Journal of Indian Academy of Oral Medicine and Radiology

: 2021  |  Volume : 33  |  Issue : 4  |  Page : 476--479

Unilateral mandibular coronoid osteoma-An unusual cause for pseudoankylosis

Karthikeya Patil1, CJ Sanjay1, M Meghana2, S Viveka1,  
1 Department of Oral Medicine and Radiology, JSS Dental College and Hospital, Mysore, Karnataka, India
2 Department of Dental, Rehabilitative Oncology, Health Care Global Cancer Centre, Bangalore, Karnataka, India

Correspondence Address:
Dr. C J Sanjay
Department of Oral Medicine and Radiology, JSS Dental College and Hospital, JSS Academy of Higher Education and Research, Mysore - 570 015, Karnataka


An osteoma is a benign osteogenic tumor characterized by compact or cancellous bone proliferation with unknown etiology, but it may arise from cartilage or embryonal periosteum. Osteomas are rare, slow growing, usually asymptomatic until their size and position interferes with functioning. This is a report of a 53-year-old male patient who complained of difficulty in opening his mouth, which was diagnosed as an osteoma of mandibular coronoid producing pseudo ankylosis, a very unusual condition. Surgical excision of the tumor was performed, followed by physiotherapy and no recurrence was observed. This case report highlights the rare causes of pseudo ankylosis with significance to early diagnosis and intervention which can prevent further complications to the patient.

How to cite this article:
Patil K, Sanjay C J, Meghana M, Viveka S. Unilateral mandibular coronoid osteoma-An unusual cause for pseudoankylosis.J Indian Acad Oral Med Radiol 2021;33:476-479

How to cite this URL:
Patil K, Sanjay C J, Meghana M, Viveka S. Unilateral mandibular coronoid osteoma-An unusual cause for pseudoankylosis. J Indian Acad Oral Med Radiol [serial online] 2021 [cited 2022 Oct 1 ];33:476-479
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Osteoma is a slow growing, benign osteogenic tumor which consists of dense bony proliferations of histologically normal membranous bone. Reactive bone hyperplasia or progressive bone ossification are said to be the causes of osteoma in the maxillofacial region. It may be classified as peripheral osteoma (arises from the periosteum), central osteoma (from endosteum), and extra skeletal osteoma (soft tissue). In craniofacial skeleton, mandible and paranasal sinuses are the most common sites.[1] Kersher et al. proposed a theory that coronoid osteomas are the result of osteochondromas after total cartilage ossification.[2] The presence of cellular pleomorphism in chondrocytes and endochondral ossification problems are suggestive of a malignant origin. Here, we describe a case of unilateral coronoid osteoma causing pseudo ankylosis. The aim of this report was to draw attention to rare causes of reduced mouth opening, and to note the scarcity of the available literature on the topic.

 Case Report

Clinical description

A 53-year-old male patient visited our OPD complaining of gradual decrease in mouth opening for six months associated with difficulty in mastication and speech. It was not preceded by any trauma, tooth ache or infection, with no association of pain or swelling. Patient gave no history of parafunctional habits. Extraoral examination revealed a slightly prominent left zygomatic area with no gross facial asymmetry. On palpation, the left zygomatic area was bony hard in consistency and non-tender. The patient and his family members were not aware of the mild asymmetry noted by the clinicians which could have possibly led to early diagnosis and management of the lesion. Bilateral TMJ were non-tender, and the movements were minimally palpable. Interincisal mouth opening was found to be about 1 mm with an inability to perform protrusive or lateral movements [Figure 1]a. Muscles of mastication were non-tender on palpation. Intraoral examination did not reveal any abnormal finding.{Figure 1}

Diagnostic assessment

Panoramic radiograph revealed the presence of a well-defined, rectangular, radiopaque mass measuring about 3 × 2 cm, with a radiolucent rim covering the anterior and antero-inferior portion of the mass overlapping the left lateral wall of maxillary sinus and the zygomatic buttress [Figure 2]a. The density of the mass was same as the adjacent bone. An additional non-contrast computed tomography scan (CT) revealed a morphological change in the condyle with hyperdense “mushroom” or “horse head” shaped bony mass in left condyle, with an irregular bony outgrowth arising from the tip of the coronoid process about 2 × 1.6 cm, invading the infratemporal space. Impingement of the lesion on adjacent arch which was evidently seen in the axial section [Figure 2]b sections. There was evidence of pseudo-arthrosis between the bony outgrowth and the anterior portion of the thinned out zygomatic arch. The CT findings were suggestive of osteoma of left coronoid process of the mandible. Correlating the clinical and radiographic features, a working diagnosis of osteoma of the left coronoid process was established. Differential diagnosis included osteochondroma, coronoid hyperplasia, osteosarcoma. Although the osteomas of coronoid process are rare it should be considered in the differential diagnosis of asymptomatic restricted mouth opening in the higher order and can prevent in delay in diagnoses and limit the investigations required for the same.{Figure 2}

Therapeutic intervention

Left coronoidectomy was performed by hemi coronal incision along with lateral swing osteotomy of the left zygomatic arch. The bony mass was surgically excised by hemi coronal approach [Figure 3]. Intraoperatively, the mouth opening improved and was recorded as 35 mm, following which contralateral coronoidectomy was performed intraorally. The resected mass was mushroom shaped and measured about 4 × 3.5 × 2.5 cm [Figure 4]a. Histopathological examination of the specimen revealed dense lamellar compact bone [Figure 4]b. It lacked the characteristic cartilaginous cap seen in osteochondroma. The histopathologic diagnosis confirmed the clinical diagnosis of osteoma.{Figure 3}{Figure 4}

Follow-up and outcome

The post-operative recovery was uneventful with improved mouth opening after two months up to 35 mm [Figure 1]b. No deficits of nerve functioning were noted, and patient was instructed to continue the physiotherapy with regular follow up [Table 1].{Table 1}


Restricted mouth opening is a commonly encountered problem by dentists. One of the most common reasons of restricted mandibular movements is extrinsic joint diseases.[3] Infection, ankylosis and arthritis are a few etiological factors that lead to progressive temporomandibular joint functional limitations.[4] Coronoid osteomas are slow growing, asymptomatic until their size and position interferes with functioning. Continuous growth may press the zygoma cortices, resulting in a visible malar bulge and zygoma resorption, followed by remodeling into a state of pseudoankylosis and trismus.[5] In 1959, Lewars reported the first case of coronoid osteoma.[6] Facial asymmetry, occlusal dysfunction and decreased mouth opening are the most common findings in coronoid osteoma.[4],[7] Similar signs and symptoms were present in our case. Although osteoma is most common in the fourth and fifth decades, lesions have been reported in people aged between 10 to 79. They occur more frequently in young adults and women.[8] This is the second case of this rare lesion reported in male. Ord et al. (1983) described a case of coronoid osteoma secondary to zygomatic-temporal fracture with paresthesia in that area. [9] In our case, there was no evidence of paresthesia. Wesley et al. and Chen et al. reported coronoid osteomas associated with Gardner's Syndrome.[6],[10] To the best of our knowledge, this the tenth case of coronoid osteoma and it was not associated with Gardner's syndrome [Table 2].{Table 2}

Coronoid osteochondromas also present as a progressive painless mass that causes progressive reduction in mouth opening.[10] The underlying cause is inconclusive, but it could be linked to abnormal periosteum activity. Exostoses can arise because of endochondral ossification around a focal point of metaplastic cartilage. Another opinion is that it develops after a trauma, when a hematoma undergoes fibrosis and leads to the production of chondrocytes. Another contributor to restricted mouth opening is Jacob's disease, which varies from osteoid osteoma in histological evidence of endochondral ossifications enclosed by hyaline cartilage.[13]

Coronoid hyperplasia can also be a significant differential diagnosis as it may occur as a reactive bone hyperplasia secondary to endocrine stimulus, trauma, enhanced temporal activity, or genetic influences.

Although panoramic radiography is a widely used screening modality, the interpretation may be difficult due to the superimposition area of the bone lesion. CT scans provide good perspectives into anatomical details, morphological changes and extensions, and it clarifies its shape, location and relationships with the neighboring structures. CT scans also aid in treatment planning and gives clue to appropriate surgical approach based on individual cases. Histopathologic examination of coronoid masses is a key tool to differentiate osteochondromas, osteomas or hyperplasia and to find evidence for the postulated etiology theories.

The goal of management in these cases is to reestablish the function of mandibular movements which aids in mastication. Based on the location, dimension, and degree of restriction the approach for surgical procedure could be through submandibular, coronoid, retromandibular, preauricular or intraoral access. This may involve myotomy of masseter and temporalis muscles. To improve functional abnormalities complete surgical removal of bony mass is recommended where in coronoid process can be accessed through intraorally or extraorally or combination of both. Extraoral approach is always preferred for larger osteomas. Care should be ensured to prevent severing to the facial nerve in which case the intraoral approach is opted, but access is compromised. Surgical procedure through intraoral approach involves complete exposure of anterior ramus.[14] The prognosis in such lesions is satisfactory and recurrence is not reported.[15] Post-surgical physiotherapy, regular mouth opening exercises and regular follow up are advised in such treated cases.


The purpose of this report was to raise clinicians' attention to rare case of coronoid osteoma, which could cause progressive asymptomatic reduction of mouth opening and should be considered in the differential diagnosis. Unless it interferes with normal functioning, surgical intervention is not required, and periodic observation is necessary in such cases. If diagnosed and treated properly, such a situation can yield significant functional and aesthetic results.


We are grateful to the patient who gave us written consent to write this story. We would like to express our gratitude to our colleagues who supported us throughout this project.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given his consent for his images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published, and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.


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