Coronoid Process Hyperplasia

3D CT reconstruction
Five year old boy with limited mouth opening since 3 years. CT scan shows enlarged coronoid processes extending above the zygomatic arches. Temporomandibular joints are normal.

Coronoid process hyperplasia (CPH) presents clinically with longstanding, progressive reduction of mandibular opening. The cause of restricted movement is impingement of the elongated coronoid process against the temporal surface of the zygomatic arch preventing further mouth opening. Clinical DD is TMJ ankylosis.

Diagnosis may be made with the presence of three features: difficulty in mouth opening, subclinical progression and hyperplastic change of the coronoid process.

CPH affects predominately young adult males, with a 5:1 male to female ratio and an average age at first presentation is 25 years.
Bilateral to unilateral incidence is about 4.7 to 1.

Reference:
Keegan M & Henry Z: University of Rochester Medial Center: Radiology: Neuroradiology Case of the Week: Case 165.

Credit: Dr Ahmed Haroun