Thyroglossal and Branchial Cysts, Sinuses, and Fistulas
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Congenital fistulas, cysts, or sinuses in the neck region consist either of branchial anomalies which arise from incomplete obliteration of pharyngeal clefts and pouches during embryogenesis or from failure of obliteration of the thyroglossal duct that was formed during the descent of the thyroid gland. The most common clinical sign is infection of the remnants, and appropriate surgical therapy is needed.
KeywordsThyroglossal duct Thyroglossal cyst Hyoid bone Thyroid gland Foramen cecum Branchial cysts Branchial sinuses Branchial cleft Facial nerve Hypoglossal nerve Laryngeal nerve
Abnormalities in the neck region are caused by a large variety of anomalies which may be congenital or acquired. Residuals from embryological structures in the neck derive either from the thyroglossal duct or from the branchial arches and constitute the most common congenital anomaly in this anatomical region accounting for up to 60% of all excised neck masses in children. Although they are congenital anomalies, they may only become evident months or years later due to local swelling discharge of fluid or inflammation. Knowledge of the embryology and neck anatomy is essential for safe surgical therapy and minimizing the risk of recurrence or unpleasant complications.
Thyroglossal Duct Remnants
Thyroglossal duct remnants present usually as a midline neck cysts or mass below the hyoid bone. Sinuses drain into the foramen cecum of the tongue. Most commonly they cause clinical problems in the first decade of life, and more than half of the cases are diagnosed before the age of 5. Rarely may they cause problems in patients of a later age.
Embryology (Sadler 2006)
The thyroid gland appears as an epithelial proliferation in the floor of the pharynx between the first pharyngeal arch and the second/third pharyngeal arch at a point later indicated as the foramen cecum. Subsequently, the thyroid descends in front, through, or behind the hyoid bone and reaches its final position in front of the trachea in the seventh week. During migration, the thyroid remains connected to the tongue by a narrow canal, the thyroglossal duct. The duct obliterates in the fifth gestational week, and the foramen cecum at the base of the tongue on one end and the pyramidal lobe of the thyroid at the other end are the normal remnants. However, if duct cells persist, they can form a cyst or a sinus which is connected to the foramen cecum but rarely a fistula with an external opening in the middle of the neck. The thyroglossal cyst may lie at any point along the thyroid gland migration but always near or in the midline. Approximately 50% of these cysts are close to or just inferior to the body of the hyoid bone. Aberrant thyroid tissue may be found anywhere along the path of the descent of the gland.
Clinical Presentation and Diagnostic Workup
In a large series, 60% of the cysts were located close to the hyoid bone, 24% behind the hyoid bone, 13% close to the pyramidal lobe of the gland, and 3% intra-lingual at the foramen cecum (Allard 1982). When located at the base of the tongue, they may cause respiratory distress or even sudden infant death (Diaz et al. 2005). During palpation, uninfected cysts are often ballotable and can be moved slightly from side to side, but not up or down. Due to their origin from the foramen cecum, the thyroid cysts move upward during swallowing or when the tongue protrudes. An ultrasound investigation is recommended as preoperative workup to prove the cystic structure of the pathology. Fluctuating cysts may drain the content into the mouth generating a foul taste (Foley and Fallat 2006). The differential diagnosis includes complete ectopic thyroid gland or parts of the thyroid, dermoid inclusion cysts, lipomas, sebaceous cysts, submental lymphadenitis, thymus cysts, or tumor (Amos and Shermetaro 2019). As mentioned above, the latter group of pathologies may be moved up and down with palpation but do not move during swallowing unless the pathology is in close connection with the hyoid bone or the thyroid gland. In particular, dermoid cysts may be located in close vicinity to the hyoid bone and should therefore be excised to avoid a recurrent pathology. If the clinical examination shows the typical up-and-down movement of the pathology during swallowing but the ultrasound shows not a cystic but a solid structure, an ectopic thyroid gland may be present. The overall incidence is 1–2%, very rare, and most of these patients have hypothyroidism. Therefore, if the ultrasound shows a solid lesion and the TSH and T3/T4 estimations indicate hypothyroidism, scintiscanning is recommended to identify the amount of functional thyroid tissue and avoid surgical resection of the functioning part of the thyroid (Radkowski et al. 1991; Wadsworth and Siegel 1994).
If the pathology presents primarily as an abscess, a horizontal incision or antibiotic therapy is recommended. The use of a drain depends on the size of the abscess. Some authors recommend antibiotic therapy alone or an additional needle aspiration of the pus in order to avoid seeding of the ductal epithelium. The parents have to be informed that a second surgical procedure with excision of the duct will become necessary as soon as the local inflammation is under control.
Branchial Cysts and Sinuses
Although branchial cysts and sinuses are most often operated on in childhood, sometimes they are not detected as a clinical problem before adulthood. They are located along the anterior border of the sternocleidomastoid muscle; however they drain into very different regions depending on their origin from one of the branchial clefts. Knowledge of the embryology and the anatomical variants is crucial to avoid surgical mistakes, thereby creating nerve lesions and significant morbidity.
Embryology (Sadler 2006)
Treatment of branchial remnants requires knowledge of the related embryology. Cysts, sinuses, and fistulas result in persisting epithelial cells within the mesoderm and are lined by squamous or columnar epithelia (Waldhausen 2006). Between 75% and 90% of the anomalies derive from the second branchial cleft, while 8–20% arise from the first cleft. Although most branchial cleft anomalies are present at birth, they may not appear until a fluid-filled cyst is formed or becomes infected. Bilateral cysts or sinuses can be observed in 10–15% of patients. Although the majority of branchial anomalies are singular events, some cases of coincidence in families point to a genetically determined abnormality. Simple cystic remnants present commonly in adolescence and adulthood, while sinuses and fistulas are usually diagnosed in infancy and early childhood. In principle, clinical manifestation should be taken as an indication for elective excision before infectious complications supervene.
Clinical Presentation and Diagnostic Workout
Remnants of the first branchial cleft occur with an incidence of approximately 5–25% of all branchial anomalies (Golf et al. 2012). They form small cysts at the retroauricular and parotid region but may extend to the area below the mandible and above the hyoid. Parotid and retroauricular lesions present usually as enlarging masses. Within the parotid, the relation to the facial nerve is critical (D’Souza et al. 2002). The most common classification divides them according to Work in two types: Work type I is of ectodermal origin and occurs medial to the concha often extending into the postauricular crease and ending in a cul-de-sac at the osseous-cartilaginous junction of the external meatus. They are usually superficial to the main facial nerve trunk. Work type II anomalies may also contain cartilage. They may have a sinus opening below the angle of the mandible and extend upward through the facial nerve to the end in or around the external auditory meatus (Work 1972). Infection of the cysts or sinus is common and pus may be discharged from the ear. According to Olsen, cysts and sinuses are usually superficial, while fistulas are deep to the facial nerve (Olsen et al. 1980; Magdy and Ashram 2013). The remnants of the first branchial cleft need to be distinguished from the preauricular pits, cysts, and sinuses which are remnants of the auditory tubercles. They are located anterior to the tragus of the ear, are often bilateral, and tend to be inherited. Diagnosis as well as surgical therapy is difficult and must avoid any damage to the facial nerve. Magnetic resonance imaging and a high-resolution CT scan are helpful to show the extent and the relationship to the external auditory canal and the middle ear, but these techniques cannot inform about the relationship of the anomaly to the facial nerve. Intraoperative continuous electrophysiological facial nerve monitoring has been shown to be useful for the location of the facial nerve and its branches (Magdy and Ashram 2013).
Remnants of the third and fourth branchial anomaly are uncommon (Golf et al. 2012). The external presentation of both tracts is similar as the remnants of the second branchial cleft along the middle to lower third of the anterior border of the sternocleidomastoid muscle. The difference between both tracts is that the third sinus passes over the superior and recurrent laryngeal nerve and between the hypoglossal and glossopharyngeal nerves and posterior to the carotid artery to end finally within the upper piriform sinus, while the fourth sinus passes deep to the laryngeal nerve but superior to the recurrent nerve. Both anomalies are predominantly on the left side, and the classical presentation is a recurrent left abscess or acute thyroiditis in childhood (Nicoucar et al. 2010; Madana et al. 2011). Further typical symptoms are recurrent respiratory tract infection, hoarseness, and painful swallowing. If the anomalies present as recurrent abscesses at the lateral side of the thyroid gland or in close vicinity to the piriform sinus, they may cause life-threatening respiratory stridor in neonates and infants or acute unilateral thyroiditis in children and adults. The appropriate diagnosis is difficult, and the cyst may evoke a false impression of acute thyroiditis. Most often these anomalies are treated as they were harmless local lymphoid abscesses, a mistake that makes later surgical excision of the tract very difficult. CT scan of the neck helps to identify the origin of such lesions. In an acute suppurative phase, external pressure onto the mass may ensue in laryngoscopically visible evacuation of pus into the piriform fossa.
Surgery of the first branchial cleft remnants is difficult, and only symptomatic forms need to be treated by local excision. At the beginning of the procedure, it is essential to expose the facial nerve and all its horizontal and lower branches. The surgical procedure should start with the identification of the main trunk of the nerve by means of a retroauricular incision. The exit of the nerve from the stylomastoid foramen can be found in a triangle formed by the sternocleidomastoid muscle, the bigastric muscle, and the external ear canal. Once the branches are isolated, minor or major parts of the parotid gland must be resected to identify the tract. Intraoperative monitoring of both mechanically elicited activity and electrically evoked responses to facial nerve stimulation with a nerve integrity monitor is useful (Magdy and Ashram 2013). The opening of the fistula to the external ear canal should be included in the resection to avoid any recurrence. Rarely, the duct opens to the middle ear or runs parallel to the Eustachian tube. The whole procedure is even more difficult in cases with a previous infection.
The special anatomy in the rare case of remnants of the third and fourth branchial cleft and the risk to damage the superior or the recurrent laryngeal nerve make the surgical procedure difficult. Several approaches have been recommended, each of them bares its specific risks. Excision with hemithyroidectomy or combined approach including catheter insertion into the piriform opening has proven to be successful (Madana et al. 2011; Pereira et al. 2004). Recently, closure of the internal opening at the piriform sinus by cauterization or injecting sclerosing material (OK-432) endoscopically into the tract of the third and fourth branch anomalies has been recommended and may be an especially helpful solution after previous repeated infections (Nicoucar et al. 2009; Nicoucar et al. 2010; Roh et al. 2006; Kim et al. 2009; Nixon and Healey 2011). In three patients with a fourth branchial pouch anomaly under 1 year of age, the sinus opening in the left piriform fossa was successfully endoscopically coagulated with a monopolar diathermy in order to seal the opening (Bajaj et al. 2011).
Conclusion and Future Directions
Branchial anomalies and thyroglossal duct cysts are common in children. Conservative observation is not indicated, but surgical therapy is most appropriate. However, detailed knowledge of the embryology and pathology of these anomalies is necessary not only for correct diagnosis but also to avoid unnecessary surgery and/or complications. In the difficult cases of the first or third and fourth branchial cleft fistulae and sinuses, a CT fistulography may provide additional information in regard to the surrounding structures. Intraoperative electrical stimulation of structures within the parotic gland might additionally be helpful to identify facial nerve branches.
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