A Case of Bilateral Bridges of a Korean Atlas

Kang, Ki Young; Baek, Jin Ghi; Kim, Hyun

Abstract

We report a case of bilateral bridges of atlas of a Korean atlas and accompanying variation of the course of the left suboccipital nerve that was observed during the practice of the human anatomy in Seonam university, college of medicine. Bridges of atlas across the groove for the vertebral artery run inferomedially from the posterior margins of the superior articular processes to the posterior margins of the grooves. Widths of the narrowest middle portions of the bridges are 5.05 mm at the left and 0.7 mm at the right. Superior and inferior widths of left bridge are 11.6 mm and 10.9 mm, and of the right are 4.45 mm and 4.65 mm respectively. Cross-sectional areas of the foramina formed by bridges of atlas are 34.7 mm 2 at the left and 29.3 mm 2 at the right. These sizes are much smaller than the sizes of the transverse foramina of the atlas at each side, but diameters of the second and third portions of the left vertebral artery are same as 4.3 mm. At the junction between the left bridge and the posterior arch distinct suture line was observed. Because of the relatively wide bridge, the left suboccipital nerve runs more laterally than the right. It turns to the posterior, pierces the obliquus capitis inferior muscle, and branches out to adjacent suboccipital muscles. Branch to the rectus capitis posterior muscles obliquely cross over the suboccipital triangle to these muscles.