E1430. Clinical Significance of Ill-Defined Spinal Epidural Fluid After Lumbar Puncture
  1. Eric Christiansen; St. Josephs Hospital
  2. Jeremy Hughes; Barrow Neurologic Institute
Ill-defined epidural fluid identifiable by MRI has been shown to be present in some patients following lumbar puncture. The clinical significance of this post dural puncture epidural fluid is indeterminate; a prior study has suggested that this epidural fluid is present in symptomatic patients although this study targeted the pediatric population only. In our experience similar ill-defined post dural puncture fluid can also be seen in the asymptomatic population and can be considered a normal imaging finding following recent dural puncture. This fluid is not well organized and dissects through the fat planes of the epidural space in distinction to the more organized extradural fluid collections which are known to occur in patients with spontaneous intracranial hypotension (SIH) related to a spinal CSF leak. Often, during the assessment of patients suspected of SIH, MR spine imaging is obtained soon after dural puncture. The presence of ill-defined epidural fluid in this setting can be a source of confusion and may be interpreted as objective evidence supporting a spinal CSF leak. The goal of this study is to determine the frequency with which nonorganized epidural fluid is present in patients following lumbar puncture and to assess for the presence of associated symptoms in these patients. We will also assess confounding factors such as needle type (cutting versus non-cutting), needle gauge, level at which LP was performed, opening and closing pressures and time from LP to MRI.

Materials and Methods:
Retrospective imaging and chart review. Relevant study participants will be identified in the Nuance mPower search engine by identifying patients who meet the inclusion criteria. Review all imaging for evidence of epidural fluid and organized epidural fluid collections.

18 of 91 (20%) patients demonstrated epidural fluid collections on MRI within 7 days of undergoing lumbar puncture. Of theses collections, 14 involved the lumbar spine with two of those cases extending to the thoracic spine, 3 cases were isolated to the thoracic spine and 1 case was isolated to the cervical spine. All cases involved the dorsal epidural space, with 1 case also involving the ventral space. Epidural collections happened more frequently with larger gauge of needle used; for 20 gauge it occurred in 50% of patients, while 22 gauge had an incidence of 16%. Univariate analysis showed an 8% decreased odds of developing ill-defined epidural fluid per 1 year increase in age. The majority of patients were asymptomatic following LP (61/91, 67%); in patients with symptoms there was no statistical significance comparing groups with epidural fluid to those without.

Epidural fluid collections are an incidental finding in a patient post lumbar puncture without significant correlation with symptomatology. It occurs more frequently with larger needle gauge and younger patient age. This finding should not prompt further workup for CSF leak and should be considered an incidental finding on MR in the setting of recent LP.