Optic Nerve Sheath Enlargement in Acute Intracranial Hypertension

Abstract

B-scan sonography can image the optic nerve and allows to measure the sheath diameter on-line. For 20 adult control subjects the optic nerve sheath (ONS) diameter ranged between 2.9 and 4.3 mm (mean 3.6). In the follow-up of 16 severe acutely brain injured patients (cerebrovascular and traumatic disease) leading to elevated intracranial pressure, ONS-diameters were significantly enlarged (mean 5.5 mm).

The underlying ONS dilatations can be explained by cerebrospinal fluid shift from the intracranial subarachnoidal compartment. Markedly enlarged ONS were found in nearly all cases and the recorded maximum diameters ranged between 3.8 and 6.9 mm. Usually papilledema was not detectable on the day of maximum ONS-diameter, but ONS dilatations were recorded as early as four hours after trauma.

Optic nerve sheath diameters exceeding 5.0 mm bilaterally always corresponded with elevated intracranial pressure and can serve as a marker for intracranial hypertension provided other neuropathies can be excluded. In this way, the authors currently use this non-invasive technique in the evaluation of acute neurological disorders at the bedside.

Key Words:

• Optic nerve sheath
• intracranial pressure (ICP)
• B-scan ultrasound