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Thyroglossal duct cyst, thyroglossal duct cyst cancer, and ectopic thyroid

Thyroglossal duct cyst, thyroglossal duct cyst cancer, and ectopic thyroid
Literature review current through: Jan 2024.
This topic last updated: Jan 17, 2023.

INTRODUCTION — Thyroglossal duct cysts (TGDCs) are the most common form of congenital cyst in the neck. Carcinoma is diagnosed in approximately 1 to 2 percent of TGDCs, most often on histopathology after a TGDC has been excised. Patients with a TGDC often have ectopic thyroid glands, which are defined as functioning thyroid tissue found anywhere other than the usual anatomic location of the thyroid gland.

In this topic, we discuss the embryology, clinical manifestations, diagnosis, and management of TGDC, TGDC cancer, and ectopic thyroid. Other types of neck mass are discussed elsewhere. (See "Evaluation of a neck mass in adults" and "Differential diagnosis of a neck mass".)

EMBRYOLOGY — The anlage of the thyroid gland forms at the foramen cecum of the tongue, which is located on the dorsum of the tongue posteriorly at the apex of the V-shaped sulcus formed by the circumvallate papillae [1]. During the fourth week of gestation, a ventral diverticulum of the foramen cecum is formed from the first and second pharyngeal pouches (the medial thyroid anlage). This diverticulum, with its narrow neck connected to the tongue, descends in the midline of the neck as the thyroglossal tract to the position of the normal thyroid in the base of the neck, where the thyroid lobes separate, by the seventh week. The path of descent is usually anterior to the hyoid bone but may be posterior to or through the bone and ends on the anterior surface of the first few tracheal rings.

The tract usually atrophies and disappears by the tenth week of gestation. Portions of the tract and remnants of thyroid tissue associated with it may persist at any point between the tongue and the thyroid (figure 1).

The pyramidal lobe can be thought of as the most caudal remnant of this tract and is present in approximately one-third of normal subjects. The lateral thyroid anlage, consisting of the C-cell precursors that arise from the neural crest portion of the fourth pharyngeal pouch, ultimately fuses with the descended medial anlage [2]. The pyramidal lobe usually arises from the isthmus of the thyroid but may arise from the medial aspect of one of the thyroid lobes or both lobes.

THYROGLOSSAL DUCT CYST — Thyroglossal duct cysts (TGDCs) are cysts of epithelial remnants of the thyroglossal tract and present characteristically as a midline neck mass at the level of the thyrohyoid membrane, closely associated with the hyoid bone.

Epidemiology and pathogenesis — Although most patients with TGDCs are children or adolescents, up to one-third are aged 20 years or older [1,3]. Males and females are equally affected. Familial occurrence of TGDCs is extremely rare, with only 21 individuals of hereditary TGDCs in seven families reported [4,5]. The most common inheritance pattern appears to be autosomal dominant [5].

TGDC arises as a cystic expansion of a remnant of the thyroglossal duct tract [1,3]. Many cystic remnants of the thyroglossal tract are never detected clinically; a postmortem study of 200 adults found a 7 percent incidence of TGDCs [6].

The stimulus for the expansion is not known; one postulate is that lymphoid tissue associated with the tract hypertrophies at the time of a regional infection, thereby occluding the tract with resultant cyst formation [7]. Alternatively, radiation therapy used to treat head and neck cancers can acutely enlarge subclinical thyroglossal duct remnants [8].

Clinical manifestations — Patients with a TGDC usually present with a mobile, soft, painless midline upper neck mass that appears to be cystic. In most cases, the cyst is at or just below the hyoid bone adjacent to the thyrohyoid membrane [1]. TGDCs are usually within 2 cm of the midline but can be more lateral and may even be more lateral than the thyroid cartilage (more typically on the left) [1].

TGDCs may occur anywhere along the thyroglossal duct tract from the foramen cecum at the base of the tongue to the level of the suprasternal notch (figure 1). However, cysts below the thyrohyoid membrane are rare. There are only two reported cases, one reaching to the suprasternal notch and the second encroaching into the superior mediastinum, descending all the way to the aortic arch. A TGDC in such a caudal location can masquerade as a thymic mass and cause confusion [9]. Very rarely, a TGDC may present in an ectopic location (eg, an endolaryngeal cyst). An intrathyroidal cyst with TGDC-like lining has also been described [10].

Classically, TGDCs move up with swallowing or protrusion of the tongue, emphasizing their close relationship with the hyoid, thyrohyoid membrane, and/or thyroid cartilage.

The mass usually causes no symptoms but may be slightly tender. Often, the patient either has an active upper respiratory tract infection or has had one in the recent past. Whether the infection leads to cyst formation or simply increases the likelihood of detection of a preexisting cyst is uncertain.

Overall, presence of a mass and infection are the two main presenting symptoms of TGDC either initially or as a recurrent episode, with infection being more common in children. Generally, adults are more likely to present with a complaint other than mass or infection, including pain, sore throat, dysphagia, hoarseness, globus, and fistula formation [11,12]. As far as location of TGDC is concerned, research has shown that the frequency of TGDC location in adults and children is the same [1,11,12].

Diagnostic evaluation — TGDC should be suspected in those who present with a cystic mass in the midline of the upper neck. Diagnosis is confirmed by imaging studies, fine-needle aspiration (FNA), and/or surgical pathology.

Imaging — For suspected TGDC, we first obtain a computed tomography (CT) scan of the neck with contrast in all adults, and we obtain magnetic resonance imaging (MRI) of the neck in children or adults with a recurrent TGDC. CT and MRI, but not ultrasonography (US), can also define the TGDC's relationship to the hyoid and other surrounding structures.

Ectopic thyroid tissue can be confused with a TGDC. If ectopic thyroid tissue is suspected on CT or MRI, we then obtain radionuclide imaging (thyroid scan) to locate all additional functioning thyroid tissue [13].

US – US of a TGDC reveals a well-defined, thin-walled, anechoic, or hypoechoic mass with posterior acoustic enhancement in the midline anterior neck [14]. US also reveals the cystic nature of a TGDC. However, US does not delineate the anatomic location of the suspected TGDC as it relates to surrounding structures, including the hyoid bone [15].

The presence of infection can change the appearance of TGDCs on US; wall thickening, loss of hypoechoic appearance, and presence of septae indicate inflammation. The loss of hypoechoic appearance occurs due to the presence of protein [16]. TGDCs with past infection or hemorrhage appear on US as heterogeneous complex cysts with internal echoes [17].

US of the neck can evaluate the TGDC, the native thyroid gland, and cervical lymph nodes in clinically suspected TGDC cancer, and some researchers recommend it as the first-line imaging modality to be employed in both children and adults [18]. However, the literature suggests that US is the most common preoperative diagnostic technique employed in children, while neck CT is used more often in adults [19].

CT – When a TGDC is suspected in adult patients, CT of the neck with contrast is the preferred imaging modality (image 1). Typically, CT imaging depicts TGDCs as well-circumscribed lesions with homogenous fluid attenuation surrounded by a thin enhancing rim [10]. CT not only helps to confirm the diagnosis of TGDC by defining the typical close relationship of the cyst to the hyoid bone but also provides accurate information regarding the size, extent, and location. It also identifies normal orthotopic thyroid tissue. Additional wall enhancement indicates an infected TGDC [16].

MRI – On MRI, uncomplicated TGDC appears dark (homogeneous low signal) on T1-weighted images and bright (homogeneous high signal) on T2-weighted images, reflecting the fluid content of the cyst [16,17]. MRI can also define the TGDC's relationship to the hyoid and other surrounding structures.

Thyroid uptake scan – Additionally, in patients suspected of having ectopic thyroid tissue, radionuclide imaging (thyroid uptake scan), US, and CT are reliable tests to identify the presence of normal thyroid gland and help to rule out ectopic thyroid tissue [20,21]. Neck palpation is not considered to be a dependable method of confirming the presence of normal thyroid glands [22].

Incidental discovery of probable TGDCs, usually on head and neck imaging performed for other conditions, is extremely rare (0.1 percent). Patients with an incidentally found TGDC should be referred to an otolaryngologist for further evaluation, regular follow-up, and surgery when symptoms arise [23].

Fine-needle aspiration — For patients with a suspected TGDC, we perform ultrasound-guided FNA in all adults, but only selectively in children with suspicious features on imaging [24]. Such imaging features include a prominent solid part, microcalcifications, asymmetric wall thickening, and hypervascularization [24].

FNA is the most reliable method for preoperative diagnosis of TGDC cancer, especially if solid elements of the lesion can be sampled under ultrasound guidance, and preoperative FNA can also be helpful to decrease cyst size [25,26]. However, given the low incidence of carcinoma in TGDCs, especially in children, preoperative biopsy of all TGDCs may not be cost effective. In one study, all 12 patients in whom the cysts contained carcinomas were at least 17 years old [25].

FNA is often used to diagnose TGDCs or to exclude other diagnoses [27]. The cytomorphologic features include colloid, macrophages, lymphocytes, neutrophils, and ciliated columnar cells, but these are not unique to TGDCs.

Laboratory tests — Thyroid function should always be assessed preoperatively in all cases of TGDCs. (See "Laboratory assessment of thyroid function".)

Differential diagnosis — TGDCs are the most common cause of all midline neck mass, followed by dermoid cysts. (See "Evaluation of a neck mass in adults", section on 'Mass localization'.)

Dermoid cyst – Dermoid cysts are due to entrapment of epithelium in deeper tissue, occurring either developmentally or post-trauma. Dermoid and sebaceous cysts tend to be quite superficial and less tethered to the underlying structures, including the hyoid bone, as compared with TGDCs. (See "Differential diagnosis of a neck mass", section on 'Dermoid cyst'.)

Branchial cleft cyst – Branchial cleft cysts can be confused with TGDCs if they are somewhat medially located. Branchial cleft cysts are often associated with a sinus tract or fistula, whereas TGDCs are not. (See "Differential diagnosis of a neck mass", section on 'Branchial cleft cyst'.)

Lipoma – Lipomas are quite superficial and have ill-defined edges.

Others – Other causes of midline neck masses include thyroid nodules, hypertrophic pyramidal lobes of the thyroid, midline lymphadenopathy, medially located salivary gland tumors, sebaceous cysts, laryngocele, and lymphatic malformations.

Management — Once diagnosed, the management of a TGDC depends on whether the cyst is infected or inflamed and whether the patient is a suitable surgical candidate.

Infected TGDC — Children with TGDCs are more likely to have some degree of infection or inflammation at presentation [28,29]. It is essential to avoid surgery during the phase of acute inflammation as this can lead to recurrence [30-32].

An infected TGDC should be managed initially with broad-spectrum antibiotics targeted toward oral flora [33].

Mild cases may be treated with a course of oral antibiotics for 10 to 14 days, such as a first-generation cephalosporin (eg, cephalexin 500 mg every 6 hours), amoxicillin-clavulanate (500 mg/125 mg every 8 hours), or clindamycin (600 mg every 8 hours). We do not recommend empirical coverage for methicillin-resistant Staphylococcus aureus (MRSA) unless identified by culture.

For more severe infections, an antibiotic regimen such as cefazolin in combination with clindamycin can be used.

Antimicrobial therapy should be directed toward the most common oral organisms, which includes various streptococcal species and oral anaerobes [34]. When possible, cultures should be obtained with a fine-needle aspirate for Gram stain, aerobic and anaerobic culture, fungal stain and culture, acid-fast bacillus stain, and mycobacterial culture [33].

Incision and drainage should only be considered in cases of abscesses that do not respond to antibiotics. Incision and drainage can allow seeding of ductal cells outside the cyst and, in turn, increase chances of recurrence [34]. Additionally, definitive surgery is easier in the absence of scar tissue or a cutaneous fistula [35].

Once the infection clears completely, patients should undergo definitive treatment for the TGDC. (See 'Uninfected TGDC' below.)

Uninfected TGDC — All TGDCs should be treated surgically with the Sistrunk procedure unless the patient is not a surgical candidate. Previously infected TGDCs are treated with Sistrunk surgery only after active infection has subsided. (See 'Infected TGDC' above.)

Surgical candidates — In suitable candidates, surgical removal of the TGDC is indicated to prevent recurrent infection and to exclude cancer.

If a TGDC is not removed, as many as one-half become infected [31], and infection before surgery is a well-described cause of recurrence [30,31]. In one retrospective series, the recurrence rate after simple cystectomy was 8 percent among children with noninfected TGDC compared with 40 percent in children with infected TGDC [31]. Similarly, among patients who underwent more extensive surgery, the recurrence rate was 1.4 percent in those with noninfected cysts compared with 14 percent in those with infected cysts [31]. Surgery is therefore best performed at initial presentation.

Approximately 1 to 2 percent of TGDCs ultimately are found to contain cancer [1,36]. The clinical features of thyroglossal duct carcinoma are very similar to those of TGDCs [1], and in the majority of cases, thyroglossal duct tract carcinomas are incidental (ie, not suspected before the operative procedure) [37]. (See 'Thyroglossal duct cyst cancer' below.)

Sistrunk procedure — The standard operation is resection of the cyst and the midportion of the hyoid bone in continuity and resection of a core of tissue from the hyoid upward toward the foramen cecum, an operation known as the Sistrunk procedure (figure 2) [38]. We prefer to resect the cyst with a cuff of surrounding tissue and strap muscle to avoid entry into the cyst, which has been implicated in cyst recurrence, and to facilitate complete removal.

The typical close relationship between a TGDC and the thyroid cartilage can result in remodeling of the laryngeal cartilage if the cyst is large [39]. However, because the cysts do not typically invade, laryngeal reconstruction is rarely required even after excision of large cysts [40].

Arborization of the superior aspect of the thyroglossal tract at and above the hyoid bone may occur and may be a reason for recurrence [30]. Recurrence after a Sistrunk procedure is rare. In such a case, a repeat or extended Sistrunk procedure is recommended. This procedure includes removal of a core of the tissue from the hyoid to the foramen cecum to encompass possible superior tract arborization [41]. The goal of a repeat Sistrunk operation is complete excision of the thyroglossal duct tract up to the tongue base, superior and posterior to the hyoid bone [42]. The overall recurrence rate after this procedure is approximately 5 percent [43].

Pathology — Histologic examination of a TGDC reveals a cyst with an epithelial lining that is columnar or squamous and may be ciliated. Some normal thyroid tissue is usually present in the wall of the cyst [2,44].

Carcinoma of the thyroglossal duct is usually diagnosed only after histologic study because there are a few clinical clues to the presence of cancer within a TGDC. Among the cancers, 88 percent are papillary carcinomas, 6 percent are squamous cell carcinomas, and the rest are Hurthle-cell, follicular, and anaplastic carcinomas [25]. There are no reports of medullary carcinoma in a TGDC [45]. (See 'Thyroglossal duct cyst cancer' below.)

Nonsurgical candidates — Percutaneous ethanol injection (sclerotherapy) is an alternative approach in patients who are not surgical candidates if the presence of malignancy can be excluded [46,47].

In a retrospective series of 68 patients, the immediate success rate of ethanol injection for the treatment of TGDCs was 81 percent, with a mean volume reduction ratio within three months of 73±31 percent [48]. After a median follow-up of 69 months, the long-term success rate was 83 percent, with a mean volume reduction ratio at last follow-up of 81±35 percent. No patients developed malignancy from the ablated TGDCs in this series.

However, sclerotherapy has lower success rates for treating TGDC when compared with surgery, and the rate of nonresponse to sclerotherapy requiring surgical intervention is higher than the rate of revision surgery after the Sistrunk procedure [49]. Additionally, histopathology evaluation is not possible with sclerotherapy. Thus, sclerotherapy should be considered for nonsurgical candidates only rather than as a mainstream therapy for TGDC.

Additionally, for nonsurgical candidates with small, noninfected TGDCs, regular surveillance with ultrasound imaging is also a good alternative.

THYROGLOSSAL DUCT CYST CANCER

Epidemiology — The incidence of primary cancer of the thyroglossal duct is less than 1 percent. Thyroglossal duct cyst (TGDC) cancer more commonly presents in the adult population. While TGDC itself shows no predilection between sexes, there is a notable female preponderance in TGDC cancer, with a female-to-male ratio of 2.3:1 reported in the literature [50].

Diagnosis — TGDC cancer is rarely diagnosed preoperatively. Malignancy may be suspected if neck ultrasonography shows probable local invasion and/or microcalcifications or if pathologic lymphadenopathy is noted clinically or by imaging [51].

Almost 75 percent of TGDC cancers are diagnosed incidentally on postoperative histopathology [52]. If the cyst is found to contain thyroid cancer, one must be sure that the cancer arose from within the cyst and is not a cystic metastasis to a midline lymph node from a primary thyroid cancer (eg, pyramidal lobe papillary thyroid cancer [PTC] or Delphian [prelaryngeal] lymph node PTC metastasis) [53,54]. Studies suggest that among patients with cancer of the TGDC, 11 to 33 percent have carcinoma within the thyroid gland [25].

The cancer is considered to have originated in the TGDC if there is histologic evidence of columnar or squamous epithelial lining in the cyst [44,55], normal thyroid follicles in the cyst wall [44], and complete absence of lymph node tissue and there is ultrasonographic evidence of a normal thyroid gland [56]. If not, the lesion may represent a lymph node metastasis from a thyroid cancer.

PTC is the most common pathologic type of TGDC cancer [25,57,58], reported in between 85 and 91 percent of cases, followed by mixed papillary and follicular cancer and squamous cell carcinoma [52]. Squamous cell cancer of the TGDC is a rare entity, with an approximately 4 percent incidence rate, and it is believed to arise from the cyst wall [52]. It carries the worst prognosis among all types of TGDC cancers and should be treated aggressively [52,59]. Medullary thyroid cancer is not found in the setting of malignancy associated with TGDC [60].

Treatment — In general, studies report that low-risk TGDC cancer cases can be treated with the Sistrunk procedure alone with observation of the thyroid gland, while high-risk patients should be treated more aggressively with thyroidectomy and possibly lymph node dissection [50,58].

Resection of the primary tumor — Low-risk TGDC cancer includes patients <55 years of age with small tumors (ranging from 1 to 4 cm) and classic histology, no extracapsular spread, no vascular invasion, negative margins, no nodal or distant metastases, and a normal thyroid gland demonstrated on imaging studies [50,58].

Low-risk TGDC cancer — Most cases of TGDC carcinoma are adequately treated by resection with the Sistrunk procedure, with a reported cure rate of 95 percent [25,61]. After review of pathology, if a surgeon is certain of the diagnosis of TGDC cancer (ie, primary thyroid gland carcinoma has been ruled out) and thyroid sonography is negative, then surgical treatment of TGDC is sufficient [36].

High-risk TGDC or metastatic cancer — A thyroidectomy is performed in cases where a primary thyroid malignancy cannot be excluded or when secondary thyroid malignancy is detected. In a retrospective review of a series that included 26 patients with TGDC cancer, approximately 60 percent also had a differentiated thyroid cancer identified [62]. (See "Differentiated thyroid cancer: Overview of management".)

Thyroidectomy is also indicated in rare cases of TGDC carcinoma that have high-risk features such as invasive tumor or positive regional lymph nodes. This is performed to facilitate I-131 treatment and diagnostic whole-body radioiodine scanning [63]. (See 'Role of adjuvant treatment for TGDC cancer' below.)

Role of lymph node dissection — Lymph node metastasis of TGDC carcinoma was previously thought to be rare [1]. However, when prophylactic neck dissection is performed at the time of resection, the incidence of lymph node metastasis is surprisingly high [62,64]. Occurrence of distant metastasis is uncommon, reported in fewer than 2 percent of cases [25,65]. The following approach to neck dissection for TGDC cancer is extrapolated from that of differentiated thyroid cancer, which TGDC cancer most closely resembles biologically. (See "Neck dissection for differentiated thyroid cancer", section on 'Choosing a neck dissection technique'.)

Papillary type TGDC cancer — For TGDC with papillary carcinoma, a therapeutic full neck dissection is performed for clinically apparent lymphadenopathy (suspicious nodes >8 mm in central neck and >10 mm in lateral neck).

A prophylactic central neck dissection (CND) is performed for large tumors, tumors in close contact with the thyroid gland, extracystic tumors that have spread to the surrounding soft tissues (T3), or macroscopic evidence of airway involvement (T4). Otherwise, no neck dissection is indicated.

Squamous cell type TGDC cancer — For squamous cell type TGDC cancer, a prophylactic central compartment and level IA dissection should be performed due to the more aggressive biology of the disease [24].

Role of adjuvant treatment for TGDC cancer — In patients with low-risk TGDC cancer treated with the Sistrunk procedure alone, the present data do not support thyroid suppression therapy. Such patients should be followed with annual clinical and sonographic cervical examination. In cases of squamous cell type TGDC cancer, some surgeons recommend adjuvant radiation therapy [52].

There are no guidelines for radioactive iodine (RAI) treatment for TGDC carcinoma. However, RAI may be considered in the presence of lymph node metastasis, concurrent thyroid cancer, or in cases of large TGDC cancer or those with aggressive pathologic features [24].

Staging and survival — TGDC papillary cancer has excellent prognosis with an overall survival rate of 95.6 percent at 10 years, and the occurrence of distant metastatic lesions is rare [24]. Nevertheless, staging TGDC carcinoma may help to more appropriately match therapeutic interventions to the extent of the disease and optimize oncologic outcomes [50]. Due to the rarity of TGDC carcinoma, however, staging of the disease has not been standardized. In a study in which the American Joint Committee on Cancer (AJCC) staging criteria for thyroid cancer were applied to TGDC carcinomas, soft tissue extension for TGDC carcinoma was considered as equivalent to extrathyroidal extension. The study found that the staging was helpful in guiding treatment decisions and standardizing management for TGDC cancer [50].

THYROID ECTOPIA — Patients with a thyroglossal duct cyst (TGDC) often have ectopic thyroid glands [22]. Thyroid ectopia is defined as functioning thyroid tissue found anywhere other than the usual anatomic location of the thyroid gland.

Ectopic thyroid tissue results from a lack of caudal migration of the thyroid gland and is thus usually located along the normal path of thyroid gland descent but is rarely found in the mediastinum, heart, esophagus, or diaphragm [13]. Ectopic thyroid tissue is derived from abnormalities in migration of the medial anlage and hence typically does not contain C cells.

Epidemiology — Failure of thyroid gland descent occurs in approximately 1 in 200,000 normal subjects and 1 in 6000 patients with thyroid disease [66]. The true incidence of thyroid ectopia is unknown due to the asymptomatic nature of some ectopic thyroid tissue.

The most common site of ectopic thyroid is a lingual thyroid. The wall of a TGDC is the second most common site for ectopic thyroid tissue [67]. The ectopic tissue is usually found in the form of small groups of follicles and is present in 25 to 65 percent of cysts examined histologically [44]. Up to 1 to 2 percent of patients presenting with what appears to be a TGDC have an ectopic thyroid gland [43].

Anatomy — Among ectopic thyroid glands, 90 percent are lingual and 10 percent occur in other sites [68].

Lingual thyroid — The entire thyroid gland can fail to descend to its normal adult orthotopic site. If the descent is completely arrested at the level of the base of the tongue, a lingual thyroid results. Partial descent can result in an ectopic gland in a sublingual or prelaryngeal position. Excessive migration can result in a substernal ectopic gland [66,68,69].

In patients presenting with a lingual thyroid, over 70 percent have no thyroid tissue in the normal location [1]. A lingual thyroid can represent the only functioning thyroid tissue, so excision could lead to severe hypothyroidism, requiring thyroid hormone replacement [70].

Enlargement of lingual thyroid tissue can be seen with upper respiratory infections (due to associated lymphoid tissue), during pregnancy, or at puberty, leading to regional symptoms such as dysphagia, dysphonia, dyspnea, or hemoptysis [66,68,71].

Carcinoma arising in a lingual thyroid is rare, with fewer than 30 cases reported in the literature [72]. (See 'Thyroglossal duct cyst cancer' above.)

Lateral nonmalignant thyroid tissue — Ectopic nonmalignant cervical thyroid tissue can be divided into (1) midline elements including an ectopic thyroid gland and TGDC remnants and (2) lateral elements including true embryologic rests, paracytic nodules, and exophytic nodules ("lateral aberrant thyroid") [2]. A patient who has a substantial amount of thyroid tissue within a lymph node in the lateral neck should be suspected to have a nodal metastasis of a small well-differentiated carcinoma of the thyroid [73-75].

True embryologic rests of normal thyroid tissue (believed to form as a result of migration error) have been described in several locations, including adjacent to the larynx, aortic arch, and heart [2] as well as within lymph nodes in the lateral neck. Strict criteria must be followed in order to exclude foci of well-differentiated thyroid cancer within the node. Such nodal embryologic rests must be small, containing only a few thyroid follicles and with none of the nuclear features of papillary carcinoma, and should be present only in the capsular region of the node [2,76,77].

Exophytic and paracytic nodules — Thyroid tissue that is not within a lymph node can occur in the lateral neck or upper mediastinum through progression of thyroid nodular disease on the surface of the gland.

Exophytic nodules are surface nodules that progressively enlarge and become detached from the main portion of the thyroid gland. Exophytic nodules are not uncommon.

Paracytic nodules are nodules that develop at some distance from the thyroid gland as a result of implantation of a small focus of thyroid tissue during a thyroid surgical procedure. Although they are rare, we have seen paracytic nodules develop adjacent to the larynx and behind the carotid artery.

Association with hypothyroidism — Most cases of thyroid ectopia manifest as simple TGDCs in conjunction with a normally developed and located thyroid gland [72]. Some thyroid ectopia function normally, but approximately one-third of patients present with hypothyroidism.

The normal thyroid gland reacts to an increase in metabolic demand by producing more thyroxine without showing abnormal enlargement. However, the ectopic thyroid tissue is dysgenetic and is unable to handle increased metabolic demand. Hence, the ectopic tissue may enlarge because of stimulation by thyrotropin (TSH). This is especially apparent during growth spurts, puberty, or pregnancy. It is usually at this time that the patient will seek medical attention either for enlarged neck swelling or for hypothyroid symptoms. If the patient presents with hypothyroid symptoms and thyroid function tests are abnormal, then further evaluation with thyroid scanning is warranted. Treatment with thyroid hormone supplementation is usually sufficient for suppression, but surgical excision may become necessary.

The preoperative detection of hypothyroidism in a patient with a midline neck mass increases the suspicion of ectopic thyroid [43]. On a rare occasion, thyroglossal ductal ectopy is found in patients diagnosed with congenital hypothyroidism associated with thyroid ectopy [78]. (See "Diagnosis of and screening for hypothyroidism in nonpregnant adults".)

Diagnostic evaluation — Ectopic thyroid is mainly diagnosed with a thyroid scan, which can localize all ectopic foci that take up radioisotope outside the native thyroid location in the neck [18]. Ultrasonography (US), CT, and MRI can augment the thyroid scan by assessing the size and anatomical location of the ectopic gland. A thyroid laboratory panel should be obtained in all ectopic thyroid cases, regardless of its location. A fine-needle aspiration (FNA) is often performed to guide management.

Management — Euthyroid patients with an asymptomatic ectopic thyroid tissue and benign cytology can be observed [51]. Treatment for ectopic thyroid tissue is indicated for hypothyroidism, local symptoms (eg, increase in size, ulceration, hemorrhage), complications (eg, respiratory distress, difficulty swallowing, obstructive symptoms, cystic degeneration), or malignancy. The treatment strategy also depends on the location of the ectopic gland, the age of the patient, and the state of the native thyroid gland. There are no consensus or guidelines, due to the rarity of the condition. The following constitutes a practical approach [18]:

Asymptomatic patients with an ectopic thyroid who are otherwise euthyroid do not require treatment. Some authors suggest follow-up for complications, while others suggest excision because of a small risk of malignant transformation [79].

Patients who develop hypothyroidism should receive thyroid hormone replacement, which should also slowly shrink the ectopic thyroid [80]. (See 'Association with hypothyroidism' above.)

Patients with complications (eg, compressive symptoms) or local symptoms (eg, bleeding or ulcerations) that are refractory to medical therapy (ie, thyroid suppression) should be treated with either excision surgery or ablation therapy. Excision can be performed transorally or externally through a pharyngotomy. Transoral excision is most suitable for small lesions [81,82], while external incision is required to remove larger lesions. In most patients with lingual thyroid, it is the only functioning thyroid tissue, and thus lifelong thyroid supplements are required post-surgery [51].

SUMMARY AND RECOMMENDATIONS

Thyroglossal duct cyst – Thyroglossal duct cysts (TGDCs) result from a failure of the thyroglossal duct to obliterate during embryonic development. They characteristically present as a nontender midline neck mass at the level of the thyrohyoid membrane and are closely associated with the hyoid bone. Classically, TGDCs move with swallowing or protrusion of the tongue. (See 'Clinical manifestations' above.)

Diagnosis of TGDC – TGDC can be diagnosed by imaging studies, fine-needle aspiration, or surgical pathology. CT of the neck with contrast and MRI are the preferred imaging modalities for TGDC in adults and children, respectively. Fine-needle aspiration should be performed in all adults with suspected TGDC but only in children with suspicious features on imaging. (See 'Diagnostic evaluation' above.)

Treatment of TGDC – For suitable surgical candidates with a TGDC, we recommend surgical excision rather than observation or nonsurgical ablation (Grade 1B). Failure to remove a TGDC could result in recurrent infection or missed cancer. (See 'Uninfected TGDC' above.)

-The standard surgical treatment is resection of the cyst and the midportion of the hyoid bone in continuity and resection of a core of tissue from the hyoid upward toward the foramen cecum, an operation known as the Sistrunk procedure. (See 'Sistrunk procedure' above.)

-TGDCs in children are more likely to have some degree of infection or inflammation at presentation. Surgery should follow antibiotics during the acute inflammation phase or else risk recurrence. (See 'Infected TGDC' above.)

-Percutaneous ethanol injection (sclerotherapy) or observation are alternative approaches in patients who are not surgical candidates. (See 'Nonsurgical candidates' above.)

TGDC cancer – TGDC cancer is a rare cancer (<1 percent) that is typically diagnosed on histopathology after excision of a TGDC. Papillary thyroid cancer is the most common pathologic type, followed by mixed papillary and follicular cancer and squamous cell carcinoma. (See 'Epidemiology' above and 'Staging and survival' above.)

Diagnosis of TGDC cancer – The cancer is considered to have originated in the TGDC if there is histologic evidence of columnar or squamous epithelial lining in the cyst, normal thyroid follicles in the cyst wall, and complete absence of lymph node tissue and there is ultrasonographic evidence of a normal thyroid gland. If not, the lesion may represent a lymph node metastasis from a thyroid cancer. (See 'Diagnosis' above.)

Treatment of TGDC cancer – In most cases of primary TGDC carcinoma, resection with the Sistrunk procedure is an adequate treatment. However, total thyroidectomy with or without lymph node dissection is performed in high-risk cases or metastatic thyroid cancer. TGDC carcinoma has an exceedingly low mortality rate. (See 'Thyroglossal duct cyst cancer' above.)

Ectopic thyroid – Patients with a TGDC often have ectopic thyroid glands, which are defined as functioning thyroid tissue found anywhere other than the usual anatomic location of thyroid gland, but usually along the normal path of thyroid gland descent. The most common site of ectopic thyroid is a lingual thyroid followed by the wall of a TGDC. (See 'Epidemiology' above and 'Anatomy' above.)

Diagnosis of ectopic thyroid – Ectopic thyroid is mainly diagnosed with a thyroid scan. A thyroid laboratory panel should be obtained because of the association of ectopic thyroid with hypothyroidism. A fine-needle aspiration is often performed to guide management. (See 'Association with hypothyroidism' above and 'Diagnostic evaluation' above.)

Treatment of ectopic thyroid – Euthyroid patients with asymptomatic ectopic thyroid tissue and benign cytology can be observed. Treatment for ectopic thyroid tissue is indicated for hypothyroidism, local symptoms (eg, hemorrhage), complications (eg, respiratory distress), or malignancy. Treatment strategies include thyroid hormone or surgical excision, depending on the location of the ectopic gland, the age of the patient, and the state of the native thyroid gland. (See 'Management' above.)

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Topic 2155 Version 25.0

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