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THYROGLOSSAL DUCT REMNANTS

Johan Fagan

The surgical management of thyroglossal of the tongue and might drain directly into duct remnants (TGDRs) requires an under- the mouth.1 standing of the embryology of the thyroid gland, as failure to include the embryologi- cal course of the thyroid gland in the surgi- cal resection increases the probability of re- currence.

Relevant Embryology

The thyroid gland originates in the base of the tongue at the foramen caecum. In early embryonic life the base of the tongue is ad- jacent to the pericardial sac. As the embryo unfolds, TGDRs may remain anywhere be- tween the pericardial sac and the foramen caecum. A persistent thyroglossal duct Figure 2: Schematic representation of the suprahyoid courses through the base of the tongue from duct branching within the muscle of the base of tongue the foramen caecum. It then passes inferi- orly, anterior to, and rarely through, the hy- Clinical presentation oid body, and often has a diverticulum that hooks below and behind the hyoid, before it TDGRs may present at any age as a cyst courses towards a thyroglossal duct cyst or (Figure 3, 4), abscess, sinus, fistula or tu- the thyroid gland (Figure 1). mour, anywhere along the embryological course of the thyroid gland.

Foramen caecum

Hyoid bone

Retrohyoid diverticulum

Thyroglossal duct cyst

Figure 1: Typical course of thyroglossal duct remnants (yellow line)

The suprahyoid ductal segment may have a branching pattern like the tips of a broom (Figure 2). These multiple ductules com- municate with secretory glands in the base Figure 3: Thyroglossal duct cyst in thyrohyoid region http://openbooks.uct.ac.za/ENTatla 21-1 Open Access Atlas of Otolaryngology, Head & Neck Operative Surgery

Lingual: 2%

Suprahyoid: 24%

Thyrohyoid: 61%

Suprasternal: 13%

Figure 4: Thyroglossal duct cyst in thyrohyoid region Mediastinal: Rarely Patients classically present with a mobile, painless mass in the midline of the neck in Figure 6: Distribution of thyroglossal duct cysts proximity of the hyoid bone. Occasionally a cyst may be off the midline (Figures 5, 10).

Figure 7: Dermoid cyst

A lingual thyroid usually presents as a mass in the base of the tongue (Figures 8, 9); this may be the patient’s only thyroid tissue in Figure 5: Thyroglossal duct cyst to left of midline over- the majority of cases. lying lamina of thyroid cartilage

Figure 6 illustrates the distribution of thy- roglossal duct cysts. 1

A cyst generally moves upward during de- glutition or protrusion of the tongue be- cause of its close anatomical relation to the hyoid bone. This is considered a reliable di- agnostic sign as it distinguishes it from other midline neck masses such as a lymph node or a dermoid cyst (Figure 7). Figure 8: Lingual thyroid

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and/or calcification on ultrasound exami- nation should raise the possibility of carci- noma, most commonly papillary. However, even if the diagnosis of thyroid cancer is suspected it does not alter the type of sur- gery (Sistrunk operation).

Surgical principles

• It is imperative to achieve a complete re- section of the TGDR and its embryonic tract so as to avoid symptomatic recur-

Figure 9: CT scan of lingual thyroid rence • A thyroglossal cyst abscess should ini- Preoperative evaluation tially be aspirated and treated with anti- biotics, not incised and drained, so as to The principal issues to determine prior to facilitate complete resection once the surgery are: infection has settled

Is it a TGDR? Unlike other midline masses, Sistrunk operation only TGDRs are treated with a Sistrunk op- eration. Therefore it is important to exclude The Sistrunk operation is the standard of other causes of midline masses prior to sur- care for TGDRs. It includes resection of en- gery such as dermoid cysts and lymph tire embryological tract i.e. the thyroglossal nodes. duct cyst, the central portion of the body of the hyoid bone, and a broad (>1cm) core of Is it the patient’s only thyroid tissue? Occa- suprahyoid muscle extending up to / close sionally a TGDR comprises the only func- to the foramen caecum. tioning thyroid tissue, and its removal re- sults in hypothyroidism. Ultrasound exam- The following description is for a cyst in the ination to establish the presence of normal thyrohyoid region: thyroid tissue is a simple investigation. Should imaging not be possible, the surgeon • Make an incision in a skin crease over should explore the neck to determine the the cyst. Note that platysma muscle may presence of a normal thyroid gland. be absent in the midline, so take care not to puncture the cyst (Figure 10) Is the patient hypothyroid? The majority of • Raise superior and inferior flaps in sub- patients with lingual thyroids are hypothy- platysmal planes. The superior flap roid. Therefore patients with lingual thy- should be raised to approximately 2cms roids should have a TSH level determined above the body of the hyoid bone prior to surgery. • Identify the infrahyoid strap muscles that are stretched over the superficial as- Does the TGDR contain thyroid cancer? pect of the cyst Thyroid cancer occurs in only about 1% of • Divide the cervical fascia vertically in operated TGDRs. A solid component the midline, separate the infrahyoid http://openbooks.uct.ac.za/ENTatlas 21-3 Open Access Atlas of Otolaryngology, Head & Neck Operative Surgery

strap muscles, and expose the cyst • Divide the inferior attachments of the (Figure 11) thyroglossal duct cyst, and mobilise the • Divide the mylohoid and geniohyoid deep aspect of the cyst from the muscles just above the body of the hyoid thyrohyoid membrane up to the hyoid bone with diathermy remaining bone with sharp dissection (Figure 13) between the lesser cornua of the hyoid • Expose the hyoid bone on either side of so as not to place the hypoglossal nerves the cyst (Figure 14) or lingual arteries at risk of injury (Figure 12)

Figure 13: Mobilise deep aspect of cyst from thyroid

Figure 10: Initial skin crease incision cartilage and thyrohyoid membrane

Figure 14: Expose hyoid bone on either side of cyst Figure 11: Expose and part infrahyoid strap muscles overlying cyst • Divide the hyoid bone about 1cm to each side of the midline with heavy scis- sors (children) or a bone cutter (Figures 15, 16) MHM

Figure 12: Divide mylohoid (MHM) and geniohyoid muscles just above body of hyoid bone Figure 15: Dividing hyoid bone

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Figure 16: Divided hyoid bone

Figure 17: Resect a 2cm wide core of tongue (hyoglos- • Next resect the suprahyoid thyroglossal sus) tissue duct. Do not attempt to identify the thy- roglossal duct, as branches of the duct may be transected in the process in- creasing the likelihood of recurrence • Using monopolar diathermy resect a 2cm wide core of tongue tissue (hy- oglossus) in continuity with the remain- der of the operative specimen, including the hyoid bone, directed at an angle of approximately 450 of the sagittal (verti- cal) plane towards the foramen caecum (Figures 17, 18, 19) • If in doubt about the required direction, Figure 18: Superimposed image (yellow) illustrates di- place a finger in the mouth and on the rection of suprahyoid dissection and extent of final re- foramen caecum as a guide. It is re- section; note proximity of vallecula to hyoid markable how much base of tongue tis- sue can be resected without interfering with speech or swallowing. Note the proximity of the hyoid bone to the val- lecula. Should the vallecula or base of tongue be accidentally entered, simply close the defect with vicryl sutures.

Figure 19: Core of tongue (hyoglossus) tissue extend- ing up to just short of foramen caecum

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determine whether the hyoid bone and su- prahyoid tissues had been resected. An MRI scan should be done to serve as a roadmap for the surgeon to find residual TGDRs (Figure 21).

Figure 20: Final defect in base of tongue up to just short of forman caecum with free floating cut ends of hyoid bone

Figure 22: MRI of recurrence demonstrating multiple cysts

Reference

Mondin V, Ferlito A, Muzzi E, Silver CE, Fagan JJ, Devaney KO, Rinaldo A. Thy- roglossal duct cyst: Personal experience and literature review. Auris Nasus Larynx 35 (2008) 11–25 Figure 21: Resected specimen

• The tongue defect (Figure 20) is then Author & Editor partially obliterated with vicryl sutures. Johan Fagan MBChB, FCORL, MMed The two cut ends of the hyoid are not Professor and Chairman approximated, but left floating free. The Division of Otolaryngology supra- and infrahyoid muscles are ap- University of Cape Town proximated in a transverse plane, as is Cape Town, South Africa the platysma muscle, and the skin is [email protected] closed over a drain • Antibiotics are not required unless the oral cavity has been entered

Recurrent TGDR

Managing recurrent TGDR becomes chal- lenging because cysts may be multifocal with the presence of fibrosis, distorted sur- gical landmarks and possible absence of hy- oid bone. It is important to obtain an accu- rate description of the original surgery to

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