What Is a Thyroglossal Duct Cyst?

A thyroglossal duct cyst refers to a congenital cyst formed in the neck that is not fully degenerated and does not disappear during the development of the early embryonic thyroid. The occurrence of thyroglossal duct cysts has no significant relationship with gender. It can occur in both men and women and can occur at any age, but it is more common in adolescents under 30 years of age. Cysts can occur anywhere from the mid-lingual tongue blind hole to the sternum notch. The most common is the upper and lower parts of the hyoid bone, which can sometimes be sideways. ^[1]

Basic Information

English name

thyroglossalcyst

Visiting department

Otorhinolaryngology

Multiple groups

Youth under 30

Common locations

Hyoid bone

Causes of Thyroglossal Duct Cyst

Thyroglossal duct cyst is a congenital, developmental cyst that originates from the residual epithelium of the thyroglossal duct. Due to the incomplete degradation of the thyroglossal duct during embryonic thyroid formation, it remains in the deep tissue of the neck, and the lumen is covered with epithelium Produce secretion accumulation and formation.

At the 4th week of embryonic development, the endoderm between the first pair of pharyngeal sacs and the ventral side of the pharyngeal cavity sinks downward, forming a diverticulum-like structure, that is, the thyroid starter, which then extends into the lower interstitial space and is in the middle of the trachea Normal thyroid was formed before; at the 6th week, the thyroglossal canal spontaneously degenerates, leaving only a shallow depression at its starting point, namely the blind tongue hole. If the thyroglossal duct is incompletely degraded during this process, the remaining epithelium can form a thyroglossal duct cyst from the middle of the neck to the thyroid gland, and the cyst can communicate with the blind tongue hole through the non-degraded thyroglossal duct.

Clinical manifestations of thyroglossal cyst

The occurrence of thyroglossal duct cysts has no significant relationship with gender. It can occur in both men and women and can occur at any age, but it is more common in adolescents under 30 years of age. Cysts can occur anywhere from the mid-lingual tongue blind hole to the sternum notch. The most common is the upper and lower parts of the hyoid bone, which can sometimes be sideways. Most of the cysts are round, grow slowly, and have no symptoms. Most of them are found by chance. The cyst is soft, with clear boundaries, and has no adhesion to the surface skin and surrounding tissues. The cyst is located below the hyoid bone. Sometimes a tough cable between the cyst and the hyoid bone can be caught. The cyst can swallow and stretch the tongue Move up and down with other actions; if the cyst is located near the blind hole of the tongue, when it grows to a certain extent, it can raise the root of the tongue, swallowing and speech dysfunction.

Cysts can communicate with the oral cavity through the blind hole of the tongue and are prone to secondary infection. When the cyst is secondary to infection, pain can occur, especially when swallowing. Neck examination showed that the surface of the cyst was red and the boundaries were unclear. When the cyst ruptured or cut through the skin and drained, a thyroglossal fistula could be formed. At this time, the cyst could disappear due to the drainage of the contents. Clinically, the primary thyroglossal fistula present after birth is also seen. The fistula of thyroglossal canal fistula is small, and the pale yellow mucus or purulent mucus can flow out for a long time. When the fistula is blocked, it can cause an acute inflammation of the fistula.

According to the Meilan staining range during surgery, and pathological section analysis during and after surgery, thyroglossal cysts can be divided into 5 types: Type I: subhyoid bone cyst or reticular fistula branch, single fistula on hyoid bone; Type : Cysts or reticular fistula branches above and below the hyoid bone; Type , superior hyoid cysts or reticular fistula branches, single fistula below the hyoid bone; Type , subhyoid cysts or reticular fistula branches Branches, suprahyoid bone fistulas closed; type V, suprahyoid bone cysts or reticular fistula branches subhyoid bone fistula atresia.

Thyroglossal duct cyst examination

1.B-ultrasound

Ultrasound showed that the cyst and capsule were intact, the boundary was clear, and the morphology was more regular. The capsule wall is thin, and the capsule is mostly a liquid dark area with good sound transmission, and a few wire-like separated echoes. In the case of co-infection, the capsule wall can be thickened and non-smooth, and echoes of weak light spots can be seen in the liquid dark area. Echoes of papillary nodules can be seen on individual capsule walls, which may be echoes of thyroid tissue. Color Doppler ultrasonography showed cystic non-echoic dark area, no blood flow signal was found in it, blood flow and frequency spectrum could be detected in the periphery, and the enlarged lymph nodes and ectopic thyroid could be distinguished by this.

2.CT inspection

You can understand the nature and size of the mass and the adjacent relationship with the surrounding tissue. Diagnostic criteria: Typical location: lesions are located between the blind hole of the tongue and the thyroid gland, mostly distributed above and below the hyoid bone, and are closely related to the hyoid bone; typical CT signs: round or oblate liquid density images, multiple capsule walls Smooth and complete, the capsule wall is rough when the infection is combined, and the shape is more irregular when the fistula is formed; enhanced scan: the lesion is not strengthened, and the capsule wall can be strengthened significantly when the infection is combined; Deformation; wall nodules: it appears as a small mound-like protrusion from the wall of the capsule to the cavity. The base is relatively wide and can be strengthened when it is enhanced.

3. Radionuclide imaging

It is also helpful for the diagnosis of this disease. It can assess the size of cysts or fistulas, understand the presence of active thyroid tissue, and help distinguish them from thyroid tumors.

4. Iodine oil contrast

The course of thyroglossal fistula can be clearly defined, but it is rarely used in clinical practice.

Diagnosis of Thyroglossal Duct Cyst

Thyroglossal duct cysts can be primarily diagnosed based on symptoms and signs such as the location of the anterior cervical cystic mass and the movement of the tongue, and the puncture can extract transparent, slightly cloudy yellow thin or viscous liquid. Imaging examinations such as B-ultrasound and CT can help to further clarify the diagnosis and understand the exact size and shape of the cyst and its relationship with the surrounding tissues.

Differential diagnosis of thyroglossal cyst

1. Chronic chronic lymphadenitis and lymph tuberculosis

Presented as a submental mass, if the tuberculosis of the lymph is ruptured, it can form a fistula forever. However, the lesions of the subphrenic lymph nodes are mostly superficial, often with parenchymal masses and tenderness, which can be identified based on the history and biopsy results.

2.ectopic thyroid

Ectopic thyroid and thyroglossal duct cysts are both congenital thyroid abnormalities, and they are closely related in embryo development. Ectopic thyroid is often located at the base of the tongue or in the pharynx of the blind hole of the tongue. It is a tumor-like protrusion with a purple-blue surface, soft texture, and clear boundaries. Patients often have unclear speech, and in severe cases, swallowing and breathing difficulties may occur. Since 75% of ectopic thyroid glands are the only functional thyroid tissue, mistaken resection will lead to severe consequences of life-long hypothyroidism. In clinical practice, attention should be paid to the identification of the two. Radionuclide scanning is the most effective method of identification. A nucleus concentration in the ectopic thyroid site or the neck can reach the thyroid tissue can make a diagnosis.

3. Parathymus

There is no connection with the hyoid bone, the mass does not move up and down with swallowing, and the B-mode ultrasound is a substantial mass, which can be distinguished from thyroglossal cysts.

4. Dermatoid cyst

It usually appears as a subcondylar mass, and can also be located in the sternal cavity. Generally, the cyst has a thick envelope, no undulation, and often adheres to the skin. It does not follow swallowing and tongue extension activities, and it can be identified by puncture and extraction of soybean residue or sebum.

5. Thyroid adenoma

The disease mostly manifests as a painless mass in the anterior cervical area and thyroid tissue, which is soft and clear in boundary, and can be moved with swallowing, but not with tongue extension, and can be identified with the help of radionuclide scanning.

6. Parotid cyst

Mostly located in the carotid side or the carotid triangle, the masses were mostly off the midline and had nothing to do with the hyoid bone. The puncture may contain skin attachments and cholesterol crystals, which need to be identified by pathological section.

7. Other neck masses

Such as thyroid conical lobes, cystic hydromas, lipomas, sebaceous cysts, sublingual cysts, laryngeal cysts, parathyroid cysts, and teratomas, etc., can be identified according to the location and characteristics of the tumor.

Thyroglossal duct cyst treatment

Surgical removal of cysts or fistulas is the main method for radically removing thyroglossal cysts or fistulas. Due to the close relationship between cysts and fistulas and hyoid bones, the middle part of the hyoid bones should be removed during surgery to prevent recurrence.

Make a horizontal incision along the neck dermatome on the surface of the cyst. The length should be sufficient to expose the surgical field. If it is a fistula, a spindle incision including the skin of the fistula should be made. If the cyst is lower, it should be peeled off. Make a transverse incision to the level of the hyoid bone. Cut the skin, subcutaneous tissue, latissimus dorsi, and anterior cervical band muscles in layers according to the incision design, reveal cysts or fistulas, and then separate them around them. Be careful not to damage the thyroid hyoid periosteum. On both sides of the part connected to the hyoid body, the hyoid periosteum and the attached muscles are cut, and both sides of the hyoid body are cut with bone scissors to remove the cyst or fistula and the part of the hyoid body that has been severed. Flush the wound cavity, completely stop bleeding, suture the fistula muscles at the root of the tongue to eliminate dead space, and suture the muscles and periosteum attached to the superficial surface of the broken end of the hyoid bone.

If the cyst is cancerous with cervical lymph node metastasis, cervical lymph node dissection is required. Postoperative pathological types are papillary or follicular carcinoma, which can be treated with thyroxine inhibition. For squamous cell carcinoma, radiation therapy is feasible after surgery. ^[2]

Prognosis of thyroglossal cyst

Thyroglossal duct cysts can have a certain recurrence rate after surgical resection. Some studies have reported that the postoperative recurrence rate of Sistrunk surgery is 3% to 5%, but there have also been reports of recurrence rates as high as 26.9%. The rate of recurrence after surgery was 33%. Most of them are papillary carcinoma, but also follicular carcinoma and squamous carcinoma. However, there is still controversy about its origin. Some people believe that it has spread from occult thyroid cancer, and some people think that it originates from ectopic thyroid tissue in the wall of the thyroid tongue duct.

references

1. Edited by Li Xuepei. Otorhinolaryngology Head and Neck Surgery. Beijing: Peking University Medical Press, 2003: 39.

2. Huang Xuanzhao, Wang Jibao, editor of Kong Weijia. Practical Otorhinolaryngology Head and Neck Surgery: People's Medical Publishing House, 2007: 608-609.