While papilledema is disc edema secondary to increased intracranial pressure, optic disc drusen (also known as pseudopapilledema and optic nerve head drusen) represent apparent optic disc swelling that simulates some features of papilledema but is secondary to an underlying, usually benign, process.
Most patients with pseudopapilledema lack visual symptoms, not unlike patients with true papilledema. In pseudopapilledema, no obscuration of the peripapillary vessels by the nerve fiber layer edema occurs. Pseudopapilledema may be unilateral or bilateral, but almost all cases of papilledema are bilateral. An extensive workup is usually unnecessary, and an experienced general ophthalmologist or neuro-ophthalmologist can correctly diagnose pseudopapilledema via an ophthalmoscopic examination.
There are a multitude of causes of true disc swelling and other disorders that may mimic disc swelling, some of which represent a morphologic variant of normal.
The optic nerve may be elevated, simply because the optic nerve enters the eye at an extremely oblique angle (tilted disc), giving a portion a more elevated aspect (usually nasally).
The optic cup may be smaller than usual in a hyperopic eye. This causes crowding of the axons, which become heaped-up and elevated as they leave the eye.
The nerve fiber layer, which is normally translucent, may be partially myelinated. This can lead to the appearance of a large cup with blurring of the disc margins.
A subtler (but common) cause of pseudopapilledema is buried disc drusen. This article focuses primarily on optic disc drusen. Disc drusen are composed of small conglomerates of mucopolysaccharides and proteinaceous material that become calcified with advancing age. These small tumors develop within the substance of the nerve tissue (bilateral in 70% of cases) and can lead to an elevated disc; they also may lead to a loss of visual field or, in rare cases, central acuity.[1] They may be inherited as an autosomal trait with irregular penetrance. Disc drusen may be associated with retinitis pigmentosa and pseudoxanthoma elasticum.
Rarely, pseudopapilledema may be caused by remnants of the congenital hyaloid system and localized gliosis. An experienced observer can almost always distinguish these entities.
Primary and metastatic optic nerve tumors can result in a swollen disc but ordinarily only when intraorbital disease is present and is seldom unaccompanied by other signs and symptoms of orbital disease, such as proptosis and motility disturbance.
A host of inflammatory, infiltrative, and infectious conditions can cause true disc edema, which may be confused with true papilledema due to elevated intracranial pressure. In these cases, the swelling is usually unilateral (with the major exception of hypertensive crisis). Examples of infectious causes include syphilis, Lyme disease, and cat-scratch disease. Examples of inflammatory disorders that cause true disc edema include anterior ischemic optic neuropathy, optic neuritis, diabetes, sarcoidosis, and leukemic infiltration. These conditions should be seen as causes of papillitis, which is a distinct entity apart from pseudopapilledema.
This condition affects 2-5% of the population. It is clinically apparent in only about 0.35% of individuals.
Mortality/Morbidity
Optic disc drusen may be associated with progressive visual field loss, more rarely loss of central acuity, and, in very rare cases, blindness. However, congenital causes are not associated with any progressive visual loss.
Race
Disc drusen are more common in whites and are believed to be less common in African Americans.
Sex
No sexual predilection exists.
Age
The condition occurs at any age, although disc drusen tend to enlarge with time and become more prominent with advancing age.
Most patients are asymptomatic. No visual symptoms are usually present.
Visual field loss
In many patients with disc drusen, visual field defects eventually develop along with afferent pupil defect, though patients usually remain symptom free.
Transient visual obscurations
A minority of patients with disc drusen experience transient visual flickering or graying out that is similar to transient visual obscurations that are sometimes seen in patients with papilledema.
Rarely, patients might experience permanent visual loss from secondary processes. For example, disc drusen may increase the risk of later developing subretinal neovascular membranes, retinal vascular occlusion, or ischemic optic neuropathy.
Visual acuity
Patients with disc drusen may eventually lose central acuity. Although unusual, this visual loss would most likely follow a long period of gradual field constriction, otherwise this should arouse suspicion of another process.
Take a history concentrating on neurologic problems and symptoms, hypertension, and febrile illness.
Perform visual acuity, color vision, and pupillary examinations. If present, document a relative afferent pupillary defect. Although the presence or absence of an afferent pupillary defect is not helpful diagnostically per se, generally, an afferent pupil defect is mild with early field loss.
Blood pressure should be checked since optic nerve swelling can be a sign of malignant hypertension, a treatable systemic medical emergency.
Perform a careful dilated fundus examination.
Edema of the nerve fiber layer that blurs the disc margins and the peripapillary vasculature is a hallmark of true papilledema. Usually, the peripapillary vessels are clearly seen in pseudopapilledema, except in such cases as myelinated nerve fibers.
The angle of the optic nerve head should be noted. A tilted disc results from an optic nerve that enters the eye at a sharply oblique angle; it usually has a characteristic appearance of a prominently elevated nasal aspect with a poorly defined or sunken temporal aspect. Patients with tilted discs may have associated marked astigmatism or high myopia.
Other anatomical variants include persistent hyaloid remnants, gliosis of the optic nerve head, and myelination of the nerve fiber layer. These entities have a characteristic appearance on dilated fundus examination.
When superficial drusen (small, white-to-yellow, granular bulging of the substance of the disc) are present, they greatly aid in the diagnosis. At other times, drusen can be deeply buried in the substance of the nerve, and the clinical diagnosis is more subtle. Buried drusen may be visualized via retroillumination of the peripapillary retina and the sclera. See the image below.
View Image
Superficial optic nerve drusen. Note the irregular disc margins with preserved vascular and perivascular detail.
In papilledema, the disc is usually hyperemic with sometimes subtle dilatation of the superficial optic nerve vessels, and an increased frequency of hemorrhages and cotton-wool spots exists. Also, Paton lines and optociliary shunt vessels may be seen with retention of the central cup until late in the course of the disease. A severely crowded nerve due to other causes (eg, hyperopia, disc drusen) may display subtle congestion of optic nerve vasculature as well.
In pseudopapilledema, the disc is yellow, the cup may be small or absent, venous congestion is not present, spontaneous venous pulsations are often present, congenitally anomalous vessels may be seen, and the disc abnormality may be familial.
It may be fruitful to examine family members for disc drusen.
B-scan ultrasonography may be useful in identifying buried disc drusen. Because drusen are calcified, they demonstrate high reflectivity on ultrasound.
While rarely indicated, a CT scan may show small areas of calcification within the disc substance, which represent calcified disc drusen. Progressive field loss, dyschromatopsia, or visual acuity loss in patients with suspected buried disc drusen or visible disc drusen warrants consideration of neuro-imaging studies to rule out occult CNS lesions, in which case a CT scan carries the advantage of possibly detecting buried disc drusen.
Fluorescein angiography can be used to rule out true papilledema, which exhibits increased dilation of the peripapillary capillaries with late dye leakage. Disc drusen may autofluoresce on fluorescein angiography, which can be seen with red-free photo techniques, using the appropriate filters.[2] (Buried disc drusen may not autofluoresce.) In Leber hereditary optic neuropathy, disc leakage is not seen on fluorescein angiography.
After studying 68 eyes with optic nerve head drusen, Merchant et al concluded that enhanced depth imaging optical coherence tomography scanning detects lesions more often and better evaluates their shape and structure than conventional testing.[3] Lee et al also found that optic head nerve drusen shows a diverse range of findings on optical coherence tomography scanning based on age and disc size.[4]
Visual field tests should be considered, especially if optic nerve drusen are suspected. Constriction of the visual field can gradually occur; patients rarely have progressive field loss that is insidious or rapid.
Stereo color photographs of the optic discs are useful to document changes.
No treatment is needed for most causes of pseudopapilledema because they represent normal physiologic variants.
Diseases possibly associated with disc drusen may need treatment, such as subretinal neovascular membrane, central retinal vein occlusion, or ischemic optic neuropathy (largely to exclude giant cell arteritis in the appropriate age groups).
A minority of patients with disc drusen (16-22%) present with progressive visual loss. Field deterioration normally occurs over many years and is generally slow and unnoticed by patients. Dramatic field loss related to vascular complications, such as anterior ischemic optic neuropathy, can rarely occur. Unfortunately, no successful therapy is available at this time.
For patients who may suffer from glaucoma, it can be challenging to differentiate progressive glaucomatous field loss from field loss due to glaucoma. Estimation of the cup-to-disc ratio is also more challenging.[5]
Mitchell V Gossman, MD, Partner and Vice President, Eye Surgeons and Physicians, PA; Medical Director, Central Minnesota Surgical Center; Clinical Associate Professor, University of Minnesota Medical School
Disclosure: Nothing to disclose.
Coauthor(s)
Joseph Giovannini, MD, Chief of Ophthalmology, Eye Surgery Center, David Grant Medical Center, Travis Air Force Base
Disclosure: Nothing to disclose.
Specialty Editors
Simon K Law, MD, PharmD, Clinical Professor of Health Sciences, Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, David Geffen School of Medicine
Disclosure: Nothing to disclose.
Chief Editor
Hampton Roy, Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Disclosure: Nothing to disclose.
Additional Contributors
Edsel Ing, MD, MPH, FRCSC, Associate Professor, Department of Ophthalmology and Vision Sciences, University of Toronto Faculty of Medicine; Active Staff, Michael Garron Hospital (Toronto East Health Network); Consulting Staff, Hospital for Sick Children and Sunnybrook Hospital, Canada
Disclosure: Nothing to disclose.
Acknowledgements
Georgia Chrousos, MD Clinical Professor, Department of Ophthalmology, Division of Neuro-Ophthalmology and Pediatric Ophthalmology Services, Georgetown University Medical Center
Disclosure: Nothing to disclose.
Brian R Younge, MD Professor of Ophthalmology, Mayo Clinic School of Medicine
Brian R Younge, MD is a member of the following medical societies: American Medical Association, American Ophthalmological Society, and North American Neuro-Ophthalmology Society
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