Abstract
Synovial chondromatosis (SC) is a rare metaplastic disease of the larger joints. It is rarely observed in smaller joints, especially in the temporomandibular joint (TMJ). This disease is considered to be metaplastic and shows no malignant tendencies, but can become locally aggressive, erode the cranial base, and even spread intracranially. To date, nine cases of spread into the intracranial space have been reported in the literature; however, the disease remained extradural in all cases. The authors present a review of the literature and report the case of a 70-year-old man with SC of the right TMJ that had eroded the cranial base, reaching the dura mater; a large intracranial mass was not present. The disease was considered to be stage 3 according to Milgram’s classification. The patient was treated surgically, the tumour mass was removed, reconstruction of the cranial base was performed using titanium mesh, and the joint was reconstructed with a temporal muscle interposition flap. Diagnostic images and intraoperative photographs are also presented.
Synovial chondromatosis (SC) is a rare pathological condition characterized by the development of cartilage nodules within the connective synovial tissue of articulating joints. This benign condition is considered to be metaplastic rather than neoplastic. It usually affects large joints, with a predilection for the knee, hip, and elbow. SC of the knee joint was first reported by Ambroise Paré in 1558, and that of the temporomandibular joint (TMJ) was first reported by Baron Albrecht von Haller in 1764. The first histological description was by Axhausen in 1933.
A review of the English-language literature by Shah et al. reported 149 studies involving 242 cases. Only 28 of these studies mentioned more than one case, and none reported more than 11 cases. However, the number of publications reported in different reviews ranges from 80 to 149. Peng et al. reported the case of a female patient with bilateral occurrence of the disease. Lieger et al. published a review of cases with intracranial extension. They reported one case and found another eight in the literature. We present herein the tenth case involving extension to the skull base.
Case report
A 70-year-old male Caucasian patient with a 5-year history of right-sided TMJ pain was referred to our department by a dentist after 5 years of unsuccessful therapy with an occlusal splint. Accurate anamnesis revealed increasing headache while chewing during the last year. A clinical examination showed slight swelling of the right TMJ with temporal pain upon maximal mouth opening. No restriction of mandibular movement was present. Panoramic X-rays showed arthrosis-like changes on the right side and resorption of the glenoid fossa. Computed tomography (CT) revealed a tumour mass that was calcified in some parts ( Fig. 1 ) and had eroded the cranial base ( Fig. 2 ). The tumour had nearly reached the intracranial space at three sites, and the mass was separated only by a blade-thin bone plate; however, in one place, the clear bony lamella covering the dura was absent. Magnetic resonance imaging (MRI) confirmed skull base erosion and excluded invasion of the dura.
A preoperative histological examination was then performed. Under general anaesthesia, the TMJ was biopsied through a modified, retrotragal approach in the manner described by Pau et al. Initial histology showed hyalinized chondral tissue covered by a synovial layer. Within the multiple chondral parts, atypical cells with large eosinophilic cytoplasm and chromatinized nuclei (some multiple, but without mitosis) were seen. The histological description was ‘joint capsule parts with atypical chondral tissue’, with the suggestion that this—together with the imaging findings—indicated SC.
The patient was then scheduled for surgical removal of the SC. The Al-Kayat–Bramley flap was modified with a retrotragal approach, in accordance with Pau et al. ( Fig. 3 ). After adapting a titanium miniplate to it, the zygomatic arch was removed to allow a better approach to the skull base and condylar head. The mandible was pulled caudally, and the tumour tissue was removed carefully, together with the entire TMJ capsule and meniscus. The glenoid fossa showed bony erosion that exposed the dura mater, which remained intact ( Fig. 4 ). Titanium mesh was used to cover the bony defect of the glenoid fossa and avoid intracranial dislocation of the condylar head through the weakened bone of the cranial base ( Fig. 5 ). The mandibular condyle was covered with a temporal muscle interposition flap ( Fig. 6 ). Finally, the zygomatic arch was repositioned and fixed with the preformed titanium miniplate. All soft tissue layers were reconstructed and a suction drain was placed to avoid the collection of blood coming from the temporal muscle and temporal flap.
The postoperative course was uneventful. The drain was removed after 2 days, the sutures were removed after 5 days, and the patient was discharged after 1 week. Histology confirmed the diagnosis, providing the same description as the preoperative biopsy.
At the 6-month follow-up, occlusion and good TMJ function were preserved with a mouth opening of approximately 4 cm ( Fig. 7 ). No pain was reported. Slight but decreasing swelling was observed in the right TMJ region. The scar was barely visible ( Fig. 8 ), and no sign of recurrence was detected in the CT scans.
Discussion and literature review
SC is considered a benign condition (metaplasia), however in the knee joint a few cases have been reported with malignant transformation to chondrosarcoma.
The pathogenesis and the aetiology of SC are unknown, however some authors have reported the disease occurring after trauma to the TMJ. Primary cases are thought to be more aggressive. Some authors have also mentioned a relationship with osteoarthritic processes. The molecular background is not precisely understood and controversy remains in the literature, due to the very low number of cases reported. The presence of increased fibroblast growth factor (FGF)-9/fibroblast growth factor receptor (FGFR)-3, FGF-2/FGFR-1, transforming growth factor beta (TGFβ) 1 and 2, tenascin, S-100 immunopositivity, Ki-67 antigen negativity, Bcl-2 expression, proliferating cell nuclear antigen (PCNA) reactivity, and bone morphogenetic proteins (BMP) 2 and 4, which are also supposed to be responsible for the metaplasia, has been described, while increased levels of FGF-2, FGFR-3 and FGF-9, and FGF-2 and FGFR-1 have also been reported. Up-regulation of interleukin 6 and vascular endothelial growth factor A has been found in the synovial fluid. Mild Ki-67 positivity has been observed in the loose bodies at the synovial membrane in Milgram’s stage 2 disease.
The histological staging of SC was published by Milgram in 1977, and this classification system has been used in all the studies available in the literature. Over 80% of patients are already at Milgram’s stage 3 when the diagnosis of SC is made. The histological (Milgram’s) staging is based on disease activity and development. Stage 1 is the early stage and represents intrasynovial metaplasia without loose bodies; perifocal macrophages may be present. Stage 2 is the transitional phase, in which synovial involvement and detached bodies are present. Stage 3 shows no more active intrasynovial disease (metaplasia), but the joint space is full of multiple detached bodies, and secondary calcification or ossification may be present. The secondary calcification is called Henderson–Jones syndrome. Fujita et al., however, also described metaplastic activity in stage 3 patients. The loose bodies in the joint space might be surrounded by a layer of synovial membrane.
Some authors have reported a female predominance of approximately 2:1, and by intracranial extension of 1.6:1. The right side is more often affected (ratio left to right = 1:1.2). Peng et al. have reported the case of a female patient with bilateral occurrence of the disease. The mean age at diagnosis ranges from 39 to 55.4 years. The onset of SC in the TMJ mostly occurs later than in other joints.
The clinical symptoms are not specific for the disease: pain, swelling, facial asymmetry, crepitations, and impaired movement of the lower jaw are the most often mentioned (see Table 1 ). Due to its rarity and non-specific symptoms, the correct diagnosis is often delayed and is made years after the onset of symptoms in most patients. In the case presented herein, the main complaint was pain in the TMJ, and the patient was referred to our institution only after the symptoms related to the skull base erosion, like headache while chewing, became apparent.
