Endoscopic-Assisted Removal of a Massive Pediatric Floor of Mouth Dermoid

A 16-year-old male presented with a floor of mouth (FOM) mass that had been increasing in size over the past 18 months. Eventual interference with speech and swallowing functions prompted surgical removal. Physical examination revealed a soft cystic lesion of the FOM, with a neck component measuring 5.0 by 6.0 cm. Computed tomography (CT) and magnetic resonance imaging (MRI) of the neck showed a 6.0 cm × 5.1 cm × 6.5 cm cystic mass, bright on T2 imaging with thin peripheral enhancement, above the mylohyoid displacing the tongue musculature superiorly and posteriorly and extending inferiorly to about the hyoid bone (Figure 1). Preoperative fine-needle aspirate showed straw-colored fluid with anucleated squamous cells with no malignant cells identified.

Figure 1.

Preoperative CT and MRI showing extent of lesion. A, Sagital CT cut at the midline showing large sublingual cyst with abutment at the hyoid bone (arrowhead). B, Axial T2 MRI showing hyperintense cystic lesion filling the floor of mouth at the level of the inferior mandible. CT indicates computed tomography; MRI magnetic resonance imaging.

Due to the size and anatomical location of the cyst, an endoscopic-assisted approach to FOM resection with cranial nerve XII monitoring was planned. The patient was nasotracheally intubated, and bilateral cranial nerve XII monitoring was prepared by placing electrodes into the lateral tongue musculature. A bite block was used for exposure, and 2-0 silk ties were used to retract the tongue superiorly. A vertical incision was made in the FOM, transfrenulum, and the muscle fibers were bluntly dissected to the level of the cyst capsule, taking care to avoid the Wharton’s duct papillae. Dissection of muscle fibers and fascial tethering was performed largely with bipolar cautery and blunt dissection with Kittner sponges. Lingual nerves were visualized bilaterally and preserved. Zero- and thirty-degree endoscopes were used to assist with the lateral, posterior, and inferior extents of the dissection (Figure 2), allowing improved visualization during dissection around the lingual nerves and submandibular ducts, and while freeing the mass from the hyoid.

Figure 2.

Endoscopic intraoperative views of floor of mouth cyst. (A) Endoscopic view showing blunt dissection of the inferior and deep margins. Detail of magnified endoscopic view (area within box, B) exhibits safer dissection under improved, high-resolution visualization.

Using this minimally invasive technique, tongue split for better gross exposure was avoided. The cyst was removed under excellent endoscopic visualization without violation of its capsule (Figure 3). The wound was closed with 3-0 Vicryl sutures and a penrose drain was placed. Minimal tongue and oropharyngeal edema was observed given narrow field of dissection, and the tracheostomy was avoided. Postoperative course was uneventful, and the patient exhibited a well-healed incision, intact tongue sensation, and full and symmetric tongue mobility at follow-up. Final pathology revealed intact dermoid cyst containing sebaceous material and serous fluid, with gross measurements of 6.8 cm × 5.5 cm × 3.3 cm.

Figure 3.

Preoperative (A) and postexcision (B) views of floor of mouth cyst. Silk sutures at tongue tip allow tongue retraction (arrow). Bilateral electrodes (arrowheads) in lateral tongue musculature are used for CN XII monitoring. CN indicates cranial nerve.

Pediatric FOM Dermoid

Dermoid cysts of the oral cavity are rare, but important entities to diagnose due to local effects on oropharyngeal and upper airway function potentially life-threatening airway compromise. ¹ A differential diagnosis including foregut duplication cyst, ranula, thyroglossal duct cyst, cystic lymphangioma, and epidermoid, dermoid, or teratoid cyst should be considered for benign FOM lesions. The FOM dermoid cysts usually exist as soft, uninterrupted masses that may adhere to the hyoid bone and may be classified by anatomic location as sublingual, submental, or submandibular. Prompt diagnosis of these lesions is imperative, as FOM cysts can enlarge rapidly or become secondarily infected, leading to local effects including submandibular gland obstruction and dysphagia. Preoperative workup includes CT and/or MRI imaging, as well as biopsy by fine-needle aspiration to aid in diagnosis. ²

Surgical removal by transcervical or transoral approach remains the definitive treatment choice. Intraoral surgery is the preferred treatment method for sublingual cysts that lie superior to the mylohyoid muscle, while transcutaneous, extraoral surgical methods are generally reserved for large sublingual cysts, or those that are submylohyoid or transmylohoid. The intraoral approach is generally preferred if the cyst measures less than 6 cm in diameter, as an extraoral approach carries a higher risk of undesirable functional and cosmetic results. With either approach, excision without disrupting capsule integrity as described here aids in avoiding cyst recurrence. ^1,3,4

Variations in Surgical Approach

Several variations to standard transoral, transcervical, or combined approaches have been described. Midline genioglossus split is a commonly described variation of the transoral technique utilized to increase exposure in cases of large FOM lesions. ^5,6 For large cystic masses, aspiration of cyst contents to decompress the mass may allow the surgeon to achieve better visualization. However, decompression or rupture of a cystic mass can make dissection more challenging, particularly when attempting to define the extent of the cyst to achieve complete excision. ⁷ Additionally, when a transoral approach is chosen, blunt dissection placing angled clamps or a small angled retractor at the base of the cyst may facilitate dissection of the base. ⁸ Eken et al described excision of a large geniohyoid dermoid cyst of the FOM using an intraoral approach with inferior-based U-shaped flap for improved early exposure, followed largely by blunt dissection. ⁹

Endoscopic assistance has resulted in successful modifications to the standard unaided transoral approach in select cases. Kim et al described an endoscope-assisted intraoral resection of a 2.0 cm × 3.0 cm external dermoid cyst below the mylohyoid muscle in an adolescent female, using endoscopy to facilitate dissection of the genioglossus and mylohyoid muscles. ¹⁰ Further, endoscopic assistance has been described for other pathologies including aided transcervical branchial cleft excision as described by Teng et al, aided transoral thyroglossal duct cyst excision as described by So et al, and aided transoral approaches to the thyroid via frenotomy incision by Woo et al. ^{11 -14}

Endoscopic-aided intraoral approach allows superior visualization and preservation of critical structures, and avoids morbidity associated with open or more invasive approaches, including transcervical incision/scar, genioglossus split, and postoperative edema necessitating tracheostomy or prolonged intubation. This technique expands the indications for transoral approach to benign FOM masses in the pediatric population, where anatomic spaces are condensed and exposure is often limited.