Midline shift may be considered significant when it exceeds roughly ~5 mm.Division is necessary to avoid counting the midline shift twice. Midline shift may be evaluated as the difference between these distances divided by two (figure below).In the absence of hydrocephalus, the third ventricle is often fairly small (visible as a pair of parallel, hyperechoic ventricular walls figure 1D above). The distance from the ipsilateral temporal bone to the center of the third ventricle is measured from both sides of the head (using the same views that are utilized to evaluate for hydrocephalus, as shown in the last section).However, the pulsatility index probably relates most directly to cerebral perfusion pressure (CPP) rather than intracranial pressure. An elevated pulsatility index within the middle cerebral artery (MCA) may suggest elevated intracranial pressure.Papilledema should be distinguished from optic disc drusen (calcifications in the optic disc which appear bright figure below) or inflammation due to optic neuritis (which is usually unilateral).However, papilledema may remain a useful ancillary finding – especially among patients who have an equivocal optic nerve sheath diameter (e.g., values fluctuating between 5-6 mm). Overall, papilledema is not as well validated as optic nerve sheath diameter.Some studies have found that ultrasonographic papilledema has good performance for the detection of elevated intracranial pressure (e.g., sensitivity in the range of ~90%).Papilledema may be noted on ultrasonography as a protrusion overlying the optic disc (figure above). If measurements are inconsistent, then they aren't providing reliable information. ⚠️ Precision may vary based on a number of different factors (e.g., whether the patient is moving their eyes, or the quality of the ultrasound machine).If all four measurements are consistently normal (6 mm), then that may increase confidence that the data is accurate. This provides an estimation of the reliability of measurement within any individual patient. Two measurements should ideally be obtained in each eye (with the probe oriented in a sagittal plane and an axial plane), yielding a total of four values.6 mm suggests elevated intracranial pressure.Interpretation is roughly as follows: ( 31025061).The most widely validated approach to estimating intracranial pressure involves measuring the optic nerve sheath diameter 3 mm behind the eye (figure below).The optic nerve itself remains the same size. ( 35001377) When intracranial pressure is elevated, the subarachnoid fluid surrounding the optic nerves swells – which widens the diameter of the optic nerve sheath. The optic nerve sheath is part of the dura surrounding the brain.
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