Ⅰ. INTRODUCTION
Osteochondroma (OC) is the most common benign bone tumor, representing 20-50% of all benign bone tumors and 10-15% of all bone tumors1). Despite its prevalence, OC rarely occurs in the craniofacial region, accounting for less than 1% of cases, due to the intramembranous ossification characteristic of craniomaxillofacial bone. The mandibular condyle is the most commonly affected site among craniofacial bones2,3). OC typically presents as a cartilage-capped exostosis and is often asymptomatic, frequently being detected incidentally1).
Synovial chondromatosis (SC) is a rare benign condition characterized by cartilaginous metaplasia within the synovial membrane, leading to the formation of intra-articular loose bodies4). While SC primarily affects large joints such as the knee and hip, its involvement in the temporomandibular joint (TMJ) is extremely rare, accounting for only 3% of reported cases5).
OC and SC in the TMJ share overlapping clinical manifestations, including malocclusion, facial asymmetry, joint sounds, and pain2,5). These nonspecific symptoms can delay diagnosis or result in misdiagnosis as more common temporomandibular disorders (TMD), particularly if patients fail to recognize the gradual changes or report their complaints.
This case report highlights two critical aspects: the rarity of simultaneous occurrence of OC and SC in the TMJ and the gradual occlusal changes associated with TMJ lesions, which can go unnoticed, increasing the chance of misdiagnosis.
Ⅱ. CASE
A 34-year-old male presented with a two-year history of progressive facial asymmetry and intermittent clicking sounds in the right TMJ. Despite these symptoms, the patient had not noticed any occlusal changes due to stable occlusion and gradual progression. Initial clinical and radiological examination showed no open bite, and teeth were generally well-aligned, albeit worn down, suggesting facial asymmetry secondary to condylar elongation and gradual occlusal adaptation (Fig. 1A). However, computed tomography (CT) revealed a mass resembling the condylar morphology, initially suggesting condylar elongation rather than a pathological lesion. Calcified bodies also observed in the joint cavity on CT, and subsequent magnetic resonance imaging (MRI) confirmed the diagnosis of OC with SC (Fig. 1C, D, E). Further evaluation with dental cast analysis indicated significant occlusal changes (Fig. 1B). Surgical intervention included condylectomy and mass excision under general anesthesia (Fig. 2A,B). Postoperatively, the patient underwent physical therapy and occlusal guidance with intermaxillary fixation screws and elastics, leading to satisfactory outcomes at the three-week follow- up. Histopathological examination confirmed the coexistence of OC and SC (Fig. 2C, D).
Ⅲ. DISCUSSION
The coexistence of OC and SC in TMJ is an exceptionally rare phenomenon. While OC and SC are well-documented individually, their simultaneous occurrence in TMJ has been reported in only a few cases4,6,7). Secondary SC, which is associated joint disorders such as osteoarthritis, avascular necrosis, osteochondritis dissecans, and rheumatoid arthritis, is uncommon, and its association with OC is even rarer6,7). The pathogenesis of the simultaneous occurrence of OC and SC remains unclear. However, several hypotheses have been proposed. First, mechanical irritation hypothesis is that continuous friction between OC and adjacent tissues may lead to the detachment of cartilage fragments, which migrate into the synovium and induce metaplastic changes. This process contributes to the formation of loose bodies, which can further progress to SC4,6,7). Second, cartilage fragments shedding hypothesis is that detached cartilage fragments from the OC may continue to grow and proliferate under the nourishment provided by synovial fluid. This mechanism facilitates the development of chondroid nodules in the subsynovium, ultimately leading to SC4,6,7). Third, although not applicable to this case, surgical trauma hypothesis is that fragments of cartilage left or implanted into the joint space during the surgical removal of an OC may provoke a strong synovial response. This reaction significantly increases the possibility of SC, particularly in cases with rapid recurrence and multiple loose bodies7).
We report this case not only due to the rarity of the simultaneous occurrence of OC and SC, but also to highlight the potential for asymptomatic and gradual changes in TMJ lesions to be misdiagnosed as TMD. In this case, at the initial visit, the panoramic radiograph did not clearly reveal the lesion, and the patient’s primary complaints, sounds in the right TMJ and mild facial asymmetry, did not strongly suggest a TMJ lesion. The cast analysis gave rise to the suspicion of occlusal changes and the presence of TMJ lesion. This suspicion was subsequently confirmed through the CT and MRI scans, which led to the diagnosis of TMJ lesion.
The treatment of OC depends on the extent of condylar involvement. Local resection is recommended when less than two-thirds of the condyle is affected, while total condylectomy is preferred for cases where more than two-thirds of the condyle is involved6). For SC, surgery remains the only effective treatment, requiring the complete excision of loose bodies and diseased synovium5,6). In this case, a combined approach involving condylectomy and the excision of loose bodies successfully resolved both pathologies. Postoperative care, including physical therapy and occlusal guidance, restored function and ensured a satisfactory recovery.
The histological characteristics of OC include endochondral ossification, a cartilage cap composed of parallel chondrocytes arranged in oblong lacunar spaces, and underlying trabecular bone2). SC is demonstrated by the presence of nodules of hyaline cartilage surrounded by synovial cells. These cartilaginous nodules frequently undergo calcification or ossification. In primary lesions, the chondrocytes may ap pear atypical with enlarged, hyperchromatic nuclei and binucleation 8).
This case demonstrates the rarity of simultaneous OC and SC in the TMJ and underscores the diagnostic difficulties posed by gradual, unnoticed occlusal changes. Advanced imaging techniques and a meticulous diagnostic approach are essential for identifying such complex TMJ pathologies. Clinicians should consider the possibility of diseases and carefully evaluate patients accordingly to ensure early and accurate diagnosis and to achieve optimal outcomes.
