Commentary

It isn't just roses that raise the issue of semantics. With the advent of the ophthalmoscope in 1851, the appearance of a swollen disc was initially referred to as “optic neuritis.” These early descriptions of optic neuritis included many cases undoubtedly related to intracranial mass lesions and therefore to increased intracranial pressure (ICP). It was not until 1908 that Parsons[1] first used the term papilledema to refer to optic disc swelling associated with ICP. Despite this definition, there has been substantial confusion about the implications of papilledema ever since. It has been a problem, particularly because both inflammation (papillitis) and ischemia (anterior ischemic optic neuropathy) may appear identical to disc swelling from increased ICP. Local ocular problems, including vitreoretinal traction, hypotony, and intermediate uveitis (pars planitis), also may cause disc swelling that cannot immediately be distinguished from disc edema caused by increased ICP.

The authors present a single case report of a patient with an acoustic neuroma presenting with disc edema. As the authors point out, disc edema has potential implications for visual function. Patients with papilledema may have long-term disc swelling without progressive deterioration in central acuity. However, disc swelling from increased ICP will cause progressive optic nerve damage in a substantial portion of patients, as demonstrated by worsening arcuate visual field defects, the eventual loss of central visual function, decreased acuity, and optic atrophy. Such an outcome was demonstrated fairly dramatically in the case of pseudotumor cerebri or “benign increased intracranial pressure” when Corbett and associates[2] reported a 70% incidence of optic nerve damage. From an ophthalmic perspective, it is therefore imperative that optic nerve function be assessed quantitatively in any patient with disc swelling. The assessment should include best corrected central acuity, quantitative perimetry (usually automated static perimetry), quantitation of afferent pupillary defect, and analysis of the nerve fiber layer. Although past authors have attempted to follow papilledema by measuring the size of the blind spot, this variable does not correlate with optic nerve function and therefore probably is not particularly helpful. Quantitative perimetry must be performed to quantitatively assess the level of optic nerve pathology. Only quantitative assessment can reveal the subtle changes that can indicate progressive damage.

In this particular case, the authors found no evidence of obstructive hydrocephalus, and reported that ICP was normal. Cerebellopontine angle tumors may increase ICP in several ways. They can block ventricular outflow from the fourth ventricle, resulting in hydrocephalus. They also can produce problems with cerebrospinal fluid (CSF) absorption from protein leaking into the CSF, causing an obstruction at the level of the pacchionian granulations. It is not surprising to find patients without evidence of ventriculomegaly who still have significant increased ICP. The lack of elevated pressure at surgery, however, does not preclude the possibility that patients still had increased ICP previously, even without ventriculomegaly. ICP can be quite variable, particularly in syndromes such as pseudotumor cerebri where intermittent plateau waves can cause disc swelling despite random measurements of normal pressure on spinal taps. As early as 1939, the following statement was made: “One determination of intracranial pressure in a case of disease of the central nervous system is no more instructive than one determination of a patient's temperature during the course of a fever.”[3]

I would agree with the authors that the most likely scenario was that elevated protein in the CSF related to their patient's acoustic neuroma was responsible for problems with CSF outflow and thus papilledema. I would suggest, however, that the only way that the elevated protein is going to cause papilledema is through increased ICP. Therefore, the term “normal pressure hydrocephalus” is inappropriate because pressure, by definition, is not elevated in normal pressure hydrocephalus and there is no evidence of disc edema. I further agree with the authors that in the setting of advanced optic nerve pathology, especially with evidence of progressive optic nerve damage, surgical excision offers a much more rapid way of normalizing ICP than treatment with the Gamma knife. The presence of papilledema alone, however, is not necessarily an indication for emergent surgery. Only evidence of progressive optic nerve damage (advancing visual field defects) would constitute a neuro-ophthalmic indication for urgent treatment. Clinical decisions on treatment modalities must include as much quantitative information about the clinical status of the patient as possible. Thus neuro-ophthalmological input can be exceedingly helpful in decision-making and management issues in similar cases.

REFERENCES

• 1 Parsons J H. The Pathology of the Eye, Vol. 4, Part 2. New York, NY; GP Putnam's Sons 1908: 1349-1365
• 2 Corbett J J, Savino P J, Thompson H S et al.. Visual loss in pseudotumor cerebri. Follow-up of 57 patients from 5 to 41 years and a profile of 14 patients with permanent severe visual loss.  Arch Neurol. 1982;  39 461-474
• 3 Ford F R, Murphy E L. Increased intracranial pressure: clinical analysis of the causes and characteristics of several types.  Bull Johns Hopkins Hosp. 1939;  64 369-398