What causes bare orbit sign in the skull on plain radiography?
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Answer:
Bare orbit sign is seen in sphenoid wing dysplasia associated with neurofibromatosis type 1 (NF1), where there is absence of the innominate line representing the greater wing of the sphenoid bone on frontal skull radiograph, resulting in a bare orbital appearance.
Why is it called so?:
It is named bare orbit sign due to the apparent lack of bony overlay across the orbital roof on frontal skull radiograph, resembling a bare or exposed orbit without the normal projection of the greater sphenoid wing.
Pathophysiology:
Sphenoid wing dysplasia in NF1 has a debated, likely multifactorial pathogenesis. Proposed mechanisms include intrinsic dysplastic maldevelopment of the sphenoid bone itself, and, in many patients, erosion and remodeling of the sphenoid wing secondary to an adjacent plexiform neurofibroma infiltrating the orbit or pterygoid fossa (sometimes termed “secondary sphenoid dysplasia”). By either mechanism, the greater sphenoid wing becomes deficient, eliminating the innominate line and enlarging the ipsilateral orbit.
Alternative names: None
Other associated named signs: None
References
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