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We describe a 53-year-old Japanese woman with absence of the posterior arch of the atlas. Computed tomography revealed that the residual posterior fragment which was displaced to the right side does not correspond to a rare ossification center in the midline and that there was no clear mass of the posterior arch except for a small fragment. Moreover, the midline center was not demonstrated as a soft tissue mass. Easy tilting of the posterior fragment on flexion-extension movement suggests that the cartilaginous arch was not present between the lateral masses and the posterior fragment of the atlas. These observations support the hypothesis that hypoplastic development of the arch plays a major role in the pathogenesis of this anomaly rather than incomplete ossification. Abnormal segmentation of the vertebrae may be implicated in the etiology of this condition, since fusion of the anterior vertebral masses between the C5-6 levels, as shown in Klippel-Feil syndrome, is also observed.

Background The typical orbito‐ocular manifestations of carotid‐cavernous sinus fistulas are conjunctival hyperemia, chemosis and exophthalmos as a result of increased fistular flow directed anteriorly in the ophthalmic veins. These congestive features are absent if the flow is directed posteriorly, resulting in “white‐eyed shunts.” We describe a rare carotid‐cavernous sinus fistula case presenting with optic neuritis‐like manifestations. Case presentation A 71‐year‐old Japanese woman developed periorbital pain, impaired visual acuity with an upper horizontal visual field defect, diminished light reflexes and a relative afferent pupillary defect in her right eye. There were no congestive features in her eyes. Intraocular pressure was normal in both eyes, but fundoscopy revealed a pale optic disc in the right eye. Serum anti‐aquaporin‐4 antibodies were negative. Although optic neuritis was suspected, high‐dose corticosteroid administration did not result in improvement. When referred to Department of Neurology, Gunma University Hospital, she showed a subtle, incomplete oculomotor nerve palsy in the right eye. Magnetic resonance angiography suggested carotid‐cavernous sinus fistula (CCF), and cerebral angiography showed fistulous drainage into the cavernous sinus and inferior petrosal sinus, and a delayed opacification of the superior orbital and angular facial veins on the right side. A diagnosis of white‐eyed shunt CCF was made, and a coil embolization procedure was carried out. However, there was no symptom improvement. Conclusions It is difficult to diagnose white‐eyed shunt CCF based only on physical findings, especially when there is an absence of ocular congestive features. We discuss the possible mechanisms underlying the optic neuritis‐like symptoms of CCF.