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OPTIC NERVE HEAD DRUSEN
Alfredo A. Sadun, Michelle Y. Wang, in Handbook of Clinical Neurology, 2011
Funduscopic features
Optic disc drusen often appear with small and crowded optic discs that have a lumpy, bumpy appearance. Drusen are most often concentrated in the nasal half of the optic disc with associated vascular anomalies such as tortuous and dilated veins, cilioretinal arteries, and optociliary shunt vessels (Erkkilä, 1976). Visible optic disc drusen appear as refractile, whitish yellow, rounded crystalline deposits embedded within the optic nerve head. Buried optic disc drusen are harder to visualize and the optic disc may have a variable appearance ranging from normal to pseudopapilledematous. Buried drusen frequently produce elevation of the disc and obscuration of the optic disc margins, making it difficult to distinguish buried drusen from true papilledema based solely on funduscopic examination. However, in true papilledema, the disc swelling extends into the peripapillary retina, causing RNFL thickening and consequently obscuration of peripapillary vasculature. In contrast, elevation from optic disc drusen is confined to the optic disc. In addition, the absence of optic disc hyperemia, obscuration of surface arteries, exudates, venous congestion, cotton-wool spots, and peripapillary circumferential subretinal fluid lines (Patton's lines) may help distinguish optic disc drusen from true papilledema (Lam et al., 2008).
The presence of a small optic disc with drusen may obscure glaucomatous cupping and both may produce arcuate-type visual field defects. Hence, it is important to recognize that both conditions may coexist in the same eye.
Christopher J. Lyons, Atchareeya Wiwatwongwana, in Handbook of Clinical Neurology, 2013
Optic disc drusen
Optic disc drusen is a common cause of pseudopapilledema. They are composed of small aggregations of mucopolysaccharides and proteinaceous material. They are deeply buried within the disc substance in childhood, but become calcified with advancing age, and emerge onto the disc surface with time, to become clinically obvious. Though generally benign, they can give rise to wedge-shaped visual field defects in the long term. Optic disc drusen may be inherited as an autosomal trait with variable penetrance. Unusual vascular branching patterns and the superficial course of the vessels over the disc substance may help to distinguish these from papilledema.
B-scan ultrasound showing an echogenic lesion within the optic nerve head can secure a diagnosis of drusen. Alternatively, autofluorescence may be apparent using a fluorescein angiography setup without injection of fluorescein. Occasional cases may require a fluorescein angiogram. Whilst profuse leakage is apparent in the early angiographic phases of the papilledematous disc, the drusen disc should never leak. However, there is late staining of the disc on the angiogram. It is important not to mistake this late staining for leakage auto-fluorescence on OCT and OCT disc features can help to secure this diagnosis.
Hans-Christoph Diener, ... David W. Dodick, in Handbook of Clinical Neurology, 2010
Diagnosis
The ophthalmological examination should be performed by a trained neuro-ophthalmologist, since it can sometimes be challenging to differentiate between papilledema and pseudopapilledema of optic disc drusen or tilted optic discs. In most patients, papilledema precedes or coincides with symptom onset, but some patients may become symptomatic shortly before appreciable disc swelling is seen on ophthalmoscopy, while in others, papilledema may evolve over hours or days to weeks. There are cases of IIH without papilledema reported in the literature, which in the acute phase may occur because papilledema has not yet developed. The diagnosis of IIH without papilledema is very likely erroneous in patients with chronic daily headache and elevated cerebrospinal pressure, most of whom have medication overuse.
Visual field defects, such as an enlargement of the blind spot, inferonasal defects, arcuate scotomas, and concentric constrictions, occur in about 96% of patients during the course of IIH (Rowe and Sarkies, 1998). Central acuity is usually preserved in early papilledema, so a decline in acuity early in the course of the disease is an ominous sign. Automated or Goldmann perimetry is necessary to detect and quantify these defects as well as to follow the course of the disease and response to therapy. Follow-up examinations are important to detect and prevent visual loss.
Lumbar puncture in the lateral decubitus position is required to show an increased CSF pressure of 200 mmH2O in non-obese and 250 mmH2O in obese patients. Many authors consider the pressure interval between 200 and 250 mmH2O a non-diagnostic gray zone. Since intracranial pressure in IIH has fluctuations, there also can be normal or even low pressure. Therefore occasionally it may be necessary to repeat lumbar punctures or even measure CSF pressure by a lumbar drain or intracranial transducer monitoring (Johnston and Paterson, 1974; Gjerris and Borgesen, 2000). CSF chemistry is normal without pleocytosis, but the protein level can be below the normal range (Johnston et al., 1991).
Neuroimaging is crucial. Standard MRI and magnetic resonace venography (MRV) should be carried out in any patient to evaluate an IIH. Unenhanced CT scan discloses space-occupying mass lesions, but to exclude venous sinus thrombosis, spiral-CT venography is an excellent tool. Elliptic-centric-ordered three-dimensional gadolinium-enhanced MRI increases the sensitivity of MRV for detecting intracranial sinovenous stenosis. Signs of raised intracranial pressure can infrequently be seen on MRI, such as an empty sella (70%), flattening of the posterior sclera (80%), dilation (45%) or tortuosity (40%) of the optic nerve sheet, or gadolinium enhancement of the optic disc (50%) (Broadsky and Vaphiades, 1998; Said and Rosman, 2004).
Jonathan D. Trobe MD, in Neuro-ophthalmology, 2008
Congenitally Elevated Optic Disc
Key Facts
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Monocular or binocular congenital crowding of the optic disc with:
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indistinct margins • dome-shaped elevation • absent physiologic cup • sometimes obvious drusen
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Often confused with acquired optic disc elevation, especially papilledema (hence the term pseudopapilledema)
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Visual field defects may enlarge but visual acuity remains normal
Clinical Findings
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Indistinct optic disc margins, dome-shaped elevation, and absent physiologic cup
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Disc vessels often have excessive tortuosity, trifurcations, or abnormal take-off
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Optic disc drusen may be evident
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Nerve fiber bundle visual field defects may be present
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they may slowly enlarge but do not impair visual acuity
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May be difficult to distinguish from acquired optic disc edema (especially papilledema) on ophthalmoscopic grounds alone
Ancillary Testing
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Red-free fundus photography, B-scan ultrasound, or orbit CT often shows occult optic disc drusen
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Late phase fluorescein angiography shows no dye leakage
Differential Diagnosis
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Papilledema
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Diabetic papillopathy
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Compressive optic neuropathy
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Pre-eruptive anterior ischemic optic neuropathy
Treatment
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None
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Retest visual fields periodically to assess whether defects are present or enlarging to the point of impairing safe driving or other visually demanding occupational tasks
Prognosis
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Visual field loss may become severe but visual acuity remains normal
Fig. 2.1. Congenitally elevated optic discs. Telling the difference between this condition and acquired optic disc elevation, especially papilledema, may be difficult! That is why this condition is often called pseudopapilledema.
Fig. 2.2. Congenitally elevated optic disc with drusen. These refractile particles reflect optic nerve axoplasmic stasis of congenital origin. Visual field loss is often present and may be slowly progressive.
Fig. 2.3. CT scan shows the drusen as bright (high attenuation) dots in the optic discs.
Optic nerve head drusen