Transorbital Ultrasound Measurement of Optic Nerve Sheath Diameter Between Pregnant Women With Severe Preeclampsia and Normal Gestations. Prospective, Controlled Trial.

The neurological alterations associated with preeclampsia depend on cerebral autoregulation, a theory that outlines the mechanisms by which the nervous system controls cerebral perfusion. However, with the loss of autoregulation, increased blood flow, edema and eventually increased intracranial pressure are triggered and may be translated into neurological manifestations such as symptoms of vasospasm, one of the criteria for severity in preeclampsia.

Nervous system manifestations frequently found in preeclampsia are headache, blurred vision, scotomas and hyperreflexia. Although uncommon, temporary blindness (lasting a few hours to a week) may also accompany severe preeclampsia and eclampsia.

The optic nerve, as part of the central nervous system, is surrounded by cerebrospinal fluid and dura mater, which forms the optic nerve sheath. Due to the connection with the intracranial subarachnoid space, the diameter of the optic nerve sheath is influenced by variations in cerebrospinal fluid pressure. Increased intracranial pressure is transmitted to the subarachnoid space surrounding the optic nerve, causing its expansion.

Recent studies suggest that an optic nerve sheath diameter greater than 5 mm correlates 100% with ICP (intracerebral pressure) greater than 20 mm Hg. Due to the simple nature of the test and the limited time required to perform it, it is an ideal non-invasive test to assess changes in mental status, severe headache, and to take the necessary measures aimed at reducing intracranial pressure.

The diagnosis of elevated intracranial pressure is challenging and critical, because early recognition and treatment are essential to prevent brain damage or death since preeclampsia with severe data remains one of the most frequent complications in our institution.

These values are not taken from the obstetric population, so this study proposes the description of a standard value for the pregnant population. There are few studies that describe a value to help us define cases of this pathology and correlate it with the signs and symptoms of severity in patients with preeclampsia.