Hyperplasia of the mandibular coronoid process is a clinical condition that causes an indolent trismus by elongated coronoid processes that impinge on the zygomatic medial surface when opening the mouth. We report a case of hyperplasia of the mandibular coronoid process which was progressive temporally and was treated by bilateral coronoidectomies.
A 10-year-old boy consulted our department with a complaint of mouth opening limitation. Maximum mouth opening (MMO) between upper and lower incisors was 20mm. Based on the image findings a diagnosis of hyperplasia of the mandibular coronoid process was made, but he and his parents did not desire treatment. Thereafter, his trismus progressed temporally and he visited our department again for treatment of hyperplasia of the mandibular coronoid process at 15 years old. The image findings showed that both enlarged coronoid processes had extended above the zygomatic arch. Bilateral coronoidectomies were performed through an intraoral approach under general anesthesia at 16 years old, and the intraoperative MMO was 50mm. Training with a mouth opening training device was started seven days after surgery, but MMO at 17 days after surgery was only 19mm. Self-training of mouth opening was continued and MMO at 15 months after surgery was 34mm. On the other hand, new island-shaped bone formation in areas of resected coronoid processes was observed on CT images three months after surgery, and the bone fragments were enlarged and connected on CT images 12 months after surgery. Therefore, continued follow-up is required for this patient.
