Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature.

Thyroglossal duct cysts are the most common congenital cysts in the neck. They are cystic dilations of epithelial remnants of the thyroglossal duct tract, just formed during the migration of the thyroid during embryogenesis. They present as midline neck masses at the level of the thyrohyoid membrane and are closely associated with the hyoid bone. Most patients present as children, although presentation at any age is possible. Males and females are equally affected, and the cysts are usually asymptomatic but they may become infected and form abscesses and draining cystulas. Cervical resection is the recommended therapy. Preop infection is associated with an increased risk of recurrence, and infection should be treated with antibiotics rather than incision and drainage, as this will lead to scarring and make later surgery more difficult.

The tuberculum impar is a medium swelling in the floor of the oral cavity of the embryo and it arises from the first brachial arch. The copula is the same thing, a medium swelling in the floor of the oral cavity; however, it arises from the second and third brachial arch. It is the junction of these two swellings that is the foramen cecum. An anlage or primordia is just an early collection of cells. It is the first evidence of the future organ or structure. And the ultimobranchial bodies come from the fourth pharyngeal pouch, and they contain parafollicular cells which merge eventually with the lateral roof of the thyroid and produce the calcitonin. We are looking at a human embryo on electron micrograph —a human embryo at 24 days—we are looking at its eventual aspect and we can see the maxillary, the frontal nasal prominence with the nasal placodes. This is the maxillary prominence, and down here you see the first arch which again the tuberculum impar arises from. And then further down, the second and third arch, which is where the copula will arrive, and then the junction of them which will be the foramen cecum. If you take this picture and cut it in its coronal plane, you get these images which again just demonstrate the tuberculum impar from the first arch and the copula from the second and third arch, and again as promised the foramen cecum at the junction which you see over here. And it is here where the anlage of the thyroid, or these early cells, form eventual diverticulum and begin to function. From here the medial anlage descends through the neck eventual to the pharyngeal gut. As it descends again it is joined by the ultimobranchial bodies which are the parafollicular C cells. The thyroid reaches its final midline pretracheal position as a bilobed diverticulum, which is connected by an isthmus around week 7 gestation. At the same time that the primitive thyroid is migrating, the hyoid bone is developing, and there has been much debate as to the position of the descent of the thyroid in the hyoid bone.

In 1977 a group of Canadian researchers took 200 adult specimens and 30 embryos at varying stages of development and examined serial step sections of the specimens. They were able to map out the path of the thyroid and to suggest "the constant and embryologically predictable relationship to the hyoid bone," which they say is anterior. At the time, however, there are people who had produced single sections through this region which demonstrated the path to the posterior to the hyoid bone which you can sort of see on this slide. It was actually the observation made in 1940 which preceded these studies of an Englishman who noted that in the development of the hyoid bone it changes shape from ovoid to crescent and when it does so the strap muscles, which would be here, pull downward on the hyoid bone causing this forward tilt. And as it does that it pulls the tract posteriorly and almost hooks it up behind the bone, and this is how you can get—if you just examine single sections—it might look like the path is posterior to the bone, but if you actually examine the serial step sections you will see that the path is truly anterior. Regardless, this just highlights the fact that the tract of the developing thyroid is closely associated with the hyoid bone, and this becomes important when we discuss the Sistrunk procedure which is the standard operation and treatment of the thyroglossal duct cyst.

During its migration the gland remains connected to the tongue by a narrow canal, the thyroglossal duct. The duct usually atrophies and disappears by week 10. Portions of the tract and remnants of thyroid tissue may persist, however, anywhere along this crescent descent from the tongue to the thyroid. The most caudal remnant of the tract is the parietal lobe which is present in one-third of people, and you can see it there. Thyroglossal duct cysts can arise anywhere there has been failure of the complete obliteration of the tract. Cystic dilations of this tract remnant result in the clinical presentation of a midline neck mass. The mass is usually asymptomatic, mobile, and located above or below the thyroid.

But what else could this be? Differential diagnosis is a congenital midline neck mass, again including thyroglossal duct cysts ,but also includeing teratomas, which are usually easily differentiated by their presentation in the neonate who is having airway obstruction due to the size of the midline neck mass. Dermoid cysts, although they can present lower in the neck, usually present in the submental area. Thymic cysts, although they can present higher in the neck, usually present in the chest and off the midline. Other things in the differential include sebaceous cysts or lipomas—which are more superficial—lymphadenopathies, lymphatic malformations, and sarcoma.

What classically differentiates the thyroglossal duct cyst from other midline neck masses is its elevation with tongue protrusion and swallowing. The mass rises in swallowing because of the tract's close association with the hyoid bone, and it rises with tongue protrusion because of the connection to the base of tongue. In children, however, it is not always as easy to detect as it is in this slide. Some patients first present with an infected midline neck mass, which usually accompanies an upper respiratory infection. There is one hypothesis that local lymphoid tissue hypertrophies with the upper respiratory infection and occludes the tract with the resultant cyst formation. Acute infection may result in abscess formation and rupture, causing a persistent sinus or fistula. It is important to note, however, that this fistula is acquired and not congenital unless it is associated with a branchial cleft remnant. Some patients with thyroglossal duct remnants never present clinically. A postmortem study of 200 adults who did not have a midline neck mass found a 7% incidence of thyroglossal duct cyst remnants. So, many people have these and just never present.

If a patient presents to you with a midline neck mass and you think it is a thyroglossal duct cyst, how do you evaluate them preoperatively? The history and physical exam remain the standard for diagnosis and therapeutic decision-making. However, if the history and physical are not classic for thyroglossal duct cysts—for example if the mass is off the midline or if the patient is a child and a physical exam is more difficult—there have been several imaging studies that have been suggested to help in the diagnosis. Ultrasound can differentiate between a cystic and a solid mass, and it can also demonstrate the presence of normal thyroid tissue. It is also noninvasive and inexpensive, so remains a used test by many clinicians. CT gets precise information about the mass size, location, and its relationship to other structures. Similarly, MRI gives detailed information about the mass but, because there are less expensive imaging studies that are adequate, it is rarely used. FNA can be used for direct tissue diagnosis when in doubt. Notice that on this list is not included a thyroid scan. Thyroid scan is not used to diagnose a thyroglossal duct cyst. We will speak more about this later.

Illustrated here is a case where CT and FNA were helpful in atypical presentation of a midline neck mass. The patient presented with a long-standing midline neck mass and hoarseness. The clinical impression was that of a Lorenzo neoplasm; however, CT showed this large cystic mass. FNA was consistent with an inflammatory cyst, and at surgery a thyroglossal duct cyst was in fact found and removed with the Sistrunk procedure, which we will speak about in a minute. Thus, CT and FNA were helpful in getting this patient the appropriate surgery instead of a big cancer operation.

Most important in a preop evaluation of a patient with a presumed thyroglossal duct cyst is to make sure that the patient has a normal functioning thyroid gland in its normal pretracheal position. Why is this so important? Well, just as you can have remnants of the tract with the formation of a cyst, you can actually have thyroid tissue anywhere along this tract from the base of tongue to the normal position of the thyroid. If you have all of your thyroid tissue with complete arrest of descent, you can see how that would be easily mistaken for a thyroglossal duct cyst. You remove it and the patient has no thyroid; in fact, in the literature there are multiple reports of patients where presumed thyroglossal duct cysts were removed and they had postop hypothyroidism progressing to myxedema in some cases.

Among ectopic thyroid glands, 90% are lingual and 10% are sublingual. This is an example of a lingual duct. In the same patient, here are her radioisotope scans which again demonstrate her only functioning thyroid tissue to be in a lingual thyroid. So what do you do? How do you avoid becoming the surgeon who boasts postop myxedema? Should you scan everyone? This is probably not cost effective or in the patient's best interest, given that only one in 200,000 people have these failures in migration. How do we best identify patients who may be at higher risk for ectopic thyroid?

A combined study was carried out by the Children's Hospital in Boston and Rainbow Babies in Cleveland that addresses this question. The authors, one of whom is Dr. Friedman, reviewed the literature as well as their own data and identified 230 patients with a presumed diagnosis of thyroglossal duct cyst. These patients underwent surgical excision and the authors reviewed the pathology. They noted that eight of these patients were found to have ectopic or aberrant thyroid tissue and not a true thyroglossal duct cyst. Of these eight patients, five had preoperative evidence of hypothyroidism. In addition, two-thirds of these patients had preop thyroid function tests, and they revealed elevated TSHs. Of the patients in the original number of 230 patients, of those who had preop thyroid function tests all of their TSHs were normal. So patients who eventually truly had a thyroglossal duct cyst on pathology had normal TSHs. So this led to the proposal that a history suggestive of hypothyroidism may identify patients more likely to have ectopic thyroid and could direct further evaluation. Here are some of the symptoms noted by the authors of Hypothyroidism. They submit that ectopic and aberrant thyroid is almost always dysgenetic, resulting in inadequate thyroid hormone production and "hypothyroidism" in these patients. The authors then proposed this algorithm which is used in the Myers operative text for management and workup of an anterior neck swelling. If a patient is clinically euthyroid on history and physical, routine thyroid function tests should be obtained. If they are normal, a patient can safely go to surgery. If they are abnormal, the patient should get a thyroid scan. If a patient presents with symptoms of hypothyroidism, they really have identified themselves as a high-risk person for having ectopic thyroid and a thyroid scan should be obtained. It is important to note that the thyroid scan is obtained for the confirmation of normal thyroid tissue and not for the diagnosis of thyroglossal duct cysts.

Current recommendations include a thorough history and physical, routine thyroid function tests, and selective use of preop thyroid scans to document presence of normal-functioning thyroid tissue. Pathologic confirmation of the diagnosis is important as rarely carcinoma can arise in the thyroglossal duct cyst.

So, you have diagnosed thyroglossal duct cyst and you are confident the patient has normal functioning thyroid tissue, and you propose surgery to the patient who says, "Why do I have to have this removed?" The indications for removal are undesirable cosmetic appearance, recurrent infection, and, again, histologic confirmation of the diagnosis, as carcinoma can arise, although this is rare. Surgical approaches have been developed over time so that now, when the procedure is properly performed, recurrence rates are reported as low as 3%. Historically, thyroglossal duct cysts were treated with simple excision or incision and drainage. This resulted in a high recurrence rate at 50%. In 1893, Schlang proposed the excision of the cyst along with the central portion of the hyoid bone, and this reduced the recurrence rate to 20%. And in 1920, Sistrunk described the procedure that is used today which reduced the recurrence rate to 3%.

Sistrunk's procedure was based upon the principles of embryology that were known at that time and included resection of the central hyoid bone as well as a cuff of tongue musculature towards the foramen cecum. The patient is placed in position as if they were to undergo a thyroidectomy. A transverse incision is made over the cyst. If there is a history of an infection or a fistula, the incision is elliptical and should include that fistula. The incision is carried through the skin and platysma. The cyst at this time is usually noted to have expanded to midline and the strap muscles are divided and the cyst is dissected free from surrounding attachments to the level of the hyoid bone. The hyoid bone is then skeletonized lateral to the cyst in the tract and the central segment is transected. Sistrunk advocated the removal of 0.25 inches of bone and the reapproximation of the bony ends with suture. Now 1.5 cm of bone is removed, and no attempt is made to reapproximate the bone. Sistrunk advocated the resection of the suprahyoid duct and a core of tissue without an attempt to isolate the duct. This concept is repeatedly emphasized in the literature with the rationale that arborization of the suprahyoid portion of the duct is common, and there is no single definitive dissection plane. Unless a core of suprahyoid tissue or tongue musculature is included in the resection, recurrence is likely.

To facilitate the resection of this core tissue, Sistrunk instructs the surgeon to place a gloved finger in the patient's mouth to identify the foramen cecum and to push the tongue forward and upward. This shortens the distance between the base of tongue and the hyoid bone. The core of tissue should be 3.0 mm on all sides and extend to the mucous membrane of the foramen cecum without actually entering the oral cavity. When you push the tongue forward this distance here, which contains the suprahyoid portion of the duct, it is brought into the surgical field making it easier to identify and dissect. The cyst's central portion of the hyoid bone and suprahyoid core of tissue are removed as one specimen, the wound is irrigated, and a Penrose drain is placed. The strap muscle and platysma are reapproximated, and the skin is closed. This procedure takes into account the embryologic origins of the thyroglossal duct remnants from the foramen cecum to its course in close proximity to the developing hyoid bone down to the normal pretracheal position. With all remnants of the tract excised, risk of recurrence is minimized.

Thyroglossal duct cysts are lined with squamous or columnar-affiliated epithelium. They can be surrounded by fibrous tissue with inflammatory cell infiltrate so that the epithelial island of thyroid tissue and mucous glands may be present. Rarely is a cyst found to contain thyroid carcinoma. Carcinoma of the thyroglossal duct cyst was first described in 1910, and since then fewer than 200 cases are reported in the literature. Cancer is usually diagnosed incidentally after the presumed cyst has been removed. It is only noted histologically. There is no difference in how a patient would present if they have a regular thyroglossal duct cyst or if they have one with "carcinoma." Eighty percent are papillary and well differentiated. Of patients noted to have a carcinoma in a thyroglossal duct cyst, 11%-33% are found to also have carcinoma in the thyroid gland. Interestingly, this statistic correlates with a "thyroid carcinoma" found in autopsy studies which is reported as high as 35%. So the question in the literature has been, "Did these cancers arise primary from the thyroglossal duct cyst or did they arise primarily in the thyroid gland?" From the literature, it seems the consensus is that these arise primarily in the thyroglossal duct cyst and this directs the workup and treatment of them. If the patient is taken to the operating room for the Sistrunk procedure and removal of the thyroglossal duct cyst, that is considered adequate surgical treatment of the carcinoma. A postoperative thyroid scan should be done to confirm that there is no carcinoma in the thyroid gland. If the scan reveals normal functioning thyroid, then no further surgery is indicated. Thyroid hormone suppression is debatable. Most sources recommend it, even the principles of management of well-differentiated thyroid carcinoma. The bottom line is that the cure rate for patients with carcinoma arising in the thyroglossal duct cyst who undergo the Sistrunk procedure and then receive thyroxine therapy is 95%.

In summary, thyroglossal duct cysts are the most common congenital cysts in the neck. Surgery is the definitive treatment, and, when performed correctly, the recurrence rate can be as low as 3%. Patients at high risk for ectopic thyroid tissue should get a thyroid scan preoperatively. Resection is indicated for cosmesis, recurrent infection, and histologic confirmation of the diagnosis. If well-differentiated carcinoma is identified, the Sistrunk procedure and thyroxine therapy are adequate treatment in the setting of a normal functioning thyroid gland on thyroid scan.

Case Presentation

GW is a 5-year-old boy with a history of a midline neck mass that increased in size with an upper respiratory infection. The mass itself was infected and was treated effectively with antibiotics. On exam, the mass was 2 cm in diameter, smooth, round, and elevated with swallowing and tongue protrusion. It was located between the hyoid bone and the thyroid gland.

On pre-operative evaluation, the patient, who had a long thin neck, had a palpable thyroid gland in the normal anatomic position. In addition, the patient did not have cold intolerance, weight gain, hypersomnolence, developmental delay, or other signs of hypothyroidism. Thyroid function tests were not performed.

Past medical history, past surgical history and ROS were otherwise negative, and the patient was not taking any medications. He had no known drug allergies.

The patient was electively taken to the operating room with a diagnosis of thyroglossal duct cyst. He underwent excision of the cyst, the tract, and a central portion of the hyoid bone without complication and was discharged home post-operative day one after the drain was removed.

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