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"Split to save": Accessing mandibular lesions using sagittal split osteotomy with virtual surgical planning.

Abstract

Large, benign intramandibular lesions are frequently removed by resection followed by extensive free tissue transfer or delayed bone grafting. We outline a protocol to remove benign mandibular lesions using sagittal split osteotomy (SSO) with virtual surgical planning (VSP) to mitigate risks involved with this effective, tissue-saving approach. Patients with benign mandibular lesions accessed by SSO with VSP during 2014 were included in this study. Computed tomographic data were imported into VSP software. Using VSP, the exact locations of mandibular lesions and the inferior alveolar nerve canal were delineated. SSO was designed virtually and provided surgeons exact measurements to gain access to lesions and to avoid vital structures intraoperatively. SSO with VSP preserved the cortical mandibular bone and the inferior alveolar neurovascular bundle in 3 patients with benign mandibular lesions. Twelve months after surgery, no patient had pathologic fracture, prolonged paresthesia (except for the patient who required inferior alveolar nerve resection), or malocclusion. No patient required bone grafting. There were no functional or aesthetic jaw deficits. SSO is an effective approach to access intramandibular lesions. The technique does not result in loss of mandibular bone, and patients return to full masticatory function compared with those who require resection and reconstruction. VSP may mitigate technical challenges associated with SSO.

Introduction

Sagittal split osteotomy (SSO) was conceived more than 60 years ago to correct maxillofacial deformities. It involves sagittal osteotomies of the mandible that allow repositioning of the dentate segment to address congenital or acquired dentofacial deformity. (1) SSO has occasionally been used as an alternative to expose and remove benign intramandibular lesions. (2-5) Advantages include avoidance of large mandibular resections for benign but extensive lesions, preservation of cortical bone and associated dentition (particularly important for growing individuals), rapid return to premorbid jaw function, and avoidance of secondary bone grafting or free tissue transfer.

Despite these advantages, SSO is underused for access to mandibular lesions because of the potential for complications, such as unintended fractures or injury to the inferior alveolar nerve (IAN). Recent advances in virtual surgical planning (VSP) may greatly reduce these risks. (3,6)

We describe how VSP can be used to plan SSO that removes mandibular lesions while preserving the entirety of mandibular cortical bone and minimizing the risk of injury to adjacent vital structures.

Patients and methods

Patients with biopsy-proven benign intramandibular lesions accessed by SSO with VSP during 2014 were included. All patients were managed by the Stanford University otolaryngology service.

Preoperative planning. Preoperative computed tomography (CT) scans in DICOM (Digital Imaging and Communications in Medicine) format are imported into VSP software (Materialise N.V.; Leuven, Belgium). Planning includes (1) localizing and demarcating the lesion of interest, (2) outlining ideal positions of osteotomies, and (3) delineating the intrabony course of the IAN to avoid severing or tearing the IAN during sagittal split.

The facial-lingual position of the IAN in the mandibular body is best seen in the coronal view, and the nerve can be traced through its entire length (figure 1). Two planned osteotomies are a ramus osteotomy extending just past the lingula and an anterior mandibular vertical osteotomy. The position of the anterior osteotomy is often dictated by the location of the lesion.

Optimal methods of fixation also can be planned before the operation with the customary combination of bicortical positional screws at the ramus and fracture plates using nonlocking screws across the vertical osteotomy at the body.

Intraoperative considerations. SSO begins with a subperiosteal exposure of the lateral mandibular body and anterior ramus including the lingula, behind which the IAN inserts and begins its intramandibular course.

The ideal incision is a linear one starting about 1 cm inferior to the mucogingival junction of the second molar. This incision is carried down to bone with a blade; this region is almost always avascular with no muscle attachments. A periosteal elevator can then be inserted through this pocket, and the lateral masseter muscle can be lifted subperiosteally with ease.

Electrocautery divides the mucosal junction between the lateral and medial pterygoid muscles along the anterior ramus. The medial pterygoid muscle is reflected to allow identification of the lingula, which is identified preoperatively using VSP. Its precise distance from the anterior border of the ramus is known, and a nerve hook can be used with a marker at the predetermined length.

A mark can be made on the saw blade so that the medial ramus osteotomy does not extend past the lingula (resulting in full-length ramus fractures) or under-extend (incarcerating the IAN after the mandible is split).

With SSO, only three osteotomies are made with the saw (medial ramus osteotomy, anterior vertical mandibular body osteotomy, and an osteotomy connecting the two). The osteotomies are followed by a controlled fracture with osteotomes (figure 2, A and B). An ideal SSO allows the mandible to open like a book (figure 2, C).

With VSP, the position of the IAN is known, providing two advantages. First, the depth of the anterior osteotomy can be planned. During the split, the osteotomes can also be guided appropriately prior to visualizing the IAN (figure 1).

After the removal of the lesion, fixation of the split mandibular cortices involves positional bicortical screws at the ramus and a fracture plate across the anterior vertical mandibular osteotomy (figure 2, D). Before fixation, maintaining occlusion with intermaxillary fixation (IMF) is important. The condyle is seated by pushing the lateral cortex of the SSO (the condylar segment) posteriorly. Jaw movement is assessed after fixation by releasing the patient from IMF. Occlusion should be as it was before surgery.

Results

Three patients treated with this approach are presented in detail. All underwent successful SSO exposure and complete removal of mandibular lesions. They achieved full recovery of mandibular function including institution of a regular diet within 6 weeks of surgery. Patient 2 required IAN resection, but the other 2 patients had full return of IAN sensation postoperatively.

Clinical scenario 1: Extensive cyst in themandibular body and ramus. A 55-year-old man presented with slowly enlarging right lower facial swelling. The CT scan showed a 6 X 3 X 3 -cm radiolucent lesion associated with a third molar dislocated to the posterior ramus (figure 3). The lesion had eroded through the buccal cortex near the mental nerve, where an incisional biopsy had been performed, and a diagnosis of dentigerous cyst was confirmed (figure 3).

SSO using VSP was performed. After the mandibular split, the cystic lining along the inner buccal and lingual cortices was removed easily in one piece along with the third molar. Bony cortices were reapproximated and fixated. The patient's jaw was banded closed for 1 week, and the patient was gradually released to full diet in 6 weeks. There were no limitations to jaw function at the 1-year follow-up. Lower facial and mandibular bony contours were preserved.

Clinical scenario 2: Inferior alveolar nerve sheath tumor. A 15-year-old boy presented with acute onset of left mental nerve paresthesia associated with intermittent left lower facial swelling. Magnetic resonance imaging of the head and neck showed infiltration of an intraosseous lesion in the left mandibular body with erosion near the mental foramen, suspicious for a peripheral nerve sheath tumor.

SSO using VSP was performed. The IAN was exposed and traced along its entire length from the ramus to the mental foramen (figure 4) after sagittal split and separation of the facial and lingual cortices of the mandible. The IAN was excised in its entirety within this region. Despite erosion of the medullary bone, bicortical positional screws at the ramus and an anterior fracture plate with nonlocking screws were adequate to maintain jaw stability. No masticatory or aesthetic deficits were apparent at the 1-year follow-up. The patient's facial growth had not been impeded by the operation.

Clinical scenario 3: Multiple cysts in the mandibular body and ramus. A 19-year-old man presented with numerous asymptomatic intramandibular radiolucencies in the ramus and body of the mandible found during routine panoramic radiography. Incisional biopsy had been performed previously in the anterior mandibular body, with removal of overlying cortical bone. Pathologic diagnosis was inconclusive. To obtain more tissue, biopsy of the lesions in the posterior ramus was necessary.

SSO using VSP was performed, and the exposure allowed for extensive visualization between the split ramus and body cortices. Multiple bony cavities with scant cystic lining were found in the ramus. With the exposure obtained, lesions within the posterior ramus were removed with endoscopic assistance. Preservation of the IAN in the ramus was also confirmed with endoscopic visualization. Biopsy was consistent with a history of giant cell granulomas that had regressed.

The patient returned to a regular diet in 2 weeks. He had no functional or aesthetic deficits at the 1-year follow-up.

Discussion

We describe three clinical scenarios in which SSO allowed optimal access to the lesion of interest in the mandible while preserving bony integrity. Classic segmental resection followed by secondary bone grafting or primary free tissue transfer are more usual approaches in these scenarios. SSO was effective in saving healthy bony tissue, preserving bony integrity, allowing patients an immediate return to premorbid occlusion and mastication, and obviating the need for reconstructive surgery. In these circumstances, VSP provided surgeons with important landmarks and measurements that assisted in carrying out SSO safely.

We propose the use of SSO with VSP for the management of (1) benign and extensive intramandibular lesions that otherwise would have required mandibular resection, (2) IAN lesions, and (3) multiple lesions within the mandibular ramus and body. This approach is particularly ideal for growing individuals because jaw development is not disrupted, in contrast with resection.

The SSO approach has been reported in the literature only sporadically. Complications related to SSO include injury to the IAN, postoperative malocclusion, and unanticipated fractures and unfavorable splits. (7,8)

Although reports demonstrate the efficacy of SSO with VSP, discussion about ways to make the SSO more predictable and reproducible for all surgeons has been inadequate. VSP helps surgeons appreciate the location of the lesion relative to other structures of interest, to design optimal osteotomies to ensure good mandibular splits, and to avoid injury to the IAN. It is also cost-effective when one considers the alternative approach, which requires resection and reconstruction. We hope that VSP encourages surgeons to consider "split to save."

Conclusion

For access to extensive or multiple benign intramandibular lesions, SSO prevents the need for extensive resection and reconstruction, avoids injury to the IAN, and allows rapid return to full jaw function. These benefits are particularly pertinent for growing individuals and medically compromised patients who are not ideal candidates for resection and reconstruction. VSP mitigates risks involved with SSO.

References

(1.) Trauner R, Obwegeser H. The surgical correction of mandibular prognathism and retrognathia with consideration of genioplasty. II. Operating methods for microgenia and distoclusion. Oral Surg Oral Med Oral Pathol 1957;10(9):899-909.

(2.) Lee HG, Rhee SH, Noh CA, Shin SH. Enucleation of large keratocystic odontogenic tumor at mandible via unilateral sagittal split osteotomy: A report of three cases. J Korean Assoc Oral Maxillofac Surg 2015;41(4):208-12.

(3.) Casap N, Zeltser R, Abu-Tair J, Shteyer A. Removal of a large odontoma by sagittal split osteotomy. J Oral Maxillofac Surg 2006; 64(12):1833-6.

(4.) Mahmood L, Demian N, Weinstock YE, Weissferdt A. Mandibular nerve schwannoma resection using sagittal split ramus osteotomy. J Oral Maxillofac Surg 2013;71(11):1861-72.

(5.) Wong GB. Surgical management of a large, complex mandibular odontoma by unilateral sagittal split osteotomy. J Oral Maxillofac Surg 1989;47(2):179-84.

(6.) Rittersma J, van Gool AV. Surgical access to multicystic lesions, by sagittal splitting of the lower jaw. J Maxillofac Surg 1979; 7(3):246-50.

(7.) Shawky M, Mosleh M, Jan AM, Jadu FM. Meta-analysis of the incidence of lingual nerve deficits after mandibular bilateral sagittal split osteotomy. J Craniofac Surg 2016;27(3):561-4.

(8.) Steenen SA, van Wijk AJ, Becking AG. Bad splits in bilateral sagittal split osteotomy: Systematic review of fracture patterns. Int J Oral Maxillofac Surg 2016;45(8):971-9.

Stanley Yung-Chuan Liu, MD, DDS; Douglas Sidell, MD; Leh-Kiong Huon, MD; Carlos Torre, MD

From the Department of Otolaryngology-Head and Neck Surgery, Stanford University School of Medicine, Stanford, Calif. (Dr. Liu); the Division of Pediatric Otolaryngology, Department of Otolaryngology-Head and Neck Surgery, Stanford University Medical Center, Stanford, Calif. (Dr. Sidell); the Department of Otolaryngology-Head and Neck Surgery, Cathay General Hospital, Taipei, Taiwan (Dr. Huon); and the Department of Otolaryngology-Head and Neck Surgery, University of Miami, Miller School of Medicine, Miami, Fia. (Dr. Torre).

Corresponding author: Stanley Yung-Chuan Liu, MD, DDS, Department of Otolaryngology, Stanford University, 801 Welch Rd., Stanford, CA 94304. Email: ycliu@stanford.edu

Caption: Figure 1. Using virtual surgical planning, the inferior alveolar nerve (IAN) can be traced through its entire intramandibular course. Illustrations courtesy of Dr. Huon.

Caption: Figure 2. Illustrations depict the process of a sagittal split osteotomy. A: Sagittal split osteotomies are initiated with a reciprocating saw. Three osteotomies are made (medial/posterior horizontal, anterior vertical, and superior connecting). B: The inferior osteotomy requires a controlled fracture using osteotomes. With virtual surgical planning, the position of the inferior alveolar nerve (IAN) is known. This guides the depth of the anterior osteotomy and the directionality of osteotomes. C: This is the point in the procedure when the ideal sagittal split osteotomy opens like a book. After splitting the distal, or dentate, segment and condylar segment of the mandibular ramus, the lesion and inferior alveolar nerve are clearly identified, and the lesion is removed without unnecessary bone loss. D: Bone cortices are reset after positioning the condylar segment upward and backward to the articular fossa. Rigid fixation is done using two bicortical screws at the ramus and a rigid plate across the anterior lower border. (In panels B to D, A = dentate segment; B = condylor segment.)

Caption: Figure 3. In this illustration and radiograph, a 6 x 3 x 3-cm cystic lesion is seen within the mandibular body and ramus with a cortical defect noted near the mental foramen. The lesion is associated with a third molar that is displaced toward the posterior ramus.

Caption: Figure 4. Illustration and photograph show the sagittal split osteotomy of the left mandible and the preoperative virtual surgical plan model in this inferior alveolar nerve sheath tumor (A = dentate segment; B = conydlar segment; IAN = inferior alveolar nerve).
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Title Annotation:ORIGINAL ARTICLE
Author:Liu, Stanley Yung-Chuan; Sidell, Douglas; Huon, Leh-Kiong; Torre, Carlos
Publication:Ear, Nose and Throat Journal
Article Type:Clinical report
Geographic Code:1USA
Date:Mar 1, 2018
Words:2378
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