Disc drusen and pseudopapilloedema

Pseudopapilloedema & Optic Disc Drusen (ODD)

Pseudopapilloedema refers to an elevated, blurred optic nerve head that mimics true papilloedema in the absence of elevated intracranial pressure. The most common cause is Optic Disc Drusen (ODD), present in approximately 1% to 2% of the population (bilateral in 75% to 85%).

Pathogenesis of Optic Disc Drusen

Optic disc drusen are acellular, calcified, hyaline concretions composed of mucopolysaccharides, amino acids, ribonucleic acid, and calcium phosphate crystals. Their formation is incompletely understood; abnormal axonal transport and crowded disc anatomy are proposed contributors. Do not present a particular mitochondrial extrusion model as an established universal mechanism.

Clinical Distinction: True Papilloedema vs. Optic Disc Drusen

• Disc Surface & Margins: In true papilloedema, the disc is hyperaemic, with a circumferential halo of nerve fibre layer opacification extending onto the peripapillary retina. In ODD, the disc is pink or yellowish, elevation is often concentrated within the scleral border, and the disc margin has an irregular, "scalloped" or "lumpy-bumpy" contour.
• Retinal Vasculature: True papilloedema exhibits dilated surface capillaries, microaneurysms, telangiectasias, and obscuration of major retinal vessels at the disc margin. In ODD, major vessels maintain crisp outlines; anomalous vascular branching (e.g., early branching, trifurcations, tortuosity) is common, but surface telangiectasias are entirely absent.
• Haemorrhages: True papilloedema frequently features peripapillary nerve fibre layer flame haemorrhages. In ODD, flame haemorrhages are rare, though deep subretinal or peripapillary haemorrhages can occasionally occur in children from choroidal neovascularisation or mechanical erosion of adjacent vessels.
• Spontaneous Venous Pulsation (SVP): Observed at the central retinal vein trunk in 80% to 90% of normal individuals. The presence of SVP makes substantial raised pressure less likely but does not independently exclude it (though its absence is non-diagnostic, as 10-20% of normal eyes lack SVP).

Multimodal Differentiation

Definitive differentiation between true papilloedema and pseudopapilloedema relies on multimodal imaging:

1. Fundus autofluorescence: Superficial drusen can be hyperautofluorescent, but buried deposits may not be. Signal alone cannot exclude superimposed oedema or other pathology.
2. B-Scan Ultrasonography: Calcified drusen possess exceptionally high acoustic density. On B-scan ultrasound, ODD exhibit bright acoustic reflectivity (hyperechogenicity) at the optic nerve head that persists at markedly reduced receiver gain, accompanied by posterior acoustic shadowing. In true papilloedema, optic disc elevation disappears when gain is lowered, and fluid distending the retrobulbar sheath may be identified (the "30-degree test").
3. Enhanced Depth Imaging OCT (EDI-OCT): The gold standard anatomical test. EDI-OCT visualizes optic disc drusen as hyporeflective cores capped by a hyperreflective, sharply demarcated margin, located in the prelaminar tissue. In true papilloedema, EDI-OCT reveals diffuse, homogeneous thickening of the peripapillary retinal nerve fibre layer (RNFL), smooth upward deflection of the internal limiting membrane, and peripapillary subretinal fluid triangles, without drusen-type cores unless optic disc drusen coexist. Drusen and true oedema can occur in the same eye.

Diagnostic Comparison: True Papilloedema vs. Optic Disc Drusen

The following table contrasts the critical differentiating features:

Diagnostic and Safety Boundaries

Papilloedema may be asymmetric or rarely unilateral. Check systemic blood pressure and neurological status; malignant hypertension and venous thrombosis must not be missed. Drugs such as tetracyclines and retinoids cause secondary intracranial hypertension rather than being classified as idiopathic risk factors. MRI plus venography is usually appropriate; CT/CT venography can be used when required by urgency or availability. Obtain lumbar puncture only after safe imaging and assessment of contraindications, in a properly positioned relaxed patient.

Adult diagnostic criteria generally use an opening pressure at least 25 cm H2O; paediatric criteria use 28 cm H2O, with 25 in a non-obese unsedated child. Interpret pressure with the full syndrome, technique and reference criteria rather than one borderline reading alone. Normal central acuity does not exclude threatening field loss.

Weight management is disease-modifying but a fixed percentage loss does not guarantee cure. Acetazolamide and monitoring are selected for vision and tolerability. Rapidly declining fields require urgent surgical assessment; shunting or optic-nerve-sheath fenestration is primarily for vision threat, not headache alone. Venous stenting is a selected specialist option with evidence and antiplatelet considerations, not a universal pressure-gradient rule.

Disc drusen can coexist with true oedema. Buried drusen may lack autofluorescence and ultrasound calcification, particularly in children; EDI-OCT is useful. PHOMS are not themselves drusen. Drusen can produce field loss and transient symptoms. Do not use jugular compression as a bedside self-test of pressure.