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Osteoblastoma of the temporal articular tubercle misdiagnosed as a temporomandibular joint disorder

Osteoblastoma of the temporal articular tubercle misdiagnosed as a temporomandibular joint disorder



International Journal of Oral & Maxillofacial Surgery, 2017-05-01, Volume 46, Issue 5, Pages 610-613, Copyright © 2017 International Association of Oral and Maxillofacial Surgeons


Abstract

The case of a 17-year-old female with a benign osteoblastoma in the temporomandibular joint (TMJ) is reported. The patient had a 2.5-year history of reduced mouth opening accompanied by tenderness and swelling in the left TMJ. Initial treatment included stabilization of the occlusion with a splint, jaw exercises, and analgesics. At first the patient's symptoms decreased, but they then increased 18 months later, prompting a cone beam computed tomography (CBCT) evaluation of the joint. The radiographic findings showed a somewhat ill-defined, radiolucent, expansile lesion containing small scattered calcifications located in the temporal articular tubercle. The lesion was removed under general anaesthesia and sent for histopathological examination. At the 12-month follow-up, the patient had normal TMJ function without clinical symptoms. CBCT examination showed a small recurrence of 3 mm. Another 12 months later, CBCT showed a 1-mm increase in the recurrence. Her function was normal, with slight tenderness lateral to the left TMJ. The decision from a multidisciplinary meeting was further annual follow-up. The present case illustrates the importance of initial radiographic examination together with clinical examination in patients with TMJ dysfunction.

Osteoblastoma is a rare benign bone tumour representing less than 1% of all bone neoplasms. The tumour normally involves the long bones, spine, and sacrum, and less than 10% of osteoblastomas are located in the maxillofacial region. Around 77 cases of osteoblastoma involving the cranial bones have been described to date in the literature, with the posterior body of the mandible being the most frequent location. Clinically the osteoblastoma may be associated with a rapid onset, dull persistent pain, and swelling. Even if the patient is treated with non-steroidal anti-inflammatory drugs (NSAIDs), there is little or no relief; this is in contrast to what is observed in patients with osteoid osteoma or other inflammatory processes.

Radiographically the lesion can be expansile, with internal structures ranging from radiolucent, to a mixed pattern with varying degrees of calcification, to a more radiopaque variant. Variations in pattern are thought to be related to the age of the tumour, although the possibility that some lesions are ‘pre-programmed’ to produce more calcified products cannot be excluded. Tooth roots may be displaced or resorbed, but the lesion, in contrast to benign cementoblastoma, never fuses with the cementum. Typically the osteoblastoma has clinical and radiographic features more consistent with a benign process, respecting cortical boundaries and not invading soft tissue.

Histopathologically, osteoblastomas are characterized by numerous plump osteoblastic cells producing and lining the haphazardly arranged lesional trabeculae of osteoid and woven bone. Numerous blood vessels are often seen in the osteoblastic and fibrous stroma filling the lesional inter-trabecular areas. Scattered multinucleated giant cells resembling osteoclasts are also generally seen. Mitotic figures may be seen, but these are usually sparse and have a normal configuration.

Osteoblastoma involving the temporomandibular joint (TMJ) area causes symptoms of pain and tenderness that can easily be misinterpreted as a TMJ disorder (TMD). About 5–15% of the adult population has some kind of dysfunction in the temporomandibular area that needs treatment. Signs and symptoms of TMD include pain associated with the TMJ and jaw muscles, pain on jaw movement, impaired jaw mobility, and locking of the jaw. Therefore the clinical examination of a patient with TMD should include an evaluation of the jaw muscles and TMJ, as well as the registration of jaw movements. Most patients with TMD symptoms are treated conservatively with splints, physical therapy, pharmacotherapy, and/or intra-articular injection. However, in situations where conservative treatment does not give the expected effect, a radiographic examination is indicated.

The clinical, radiographic, and histopathological findings in a case of osteoblastoma located in the TMJ are reported herein.

Case report

Clinical and radiographic findings

The patient, a 17-year-old female, had a 2.5-year history of reduced mouth opening accompanied by tenderness and swelling in the left TMJ area. Her initial treatment included clinical examination, stabilization of the occlusion with a splint, jaw exercises, and analgesics. At first, the patient's symptoms decreased, but they then increased 18 months later, prompting a cone beam computed tomography (CBCT) evaluation of the TMJ. Radiographic findings showed a somewhat ill-defined, radiolucent, expansile lesion containing small scattered calcifications. The lesion was located within the articular eminence of the temporal bone and had expanded the bone structure ( Fig. 1 a) . The lesion measured 11 × 8 × 8 mm and had a well-defined cortical border towards the articular surface of the eminence, but was radiographically ill-defined within the temporal bone.

(a) Sagittal and frontal CBCT showing a somewhat ill-defined radiolucency with scattered small foci of calcification in the articular eminence of the temporal bone; pre-operative examination, September 3, 2013. (b) Sagittal and frontal CBCT showing healing at 6 months after surgery; examination, May 8, 2014. (c) Sagittal and frontal CBCT showing signs of recurrence in the articular eminence of the temporal bone; examination, May 24, 2016.
Fig. 1
(a) Sagittal and frontal CBCT showing a somewhat ill-defined radiolucency with scattered small foci of calcification in the articular eminence of the temporal bone; pre-operative examination, September 3, 2013. (b) Sagittal and frontal CBCT showing healing at 6 months after surgery; examination, May 8, 2014. (c) Sagittal and frontal CBCT showing signs of recurrence in the articular eminence of the temporal bone; examination, May 24, 2016.

Surgical procedure and follow-up

Due to clinical symptoms and radiographic findings suggestive of a tumour with features of osteoblastoma, surgical removal was scheduled. Surgery was performed under general anaesthesia. The TMJ was exposed with a pre-auricular approach, according to Rowe, to gain access to the articular tubercle. The tumour was identified in the lateral part of the tubercle and excised after removal of the lateral part of the zygomatic arch. After removal, the surface of the tubercle was smoothened with a rotary instrument. Initial healing was uneventful, and at the 6-month follow-up, no clinical or radiographic (CBCT/CT) signs of recurrence were seen ( Fig. 1 b). At the 12-month follow-up, CBCT examination showed a small recurrence with a diameter of 3 mm. The patient had normal function in the TMJ, without any symptoms. She was seen again after another 12 months. At this time, the patient had normal function in the left TMJ, with mild tenderness lateral to the left TMJ. A new CBCT showed a 1-mm increase in the recurrence ( Fig. 1 c). The case was then discussed in a multidisciplinary meeting, and because only mild symptoms were present, the patient was planned for further annual follow-ups.

Histopathological findings

Histopathologically, the lesion showed uniform, interlacing trabeculae of woven bone lined by plump osteoblastic cells with pale-staining nuclei, minimal pleomorphism, and minimal mitotic activity. A characteristic prominent vascular pattern was seen, as well as scattered multinucleated cells. No necrosis or chondroid production was seen ( Fig. 2 ).

This medium-power photomicrograph shows interlacing trabeculae of immature bone that are lined by plump osteoblastic cells and supported by a vascular stroma.
Fig. 2
This medium-power photomicrograph shows interlacing trabeculae of immature bone that are lined by plump osteoblastic cells and supported by a vascular stroma.

Discussion

Benign osteoblastoma involving the TMJ area is very rare, with only six cases reported. The mean age of these six cases (four male and two female) is higher than that of the patient reported here, at 26 years (range 14–48 years). As in the present case, all six previously reported cases demonstrated pain in the joint area, together with swelling for a majority of them. The radiographic features are described in all of these cases as rather well-defined expansile lesions containing small scattered calcifications. The majority of the TMJ cases are found in the condyle, in contrast to the case presented here, in which the articular eminence of the temporal bone was involved. In concordance with the previously described lesions, the present case had symptoms suggestive of a TMD. Despite therapy with a splint and NSAIDs, the pain and swelling in the TMJ area persisted. Further analysis using a CBCT scan showed an expansile lesion, partly well-defined and without any periosteal reaction, suggestive of a benign tumour with features of osteoblastoma in the articular tubercle (temporal bone).

Based on the radiographic findings, the treatment of choice was conservative surgical excision. If the radiographic features had raised suspicion of a malignancy, more aggressive treatment would have been considered. Osteoblastomas can be either benign or ‘aggressive’. The ‘aggressive’ type in particular must be distinguished from osteosarcoma, and in the case of an aggressive osteoblastoma, long-term follow-up is recommended in order to exclude misdiagnosis.

Osteoblastoma and osteoid osteoma are histopathologically very similar, and diagnosis is often based on the size of the lesion, with an osteoid osteoma being less than 1 cm in diameter and an osteoblastoma being larger than 2 cm. There are, however, exceptions, and osteoblastomas of 1–2 cm have been reported in some anatomical sites. Nevertheless, this distinction based on size seems to be of little importance for the patient.

This case report describes an osteoblastoma in the TMJ region that required complete surgical removal, including a modest margin to minimize the risk of adverse effects on the surrounding joint structures. Recurrences after complete excision are uncommon. The present patient has now been followed for 3 years since surgery, with CBCT scans showing a small slow-growing recurrence. Due to only mild symptoms so far, no further action other than annual follow-ups is planned.

Benign osteoblastoma involving the TMJ is very rare, but should be considered in the differential diagnosis of expansile painful lesions with a mixed radiolucent/radiopaque appearance. In these cases, surgical excision and long-term follow-up including clinical and radiographic examinations is recommended. The present case illustrates the importance of initial radiographic examination together with clinical examination in patients with TMJ dysfunction.

Funding

None.

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