Transzygomatic approach for the resection of large condylar osteochondromas using computer-assisted preoperative planning

Abstract

The purpose of this study was to evaluate the outcomes of patients with large osteochondromas (OCs) treated via transzygomatic approach for exposure and local resection. All patients with large OCs treated by transzygomatic approach from 2006 through 2014 were investigated. The inclusion criteria were (1) condylar OC of exogenous type; (2) a mass that could be treated only via transzygomatic approach, as assessed using computer-assisted preoperative planning. The preliminary results evaluated included recurrence, joint form and function, occurrence of facial deformity, facial nerve function, and the condition of the zygomatic arch fixation. Other parameters assessed included tumour size and location and the length of follow-up. Ten patients with OCs were included in this study. All masses were located anteromedial to the condyle; the average maximal diameter was 33.15 mm. During follow-up (average 28.5 months), the average maximum inter-incisal opening increased from 25.4 mm to 32.0 mm. Nine patients recovered without recurrence, a change in occlusion, secondary deformity, or nerve dysfunction. One patient had severe disc perforation and condylar resorption. The transzygomatic approach is applicable for the resection of large condylar OCs protruding anteromedially into the infratemporal space. Surgical simulations may help to identify the indications for this approach and to design the surgery.

Osteochondroma (OC) is defined as a cartilage-capped bony protrusion on the external surface of the bone. In the craniofacial region, the condyle is the most common site affected by OC.

In a previous study, it was found that 65.8% of all condylar OCs of exogenous type protruded anteriorly or anteromedially from the condyle. Due to their extension into the infratemporal space with the zygomatic arch obstructing the access, there are risks associated with the surgical exposure and local resection of these masses. Thus, a transzygomatic approach to the infratemporal space is now recommended. However, neither a detailed surgical procedure nor long-term follow-up results have been presented in the literature.

Therefore, the cases of patients with condylar OC resected via transzygomatic approach were investigated in this study. As computer-assisted surgical design is now widely applied, computer-assisted surgical simulation was also used in this study. The core concerns of this study were the following: (1) For what type of condylar OC is the transzygomatic approach indicated? (2) How can the computer technique help in the design of the access? (3) Are there any critical techniques in this approach? (4) How do patients recover after surgery?

Materials and methods

This study was performed in accordance with the Declaration of Helsinki on medical protocol and ethics. The regional ethics review board approved the study.

Patients

The study included patients with large OCs of the mandibular condyle treated using the transzygomatic approach between January 2006 and December 2014. The inclusion criteria were (1) condylar OC of exogenous type; (2) a mass that could be treated only via transzygomatic approach, as assessed using computer-assisted preoperative planning. The exclusion criteria were (1) OC of a diffuse type; (2) a mass that could be removed without the zygomatic arch osteotomy.

The study patients were five males and five females with an average age of 41 years (range 21–83 years). The clinical symptoms mainly included pre-auricular swelling and pain, mandible deviation, abnormal occlusion, and a limitation or deviation of mouth opening.

All of the patients underwent computed tomography (CT) and magnetic resonance imaging (MRI) examinations before surgery. The CT examination was performed from the orbit floor to the hyoid bone. The MRI examination was performed in both closed mouth and open mouth positions: the T1-weighted sequence was used in the sagittal plane in closed mouth position, while the T2-weighted sequence was applied in the sagittal and coronal planes in open mouth position. The typical CT and MRI features helped in the primary diagnosis of OC.

Computer-assisted preoperative planning

Computer-assisted preoperative planning was performed in every case, with the following steps: (1) the CT data were transferred into Mimics software (Materialise NV, Leuven, Belgium) to reconstruct and differentiate the maxilla, mandible, and the mass; (2) the osteotomy lines were designed to resect the mass; (3) it was attempted to move the resected mass through the space between the zygomatic arch and the sigmoid notch; (4) if it was difficult to move the mass through that space, an attempt was made to remove the mass whole or piecemeal with the zygomatic arch osteotomized.

Surgical procedure

Under general anaesthesia, a modified pre-auricular incision was made. The tissue was dissected anteroinferiorly to the level of the zygomatic arch and temporomandibular joint (TMJ) capsule. The temporal fascia was then cut to expose the zygomatic arch. Two osteotomy lines were marked: the anterior one was the boundary between the zygomatic body and arch, while the posterior one was the boundary between the arch and the joint eminence. The zygomatic arch osteotomies were completed and the arch displaced downward with the masseter muscle still attached.

The joint capsule was then opened and local resection of the mass (total or piecemeal) was performed. The lateral pterygoid muscle needs to be detached from the tumour/condyle interface in order to remove the tumour/condyle. The mass was then taken out through the approach created by the temporary removal of the zygomatic arch. Intraoperative frozen tests were performed to confirm the diagnosis of OC.

Afterwards, the zygomatic arch was repositioned and fixed with titanium plates. Repositioning of the disc or a new interposition (soft tissue flap) preparation was selected according to the disc form and location. A fat flap (buccal fat pad flap, temporal fascia fat flap, or abdominal free fat flap) was transferred to fill the defect ( Table 1 ). All patients received elastic traction and orthodontic or orthognathic treatment according to the occlusion.

Evaluation of the parameters

This was a descriptive study. The preliminary results were evaluated based on the guidelines of the American Association of Oral and Maxillofacial Surgeons (AAOMS) and included (1) the recurrence rate; (2) the TMJ form seen on CT and MRI; (3) TMJ function represented by the measurement of maximum inter-incisal opening (MIO); (4) the occurrence of a secondary dentomaxillofacial deformity; (5) facial nerve function; (6) the condition of the zygomatic arch fixation seen on postoperative CT. Other parameters assessed included the tumour size and location and the length of follow-up.

Results

Radiological findings and surgical simulation results

Preoperative CT showed that the mass in all cases had a similar form and location ( Fig. 1 A): it protruded anteromedially into the infratemporal space with a stalk to the condylar head, and the involvement of the condylar surface was less than 50%. The maximum diameter of the mass ranged from 17.22 mm to 48.00 mm, with an average of 33.15 mm ( Table 1 ). Computer-assisted planning showed that none of the masses could be taken out through the space between the zygomatic arch and the sigmoid notch ( Fig. 1 B). Only through osteotomy of the zygomatic arch could the masses be taken out whole or piece by piece.

Fig. 1
Use of the transzygomatic approach: case presentation (patient 2). (A) Preoperative CT showing the mass arising from the condyle and extending into the infratemporal space. (B) Computer-assisted preoperative planning. (C) Exposure and resection of the mass; the white arrow indicates the condylar OC, the yellow arrow indicates the defect left after the mass was removed, and the blue arrow indicates the repositioning of the zygomatic arch with the masseter muscle attached. (D) 3D CT reconstruction of the patient after surgery, showing the well-fixed zygomatic arch, without condylar resorption.

Table 1
Summary of patients with condylar osteochondroma undergoing the transzygomatic approach.
No. Age (years) Sex Size of OC (mm) Surgical notes Follow-up (months) MIO (mm) Recurrence Deformity Nerve disorder
Preop. Postop.
1 37 M 17.22 × 14.40 × 9.51 51 35 37 No No No
2 30 F 26.14 × 34.07 × 24.00 49 8 30 No No No
3 30 F 29.96 × 29.38 × 48.00 Buccal fat pad flap applied in the defect 33 15 31 No No No
4 83 F 19.48 × 29.38 × 21.39 Temporal fascia fat flap applied in the defect 28 13 30 No No No
5 27 M 17.88 × 23.31 × 15.33 3 25 25 No Anterior disc displacement with huge perforation; condylar resorption; ankylosis No
6 34 M 44.39 × 43.11 × 29.06 Piecemeal resection of OC; abdominal free fat and temporal fascia fat flap applied to replace the disc and fill the defect 20 15 30 No No No
7 47 M 33.20 × 38.20 × 33.99 Temporal fascia fat flap applied to the defect 36 48 40 No No No
8 40 M 26.63 × 20.33 × 18.04 Disc repositioning with temporal fascia fat flap applied 30 30 32 No No No
9 60 F 37.12 × 35.48 × 30.53 18 35 30 No No No
10 21 F 33.14 × 33.16 × 32.19 Temporal fascia fat flap applied to the defect 17 30 35 No No No
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Dec 15, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Transzygomatic approach for the resection of large condylar osteochondromas using computer-assisted preoperative planning
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