Lateral Molar Approach-Driven Transoral Endoscopic Procedure for Benign Infratemporal Fossa Tumor Resection

Summary

Here, we present a protocol to resect benign infratemporal fossa tumors via an endoscopic-assisted transoral lateral molar approach with low-temperature plasma ablation and intraoperative mandibular nerve monitoring. This minimally invasive technique prioritizes anatomical preservation, functional recovery, and avoidance of external scarring, demonstrating feasibility for well-demarcated lesions ≤4 cm in diameter.

Abstract

Benign infratemporal fossa tumors necessitate complete resection while preserving neurovascular integrity. Conventional open approaches risk delayed bone healing, occlusal dysfunction, severe facial scarring, and iatrogenic neurovascular injury. We propose an endoscopic-assisted plasma ablation technique via a lateral molar transoral approach to address these limitations.

A 55-year-old female with a 2.5 × 2 cm right infratemporal fossa tumor underwent the novel procedure. A 4-5 cm mucosal incision lateral to the molar established an osteotomy-free corridor along the mandibular ramus. The technique integrated a 4-mm 0° rigid endoscope for magnified visualization and a low-temperature plasma ablation device for extracapsular dissection with simultaneous cutting/coagulation, minimizing thermal damage. Intraoperative neurophysiological monitoring safeguarded the mandibular nerve. Postoperative recovery metrics, MRI, and histopathology were analyzed.

Complete tumor resection was achieved in 122 min with 50 mL blood loss. Postoperative MRI confirmed no residual lesions, but they were replaced by fibrotic scar tissue. Mandibular function (physiological mouth opening ≥35 mm) and facial sensation recovered by postoperative day 3. No hematoma, infection, or neurological deficits occurred. Histopathology confirmed a benign vascular malformation (SMA+, CD31/CD34+). Aesthetic outcomes were optimal, with no visible scarring (patient satisfaction: 10/10).

The endoscopic-assisted plasma ablation technique via a transoral lateral molar approach enables precise, minimally invasive resection of anteromedial infratemporal fossa tumors (≤4 cm), avoiding osteotomy and external incisions. Synergizing anatomic landmark guidance, energy-selective ablation, and intraoperative neuroprotection, this method optimizes functional preservation and aesthetic outcomes while adhering to microsurgical principles. Standardization requires advanced endoscopic skills and warrants further validation in larger cohorts.

Introduction

Infratemporal fossa (ITF) tumors, as relatively rare lesions in the head and neck region, present significant challenges in skull base surgery due to their deep-seated location and obscuration by surrounding structures, complicating both diagnosis and treatment^1,2,3. Benign tumors dominate this region, accounting for approximately 74% of cases (e.g., schwannomas and nasopharyngeal angiofibromas), while malignancies often arise from adjacent structure invasion or distant metastasis (with adenoid cystic carcinoma being the most common)⁴. Anatomically, the ITF is bounded anteriorly by the posterolateral wall of the maxilla, posteriorly by the root of the styloid process and part of the temporal bone, medially by the lateral pterygoid plate, laterally by the ascending ramus of the mandible, and superiorly by the infratemporal surface of the greater wing of the sphenoid bone. This compartment communicates with the pterygopalatine fossa and middle cranial fossa via natural bony channels such as the foramen ovale and spinosum, facilitating tumor spread along fascial planes and complicating surgical boundary delineation⁵. Notably, the proximity of this region to critical neurovascular structures-including the internal maxillary artery, mandibular nerve, and pterygoid venous plexus-often results in insidious early symptoms, leading to delayed diagnosis when tumors have already reached substantial size, thereby amplifying surgical risks.

Conventional open approaches (e.g., submandibular or zygomatic osteotomy routes) require extensive soft tissue dissection and mandibular or zygomatic bone resection to achieve adequate exposure, resulting in significant collateral trauma. Literature reports intraoperative blood loss averaging 500-1000 mL^6,7, alongside risks of postoperative complications such as parotid gland injury, cranial nerve palsy, cerebrospinal fluid leakage⁸, temporomandibular joint dysfunction, and trismus⁹. Additionally, postoperative facial scarring and asymmetry^10,11 render these approaches suboptimal for modern minimally invasive and aesthetic demands, limiting their use to large or malignant tumors requiring radical resection.

Existing non-transoral endoscopic techniques for ITF tumor resection remain constrained by critical limitations. The transnasal approach, hindered by tortuous anatomical pathways, obscures lateral visualization, impeding access to tumors in the lateral quadrant¹². The Caldwell-Luc route necessitates anterior maxillary wall resection, risking injury to the superior alveolar nerve¹³. Furthermore, non-natural cavity approaches exacerbate blind spots through spatial compression, increasing iatrogenic injury risks to the internal carotid artery and cranial nerves. In contrast, the transoral lateral molar approach combined with plasma ablation and 0° rigid endoscope establishes a surgical corridor via natural anatomical spaces, eliminating the need for osteotomy or external incisions. The 0° rigid endoscope provides direct axial access to the ITF core through the molar region, overcoming lateral blind zones inherent to traditional angled scopes, particularly enhancing exposure of deep-seated tumors medial to the mandibular ramus and posterior to the lateral pterygoid plate. The plasma ablation system enables simultaneous cutting and precise hemostasis in low-temperature mode, with a large-bore suction channel optimizing visual clarity. Integration of anti-gravity unidirectional fluid control ensures dynamic balance between saline irrigation and aspiration, mitigating thermal damage and electrical leakage risks¹⁴. Miniaturized instruments facilitate manipulation within narrow anatomical spaces, allowing single-port integration of endoscope and plasma ablation tools to avoid multi-port interference. Angular adjustments enable comprehensive quadrant management, offering a minimally invasive, functionally preservative, and safe solution for localized tumors ≤4 cm in maximum diameter.

Case Presentation
A 55-year-old female patient was diagnosed with a space-occupying lesion at the right skull base during an evaluation at another hospital one month ago. Contrast-enhanced magnetic resonance imaging (MRI) revealed a 2.5 × 2 cm well-demarcated, moderately enhancing lesion in the right masticator space. Physical examination demonstrated symmetrical facial contour, normal mouth opening, and no palpable swelling or tenderness in the right lesion area. Mandibular nerve function tests showed no pathological alterations. The diagnosis favored a vascular malformation. After discussing surgical risks and the potential to avoid external scarring, the patient consented to an endoscope-assisted transoral lateral molar approach with plasma ablation and standard intraoperative nerve monitoring of the mandibular nerve.

Protocol

The procedure described here was approved and conducted following the guidelines of the human research ethics committee of West China Hospital of Stomatology, Sichuan University, Chengdu, China.

1. Instrument preparation

1. Ensure the availability of sterilized surgical instruments and equipment, including the following critical items: an intraoperative neurophysiological monitoring system for the mandibular nerve, an endoscope, a plasma ablation device, an electrosurgical unit, and standard surgical instruments.

2. Preoperative imaging and patient preparation

1. Perform preoperative high-resolution MRI with three-dimensional reconstruction to delineate the tumor's spatial relationships with the internal maxillary artery, mandibular nerve, and lateral pterygoid plate. Assess tumor capsule adhesion to critical structures, including the mandibular nerve, internal maxillary artery, skull base dura, and pterygoid venous plexus (Figure 1).
2. Position the patient supine with the head rotated to the unaffected side and shoulders elevated to achieve mild neck extension.
3. Administer general anesthesia via nasotracheal intubation.
4. Disinfect the intra- and extraoral regions using 0.5% povidone-iodine solution. Drape the surgical field to cover the face and neck while preserving a transoral operative corridor.
5. Plan the surgical access incision in the right lateral retromolar region, meticulously avoiding the parotid duct and neurovascular bundles. Mark the incision site with methylene blue (Figure 2A).

3. Surgical approach establishment

NOTE: The procedure was performed by a surgical team comprising an attending surgeon, surgical assistant, and scrub nurse. The attending surgeon operated while holding the endoscope in the left hand and surgical instruments in the right hand.

1. Make a 5 cm longitudinal incision in the non-functional zone of the right buccal mucosa, anterior to the pterygomandibular ligament. Incise the mucosa and submucosal layers to expose the buccinator muscle.
2. Divide the buccinator muscle to reveal the buccal fat pad. Partially resect the buccal fat pad if it obstructs the visual field. Retract the buccinator muscle laterally.
3. Gently displace the parotid duct along the anterior margin of the pterygomandibular ligament using a periosteal elevator to preserve its integrity.
4. Perform meticulous dissection and partial resection of the buccal fat pad (Figure 2B) to expose the anterior borders of the right masseter and medial pterygoid muscles ( Figure 2C).
5. Create a domed operative space using an endoscope combined with a flexible titanium mesh retractor.
6. Adjust the endoscope's focal length, magnification, and illumination to achieve a clear visual field spanning from the anterior margin of the mandibular ramus to the posterior boundary of the lateral pterygoid plate.

4. Tumor exposure and resection (Figure 3)

1. Set the low-temperature plasma ablation device to bipolar output mode for cutting and adjust the power to 330 W ± 20% under a 250 Ω load. Use it to incise the masseter and medial pterygoid muscle attachments at the anterior margin of the mandibular ramus, exposing the ramus.
2. Dissect medially along the anterior mandibular ramus into the pterygomandibular space while meticulously preserving the lingual nerve. Further dissect the lingual nerve along the medial aspect of the mandibular ramus (Figure 3A).
3. Dissect the medial pterygoid muscle superiorly along the medial surface of the ramus, incise it, and access the ITF to expose the tumor (Figure 3B).
4. Confirm endoscopic visualization of a fully encapsulated tumor approximately 2 cm in diameter located medial to the mandibular ramus and adjacent to the anterior condylar border. Omit coronoidectomy if no obstruction is observed in the coronoid process.
5. Initiate intraoperative electrophysiological monitoring of the mandibular nerve.
6. Resect the tumor en bloc using the plasma ablation device 1 mm beyond the tumor capsule (Figure 3C).
7. Maintain the plasma ablation device in bipolar output mode if encountering bleeding from the pterygoid plexus or maxillary artery during dissection, but reduce the power to 60 W ± 20% under a 250 Ω load for precise hemostasis. Ensure continuous irrigation of conductive fluid (e.g., saline) throughout the procedure to dissipate heat and prevent thermal injury to surrounding tissues.
8. Continue these steps until complete tumor separation is achieved finally (Figure 3F).
9. Immediately send the resected specimen for intraoperative frozen section analysis to confirm the benign or malignant nature of the ITF tumor (Figure 3G).
10. Proceed with the surgical plan if the analysis confirms benign pathology. Smooth the mandibular bone prominence using a diamond-coated drill.
11. Irrigate the surgical cavity endoscopically to ensure no residual tumor capsule remains.
12. Pack and secure absorbable hemostatic gauze and a drainage strip in place. Reapproximate the muscle, fascia layers, and mucosal flap and close the incision with interrupted 3-0 absorbable sutures (Figure 3D, E). Ensure precise deep-to-superficial layer alignment to prevent dead space formation and avoid nerve injury.

5. Postoperative management

1. Administer aggressive fluid resuscitation and supportive therapy during the early postoperative period. Remove the drainage tube if the drainage volume is <10 mL within 24 h and no active bleeding is observed.
2. Initiate a cool liquid diet within 24 h postoperatively and gradually transition to soft foods. Assess mouth opening daily until the physiological range (≥35 mm) is restored.
3. Optimize nutritional intake to enhance immune resilience and maintain rigorous oral and surgical site hygiene. Remove sutures one week postoperatively.
4. Schedule clinical reviews at 1, 3, 6, and 12 months postoperatively. Advise patients to seek prompt evaluation for any discomfort.

Results

Imaging evidence
Preoperative contrast-enhanced MRI revealed a well-circumscribed, round mass in the right ITF with moderate homogeneous enhancement. The tumor adhered to the medial periosteum of the mandibular ramus and was partially encircled posteriorly by the pterygoid venous plexus. The internal maxillary artery abutted the tumor's superior pole without evidence of infiltration. Postoperative MRI at 3 months confirmed complete tumor resection with no residual or ...

Discussion

ITF tumors, as rare entities in the head and neck region, are primarily managed by surgical resection as the definitive curative approach. The clinical challenge arises from their deep-seated anatomical location and proximity to the internal carotid artery and cranial nerve complexes. Early-stage tumors often present with nonspecific symptoms -- such as unilateral nasal obstruction, facial dull pain, or limited mouth opening -- mimicking sinusitis or temporomandibular joint disorders, leading to delayed diagnosis until t...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0° Rigid Endoscope	KARL STORZ SE & Co. KG	1216AA	Provides intraoperative vision
3-0 absorbable surgical suture	Johnson (Suzhou) Medical Devices Co., Ltd.	VCP177D	Tissue suturing
High-Frequency Electrosurgical Unit	Guangdong Baisheng Medical Equipment Co., Ltd.	OBS-350A	Precise tissue cutting and coagulation
Plasma ablation system	BONSS MEDICAL	ADS413	Synchronous cutting at low temperature to stop bleeding, prevent heat loss and leakage, and ensure a balanced field of vision.
SURGICEL SNoW Absorbable Hemostat	Ethicon LLC	3013SP	Used for endoscopic surgical bleeding control.