pregnant woman;
- TORCH infections;
- contact with toxic substances: chemicals, radiation;
- thyroid diseases in a pregnant woman.
The thyroid gland is located on the front surface of the neck, adjacent to the trachea in front at the level of 2-5 rings, and to the larynx – on the sides. Partially with its lobes, the gland is adjacent to the thyroid cartilage, from which the name of the organ originated. The formation of the thyroid gland begins at the 3rd-4th week of embryonic development from the cells of the endoderm of the primary pharyngeal intestine. First, at the level of 1-2 pairs of gill pockets, a protrusion of the ventral pharyngeal wall is formed, then the rudiment of the future gland migrates along the so-called thyroglossal (thyroid-lingual) pathway: from the oropharynx to the level of the trachea.
By the 7th week of gestation, the thyroid tissue reaches its normal anatomical position, after which the morphogenesis of the gland begins. The causes and mechanisms of incomplete migration of the thyroid germ are largely unclear.
In the vast majority of cases, it remains at the level of the root of the tongue, in other cases, migration stops at the level of the hyoid bone, in the third it is interrupted in various structures of the head and neck (pituitary gland, iris, palatine tonsils, trachea, carotid bifurcation, etc.). Sometimes, for unknown reasons, the thyroid rudiment goes beyond the thyroglossal tract – in in this case, the gland is displaced into the abdominal cavity, the pelvis.
In modern endocrinology, there are two anomalies of the position of the thyroid gland ‒ dystopia and ectopia. Both of these terms denote the absence of a thyroid gland in a typical place and are often used interchangeably. However, some authors pay attention to certain semantic nuances:
- dystopia is a displacement of thyroid tissue along the thyroid duct (in the area of the root of the tongue, pharynx, larynx, trachea, esophagus, mediastinum);
- ectopia is the location of the thyroid gland outside the thyroglossal duct (in the heart, sex glands, etc.).
Separately, an aberrant goiter is isolated – an abnormally located additional thyroid tissue, along with a normally located gland. The most common are the following variants of ectopia-thyroid dystopia:
- lingual (70-90%);
- intralaryngotracheal (7%);
Cases of thyroid ectopia in submandibular lymph nodes, palatine tonsils, carotid artery bifurcation, eye iris, pituitary gland have also been described in the head and neck area.
With the retrosternal form, the gland can be ectopic into the esophagus, heart (chambers, septa, pericardium), the wall of the ascending aorta, the thymus gland; with abdominal and retroperitoneal ‒ into the diaphragm, stomach, gallbladder, duodenum, small intestine, pancreas, adrenal gland. Pelvic dystopia is fixed in the fallopian tubes, uterus, ovaries, vagina. In rare cases, the ectopic thyroid gland is simultaneously detected in two or even three different atypical areas.
Clinical manifestations are determined by the localization of the ectopic thyroid gland and its functional activity. In 7-10% of people, pathology is not accompanied by any manifestations, the fact of its presence is detected at autopsy after death for other reasons. In about a third of patients, thyroid ectopia is associated with hypothyroidism, less often accompanied by thyrotoxicosis.
Hypothyroidism can have varying degrees of severity – from subclinical (70%) to manifest (30%). Clinical manifestation is usually provoked by stress, hard physical work, infectious diseases, hormonal fluctuations (puberty, pregnancy). At the same time, apathy, lethargy, weakness, chilliness, pasty skin, a tendency to gain weight are noted. Ectopic thyroid is one of the most common causes of congenital hypothyroidism in children.
Thyrotoxicosis syndrome is characterized by irritability, tearfulness, trembling in the body, sweating. There is tachycardia, increased stool, progressive weight loss, exophthalmos. Women develop menstrual dysfunction up to amenorrhea, men – decreased libido and potency.
Goiter of the tongue root (lingual ectopia) is accompanied by sore throat, cough, dysphagia, dysphonia. Cases of sleep apnea have been described. With ectopic thyroid in the trachea, there is difficulty breathing, tachypnea, cyanosis of the skin, in infants – the occlusion of the large fontanel.
Traumatization of the lingual goiter leads to recurrent bleeding from the oral cavity, abscessing. With intralaryngotracheal localization of the thyroid tissue in children, there is often an obstruction of the VDP, death from asphyxia may occur. Sometimes autoimmune thyroiditis, benign tumors (adenomas) develop in ectopic tissue.
In 1% of cases, malignant neoplasia occurs: carcinomas (follicular, papillary, medullary), lymphomas, immature teratomas. Removal of ectopic tissue, mistaken for a neoplasm, can cause the development of severe postoperative hypothyroidism (myxedema) and hypoparathyroidism (tetany).
Endocrinologists, endoscopists, radiologists, ultrasound diagnosticians take part in the diagnosis. When conducting research, it is necessary not only to establish the fact of ectopia and identify its localization, but also to evaluate the function of the thyroid gland, to conduct a differential diagnosis.
- Inspection. When examining the neck, the thyroid gland is not palpated in the usual place, but a seal can be felt in the hyoid bone or in the side of the neck. Lingual ectopia is detected during pharyngoscopy, has the appearance of whitish or reddish tissue of a soft consistency with a smooth or uneven surface, often with hemorrhages, ulcerative defects.
- Endoscopy. Laryngotracheobronchoscopy, esophagogastroscopy are informative for intraluminal localization of ectopic tissue, serve to detect stenotic changes in the trachea, esophagus, and endoscopic biopsy.
- Ultrasound. Sonography reveals the absence of thyroid tissue in a typical place, but helps to detect it in other parts of the neck. Ultrasound monitoring is also used for navigation during aspiration puncture biopsy.
- Computed tomography. Depending on the intended localization, CT of the soft tissues of the neck, CT of the mediastinum, abdominal cavity, retroperitoneal space, small pelvis is performed.
- Scintigraphy. Radionuclide diagnostics using 123I, 999mTc allows visualizing the entire ectopic tissue in the body, differentiating aberrant goiter from thyroid dystopia.
- Laboratory diagnostics. To assess the functional activity of ectopic tissue, thyroid hormones (TSH, T3, T4) and antibodies to TPO are determined.
Lingual ectopia has to be differentiated with tumor processes of the root of the tongue: hemangioma, lymphangioma, fibroma. With a sublingual arrangement of the thyroid gland, it is necessary to exclude the following pathological processes:
- metastatic tumors;
- congenital neck cysts (lateral, median, dermoid, epidermoid);
- cystic hygroma (neck lymphangioma);
- echinococcal cyst;
- cervical lymphadenopathy, etc.
With an asymptomatic course of pathology, treatment is not carried out, dynamic monitoring is established for the patient. Suppressive therapy with synthetic thyroxine analogues is prescribed to patients with lingual, sublingual, cervical, intratracheal ectopia and concomitant hypothyroidism. Its purpose is to reduce the volume of thyroid tissue. Radioiodotherapy is also successfully used, which contributes to the destruction of the ectopic gland.
With the ineffectiveness of conservative tactics, in urgent situations (with increasing obstruction of the VDP, bleeding), malignancy, cystic degeneration, surgical methods are resorted to. Some clinicians are of the opinion about the mandatory surgical excision of lingual ectopia. Methods of transoral, submandibular, cervical access with pharyngotomy are proposed.
Operations are performed using endoscopic control, radio frequency and laser destruction, and robotic technologies. For the prevention of postoperative hypothyroidism, autotransplantation of thyroid tissue is possible, in other cases, after removal of ectopia, lifelong hormone replacement therapy with thyroid hormones is prescribed.
Prognosis and prevention
Asymptomatic ectopic thyroid can go unnoticed and in no way affect the quality and duration of life. The greatest danger is ectopia associated with hypo- or hyperthyroidism, obstruction of the respiratory system, bleeding. The results of treatment of thyroid ectopia are mostly satisfactory, however, it should be remembered that lifelong HRT after thyroidectomy is necessary.
Specific preventive measures have not been developed. When planning pregnancy and in the early stages of gestation, possible teratogenic factors (infections, contact with household and industrial chemicals, medicines, radiation) should be avoided.