Prebasioccipital Arch

Description

Pre-basioccipital arch (thin arrows), a U-shaped bony valance on the ventral lip of the anterior foramen magnum rim. This results from complete preservation of the hypochordal bow of the proatlas

MRI cranio vertibral junction (CVJ) showing pre basioccipital arch with a U-shaped bony prominence on ventral lip of anterior lip of foramen magnum and a well-defined oval corticated space-occupying lesion anterioinferior to the basion that was as contrasting as bone, indicating a possible third occipital condyle (condylus tertius) white arrow.

Name

• Prebasioccipital arch

General

• Rare anatomical variant of the occipital bone
• Part of the spectrum of occipital vertebrae

Epidemiology

• Very rare
• One study found prevalence to be 0.025%

Clinical Presentation

• Typically incidental finding
• Can theoretically cause neck pain if it articulates with axis or atlas
• Clinical significance is not well described in the literature

Radiographic Features

• U shaped bone arch arising from the inferior surface of the clivus
• It is draped across the anterior rim of the foramen magnum between the tips of the occipital condyles
• It may exist as an accessory ossicle or be fused with the occipital bone

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Clinical Significance

• Clinical significance is not well understood or described

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See Also

• Accessory Bones Main
• HEENT Anatomy Main

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