Jacob's disease: report of two cases and review of the literature.

Jacob's disease is a rare condition consisting of new joint formation between the coronoid process of the mandible and the inner aspect of the zygomatic arch. Strictly speaking, it was first described by the French anatomist Oscar Jacob in 1899, although in 1853 von Langenbeck had described coronoid process hyperplasia. The pathogenesis of both conditions remains unknown. In this paper we present two new cases and a complete review of the literature on Jacob's disease, of which we have found only 12 cases. Due to the low prevalence of this condition, its diagnosis is not straight forward.