Justin G. Peacock, MD,PhD, Vincent M. Timpone, MD Doing More With Less: Diagnostic Accuracy of CT in Suspected Cauda Equina Syndrome ASNR 2016 Electronic Scientific Poster, eP-199 Justin G. Peacock, MD,PhD, Vincent M. Timpone, MD San Antonio Military Medical Center, Dept of Radiology

Disclosures No financial disclosures. The views expressed in this presentation are solely those of the authors and do not represent an endorsement by or the views of the Department of Defense, or the United States Government.

Background-Purpose Cauda equina syndrome (CES) requires emergent imaging to rule out compressive lesions on the cauda equina which could necessitate emergent surgical decompression. MRI is the established imaging gold standard to screen for the various etiologies that can account for CES to include degenerative disc disease, trauma, neoplasm, infection, and hematoma. The clinical presentation of CES is defined by a broad range of symptoms and physical exam findings to include severe low back pain, bilateral sciatica, lower extremity weakness, bladder/bowel dysfunction, saddle numbness or reduced rectal tone. Some of these symptoms are common and nonspecific to CES, presenting the clinician with the diagnostic challenge of deciding which patients warrant further evaluation with MRI. Studies have demonstrated that the vast majority of MR scans performed to evaluate for CES do not demonstrate concordant pathology, however these scans are nonetheless frequently ordered given the significant impact of missing or delaying a diagnosis of CES1, 4-6, 9.

Background-Purpose While CT is sometimes performed as a complimentary imaging modality to evaluate osseous integrity in patients with CES, the diagnostic accuracy of CT in detecting significant spinal stenosis and cauda equina impingement compared to MRI is not well defined in the literature. The purpose of this study was to evaluate whether CT could reliably identify significant spinal stenosis and rule out cauda equina impingement in patients presenting with clinically suspected cauda equina syndrome.

Methods Over a 12-month period clinical and imaging data of 4,691 consecutive lumbar spine MRI examinations performed at our institution were reviewed. This study was Health Insurance Portability and Accountability Act compliant and was approved by our institutional review board. 151 patients met the following inclusion criteria: Acute neurologic symptoms with clinical suspicion of cauda equina syndrome (symptoms include: severe low back pain, bilateral sciatica, lower extremity weakness, bladder/bowel dysfunction, saddle numbness or reduced rectal tone). CT of lumbar spine performed within 48h of MRI. No interval surgery or significant change in symptoms between CT or MRI.

Methods We analyzed by visual inspection the percentage thecal sac effacement (≥ 50% , <50%) on lumbar spine CT and percentage thecal sac effacement (≥ 50% , <50%) on lumbar spine MRI. Percentage thecal sac effacement (PTSE) was determined by visually inspecting the area of thecal sac at the most stenotic level using axial and sagittal planes and comparing it to a normal level above or below the stenosis. Presence or absence of cauda equina impingement on MRI was also recorded. Cauda equina impingement was defined as complete effacement of CSF within the thecal sac secondary to an extrinsically compressing lesion.

Methods Images were reviewed independently by 2 radiologists; a CAQ certified neuroradiologist with 8 years of experience, the other a radiology resident with 1 year of radiology experience. Interpreting radiologists were blinded to all clinical and imaging report information. MR images were reviewed 2 weeks following review of CT images with readers blinded to the CT interpretation. Any disagreements were resolved by consensus. .

Results Demographic and Clinical Characteristics of Study Population Patients (n) 151 Female n(%) 46 (30.5%) Age (years), mean (SD) 54.5 (± 19.5) MR-PTSE ≥50% n(%) 40 (26.5%) MR-PTSE <50% n(%) 111 (73.5%) Cauda equina impingement (CEI) n(%) 19 (12.6%) MR-PTSE ≥50% -Degenerative changes n(%) 23 (15.2%) MR-PTSE ≥50% -Traumatic osseous retropulsion n(%) 12 (8%) MR-PTSE ≥50% -Neoplastic n(%) 3 (1.9%) MR-PTSE ≥50% -Hematoma n(%) 1 (0.7%) MR-PTSE ≥50% -Infection n(%)

Results Based on CT alone, readers determined PTSE<50% in 97/151 cases, and PTSE ≥50% in 54/151 cases. Reader sensitivity for detection of MR-PTSE ≥50% using CT alone was 98%, specificity 86%, PPV 72%, NPV 99%. 19/40 cases of MR-PTSE ≥50% had cauda equina impingement. No cases read as CT-PTSE<50% were found to have cauda equina impingement. Inter-reader agreement for CT-PTSE was good (kappa=0.62). No significant difference in results when CT exams stratified for presence of IV contrast.

Results Representative cases from study:

Results A C Figure 1. Normal Lumbar CT (A,B) and MRI (C,D). With appropriate window-level adjustment on CT, note the level of soft tissue contrast within the lumbar spine, including bone (red), disc (blue), thecal sac (green), and epidural fat (yellow). The average Hounsfield unit (HU) values for bone, disc, thecal sac, and epidural fat were 363, 90, 27, and -107 respectively. B D

Results A C Figure 2. 41 yo male with severe low back pain. CT (A,B) demonstrates degenerative stenoses, most significant at L2/3 (solid arrow). Readers determined PTSE was <50%. MRI (C,D) confirms PTSE<50%, and no evidence of cauda equina impingement. B D

Results A C Figure 3. 61 yo male with acute bilateral decreased lower extremity paresthesias. CT (A,B) demonstrates degenerative stenoses, most significant at L3/4 and L4/5 (solid arrow). Readers determined PTSE was ≥50%. MRI (C,D) confirms PTSE ≥50%, and demonstrates early impingement of the cauda equina. B D

Results A C Figure 4. 55 yo male with severe low back pain following fall off of roof. CT (A,B) demonstrates L3 burst fracture with osseous retropulsion into the spinal canal (solid arrow). Readers determined PTSE was ≥50%. MRI (C,D) confirms PTSE ≥50%, and demonstrates impingement of the cauda equina. B D

Results A C Figure 5. 59 yo male with metastatic renal cell carcinoma with worsening left lower extremity pain and difficulty ambulating. CT (A,B) demonstrates sclerotic osseous metastasis at L3, with hyperdense soft tissue component bowing and thinning posterior vertebral body wall (solid arrow). Readers determined PTSE was ≥50%. MRI (C,D) confirms PTSE ≥50%, and demonstrates impingement of the cauda equina by tumor. B D

Results A C Figure 6. 65 yo female with severe low back pain with bilateral lower extremity radiculopathy. CT (A,B) demonstrates degenerative stenoses most significant at L4/5 and L5/S1 (solid arrow). Readers determined PTSE was ≥50%. This case proved to represent a false positive as MRI (C,D) demonstrates a PTSE < 50% and no evidence of cauda equina impingement. B D

Conclusion CT-PTSE ≥ 50% predicts significant spinal stenosis on MRI in patients with clinically suspected cauda equina syndrome. CT-PTSE < 50% appears to reliably rule out cauda equina impingement. This imaging marker may serve as an additional tool to the clinician in deciding whether MRI can be deferred.

Limitations Retrospective design. Majority of cases were degenerative or traumatic osseous stenoses. Few cases of tumor, infection or hemorrhage. Variable CT imaging quality, predominantly secondary to streak artifact from differences in patient upper extremity positioning, body habitus, and inclusion of both IV and noncontrast exams.

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