Neurilemmomas (Schwannomas) typically present like cavernous haemangioma and have a similar scan appearance, and neurofibromas usually form a mass in the supraorbital nerve, with slowly progressive proptosis and hypoglobus; resection of these tumours, when causing loss of orbital function, is curative. In contrast, plexiform neurofibromas diffusely affect the anterior orbital tissues, especially in the upper eyelid and lacrimal gland, and resection is difficult and does not eliminate the disease.
Primary optic nerve tumours, either meningioma or glioma, are usually benign and present in childhood or young adults. Gliomas cause proptosis and mild visual loss and CT scan shows a fusiform enlargement of the optic nerve (Figure 12.16); MRI is particularly useful for demonstrating changes in the intracanalicular and intracranial portions of the nerve. Gliomas require neurosurgical resection, if progressing to threaten the optic chiasm, or orbital resection if causing gross proptosis. Optic nerve meningiomas do not cause significant proptosis, but profound visual failure due to impairment of optic nerve perfusion. CT scan typically shows a diffuse expansion of the optic nerve and, in some cases, calcification within the optic nerve sheath (Figure 12.17) and MRI may demonstrate a normal or small nerve passing through an enlarged sheath. Neurosurgical resection of optic nerve meningiomas may be considered in younger people, in whom the tumour appears to have a more active course and risks intracranial involvement.
There are many rare diseases that affect the orbital bones, but the commonest is sphenoid wing meningioma. This tends to present in middle age with chronic variable lid swelling, chemosis and mild proptosis. The CT scan shows hyperostosis of the greater wing of the sphenoid with en-plaque soft tissue on the lateral wall of the orbit, the temporalis fossa or the middle cranial fossa (Figure 12.18). Although a metastasis may very rarely present with a similar radiological appearance, the
clinical behaviour is different - with sphenoid wing meningioma progressing very slowly and usually not requiring any active treatment; biopsy is indicated if a rapid progression is suggestive of metastatic disease.
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