Transantral Approach With an Optical Navigation System for Cystic Lesions at the Pterygoid Process

Abstract

A 48-year-old woman with hypernasality symptoms and discomfort in the right maxillary area was diagnosed with cystic lesions at the pterygoid process and linguoposterior mandible area. Cyst enucleation was performed through a transantral approach with an optical navigation system. A bony window on the anterior sinus wall was created, and an optical navigation system was used to locate the cystic lesions. After the cystic mass was removed, the bony window was repositioned with prebent plates. Both cystic lesions were diagnosed as postoperative maxillary cysts, and no other complications were observed.

Cystic lesions in the pterygoid process are very uncommon, and few cases have been reported.¹ The involved surgical areas are typically deep in location and in proximity to various arteries and cranial nerves. As a result, the lesions are difficult to access, resulting in challenging excision.

As an approach to a pterygoid process structure, an endoscopic transnasal approach has been proposed.^2,3 An endonasal approach accompanied by with nasal antrostomy, ethmoidectomy, and sphenoidectomy can remove lesions in the pterygoid plate area conservatively without forming scars on the skin or in the oral cavity.³ Additionally, if accompanied by transnasal septotomy, access from a wider angle may be possible, decreasing surgical difficulty. However, this approach has a limited field of view and restrictive working angle, making it difficult to perform in emergency situations. In addition, it is important to avoid damage to major anatomical structures encountered during this approach.

On the other hand, a transantral approach (TAA) through an intraoral incision can be a good option to approach the pterygoid process. Accessing the retroantral space through the anterior wall of the maxillary sinus provides a wider field of view and a larger working angle, enabling direct vision. A disadvantage of this approach is that the removed anterior sinus wall must be reconstructed. However, this can be resolved by prebending the plate and providing screw fixation when forming the window after removing the specimen and by repositioning and refixing the bony window.

Navigation-assisted surgery using optical navigation systems has been used in various fields of surgery.⁴ It can accurately locate critical anatomical structures, mapping the safest way to reach the specimen, and provide orientation around which safe and reliable surgery can be performed.⁴ As a result, the optical navigation system has become an important element in complex surgeries of the craniomaxillofacial area. It could be helpful to achieve anatomically accurate reduction and symmetric correction with the mirroring technique in trauma patients, playing a critical role in the detection and removal of foreign bodies.^4–7 In the TAA with the aid of an optical navigation system even through a small bony window, the position of the retroantral area where the cystic lesion is located can be identified, and orientation for safe and accurate access could be provided.

Based on this TAA, this study proposes the benefits of the navigation-assisted TAA compared to the conventional method in accessing a rare lesion of the pterygoid plate.

CASE PRESENTATION

A 48-year-old female patient had visited the department of oral and maxillofacial surgery of our hospital with hypernasality symptoms and discomfort in the right maxillary area. She stated that she had history of uvoplasty, mandibuloplasty, and genioplasty ~30 years prior. She also had undergone surgical enucleation of a left mandibular cystic lesion almost 20 years previous, with the biopsy result indicating a surgical ciliated cyst. However, the patient had no experience with paranasal sinus surgery, rhinoplasty, cartilage grafting, or extraction of maxillary teeth. Computed tomography examination revealed cystic lesions at the pterygoid process and linguoposterior mandible area (Fig. 1). The left pterygoid and left mandible lesions had corticated margins and exhibited low attenuation on imaging. The patient was diagnosed with a recurring cystic lesion and was scheduled to undergo mass excision of the mandible and pterygoid process cystic lesions under general anesthesia.

FIGURE 1: Preoperative computed tomography radiograph and schematic diagram of the transantral approach. A and B, Sagittal and axial view with diagram of the bony window (green ellipse) approximating the locating probe. C, Axial view with a diagram of removing retroantral wall using surgical bur through the bony window. D, Axial view with a diagram of the repositioned bony window with metal plates and screws.

Surgical Technique

Cyst enucleation surgery with the navigation-assisted TAA was performed under general anesthesia. After the left maxillary vestibular incision, a bony window for the TAA was designed, two 8-hole plates were prebent, and screw holes were made. After removing the plate and screws, an osteotomy was created with a 1-mm round bur to minimize bony gap and promote the continuity of the maxillary sinus bony wall (Figs. 1, 2A). Afterward, the bony window was separated and the Schneiderian membrane was removed to provide a proper field of view. The optical navigation system (BrainLAB) was used to navigate to the location of the cystic mass (Figs. 1A, B, 2B). After determining the location of bone preparation through BrainLAB navigation system, bone grinding was performed at the optimal location to access and expose the cystic mass. Then, the cystic mass was enucleated (Fig. 2C) and transferred for biopsy to the Department of Oral Pathology. The cystic mass located at the left mandible was also enucleated completely. Subsequently, the bony window with the plate was repositioned and fixed with screws (Fig. 2D).

FIGURE 2: Surgical procedure. A, After subperiosteal elevation, the bony window for the approach to the posterior sinus wall was designed and an osteotomy for the bony window was completed. B, BrainLAB navigation was used to detect the posterior sinus wall close to the lesion. The location on the computed tomography was co-related using a navigation probe. C, The lesion was exposed after grinding the posterior wall of the maxillary sinus, and the cystic mass was removed. D, The bony window plate was prebent and fixed with screws to reposition and stabilize the bony window after enucleation.

Histopathology

Histologic examination confirmed the diagnosis of cysts on the left pterygoid process and left posterior mandible. Following the examination, both cystic lesions were pathologically diagnosed as postoperative maxillary cyst (POMC). Staining with hematoxylin and eosin, cytokeratin 7, and VE1 showed the respiratory characteristics of this epithelium and confirmed the final diagnosis of a mandibular recurred surgical ciliated cyst and left pterygoid plate POMC. The cysts were lined with respiratory epithelium and pseudostratified columnar epithelium, and an inflammatory reaction was observed below the cystic wall (Fig. 3).

FIGURE 3: Hematoxylin and eosin staining of the mass with ×10 magnification. The cyst is lined with respiratory epithelium and pseudostratified columnar epithelium, and an inflammatory reaction was observed below the cystic wall.

DISCUSSION

Most cyst enucleation surgeries for the pterygoid process have used endoscopic, endonasal, or transpterygoid approaches. In this report, the patient underwent cyst enucleation surgery in the pterygoid process through a per-oral TAA. The endoscopic endonasal approach has proven to be advantageous for the removal of cystic lesions. However, since pterygoid plates are deeply located and are in the proximity of various vessels and cranial nerves, there is difficulty in sufficient vision and instrument operation during surgery. Therefore, it remains difficult to safely and completely remove such masses.

The per-oral TAA implemented in this study minimized the amount of bone removed using an optical navigation system, minimized complications, and maximized bone healing and regeneration of the Schneiderian membrane by repositioning the bony window.⁸ In addition, this approach allows a wide field of view and operation of instruments, enabling faster surgery and more efficient operation for surgeons.

In particular, an optical navigation system was used for the TAA of this case. This made it easy to identify the location of the lesions in the pterygoid plate and retroantral space. When approaching the lesion, surrounding critical anatomical structures like the maxillary artery were observed and the orientation verified, enabling a safer and more rapid surgical approach.^6,7

POMC is considered a delayed complication, occurring many years after surgical intervention of the maxilla involving the sinus membrane area, especially Caldwell-Luc procedures. These cysts are histologically lined by respiratory type pseudostratified columnar ciliated epithelium. Variable symptoms and complications related to POMCs include swelling, dysesthesia, hypernasality, and pain and discomfort in the mandible and maxillary teeth. The surgical ciliated cyst, which is pathologically very similar to POMC, is very rare and typically occurs in areas of the maxilla that have experienced previous surgical intervention (orthognathic surgery, rhinoplasty, or plastic surgery). Only 12 such clinical cases have been reported.⁹ Treatment of a surgical ciliated cyst involves simple enucleation, as with POMC, and shows a low recurrence rate. Since all related surgeries were denied according to the patient, the causes of the lesions in the mandible with subsequent recurrence remain unclear. In this case, diagnosis was difficult because history of the related operation was not reported, and a ciliated cyst of the mandible recurred in multiple locations after 20 years.

This study will serve as an important reference for diagnosis, treatment planning, and approach to surgical ciliated cysts and POMCs with an important implication for long-term follow-up. In addition, as a method for removing lesions located in the retroantral space, the TAA using an optical navigation system is expected to be presented as an effective alternative.