Evaluation of Joint Formation in Coronoid Process Hyperplasia (Jacob’s Disease) on CT and MR Imaging

Background Jacob’s disease is a rare pathology characterized by elongation/ enlargement of coronoid process of mandible with formation of pseudoarticulation with zygomatic arch. It presents clinically as restricted mouth opening and is often misdiagnosed as temporomandibular joint pathology. Case Presentation We performed cross sectional imaging and evaluation of Jacob’s disease in a 14-year-old girl with restricted mouth opening, CT images including Multiplanar Reconstruction and Volume Rendered Technique revealed enlarged left coronoid process of mandible while open mouth CT images and MR images concluded the presence of joint between enlarged coronoid process and zygomatic arch. Conclusions Coronoid process hypertrophy and Jacob’s disease are important differentials which should be considered in evaluation of restricted mouth opening. We propose that apart from CT, MR imaging should be considered in such cases for better pre-operative evaluation of joint formation.