Correlation between Optic Nerve Sheath Diameter and clinical improvement after lumbar Epidural Blood Patch in case of Spontaneous Intracranial Hypotension.

Spontaneous intracranial hypotension (SIH) was first described in 1938. Because CSF leakage is the reason of SIH, this disease also has been named spontaneous intracranial hypovolemia. Mostly leaking sites are in the thoracic spine or at the cervicothoracic junction. Patients may have a history of trivial traumatic injury, or may have no definite history of injury. The imaging findings of SIH derived from CSF volume depletion usually show brain sagging and related complaints. SIH is characterized by orthostatic headache (OH), and DPME (diffuse pachymeningeal gadolinium enhancement) on magnetic resonance imaging (MRI), evidence of CSF leakage on conventional myelography, CT myelography or cisternography, CSF opening pressure LESS THAN 60 mmH2O in sitting position unrelated to lumbar puncture and definite trauma. OH, as defined by the International Headache Society, is a headache that occurs within 15 minutes of an upright position and is relieved within 30 minutes of recumbency.The OH characteristics may change over time, resulting in a daily chronic headache or paradoxical headache, with worsening in supine position. Various additional symptoms, like neck pain, neck stiffness, nausea, photophobia, vomiting, tinnitus, diplopia, and decreased level of consciousness have been described . Three causes, first described by Schievink et al. in 2016, that may lead to spinal CSF loss include ventral dural tear (type 1), leaking nerve root diverticulum (type 2) or a CSF-venous fistula (CVF; type 3)

SIH is primarily treated conservatively. When more aggressive treatment is required i.e. initial conservative measures failed, an epidural blood patch (EBP) is the modality of choice. Historically, lumbar EBP has been used regardless of leak site because of its low risk and the ability of blood to travel many levels from the site of injection. Mokri B explained mechanisms that are involved in relieving the headache. The immediate headache-relief occurs when the blood inflow presses the dura mater and causes CSF volume replenishment. The secondary long-lasting relief is achieved by sealing of leak by blood inflow. The amount of blood injected in SIH patients has varied in different reports. Usually, 20 ml of autologous blood is used in the lumbar spine level in case of non-targeted EBPs. Performing an EBP on SIH patients has shown persistent symptomatic relief in up to 90% of the cases in previous studies.

Ultrasound evaluation of the optic nerve sheath diameter (ONSD) has emerged in recent years as a useful non-invasive tool for estimating ICP or detecting intracranial hypotension and hypertension. It is a safe technique that can be conducted at the bedside, in real time, and is reproducible, relatively low cost, and does not carry the risks of radiation and CNS infections. ONSD is currently considered the best non-invasive modality for dynamic estimation of ICP . POCUS measurements have shown ONSD to be significantly correlating with ICP . ICP can be calculated using the formula ONSD: nICPONSD = 5.00 × ONSD - 13.92 mmHg . This is thus necessary in assessing patients in whom invasive ICP monitoring is either unavailable or is contraindicated or resource-poor areas where MRI or CT myelography/ cisternography is not easily available. An increase or decrease in fluid in the subarachnoid space can cause the ONSD to widen or narrow. The validity of using ultrasound measurements of the ONSD to assess intracranial pressure has been demonstrated, and this non-invasive and safe method has been used to assist in clinical diagnosis. It is hypothesized that the resolution of SIH can be predicted by ONSD. This study is thus being conducted to observe the correlation between ONSD measured non-invasively with symptom relief after EBP.