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Foster Kennedy syndrome is characterized by optic atrophy in one eye and papilledema in the other caused by a frontal lobe mass ipsilateral to the atrophic optic nerve. It was first described by Foster Kennedy in 1911 in a case series of 6 patients with expanding frontal lobe lesions.
Optic nerve atrophy with contralateral optic disc edema in the absence of an intracranial mass has been coined pseudo-Foster Kennedy syndrome and is seen most often with nonsimultaneous bilateral nonarteritic anterior ischemic optic neuropathy (NAION).
Here, we report an additional case of pseudo-Foster Kennedy syndrome due to IIH.
Case Report
A 36-year-old overweight female patient (BMI 26.6 m/kg) was referred to the neuro-ophthalmology clinic by an optometrist who incidentally noticed optic disc edema in the right eye and a pale optic disc in the left eye during a routine eye examination. The patient denied blurry vision, transient visual obscurations, diplopia, headache, and tinnitus. She had no notable medical history and denied any previous trauma and the use of any medications including oral contraceptives, vitamin A derivatives, or any recent antibiotics.
During our initial assessment, her best corrected visual acuity was 20/20 OD and 20/30 OS. She had a relative afferent pupillary defect in the left eye and intraocular pressures of 10 mm Hg in each eye. She correctly identified 12 of 12 Ishihara colour plates in the right eye and saw the control plate, and 0 of 12 plates in the left eye. Her extraocular movements were full and there was no proptosis. Her anterior segment examination was normal. Dilated fundus examination revealed grade II optic disc edema in her right eye and a pale atrophic left optic disc (Fig. 1). The macula and peripheral retina appeared normal in each eye. Humphrey 24-2 visual field testing revealed a constricted visual field in the left eye with a mean deviation of –27.51 dB and a normal visual field in the right eye with a mean deviation of –1.96 dB (Fig. 2). The neurologic examination was unremarkable. Cardiovascular, respiratory, and head and neck clinical examinations were also within normal limits.
Fig. 1Optic disc photographs show optic disc edema in the right eye (RE) and optic atrophy in the left eye (LE).
A magnetic resonance (MR) image of the brain revealed tortuosity of the optic nerves and flattening of the posterior globe. There were no space-occupying lesions. An MR angiogram was normal. MR venogram revealed narrowing of bilateral transverse sinuses, but no evidence of venous thrombosis. A lumbar puncture was performed in the left lateral decubitus position with an opening pressure of 28 cm water. Cerebrospinal fluid analysis including cell counts, protein, and glucose were within normal limits.
In addition to recommending weight loss, the patient was started on oral acetazolamide 250 mg bid. She was seen in follow-up 3 times since the time of diagnosis. Although there was no reduction in her weight, she remained asymptomatic and was tolerating the medication well. Her visual acuity during the last visit at 9 months was unchanged in the right eye and had improved to 20/25 OS. The left optic disc remained atrophic and right optic disc edema evolved to grade I papilledema. As she still had papilledema, she was advised to continue acetazolamide and continue weight loss.
Discussion
Before the availability of neuroimaging, Foster Kennedy syndrome was thought to be pathognomonic for a space-occupying lesion in the basofrontal area on the side of optic atrophy, and exploratory craniotomy was performed to locate the mass.
Negative exploratory craniotomies subsequently led to description of other noncompressive causes, which are termed pseudo-Foster Kennedy syndrome (Table 1). The largest case series of pseudo-Foster Kennedy syndrome was published by Francois and Neetens in 1955, reporting that the top 3 causes were “arteriosclerosis and hypertensive cardiovascular disease, optochiasmatic arachnoiditis, and internal carotid aneurysms.”
More recent literature clearly implicates bilateral (nonsimultaneous) NAION as the most common cause, by far, of pseudo-Foster Kennedy syndrome (which is almost certainly what is implied by “atherosclerosis and hypertensive cardiovascular disease” in historical reports).
IIH encompasses patients with isolated increased intracranial pressure that is not related to intracranial compressive lesions, cerebral venous thrombosis, or a meningeal process. Approximately one fourth of patients, such as the one described in this report, are asymptomatic and diagnosed on routine eye examination.
Papilledema can result in slowly progressive visual loss, and up to 25% of patients with IIH develop secondary optic atrophy and permanent visual loss.
Papilledema is swelling of the optic nerve head caused by increased intracranial pressure and is usually bilateral. However, asymmetric papilledema is not uncommon in IIH, and it is thought to be related to differences in impedance to cerebrospinal fluid flow from trabeculations within the subarachnoid space of the optic nerve sheath.
this patient had papilledema in one eye and optic atrophy in the other: pseudo-Foster Kennedy syndrome. In our case, it may be that the atrophic optic nerve had the most severe optic disc edema initially, leading to optic atrophy, with relative preservation of less affected optic nerve, which continues to manifest optic disc swelling.
Evolution of optic atrophy in papilledema depends on the severity and persistence of the elevated intracranial pressure. Postpapilledema optic atrophy can happen within weeks or days, even before the phase of chronic papilledema, if the intracranial pressure rises rapidly and remains constantly high. In other cases with chronic papilledema, the optic disc swelling can gradually melt away into optic atrophy over a period of months to years. After the development of optic atrophy, papilledema does not occur without the presence of sufficient viable optic nerve fibres. Another potential cause of optic atrophy in this setting is a superimposed NAION or some other cause of optic atrophy before the development of IIH. These alternative explanations cannot be excluded particularly because the patient was asymptomatic and she was found to have to this condition during a routine eye examination.
References
Kennedy F.
Retrobulbar neuritis as an exact diagnostic sign of certain tumors and abscesses in the frontal lobes.
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