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Fatal Herpes Simplex Infection during Chlorambucil Therapy for Sarcoidosis

techniques include lumbar peritoneal shunting or subtemporal decompression, both of which are major neurosurgical procedures; lumbar peritoneal shunts also have a high failure rate. Optic nerve sheath decompression is probably safer and simpler and has been shown to preserve vision in papilloedema of different aetiologies (Kaye et al. 1981, Keltner et al. 1977). Early surgical intervention carries the surgical risks of optic nerve damage in a disease which may resolve spontaneously, whereas late intervention may allow optic atrophy with irretrievable visual loss. Serial perimetry and visual acuities help determine the necessity for intervention, but the exact timing is controversial. The mechanism of action of optic nerve sheath decompression may be by a lowering of intracranial pressure due to CSF leak from the dural window into the orbit. Filtering fistulas have been demonstrated following optic nerve sheath decompression for papilloedema, and bilateral resolution of papilloedema following unilateral optic nerve sheath decompression has been reported (Keltner et al. 1977), which would support CSF leak as a mechanism of action. Our case showed unilateral resolution of papilloedema following unilateral optic nerve sheath decompression, with no postoperative fall in CSF pressure. This suggests a local decrease in pressure on the optic nerve head as the mechanism for resolution of papilloedema. Hayreh (1968) and Davidson (1969) have reported obliteration of the optic nerve dural window and adjacent subarachnoid space by fibroblasts following optic nerve sheath decompression. Such obliteration would prevent transmission of raised intracranial pressure along the subarachnoid space to the optic nerve head, and this is the probable mechanism for the resolution of papilloedema and field defects in this case.