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The differential diagnosis of retrobulbar processes as detected by computed tomography or magnetic resonance imaging (MRI) comprise a variety of pathological processes. While the most frequent diagnoses are tumours or inflammation, others are incidental findings that might point to an underlying cause. Among the latter is enlargement of the optic nerve sheath, an expansion of the cerebrospinal fluid space around the optic nerve that in some cases is linked to raised intracranial pressure.1
The so called “optical nerve sheath ectasias” or meningoceles are a rare finding, with only around 40 documented patients.2,3 The appearance of these ectasias has been described as tube‐like. Aneurysm‐like ectasias of the optical nerve sheath have not been reported so far. We present a case of bilateral aneurysm‐shaped ectasia of the optic nerve sheath associated with bilateral subdural haematomas and presumably with temporarily raised intracranial pressure.
A 36 year old female patient presenting with a history of focal Jackson seizures in her right arm two months ago, and being repeatedly beaten by her husband, complained of impaired vision and headaches for two days. Ophthalmoscopy revealed bilateral papilloedema, and MRI showed bilateral chronic subdural haematomas, empty sella, and bilateral, aneurysm‐like ectasia of the optical nerve sheaths (fig 11).). After neurosurgical evacuation of the subdural haematomas, the appearance of the optic nerve head normalised and clinical examination was unremarkable at three and six months after the intervention. On MRI, the ectasia of the optic nerve sheaths remained unchanged.
Ectasia of the optic nerve sheath is a rare finding in imaging studies, and various terms have been used to desribe this entity: arachnoid cyst,4 optic hydrops,5 patulous subarachnoid space,6 and meningocele.2
Concerning pathogenesis and associated diseases, Shanmuganathan et al7 reviewed the literature and identified a patient group with associated progressive hyperopia and choroidal folds.
Lövblad et al reported three patients with neurofibromatosis type 1 and tube‐like ectasia of the optic nerve sheath.8 In neurofibromatosis type 1, dural ectasias are a typical finding and are most often present in the spinal canal.9,10 In contrast to an enlargement of the optic nerve sheath by optic gliomas, which are also common in neurofibromatosis type 1, the ectasias are isointense to cerebrospinal fluid.
Hansen and Helmke1 investigated the optic nerve sheath response to pressure during CSF absorption studies in 12 patients undergoing neurological testing, and found that changes in the diameter of the sheath followed changes in the intracranial pressure.
In our case, neither progressive hyperopia, choroidal folds, nor features of neurofibromatosis were present. The intracranial pressure was at least temporarily raised, but the morphological changes remained after normalisation of the intracranial pressure.
The morphology of the optic nerve sheath ectasia in our case is different from what has been reported previously. Whereas previous reports describe a tube‐like enlargement, in our case it was aneurysm‐like.
Vascular aneurysms usually arise from weak parts of the vessels, from the vascular division sites. In our case the aneurysm‐like ectasia of the optic nerve may have been pre‐existing and only accidently detected. Alternatively, one may hypothesise that a focal weakness in the optic nerve meninges may have been induced by some indirect trauma to the orbit. The increased pressure within the optic nerve sheath may then have contributed to the formation of the optic nerve sheath aneurysm.
Competing interests: None declared.