Commentary

This interesting case suggests that papilledema may result from intracranial pathology provoking high cerebrospinal fluid (CSF) protein without the hallmark of increased intracranial pressure (ICP). The authors speculate that the increased CSF protein impaired reabsorption of CSF in their patient, causing communicating hydrocephalus that produced papilledema and visual deterioration.

Traditionally, disc edema with normal ICP has been associated with local ophthalmologic processes such as central vein obstruction, hypertension, optic neuritis, ischemic neuropathy, compressive neuropathy, scleritis, uveitis, diabetes, toxicity, or infection. Bilateral disc edema with increased ICP is characteristic of pathology beyond the optic nerve itself. The level of protein in this patient's CSF was quite high, a condition known to be caused by a variety of intracranial and intraspinal tumors. An increase in the level of protein in the CSF has been postulated to increase ICP by decreasing absorption of CSF by blocking all semipermeable membranes of the arachnoid granulations. This mechanism was described by Gardner and colleagues[1] in 1954. Given this hypothesis, the absence of hydrocephalus in this patient indicates rather mild cerebral edema from the elevated CSF protein levels. Furthermore, all previous descriptions of the complications related to elevated CSF protein have included papilledema associated with increased ICP. This report now suggests the undescribed entity of papilledema associated with normal ICP.

The authors concede that the true opening pressure could have been lowered iatrogenically during general anesthesia. They also speculate that ICP might have been elevated intermittently as in normal pressure hydrocephalus. It is important to point out that disc edema may develop in a gradual, stepwise process that may proceed within a time frame of normal ICP. The authors also suggest that intermittent blockage of the fourth ventricle might have served as a mechanism for the stepwise development of papilledema without being associated with an obvious increase in ICP.

This patient's visual complaints, disc appearance, and ophthalmologic details were rather vague. The visual deterioration to 6/9 or 20/30 Snellen acuity is mild. Although patients with papilledema initially may have mild degrees of visual loss, the authors do not exclude simple refractive errors. The authors describe an enlarged blind spot but failed to investigate this visual field change with a more enlightening full-threshold static perimetry. Had this study been performed, it may have shown a defined scotomatous field defect rather than simple enlarged blind spots. Enlarged blind spots also can be associated with simple optic nerve drusen (congenital anomalous disc elevation), which can mimic disc edema. Furthermore, there is no mention that the visual field defects ever resolved after resection of the acoustic neuroma. Finally, the photographs of the optic nerve are not revealing enough to exclude the possibility of simultaneously present disc drusen. Intravenous fluorescein angiography would have been very useful to distinguish the perfusion patterns of drusen, papilledema, and inflammatory or infiltrative processes. Likewise, contrast sensitivity could have been useful to identify diseases that depress nerve conduction as opposed to nonpathologic anatomic variants with normal conduction.

Despite the limited ophthalmologic details, magnetic resonance imaging showed the large acoustic neuroma compressing the fourth ventricle, and the lesion was removed expeditiously.

This case is important because it highlights possible causes of disc edema associated with normal ICP other than local ophthalmologic processes. This is a unique departure from accepted thinking. Therefore, any patient with a swollen disc should be evaluated thoroughly. This evaluation should include comprehensive neuro-ophthalmologic investigations with full-threshold static perimetry. Although the demise of optic neurons with papilledema is a relatively slow process, space-occupying masses should be treated promptly to minimize optic nerve morbidity. When deciding to forego the use of stereotactic neurosurgical technology in lieu of more immediate surgical decompression, however, the physician should consider all variables, including the degree and duration of papilledema, level of surgical expertise, and finally, the availability of stereotactic technology, rather than the mere presence of disc edema itself.

REFERENCE

• 1 Gardner W J, Spitler D K, Whitten C. Increased intracranial pressure caused by increased protein content in the cerebrospinal fluid; an explanation of papilledema in certain cases of small intracranial and intraspinal tumors, and in the Guillain-Barré syndrome.  N Engl J Med. 1954;  250 932-936