INTRODUCTION — Thyroglossal duct cysts (TGDCs) are the most common form of congenital cyst in the neck. They 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. Although most patients with TGDCs are children or adolescents, up to one-third are aged 20 years or older [1,2]. Males and females are equally affected.

Patients with a TGDC often have ectopic thyroid glands. (See 'Thyroid ectopia' below.)

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 [2]. 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, which arises from the neural crest portion of the fourth pharyngeal pouch, ultimately fuses with the descended medial anlage [3]. 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.

A thyroglossal duct cyst arises as a cystic expansion of a remnant of the thyroglossal duct tract [1,2]. 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 [4]. Many cystic remnants of the thyroglossal tract are never detected clinically; a postmortem study of 200 adults found a 7 percent incidence of thyroglossal duct cysts [5].

CLINICAL FEATURES — Patients with a TGDC usually present with a midline upper neck mass that is cystic. The mass usually causes no symptoms but may be slightly tender. Often the patient has or recently had an upper respiratory tract infection, but whether the infection leads to cyst formation or simply increases the likelihood of detection of a preexisting cyst is uncertain.

The cyst 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). In most cases, the cyst is at or just below the hyoid bone adjacent to the thyrohyoid membrane [2]. 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 location can masquerade as a thymic mass and cause confusion [6].

TGDCs are usually within 2 cm of the midline [7] but can be somewhat more lateral and may even be lateral to the thyroid cartilage (more typically on the left). The typical cyst does, however, maintain a close relationship to the hyoid, thyrohyoid membrane, or thyroid cartilage. Classically, TGDCs move up with swallowing or protrusion of the tongue, emphasizing their close relationship with the hyoid/larynx complex.

The typical close relationship between a TGDC and the thyroid cartilage can result, if the cyst is large, in remodeling of the laryngeal cartilage [8]. However, because the cysts do not typically invade, laryngeal reconstruction is rarely required even after excision of large cysts [9].

Familial occurrence of TGDCs has been reported but is extremely rare, with 21 individuals of hereditary TGDCs in seven families reported [10,11]. The most common inheritance pattern appears to be autosomal dominant [11].

In addition, radiation therapy used to treat head and neck cancers can acutely enlarge subclinical thyroglossal duct remnants [12]. Hence, radiologists, radiation oncologists, and the surgeons should be aware of this possibility when evaluating patients after radiation therapy. Very rarely, a TGDC may present in an ectopic location (eg, an endolaryngeal cyst). In such cases, an open procedure is preferred over an endoscopic surgical approach [13]. An intrathyroidal cyst with thyroglossal duct cyst-like lining has also been described [14].

THYROID ECTOPIA — Thyroid ectopia is defined as functioning thyroid tissue found anywhere other than the usual anatomic location of thyroid gland. Ectopic thyroid is usually located along the normal path of thyroid gland descent but rarely can also be found in the mediastinum, heart, esophagus, or diaphragm [15]. Ectopic thyroid tissue is derived from abnormalities in migration of the medial anlage and hence typically does not contain C cells.

Failure of thyroid gland descent occurs in approximately 1 in 200,000 normal subjects and 1 in 6000 patients with thyroid disease [16]. The true incidence of thyroid ectopia is not known 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 [17]. 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 [18]. Up to 1 to 2 percent of patients presenting with what appears to be a TGDC have an ectopic thyroid gland [19].

Association with hypothyroidism — Most cases of thyroid ectopia manifest as simple TGDCs in conjunction with a normally developed and located thyroid gland [20]. Some thyroid ectopia function normally, but approximately one-third of patients present with hypothyroidism.

If hypothyroidism develops, the mass may enlarge as a result of stimulation by thyrotropin (TSH). Ectopic thyroid tissue may enlarge during puberty or pregnancy. 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 [19]. On a rare occasion, thyroglossal ductal ectopy is found in patients diagnosed with congenital hypothyroidism associated with thyroid ectopy [21]. (See "Diagnosis of and screening for hypothyroidism in nonpregnant adults".)

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 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 [16,22,23].

Among ectopic thyroid glands, 90 percent are lingual and 10 percent occur in other sites [22]. In patients presenting with a lingual thyroid, over 70 percent have no thyroid tissue in the normal location [2]. A lingual thyroid can represent the only functioning thyroid tissue, so excision could lead to severe hypothyroidism, requiring thyroid hormone replacement [24].

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 [16,22,25].

Carcinoma arising in a lingual thyroid is rare, with fewer than 30 cases reported in the literature [20]. (See 'Thyroglossal duct cyst carcinoma' below.)

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") [3]. 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 [26-28].

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 [3] 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 [3,29,30].

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.

DIFFERENTIAL DIAGNOSIS — TGDCs are the most common cause of a midline neck mass, followed by dermoid cysts. Dermoid and sebaceous cysts tend to be quite superficial and less tethered to the underlying structures, including the hyoid bone, as compared with TGDCs.

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.

Lipomas are quite superficial and have ill-defined edges.

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

Fine-needle aspiration — Fine-needle aspiration (FNA) is often used to diagnose TGDCs or to exclude other diagnoses [31]. The cytomorphologic features include colloid, macrophages, lymphocytes, neutrophils, and ciliated columnar cells, but these are not unique to TGDCs.

IMAGING — Palpation to confirm the presence of normal thyroid gland is thought not to be reliable by pediatric surgeons [32]. Radionuclide imaging, ultrasonography, and computed tomography (CT) are undoubtedly more reliable tests to identify the presence of thyroid tissue [33,34]. (See "Overview of the clinical utility of ultrasonography in thyroid disease".)

CT — In a suspected case of TGDC, CT of the neck with contrast is the most preferred imaging modality (image 1). Typically, CT imaging depicts TGDCs as well-circumscribed lesions with homogenous fluid attenuation surrounded by a thin enhancing rim [35]. It 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 information regarding the size, extent, and location. It also identifies normal orthotopic thyroid tissue. Additional wall enhancement indicates an infected TGDC [36].

MRI — On magnetic resonance imaging (MRI), water characteristics are seen (ie, dark on T1- and bright on T2-weighted images) [36]. MRI can also define the cysts' relationship to the hyoid and other surrounding structures.

Ultrasonography — Ultrasonography (US) is a very useful modality for thyroid glands and will reveal the cystic nature of a TGDC but does not provide information about the relationship to surrounding structures including hyoid bone [37]. US imaging of a TGDC reveals a well-defined, thin-walled, anechoic, or hypoechoic mass with posterior acoustic enhancement in the midline anterior neck [38].

The presence of infection can change the appearance of TGDCs on US; wall thickening and loss of hypoechoic appearance may be noted. Additionally, the cyst fluid can also contain protein, causing the normal uniform hypoechoic appearance to be lost [36].

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

Incidentally found TGDC — 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 [39].

THYROGLOSSAL DUCT CYST CARCINOMA — The incidence of primary carcinoma of the thyroglossal duct is less than 1 percent. TGDC carcinoma more commonly presents in the adult population. While TGDC itself shows no gender predilection, there is a notable female preponderance in TGDC carcinoma, with a female-to-male ratio of 2.3:1 reported in the literature [40].

The majority of TGDC carcinomas are papillary-type thyroid cancer [41-43]. Thus, if the cyst is found to contain thyroid cancer, one must be sure that the carcinoma 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) [44,45]. Studies suggest that among patients with carcinomas in TGDCs, 11 to 33 percent have carcinoma within the thyroid gland [41].

TGDC carcinoma is typically diagnosed on final pathology. The carcinoma is considered to have originated in the TGDC if there is histologic evidence of columnar or squamous epithelial lining in the cyst [18,46], normal thyroid follicles in the cyst wall [18], and complete absence of lymph node tissue, and there is ultrasonographic evidence of a normal thyroid gland [47]. If not, the lesion may represent a lymph node metastasis from a thyroid cancer.

Most cases of TGDC carcinoma are adequately treated by resection with the Sistrunk procedure, with a reported cure rate of 95 percent [41,48]. After review of pathology, if a surgeon is certain of the diagnosis of TGDC carcinoma (ie, primary thyroid gland carcinoma has been ruled out) and thyroid sonography is negative, then surgical treatment of TGDC is sufficient [49]. 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 [50]. (See "Differentiated thyroid cancer: Overview of management".)

In general, studies report that low-risk TGDC cancer cases can be treated with the Sistrunk procedure alone with observation of the thyroid, while high-risk patients should be treated more aggressively [40,43]. Low-risk TGDC cancer includes patients <45 years of age with small tumors (ranging from 1 to 4 cm) with classic histology, no extracapsular spread, no vascular invasion, negative margins, no nodal or distant metastases, and a normal thyroid gland demonstrated by imaging studies [40,43].

Thyroidectomy is also indicated in rare cases of TGDC carcinoma that have invasive tumor or positive regional lymph nodes. This is done in anticipation of the need for I-131 treatment and diagnostic whole-body radioiodine scanning [51].

Lymph node metastasis of TGDC carcinoma was previously thought to be rare [2]. However, if prophylactic neck dissections are performed at the time of resection, the incidence of lymph node metastasis is surprisingly high [52]. In a series of 18 patients with papillary cancer arising in a TGDC, most (16/18) patients underwent neck dissection of the central and/or lateral compartments. Lymph node metastases were found in 75 percent (12/16) of the patients in this series [52] and 88 percent in a retrospective review of 26 patients [50]. In addition, 56 percent had small foci of papillary cancer in their thyroid glands, but these patients accounted for only one-half of the patients who had positive nodes [52]. Occurrence of distant metastasis is uncommon, reported in fewer than 2 percent of cases [41,53].

TGDC carcinoma has an exceedingly low mortality rate. Nevertheless, staging TGDC carcinoma may help to more appropriately match therapeutic interventions to the extent of the disease and optimize oncological outcomes [40]. 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 was 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 [40].

Papillary thyroid cancer is the most common pathological type of TGDC cancer, reported between 85 and 91 percent of cases, followed by mixed papillary and follicular cancer and squamous cell carcinoma [54]. TGDC papillary carcinoma has excellent prognosis, and the occurrence of distant metastatic lesions is rarely reported. Squamous cell carcinoma of the TGDC is extremely rare (about 4 percent of all TGDC cancers) and is believed to arise from the cyst wall. It carries the worst prognosis amongst all types of TGDC cancers and should be treated aggressively [54,55]. Medullary thyroid cancer is not found in the setting of malignancy associated with TGDC [56].

INFECTED THYROGLOSSAL DUCT CYST — Most TGDCs have some degree of infection or inflammation at presentation [57]. It is essential to avoid surgery during the phase of acute inflammation as this can lead to recurrence [58-60]. An infected TGDC should be managed initially with antibiotics, followed by definitive surgery once the infection has resolved. Once the infection clears completely, the patient should undergo an elective Sistrunk procedure. (See 'Sistrunk procedure' below.)

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 [61]. Additionally, definitive surgery is easier in the absence of scar tissue or a cutaneous fistula [62].

Microbiology — The cysts are usually infected by oropharyngeal flora; hence, antibiotics should be directed toward the most common oral organisms, which include various streptococcal species and oral anaerobes [61]. 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 [63].

Antibiotics — Successful treatment requires broad-spectrum antibiotics targeted toward oral flora [63].

Mild cases may be treated with a course of oral antibiotics, such as a first-generation cephalosporin (cephalexin 500 mg PO every 6 hours), amoxicillin-clavulanate (500 mg/125 mg PO every 8 hours), or clindamycin (600 mg PO every 8 hours). We do not recommend empirical coverage for methicillin-resistant Staphylococcus aureus (MRSA) unless identified by culture. (See "Methicillin-resistant Staphylococcus aureus (MRSA) in adults: Treatment of skin and soft tissue infections".)

For more severe infections, an antibiotic regimen such as cefazolin in combination with clindamycin can be used (table 1). (See "Antimicrobial prophylaxis for prevention of surgical site infection in adults", section on 'Head and neck surgery'.)

SURGERY — Patients with TGDCs should be treated surgically with the Sistrunk procedure unless the patient is not a surgical candidate. (See 'Sistrunk procedure' below and 'Sclerotherapy' below.)

If a TGDC is not removed, as many as one-half become infected [59], and infection before surgery is a well-described cause of recurrence [58,59].

●In one retrospective series, the recurrence rate after simple cystectomy was 8 percent among children whose cysts had not been infected, compared with 40 percent in children whose cysts had been infected [59]. Similarly, among patients who underwent more extensive surgery, the recurrence rate was 1.4 percent in those with noninfected cysts as compared with 14 percent in those with infected cysts [59]. Surgery is therefore best performed at first presentation.

●Approximately 1 to 2 percent of TGDCs ultimately are found to contain cancer [2,49]. The clinical features of thyroglossal duct carcinoma are very similar to those of TGDCs [2], and in the majority of cases thyroglossal duct tract carcinomas are incidental (ie, not suspected before the operative procedure) [64].

Preoperative evaluation — Patients with a TGDC often have ectopic thyroid glands (see 'Thyroid ectopia' above). In a survey of 368 surgeons (including pediatric, general, and head and neck surgeons), 57 percent had encountered ectopic thyroid tissue among patients with TGDCs [32].

Before any surgery is planned, it is important to determine whether patients with a TGDC have thyroid tissue in the normal site. It is essential to determine whether a patient has ectopic thyroid tissue as this can be involved with benign or malignant thyroid disease.

Ectopic thyroid tissue can be confused with a TGDC. All cases of thyroid ectopia should have thyroid function tests, ultrasonography, and a thyroid scan performed to locate additional functioning thyroid tissue [15]. (See "Laboratory assessment of thyroid function" and "Overview of the clinical utility of ultrasonography in thyroid disease".)

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 upwards toward the foramen cecum, an operation known as the Sistrunk procedure (figure 2) [65]. Arborization of the superior aspect of the thyroglossal tract at and above the hyoid bone may occur and may be a reason for recurrence [58]. 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 [66]. 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 [67]. The overall recurrence rate after this procedure is approximately 5 percent [19].

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. Patients with infected cysts should receive antibiotic therapy and not undergo incision and drainage, because the latter can lead to scarring and make later surgery more difficult. Preoperative fine-needle aspiration can be helpful to decrease cyst size and in some cases may lead to identification of TGDC carcinoma, if solid elements of the lesion can be sampled [41].

A new modification of the repeat Sistrunk operation, suture-guided transhyoid pharyngotomy, has also been proposed to allow the surgeon better visibility of normal structures and direct access to the tissues between the hyoid bone and the foramen cecum [67]. A single series of eight of these procedures, all done successfully by a single surgeon, has been reported. As the procedure is new and the experience is limited, the suture-guided modification of the Sistrunk operation is not recommended at this time.

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 [3,18]. 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 [41]. There are no reports of medullary carcinoma in a TGDC [68].

Fine-needle aspiration biopsy is the most reliable method for preoperative diagnosis of thyroid cancer, especially if done with ultrasound guidance [69]. 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 [41].

SCLEROTHERAPY — Percutaneous ethanol injection is an alternative approach in patients who are not surgical candidates if the presence of malignancy can be excluded [70]. It is effective in only one-third of cases. Prospective and long-term observational studies will determine recurrence rates with this approach [71].

SUMMARY AND RECOMMENDATIONS

●Thyroglossal duct cysts (TGDCs) characteristically present as a midline neck mass at the level of the thyrohyoid membrane, closely associated with the hyoid bone. Although most patients with TGDCs are children or adolescents, up to one-third are aged 20 years or older. (See 'Introduction' above.)

●TGDCs usually present as a nontender mass within 2 cm of the midline but can be more lateral. The typical cyst maintains a close relationship to the hyoid, thyrohyoid membrane, or thyroid cartilage. Classically, TGDCs move with swallowing or protrusion of the tongue. Most TGDCs have some degree of infection or inflammation at presentation. (See 'Clinical features' above.)

●The differential diagnosis includes dermoid cysts, sebaceous cysts, and thyroid ectopia. (See 'Differential diagnosis' above.)

●Computed tomography (CT) of the neck with contrast and ultrasonography are the preferred imaging modalities. (See 'Imaging' above.)

●Patients with TGDCs should be treated surgically unless the patient is not a surgical candidate. Surgery should be avoided during the acute inflammation phase as this can lead to recurrence. (See 'Surgery' above.)

●Infection is the most common complication of TGDCs. An infected TGDC typically presents as a tender mass, with or without fever, and may have a draining sinus. On ultrasonography, it may lose normal hypoechoic appearance. An infected TGDC should be managed initially with antibiotics, followed by definitive surgery once the infection has resolved. (See 'Infected thyroglossal duct cyst' 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 upwards toward the foramen cecum, an operation known as the Sistrunk procedure. (See 'Sistrunk procedure' above.)

●Patients with a TGDC often have ectopic thyroid glands. Some thyroid ectopia function normally, but approximately one-third of patients present with hypothyroidism. Treatment with thyroid hormone supplementation is usually sufficient for suppression, but surgical excision may become necessary. (See 'Thyroid ectopia' above.)

●The preoperative detection of hypothyroidism in a patient with a midline neck mass increases the suspicion of ectopic thyroid tissue. (See 'Association with hypothyroidism' above.)

●Ectopic thyroid tissue can be confused with a TGDC. All cases of thyroid ectopia should have thyroid function tests, ultrasonography, and a thyroid scan performed to locate additional functioning thyroid tissue. (See 'Preoperative evaluation' above.)

●Incidentally detected TGDC on head and neck imaging should be referred to an otolaryngologist for evaluation, regular follow-up, and surgery when symptoms arise. (See 'Incidentally found TGDC' above.)

●Before any surgery is planned, it is important to determine whether patients with a TGDC have thyroid tissue in the normal site or any ectopic thyroid tissue, as this can be involved with benign or malignant thyroid disease. (See 'Preoperative evaluation' above.)

●The incidence of primary carcinoma of the thyroglossal duct (TGDC carcinoma) is less than 1 percent. TGDC carcinoma is typically diagnosed on final pathology. Once the diagnosis of primary carcinoma of TGDC is completely established, in most cases of TGDC carcinoma, resection with the Sistrunk procedure is an adequate treatment. However, total thyroidectomy is performed in high-risk cases and in some rare situations. (See 'Thyroglossal duct cyst carcinoma' above.)