Post-void bladder ultrasound in suspected cauda equina syndrome—data from medicolegal cases and relevance to magnetic resonance imaging scanning

Abstract

Objective Post-void residual (PVR) scans of less than 200 ml are increasingly being used to rule out the likelihood of cauda equina syndrome (CES) and to delay emergency MRI scanning in suspected cases. This study was done to review a series of 50 MRI confirmed cases of CES and to test the hypothesis that a PVR of less than 200 ml was unlikely to be present. Methods Fifty consecutive medicolegal cases involving CES were audited. Records were reviewed to see if PVR scans were done. MRI scans were reviewed, clinical and radiological diagnosis reviewed, and treatment recorded. Results Out of 50 CES cases, 26 had had PVR scans. In 14/26 (54%) the PVR scan was ≤ 200 ml. In one case, the CES diagnosis was in question leaving 13/26 (50%) cases where there was a clear clinical and MRI diagnosis of CES despite the PVR being ≤ 200 ml. All 13 were classified as incomplete cauda equina syndrome (CESI) and all proceeded to emergency decompression. Conclusions This study is the first in the literature to demonstrate that there is a significant group of CES patients who require emergency decompression but have PVRs ≤ 200 ml. The results demonstrate the existence of a significant group of CESI patients whose bladder function may be deteriorating, but they have not yet reached the point where the PVR is over 200 ml. Given the accepted understanding that CESI is best treated with emergency decompression, such patients are likely to have worse outcomes if MRI scanning and therefore surgery is delayed. We recommend the following: PVR is recommended as an assessment tool in suspected CES. A PVR of ≤ 200 reduces the likelihood of having CES but does not exclude it; clinical suspicion of CES should always lead to an MRI scan. Further investigation of PVR as a prognostic tool is recommended.

How to assess the long-term recovery outcomes of patients with cauda equina syndrome before surgery: a retrospective cohort study

“…In addition to placing a physical and economic burden on patients, the effectiveness of such measurement tools varies depending on the literature 5 . Measurement of the bladder residual urine volume may often provide inaccurate information; nearly 60% of patients with confirmed CES have less residual urine than the currently recognized diagnostic threshold of 200 ml 28 , 29 . Hellstrom and Podnar et al .…”

Diagnosis of cauda equina syndrome in the emergency department

“…However, normal bladder emptying is insufficiently sensitive to exclude CES [9] and over-reliance on bladder scanning may provide false reassurance and contribute to diagnostic delay. Although bladder scanning showed promise as an adjunct in earlier diagnostic studies [32,33], three subsequent reports have highlighted that up to 80% of patients with confirmed CES have a post-void residual <200ml [9,34,35]. Bladder scanning may therefore have a role in ruling in CES but should not be used to exclude the diagnosis [34].…”

“…Although bladder scanning showed promise as an adjunct in earlier diagnostic studies [32,33], three subsequent reports have highlighted that up to 80% of patients with confirmed CES have a post-void residual <200ml [9,34,35]. Bladder scanning may therefore have a role in ruling in CES but should not be used to exclude the diagnosis [34]. Bladder scanning may also be helpful in identifying painless urinary retention requiring early catheterisation [35].…”

“…Transfer of patients between hospitals for the purposes of diagnostic imaging is expensive [51] and uncomfortable in cases of severe back pain but may be necessary in some cases. Systems should accept a substantial proportion of "negative" scans and not chase higher yields because it is critical not to miss cases of CES [34]. Protocols that facilitate direct ED access to emergency MRI can expedite imaging for suspected CES without overburdening radiology services [52,53].…”

Research

“…A team from Oxford (UK) have stepped up and put this hypothesis to the test in an interesting way, reporting on the 50 most recent medicolegal reports concerning patients who were litigating in relation to CES. 4 All patients’ notes were reviewed for PVR volume, CES signs, and MRI findings. Overall, 26 patients had a record of PVR being measured, of whom 13 showed a PVR ≤ 200 ml.…”