Surgical excision of osteochondroma on mandibular condyle via preauricular approach with zygomatic arch osteotomy

Reconstruction and differentiation of tumor mass and surrounding structures were done using Mimics (Materialize NV, Leuven, Belgium). In a mandible only view, tumor mass could be observed at all directions. Resection line of tumor mass was identified (Fig. 4). We could anticipate that zygomatic arch obstructed access to the resection line and removal of the resected mass; thus, we plan zygomatic arch osteotomy. The tumor mass was about 20 × 20 × 15 mm; the size of zygomatic arch osteotomy was enough to be 15 mm for drawing out the resected mass.

Under general anesthesia, a preauricular incision was made. Dissection and bleeding control was done until zygomatic arch and temporomandibular joint capsule appeared. Two osteotomy lines were made. A posterior one was made at the foremost point of articular eminence while an anterior one was made at 15 mm in front of the posterior line. Zygomatic arch osteotomies were completed, and the fragment was displaced downward with the masseter muscle still attached. The joint capsule was incised, and the lateral pterygoid muscle was dissected to expose the tumor mass. Tumor mass was resected with saw. The surface of condyle was smoothed with round bur. Tumor mass was sent to the Department of Pathology. The zygomatic arch fragment was repositioned and fixed with a four-hole straight shape miniplate (Fig. 5). Finally, normal occlusion and proper midline relationship were checked (Fig. 6).

After the operation, intermaxillary fixation was done for 2 weeks with rubber rings. A month later, normal occlusion with proper dental midline was maintained (Fig. 6).

CT was taken immediately after the operation. It confirmed that the tumor mass was removed (Fig. 7).

Pathologic diagnosis of the tumor mass was the osteochondroma (Fig. 8).

There are many theories about the etiology and pathogenesis of cartilage-capped and exophytic bony growths. They can occur in bones formed by endochondral ossification. They can also develop from displacement of the lateral portion of the growth plate which then proliferates in a direction diagonal to the long axis of the bone and away from the nearby joint [8]. In our patient, exophytic projection was extruded from the lateral portion of the condyle head with a direction diagonal to the long axis of the condyle. The peripheral part of the physis has been considered as a hernia from the growth plate [9]. This hernia may be idiopathic or traumatic. Regardless of the cause, the result is an abnormal extension of metaplastic cartilage responding to factors that cause exostosis growth by stimulating the growth plate. Development of these tumors in the mandibular condyle tends to support the theory that epiphyseal cartilage is idly located on the bone surface. It has been suggested that stress in the tough insertion region where local accumulation of cartilage dislocation is present can induce the formation of these tumors [2]. This could explain the fact that in the mandible, these lesions often arise at the coronoid process attached to temporalis and anteromedial condylar region attached to lateral pterygoid muscle insertion. Some authors also believe that trauma might play a role in the formation of these lesions [1].

Histopathological findings are crucial to the diagnosis of osteochondroma. Histologic examinations include a cartilaginous cap similar to that seen in a normal cartilage, endochondral ossification, cartilaginous islands in the subcortical bone, and a marrow space contiguous with the underlying bone (Fig. 8). It has been reported that the cartilaginous cap might be 10 mm or greater in thickness in the axial skeleton [10]. However, it tends to be thinner in the maxillofacial region. It might be absent in long-standing cases [10].

When considering treatment, the growing state and the type of osteochondroma are crucial. Growth status can be judged by repeated occlusal evaluation or bone scintigraphy. If an active growth is noticed in a child and the asymmetry is large, subtotal condylectomy is usually performed. However, in adult patient with the same symptoms, both side condylectomy and orthognathic surgery should be included. After such condylectomy, lateral open bite on the contralateral side might occur unless some kind of reconstruction is performed. A costochondral graft or a total stock joint prosthesis may be used. However, it has disadvantages such as exploration of the second surgical site, donor site morbidity, and bone resorption. A total joint prosthesis has disadvantages of high cost, material wear and potential failure, and restricted use in the growing patient [11, 12]. An alternative method might be vertical osteotomy of the ramus and advancing it superiorly to form a new condyle underneath the disc as described previously [13]. Locally derived bone graft attached to the medial pterygoid muscle has been utilized [14]. Some authors have proposed conservative condylectomy with less complications [15]. This protocol is applicable to osteochondromas involving the head of the condyle without extension of tumor into the neck. In patients with osteochondroma, the condylar head usually enlarges fairly and the neck of the condyle is significantly thickened [13]. Such neck thickening makes it possible to reproduce the remaining condylar stump for functioning as a “new” condylar head. The articular disc is then repositioned onto the “new” condyle and stabilized [13].

If the condition is inactive and there is no TMJ symptom, the reason for surgical intervention can be cosmetic or associated with dysfunction of mastication. In this situation, treatment can be chosen depending on osteochondroma classification. In type 2 with globular expansion, condylectomy should be performed as described above. In type 1 with protruding expansion, just local excision is sufficient. Some excellent outcomes have been reported for type 1 [12]. In this study, the patient’s age was 37 years old. There was a mild bone activity on the condyle head in the three-phase bone scan. Exophytic bony protrusion area was approximately 2 × 2-cm sized, heading for anteromedial of the condyle. It was type 1 osteochondroma. Based on these facts, we decided to do local excision.

After 3D reconstruction of the CT images, the tumor mass was growing to anteromedial side of the mandibular condyle; thus, it might be difficult to approach to the mass through only preauricular incision due to the obstruction of zygomatic arch (Fig. 4). To allow the access of cutting instruments to the anteromedial side of the mandibular condyle and removal of the excised tumor without extension of incision or dissection, we planned zygomatic arch osteotomy over the tumor mass. During the surgery, zygomatic arch osteotomy provided easy access to anteromedial portion of the condyle without additional incision or wide dissection, and tumor mass was drawn out with only 4 cm of preauricular incision with zygomatic arch osteotomy. Though minimally invasive procedure in this study cannot be applied in all osteochondroma cases, it can be one of the simple treatments for not-growing type 1 osteochondromas.

The malignant potential and risk of recurrence are the major drawbacks of conservative procedure. The recurrence rate for solitary osteochondromas in long bone is approximately 2% [16]. Of all the condylar osteochondromas reported, three have shown recurrence [15, 17, 18]. For the three cases, excision and condyloplasty rather than condylectomy were done as the initial procedure [1]. Because of a short follow-up period, we cannot evaluate recurrence for this case. However, based on mild bone activity in three-phase bone scan and other cases in the literature, it is expected that there will be no recurrence.