Thyroglossal Duct Cyst Imaging

Updated: Oct 16, 2015
  • Author: Omar Islam, MD, FRCPC; Chief Editor: L Gill Naul, MD  more...
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Overview

Overview

Thyroglossal duct cyst (TDC) is usually diagnosed clinically, but ultrasonography is the preferred imaging technique in children. The 2 most common complications of TDC are infection and malignancy, the latter of which occurs in 1-4% of cases. [1, 2, 3]

TDC is the most common nonodontogenic cyst in the neck, representing approximately 70% of all congenital neck abnormalities. [4, 5] It occurs as a result of anomalous development and migration of the thyroid gland during the fourth through eighth weeks of gestation. It is a cystic remnant along the course of the thyroglossal duct between the foramen cecum of the tongue base and the thyroid bed in the visceral space of the infrahyoid neck. [6, 7, 8]

When examined pathologically, TDCs have a variable number of histologic components, including columnar, cuboidal, and/or non-keratinized stratified squamous epithelium. [9] Ectopic thyroid tissue is present in a proportion of TDCs, with estimates ranging widely, from 1.5 to 62%. [4, 10]

TDC typically presents in children and young patients, with an average age at presentation of 6 years. About 50% of patients present before 20 years of age, but a significant percentage (15%) present after 50 years of age. [4, 11] Renard et al reviewed 146 cases of thyroglossal duct carcinoma and found that the average age was 39 years (range, 6–81 years). The squamous type of thyroglossal duct carcinoma tends to arise in an older age group, with an average age of 54 years at presentation. [12, 13]

In children, TDCs are diagnosed clinically. Imaging is used to confirm the clinical diagnosis and identify the presence of the thyroid gland. Most authorities feel that ultrasound is the most appropriate initial imaging technique for TDC. Ultrasound is readily available, inexpensive, non-invasive, and does not involve ionizing radiation or sedation, which is particularly important in children. CT and MRI are useful for determining the full extent of the lesion and its sometimes complex relationship to surrounding structures such as the hyoid bone. [14, 15, 16, 17]

In adults, CT is the preferred modality for several reasons:

  • TDC is less frequently diagnosed in adulthood, so the differential is broader
  • The radiation risk is lower in adults than in children
  • The risk of carcinoma is substantially higher in adults, and CT can better identify the suggestive features of malignancy

Ultrasound may not depict the deep extent of hyoid and infrahyoid TDCs, and it cannot reliably assess the region of the tongue base in the setting of suprahyoid TDCs.The thyroglossal duct is intimately related to the hyoid bone, and CT depicts this relationship best in hyoid lesions. MRI is preferred for lesions at or near the tongue base. The major disadvantage of CT is ionizing radiation. Both CT and MRI usually require sedation, and are more expensive to perform than ultrasound. [16]

Anatomy

Approximately 65% of TDCs are located between the hyoid bone and thyroid gland. Fifteen percent occur at the level of the hyoid bone and 20% occur above it. Lingual TDCs are rare, accounting for 1-2% of all TDCs. In a series of 300 TDCs only 2 (0.67%) were in the region of the foramen cecum. [18] Cysts in this location may be associated with dysphagia and respiratory arrest. The low incidence of lingual TDC may be because the thyroglossal duct begins to atrophy from the oral side. [19, 20, 21, 22, 23]

Thyroid carcinomas in TDCs

Virtually every type of thyroid carcinoma has been identified within a TDC, including, in descending order of frequency, papillary, mixed follicular-papillary, squamous, follicular, anaplastic and Hurthle cell carcinoma. [24, 25, 26, 27]

In 80% of cases, TDC carcinoma is of papillary cell origin. [28, 29] This is of radiologic significance, because the presence of calcifications in papillary carcinomas is one of the key imaging findings indicative of malignancy in TDC. [26] There are no documented cases of medullary carcinoma arising in TDC. This is not surprising, because medullary carcinomas arise from parafollicular cells originating from the ultimobranchial bodies of the fourth branchial pouch rather than the thyroid anlage.

Invasion into surrounding soft tissue is seen in only 17% of thyroglossal duct carcinomas. Metastatic disease is present in 1.3%, which is much lower than the rate from carcinoma arising in the thyroid gland. [30] Regional lymph nodes metastases occur in 8% of cases. [4, 25] Coincident orthotopic thyroid gland carcinoma occurs in 14-25% of cases. [10, 31]

Surgical intervention is the primary therapy for large TDCs. Recently, the effect of ethanol sclerotherapy on TDCs was investigated. [32] In a small study of 8 patients, under sonographic guidance, ethanol was slowly instilled into the thyroglossal duct cavity after the cyst fluid was aspirated. The procedure was performed in an outpatient setting. Although ultrasound-guided sclerotherapy has been well established for benign thyroid cysts, it has been challenged for various nonthyroid cysts; however, it has become an accepted alternative for benign nonthyroid cystic neck masses. [33]

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Computed Tomography

Computed tomography (see the images below) has a high degree of diagnostic accuracy for thyroglossal duct cysts (TDC). The most helpful features in the differential diagnosis are the midline location, most often at or below the hyoid bone, and the intimate relationship of infrahyoid TDCs to the strap muscles. CT better evaluates the potential for thyroglossal duct carcinoma and is thus preferred in adult patients. [15]

Axial-enhanced CT scan of the neck at the level of Axial-enhanced CT scan of the neck at the level of the thyroid cartilage demonstrates a subtle hypodense lesion deep to the strap muscles, asymmetrically to the right of midline.
Enhanced CT of the neck in the same patient as in Enhanced CT of the neck in the same patient as in the previous image shows ectopic thyroid tissue deep to the right strap muscle anterior to the cricoid bone. This conforms to the expected course of the right thyroglossal duct.
Axial contrast-enhanced CT shows a large cystic le Axial contrast-enhanced CT shows a large cystic lesion at the level of the thyroid cartilage, slightly to the right of midline, embedded in the right strap muscles, consistent with a TDC.
Axial contrast-enhanced CT shows a rim of enhancin Axial contrast-enhanced CT shows a rim of enhancing thyroid tissue (white arrow) along the inferior aspect of the TDC. This communicated with the native thyroid gland via a thin band of tissue (see the following image).
Sagittal contrast-enhanced CT in the same patient Sagittal contrast-enhanced CT in the same patient as in the previous image nicely demonstrates a thin band of tissue (white arrow) connecting the TDC with the native thyroid gland inferiorly.
Sagittal CT image in a 76-year-old man with a rapi Sagittal CT image in a 76-year-old man with a rapidly enlarging neck mass shows a large infrahyoid cystic lesion representing pathologically proven thyroglossal duct cyst carcinoma. Image courtesy of Barton F. Branstetter IV, MD.
Axial CT image in a 22-year-old female with hoarse Axial CT image in a 22-year-old female with hoarseness and a midline mass shows a partially calcified cystic mass in the pre-epiglottic space at the level of the thyroid cartilage. The lesion represents pathologically proven thyroglossal duct cyst carcinoma. Image courtesy of Barton F. Branstetter IV, MD.

Reede et al performed a retrospective analysis of 12 preoperative cases of TDC and 2 cases with postoperative complications and described the typical CT appearance of a TDC as a well-circumscribed, low-density lesion with peripheral rim enhancement. Occasionally, increased attenuation, internal septations, and indistinctness of surrounding tissue planes are seen and are presumably the result of prior infection. Thyroid cartilage erosion and laryngeal extension are both extremely rare. [34]

Calcifications and soft tissue nodules in the wall of the cyst are important features suggestive of TDC carcinoma. [26, 27] Branstetter et al retrospectively reviewed 6 cases of TDC carcinoma and found that all 6 had either a dense or enhancing mural nodule, calcification within the cyst, or both. [35]

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Magnetic Resonance Imaging

Magnetic resonance imaging (see the images below) provides a high degree of diagnostic accuracy for thyroglossal duct cysts (TDC), but it is rarely required for the diagnosis. Although TDCs are invariably hyperintense on T2-weighted images, T1-weighted signal intensity is variable. King found that 56% (9 out of 16) of TDCs were isointense or hyperintense on T1-weighted images, while the remaining 44% (7 out of 16) were hypointense. [36]

In this axial T2-weighted MRI, at the level of the In this axial T2-weighted MRI, at the level of the hyoid bone, there is a fluid signal intensity mass extending anteriorly from the pre-epiglottic space into bilateral strap muscles.
Axial inversion recovery sequence in the same pati Axial inversion recovery sequence in the same patient as in the previous image shows the tongue base component of the hyperintense thyroglossal duct cyst nicely. Note the relationship of the mass deep to the hyoid bone at this level.
After the administration of intravenous gadolinium After the administration of intravenous gadolinium, the thyroglossal duct cyst wall shows enhancement on this axial T1-weighted postcontrast fat saturation sequence. This may indicate superimposed infection.
Axial T1-weighted image demonstrates the mass to b Axial T1-weighted image demonstrates the mass to be low signal, representing cyst fluid.
Axial inversion recovery MRI sequence in an elderl Axial inversion recovery MRI sequence in an elderly patient demonstrates a fluid-signal intensity mass embedded in the strap muscles just off the midline at the level of the hyoid bone.
Axial T1-weighted image obtained following intrave Axial T1-weighted image obtained following intravenous gadolinium administration demonstrates peripheral rim enhancement of the thyroglossal duct cyst.
A sagittal T1-weighted postcontrast image in the s A sagittal T1-weighted postcontrast image in the same patient as in the previous image nicely depicts the midline thyroglossal duct cyst and its location relative to the airway, tongue base, hyoid bone, and strap muscles.

In a report of 2 cases of TDC, Blandino found high T1-weighted signal intensity in both lesions. [37] The high T1-weighted signal intensity is thought to be due to thyroglobulin or hemorrhage. Peripheral rim enhancement is sometimes observed on postcontrast images and is suggestive of previous infection.

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Ultrasonography

On ultrasonography (see the images below), most thyroglossal duct cysts (TDCs) appear as unilocular lesions with thin walls and posterior acoustic enhancement. TDCs are highly variable in echogenicity. Ahuja et al studied 23 clinically diagnosed TDCs in children and found 3 appearances [38] : 3 lesions (13%) were anechoic, 13 lesions (56.5%) were hyperechoic, and 7 lesions (30.5%) were heterogeneous.

Ultrasound image demonstrates a midline infrahyoid Ultrasound image demonstrates a midline infrahyoid unilocular mass with a homogeneously hypoechoic internal echotexture, typical of a TDC.
Ultrasound image in the same patient as in the pre Ultrasound image in the same patient as in the previous image demonstrates normal thyroid tissue inferior to the TDC.

In another study by Ahuja et al, 40 clinically suspected TDCs in adults were found to have variable sonographic appearances ranging from a typical anechoic cyst to a pseudosolid appearance. [39] Four patterns of TDCs were identified: 11 lesions (28%) were anechoic, 7 lesions (18%) were hypoechoic with low-level echoes, 11 lesions (28%) were hyperechoic, and 11 lesions (28%) were heterogeneous.

Surrounding soft tissue edema, regional reactive lymphadenopathy and a sinus tract to overlying skin may be demonstrated. [40] Doppler interrogation should be performed on initial ultrasound to identify any solid vascular component.

While most TDCs can be confidently diagnosed by ultrasonography, the presence or absence of functioning thyroid tissue within the TDC may be difficult to ascertain. The same holds true for thyroid tissue extending superiorly or inferiorly from the TDC. A solid nodular component may be difficult to identify, particularly within a uniformly hyperechoic TDC. For this reason, Doppler interrogation should always be performed in cases of suspected TDC. [17]

In adults, the findings of carcinoma may be inevident on ultrasound.

In a retrospective chart review of 44 patients younger than 18 years who had undergone surgical excision of midline neck masses to determine and compare the accuracy of different imaging modalities, including ultrasound, MRI, and CT in the diagnosis of TDCs in children, ultrasound was the preferred examination given its comparable accuracy, ease of administration, and lower cost. [41] Ultrasound had a sensitivity of 75% in the diagnosis of TDCs. In addition, the added risks of general anesthesia with MRI and ionizing radiation with CT are not justified in this setting, given their equivalent or inferior performance when compared with ultrasound in this cohort.

The following entities can have sonographic findings similar to TDC:

  • Branchial cleft cysts: these cysts can usually be differentiated from TDCs by their characteristic lateral location in the neck; however, TDCs located off the midline could be mistaken for branchial cleft cysts, as their sonographic appearances are similar [38]
  • Cystic hygromas: these lesions have characteristic cystic spaces of varying sizes with intervening septa, allowing for easy differentiation from TDCs
  • Hemangiomas: these lesions are typically hypoechoic, with vascular spaces, and may demonstrate the presence of flow with color flow Doppler; the presence of phleboliths may also aid diagnosis [42]
  • Lipomas: these lesions have a characteristic feathery pattern on ultrasound with multiple bright reflectors [39]
  • Lymph nodes: lymph nodes are hypoechoic, are often multiple, and demonstrate the presence of an echogenic hilus; a suppurated node in the prevascular space might be mistaken for an infected TDC
  • Dermoid inclusion cysts: these lesions may be confused with TDC, particularly when they are located in the vicinity of the hyoid bone; however, dermoid cysts lie superficial to the strap muscles and usually have visible fat components on CT.
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Nuclear Imaging

There is controversy regarding the need for preoperative thyroid scintigraphy in patients with a presumed thyroglossal duct cyst (TDC). [40] Proponents argue that scintigraphy may be more sensitive than CT or MRI for detection of ectopic thyroid tissue in the neck and that the excision of a TDC in a patient with no additional functioning thyroid tissue might result in permanent hypothyroidism. [43]

Other experts do not feel that preoperative scintigraphy is necessary, arguing that a properly performed Sistrunk procedure will remove all ectopic thyroid tissue regardless of whether it was identified on preoperative imaging and that scintigraphy results in an unnecessary radiation dose to the neck, especially in pediatric patients.

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