Female patient, 44 years old, referred to our unit due to an increase in volume in the zygomatic region and progressive limitation of mouth opening of 10 months of evolution. The medical history was not relevant. The extraoral physical examination showed facial asymmetry due to an increase in volume in the left cheek, with diffuse limits, bony consistency, painless, with normal skin appearance. The mouth opening was 30 mm. The temporomandibular joint (TMJ) was normal on palpation, with no noises or pain on opening. On orthopantomography we observed an enlarged left coronoid process. The diagnostic hypothesis was a coronoid tumour.

An incision was made over the anterior border of the mandibular ramus, disinserting all the insertions of the temporalis muscle. A fibrous pseudocapsule was found around the enlargement, which was released. Coronoidectomy was performed. The buccal opening was immediately restored to 43 mm. The postoperative course was uneventful, and the patient was discharged after 48 hours.
Histopathological study reported the presence of fibres, neoformation bone and hyaline cartilage tissue. The diagnosis was osteochondroma. Subsequent check-ups were uneventful. Definitive discharge was given at 10 months, with almost complete remodelling of the cheek deformity.