Simultaneous lateral and posterior ponticles resulting in the formation of a vertebral artery tunnel of the atlas: case report and review of the literature.

The foramen arcuale is infrequently found and is potentially a clinically/surgically significant anatomical variation of the atlas. When present, the vertebral artery travels through this bony ring after exiting the transverse foramen of the atlas and prior to entering the cranium. We present a case of an adult female skeleton noted to harbor both a foramen arcuale and a lateral ponticle that resulted in the formation of a canal for the vertebral artery. The literature regarding these osteological structures is reviewed regarding their presence and potential clinical significance. The simultaneous occurrence of fully developed lateral and posterior ponticuli resulting in encasement of the third part (atlantal segment) of the vertebral artery appears to be very rare. Based on the literature regarding only foramina arcuale and their presence predisposing one to symptomatic entrapment, additional compression, as seen in our specimen, of the vertebral artery by a lateral ponticle could very likely result in stenosis of the vertebral artery.