The Double Transverse Foramen

The double transverse foramen in the cervical spine is a normal variant that, according to the literature, occurs most often in the C6 vertebra transverse process, with decreasing frequency above and below.  It is claimed that the vertebral artery splits at these accessory foramen (which are always smaller), and rejoins distally, although this is controversial, and it is not entirely clear from the literature whether the accessory foramen usually contains artery, vein, nerve, neither, or some combination. 

Bilateral transverse foramina incidentally noted at C5 on this trauma patient.

Bilateral transverse foramina also incidentally noted at C6 on this trauma patient.  C6 is the most common level to find double transverse foramina.

One source claims that accessory foramina occur in 1.6% of observed cervical spines. The duplication is thought to represent the failure of controlled regression of two intersegmental arteries and a segment of the primitive dorsal aorta.  An extremely rare triple transverse foramen has been reported.

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2. Wysocki J, Bubrowski M, Reymond J, Kwiatkowski J. "Anatomical variants of the cervical vertebrae
and the first thoracic vertebra in man" Folia Morphol. Vol. 62, No. 4, pp. 357–363
3. Murlimanju BV, et al. "Accessory Transverse Foramina in the Cervical Spine: Incidence, Embryological Basis, Morphology and Surgical Importance" Turkish Neurosurgery 2011, Vol: 21, No: 3, 384-387