Can papilledema be diagnosed by measuring the optic nerve via ultrasound?

From the Guidelines

Yes, optic nerve sheath diameter measurement using ultrasound can help diagnose papilledema, as supported by the most recent evidence from 2020 1. To perform this:

• Use a high-frequency linear transducer (7-15 MHz)
• Place the probe gently on the closed eyelid
• Measure the optic nerve sheath diameter 3mm behind the globe
• A measurement >5mm is suggestive of increased intracranial pressure and papilledema This technique is based on the fact that increased intracranial pressure causes cerebrospinal fluid to accumulate around the optic nerve, enlarging its sheath. Ultrasound provides a quick, non-invasive way to visualize this enlargement. While useful as a screening tool, it should not replace a thorough ophthalmologic examination when papilledema is suspected. False positives can occur, so clinical correlation is important. This method is particularly valuable in emergency settings or when fundoscopy is challenging. Some studies suggest that MRI of the head and orbits is the most useful imaging modality for initial evaluation of the child presenting with papilledema and signs of raised intracranial pressure 1. However, the use of ultrasound to measure optic nerve sheath diameter is a valuable adjunct in certain situations, such as in emergency settings or when other imaging modalities are not available. It's worth noting that the evidence on the use of ultrasound to measure optic nerve sheath diameter is not universally consistent, with some studies reporting varying cut-off values and efficacy 1. However, the most recent evidence from 2020 1 supports its use as a helpful tool in detecting changes in optic nerve sheath diameter indicative of raised ICP in children.

From the Research

Diagnosis of Papilledema using Ultrasound

• Papilledema can be diagnosed by measuring the optic nerve sheath diameter (ONSD) via ultrasound, but the accuracy of this method is still a topic of debate 2, 3, 4, 5, 6.
• Studies have shown that ultrasound measurement of ONSD has a sensitivity of 46.9% to 92% and a specificity of 54% to 87% for diagnosing papilledema 2, 3, 4.
• The accuracy of ultrasound measurement of ONSD can be affected by the technique used, with some studies suggesting that the coronal technique may be more accurate than the axial technique 6.
• Comparison of ultrasound measurements with MRI measurements has shown that ultrasound can be a useful tool for predicting raised intracranial pressure, but the correlation between the two methods is not always significant 4, 5.

Factors Affecting Ultrasound Measurement of ONSD

• The accuracy of ultrasound measurement of ONSD can be affected by the experience of the operator, with novice emergency physicians having a lower sensitivity and specificity than experienced ophthalmologists 3.
• The quality of the ultrasound image can also affect the accuracy of the measurement, with some studies suggesting that the inferior and transverse orientations may be superior to the sagittal orientation 5.
• The cutoff value for ONSD can also affect the accuracy of the diagnosis, with some studies suggesting that a cutoff value of 6.2 mm may be more predictive of high intracranial pressure than other values 6.

Comparison with Other Diagnostic Methods

• Ultrasound measurement of ONSD has been compared with other diagnostic methods, such as fundoscopy and MRI, and has been shown to have a lower sensitivity and specificity than these methods 2, 3, 4.
• However, ultrasound measurement of ONSD has the advantage of being a non-invasive and relatively quick procedure, making it a useful tool for emergency physicians and other healthcare professionals 3, 4.