forming a bony opening through which the vertebral artery (VA) enters the vertebral canal. Block vertebra is a synostosis of at least two vertebral bodies that did not separate during the embryological development. It is worth distinguishing it from the Klippel-Feil syndrome, as the latter oftentimes involves other abnormalities (namely skeletal) and is typically diagnosed in childhood. Both variants could potentially lead to an impairment of the blood flow through the VA. Case report: The following case report presents a finding of two anomalies of the cervical spine, found in a 38 y.o. female patient suffering from dizziness. A synostosis of the C4 and C5 vertebral bodies, arches and zygapophysial (facet) joint, was noted by the examining radiologist, with marked narrowing of the intervertebral foramen. Furthermore, second anatomical variation in the form of the complete bilateral arcuate foramen was identified superior to the groove for the VA on the upper surface of the posterior arch of the atlas. Conclusions: To the best knowledge of the authors, this case report is the first to present a co-existing block vertebra and bilateral complete arcuate foramen. Common presence of at least two anatomical variations that could have a synergistic clinical effect could possibly be termed 'tandem anomaly.' Notwithstanding, identification of a single anomaly explaining a patient's symptoms does not absolve the medical professionals from searching for any other potential variations that could also be present and could further influence the clinical picture.
Keywords: anatomy; arcuate foramen; radiology; vertebral artery; vertebral synostosis.