The bare orbit sign, is described as a characteristic appearance of the orbit, seen when the innominate line is absent. The innominate line is a projection of the greater wing of the sphenoid, and its absence or destruction is responsible for this appearance.
It is the classical frontal radiograph sign of neurofibromatosis type I (NF1). In addition to the bare orbit sign, it is accompanied by an egg-shaped enlargement of the anterior orbital rim, bony defect in the posterior orbit and anteroposterior enlargement of the middle cranial fossa.
The bare orbit sign may also be seen in destruction of the sphenoid wing, most commonly due to neuroblastoma metastases.
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