A prospective study of the role of bladder scanning and post-void residual volume measurement in improving diagnostic accuracy of cauda equina syndrome

Abstract

Aims Diagnosis of cauda equina syndrome (CES) remains difficult; clinical assessment has low accuracy in reliably predicting MRI compression of the cauda equina (CE). This prospective study tests the usefulness of ultrasound bladder scans as an adjunct for diagnosing CES. Methods A total of 260 patients with suspected CES were referred to a tertiary spinal unit over a 16-month period. All were assessed by Board-eligible spinal surgeons and had transabdominal ultrasound bladder scans for pre- and post-voiding residual (PVR) volume measurements before lumbosacral MRI. Results The study confirms the low predictive value of ‘red flag’ symptoms and signs. Of note ‘bilateral sciatica’ had a sensitivity of 32.4%, and a positive predictive value (PPV) of only 17.2%, and negative predictive value (NPV) 88.3%. Use of a PVR volume of ≥ 200 ml was a demonstrably more accurate test for predicting cauda equina compression on subsequent MRI (p < 0.001). The PVR sensitivity was 94.1%, specificity 66.8%, PPV 29.9% and NPV 98.7%. The PVR allowed risk-stratification with 13% patients deemed ‘low-risk’ of CES. They had non-urgent MRI scans. None of the latter scans showed any cauda equina compression (p < 0.006) or individuals developed subsequent CES in the intervening period. There were considerable cost-savings associated with the above strategy. Conclusion This is the largest reported prospective evaluation of suspected CES. Use of the PVR volume ≥ 200 ml was considerably more accurate in predicting CES. It is a useful adjunct to conventional clinical assessment and allows risk-stratification in managing suspected CES. If adopted widely it is less likely incomplete CES would be missed. Cite this article: Bone Joint J 2020;102-B(6):677–682.

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

“…they could void and were therefore CESI, we found 13 cases where the PVR was less than 200 ml, and the diagnosis was confirmed on MRI. Our patients are not exactly the same as the patients reported by Katzouraki et al 7 . Case 12 had bladder symptoms but normal perineal sensation and anal tone with a positive MRI.…”

“…Worryingly, in our medicolegal practice, we are increasingly seeing doctors say that, because the symptoms and signs of CES are not diagnostic and because the PVR is a quantitative measurement, a PVR ≤ 200 ml indicates that the patient does not have CES even in the presence of objective signs. If it was thought that a PVR ≤ 200 ml did not require an MRI (which is not what Katzouraki et al 7 recommended), all 13 of our cases would have been missed. We believe that in some centres, PVR is being used in an uncritical way.…”

“…Unfortunately, no symptom or sign or combination accurately predicts CE compression on MR imaging [2][3][4], which leads to large numbers of negative MRIs performed so that a diagnosis of CES is not missed. A retrospective and then a prospective study of PVR in the assessment of potential CES patients have been performed [6,7]. The prospective study was of 260 suspected CES patients.…”

“…They had deferred MRIs, no MRI was positive, no patient underwent surgery, and none developed CES subsequently. The authors said that in patients with no objective signs of CES and a PVR ≤ 200 ml urgent/emergency, MR imaging is not justified, and MR imaging can safely be deferred to an outpatient basis during normal working hours 7 . In a subsequent letter 12 , the authors said that such patients can be managed on a routine basis "using the local radiculopathy pathway".…”

A Systematic Review of the Value of a Bladder Scan in Cauda Equina Syndrome Diagnosis

“…More recently, from the same institute in 2020, Katzouraki et al followed 260 patients and found a similar predictive value of 200 ml with CE compression on MRI, and where candidates underwent subsequent surgery (P<0.0001, Fisher's exact test). The PVR volume >200 ml had a sensitivity of 94% in predicting CES and specificity 66.8%, with 29.9% positive predictive value and 98.7% negative predictive value [14].…”