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 arises from biallelic inactivation of the NF1 gene in mesenchymal cells during embryonic skull base development, leading to defective ossification and bony resorption of the greater sphenoid wing, which enlarges the ipsilateral orbit and eliminates the innominate line projection.
Alternative names: None
Other associated named signs: Moya moya syndrome in neurofibromatosis type 1
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