The longer I do anesthesia, the more I realize that not knowing the details about the surgeries that I see every day can cause unexpected problems with the anesthesia.
The Case
My colleague was doing anesthesia recently for a healthy adult with a thyroglossal duct cyst that had repeated become infected. This patient had a normal airway and was easy to ventilate and intubate. The surgery was uneventful. Knowing that airway management had been easy at the start, my colleague elected to extubate the patient still deeply anesthetized in order to avoid any coughing during wake-up. Coughing and bucking against an endotracheal tube can potentially cause some bleeding at the surgical site, which he wanted to avoid.
However, as soon as he removed the endotracheal tube he had a very difficult time ventilating the patient. Insertion of an oral airway did not help, despite the fact that the patient had no visible swelling nor any signs of laryngospasm. After pulling forward on the mandible and applying positive pressure assistance, ventilation slowly improved as the patient emerged from anesthesia. After awakening, the patient did fine and had no problems in the recovery area.
Removal of the Hyoid Bone Can Cause Problems
After finishing this unexpected and nerve-wracking experience, my colleague did some on-line research about thyroglossal duct cyst surgery and what he found startled us. For example, I didn’t know that when a surgeon excises a thyroglossal duct cyst, that he or she usually takes out the middle section of the hyoid bone, the section between the two lesser horns. This operation is called a Sistrunk procedure.
In embryonic development, the thyroid gland moves from its origin near the hyoid bone at the base of the tongue down a tract known as the thyroglossal duct, to its final position in the neck. Parts of this duct can remain intact, and can later form cysts or tracks that can communicate with the skin, leading to lumps and/or infections. Excision of these thyroglossal duct cysts is fairly common. The surgeon takes the cyst, the tract, plus the section of hyoid the tract is attached to, in order to prevent recurrence. This is considered a low risk procedure that doesn’t usually cause functional airway problems because scar tissue quickly forms in this area, functionally re-establishing these relationships.
The Anatomy
However, acutely the situation can be quite different. The hyoid is in a very strategic location. Let’s look at the anatomy. The hyoid bone, although free floating, is the biomechanical center of many ligaments and muscles attaching the larynx in the area at the base the tongue. There are many balancing forces pulling in opposing directions at this spot. The final balance tends to keep the larynx stable and the airway open.
The balance of forces of the muscles and ligament of the larynx depend partially on the biomechanical focal point of the hyoid bone.
Surgical disruption of the hyo-epiglottic membrane by removing the center section of hyoid allows the now unopposed supra and infrahyoid muscles to pull the entire larynx cephalad and allows the epiglottis to tip forward over the glottis. In addition, the base of the tongue can slide downward, pushing the epiglottis over the glottis. With normal muscle tone this is usually not a problem. However with loss of muscle tone, as in this case with the patient still anesthetized, the airway could be difficult to keep open. We think that happened in this case. Difficult reintubation has been reported after thyrogossal duct excision in the immediate postoperative period related to this anatomical change.
After removal of the center section of hyoid during a thyroglossal duct excision, the larynx tends to rise, the tongue slides downward, and the now unbalanced forces pull the epiglottis downward over the glottis. Airway obstruction can occur until muscle tone is restored.
Of course any edema or hematoma formation would only exacerbate this tendency to obstruct the airway. While extremely rare, other potential complications of the Sistrunk procedure include resection of other parts of the larynx, especially in the small child where identification of laryngeal anatomy can be more challenging. As you might imagine this could be quite catastrophic.
I honestly don’t know if having had a thyroglossal duct cyst repaired in the past predisposes a patient to airway obstruction or difficult intubation in the future. However, I will certainly be more mindful, as well as prepared in the future when I get this history from a patient. And I will have more respect for this simple procedure. I’ve included a couple of links below for those of you who want to read further.
This experience is a reminder that we not only need to be expert at our own profession, but we also need to be mindful of the details of the procedures that our surgical colleagues perform with our help.
May the force be with you.
Further reading:
