Endoscopic Assisted Removal of a Massive Pediatric Floor of Mouth Dermoid

Introduction

Dermoid cysts of the oral cavity are rare, but important entities to diagnose due to local effects on oropharyngeal and upper airway function. Surgical removal by transcervical or transoral approach remains the definitive treatment choice. We present an adolescent male with a large floor of mouth (FOM) dermoid and a technique for surgical resection using an endoscopic-assisted, transoral approach.

Case

A 16-year-old male presented with a FOM mass which had been increasing in size over the past 18 months. He denied symptoms of dysphagia, shortness of breath, fevers, chills, or weight loss associated with the emergence of the mass; however, eventual interference with speech and swallowing functions prompted surgical removal. Physical examination revealed a 5.0 centimeter (cm), 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 large (6.0 × 5.1 × 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 abut the hyoid bone (Figure 1). Pre-operative fine needle aspirate showed straw colored fluid with anucleated squamous cells with no malignant cells identified. A differential diagnosis including foregut duplication cyst, ranula, thyroglossal duct cyst, cystic lymphangioma, and epidermoid, dermoid or teratoid cyst was considered.

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.

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, trans-frenulum, 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 anteriorly.

Figure 2. Endoscope assisted intraoperative views of floor of mouth cyst.

Identical views showing assisted blunt dissection of the inferior and deep margins. Detail of magnified endoscopic view (area within box, 2B) 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. Postoperatively, the patient was admitted to the intensive care unit intubated for airway monitoring. Drain removal and extubation occurred on post-operative day (POD) one. The patient tolerated a soft diet following extubation, and was discharged on POD three after an uncomplicated recovery. He returned for follow up three weeks post-operatively with a well healed incision, intact tongue sensation, and full and symmetric tongue mobility. Final pathology revealed intact dermoid cyst containing sebaceous material and serous fluid, with gross measurements of 6.8 × 5.5 × 3.3 cm.

Figure 3. Preoperative (A) and Post-excision (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.

Discussion

Pediatric Floor of Mouth Dermoid

FOM dermoid cysts usually exist as soft, uninterrupted masses that may adhere to the hyoid bone. These may be further 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, dysphagia, or potentially life threatening airway compromise.¹ Preoperative workup includes CT and/or MRI imaging, as well as biopsy by fine needle aspiration (FNA). Although FNA does not obviate the need for preoperative imaging, it is thought be safe, cost-effective, and reliable in diagnosis of FOM lesions.^2–4

Intraoral surgery is the preferred treatment method for sublingual cysts that lie superior to the mylohyoid muscle, while transcutaneous, extra-oral surgical methods are generally reserved for large sublingual cysts, or those that are submylohyoid or transmylohoid. The intra-oral approach is generally preferred if the cyst measures less than 6 cm in diameter, as an extra-oral approach carries a higher risk of undesirable functional and cosmetic results. Ohta et al described excision of a 5.5 × 6.5 sublingual dermoid in an adult patient, leading to successful enucleation of the mass and avoiding cervical scar; however, further challenges in visualization and access exist in the smaller pediatric patient.⁵ Both transoral and transcervical methods rarely result in cyst recurrence, though excision without disrupting capsule integrity as described here aids in avoiding this complication.^1,6,7

Variations in Surgical Approach

Several variations to standard trasoral, 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.^8–10 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.^11,12 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.¹³ 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.¹⁴ Notably, this technique describes aspiration of cyst contents to facilitate exposure prior to inferior dissection.¹⁴

Advances in endoscopic assistance technology have led to improved visualization of the surgical field and are of particular interest in pediatric otolaryngology, where anatomic spaces are condensed and exposure is often limited. 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 × 3.0 cm external dermoid cyst below the mylohyoid muscle in an adolescent female.¹⁵ This group utilized endoscopy to facilitate dissection of the genioglossus and mylohyoid muscles, further exhibiting that an aided transoral technique can be effective to access the submentum and anterior neck.¹⁵ 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.^16–19

Endoscopic-aided intraoral approach allows superior visualization, 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.

Abbreviations

cm

Centimeter

CT

Computed Tomography

FNA

Fine Needle Aspiration

FOM

Floor of Mouth

MRI

Magnetic Resonance Imaging

OC

Oral Cavity

POD

Post-Operative Day