1. Mallinckrodt Institute of Radiology Washington University in St. Louis
Speed and Accuracy of Hyperacute Stroke CTA Interpretation by Radiology Trainees
Submission Number: 1335
James W. Berger, Thomas Madaelil, Colin P. Derdeyn, Michelle Miller-Thomas, Katie Vo, Jin-Moo Lee, Peter Panagos, Andria Ford, Jennifer Williams, Manu S. Goyal
Mallinckrodt Institute of Radiology
Washington University in St. Louis
Saint Louis, MO, USA
Submission Number: 1335

2. Disclosures
Manu Goyal: Funded by RSNA and McDonnell Center for Systems Neuroscience. No financial interests related to this work.
No other author disclosures

3. Introduction
Randomized clinical control trials show that endovascular mechanical thrombectomy (EVT) is superior to standard medical care in acute ischemic stroke due to large vessel occlusion (LVO).1–5
These trials used head and neck computed tomographic angiography (CTA) predominantly to detect LVO non-invasively in patients who otherwise meet inclusion criteria for EVT.6
Time to reperfusion and recanalization are significant factors in determining the efficacy of EVT . Thus, optimizing the speed and accuracy of detecting LVO is critical to identify patients for EVT and maximize their outcomes.

4. Introduction
At our institution a new resident driven image interpretation and communication protocol was developed and implemented to improve door to endovascular treatment time in the emergency department.
As a patient undergoes CTA for stroke in the ED, a radiology resident reviews the CTA immediately after it is obtained and then provides a preliminary impression—in particular whether LVO is present or not—to the neurology and/or ED physicians available in the scanner room.
CTAs are subsequently also reviewed for accuracy by an interventional or diagnostic neuroradiology.
The speed and accuracy of resident-based preliminary CTA impressions for detection of LVO are unknown. We therefore prospectively collected and retrospectively reviewed the time and specifics of their preliminary impressions relative to the CTA time and final diagnosis, respectively.

5. Methods
This study was approved by the Washington University School of Medicine Institutional Review Board. This study was performed at the Barnes Jewish Hospital, which is the main quaternary hospital for our institution, serves the greater St. Louis area, and receives patients transferred from other hospitals several hundred miles away.
Electronic search of our radiology information system was used to identify consecutive patients presenting with hyperacute stroke and who underwent CTA in the 6 month period between 3/30/2015 and 9/30/2015.

6. Methods
Our hyperacute stroke CTA protocol includes a noncontrast head CT followed by head and neck CTA from the level of the aortic arch to the skull vertex, most often performed on a 128 row detector FLASH Siemens CT Scanner with 100 mL of iodinated contrast and bolus tracking.

7. Methods
After acquisition, sagittal and coronal maximum-intensity projections (MIPS, 30mm x 5mm) are created by the technologist and sent to the PACS workstation for review. The images and reconstructions are also available for immediate review following the acquisition on the technologist workstation in the CT scanner control room.

8. Methods
After acquisition, sagittal and coronal maximum-intensity projections (MIPS, 30mm x 5mm) are created by the technologist and sent to the PACS workstation for review. The images and reconstructions are also available for immediate review following the acquisition on the technologist workstation in the CT scanner control room.

9. Methods
The on-call diagnostic radiology residents were asked to document their initial radiology resident impression (IRRI) of hyperacute stroke CTA examinations on a formatted index card available in the CT control room. 

10. Methods
During and after the study period, the cards, dictated reports, and EMR were all reviewed together to determine the IRRI reported to the neurology and/or ED team and the time this was reported.

11. Methods Major change: Minor change:
In addition to the IRRI, we also recorded the time the CTA scan was performed, the time and content of the dictated preliminary report, the time and content of the final report including any noted discrepancies in interpretation.
Discrepancy in interpretation between the IRRI and the final report and/or catheter angiography findings was categorized as major or minor.
Major change:
-possibly altered immediate clinical management in particular with regards to the presence or absence of LVO.
Minor change:
-all other changes that might influence subsequent clinical management beyond the endovascular time window.

12. Results
During the study period 100 consecutive hyperacute stroke CTAs were performed at our institution. The IRRI was found in various locations, most often the stroke neurology consult note, the preliminary radiology report or IRRI index card, and the emergency room patient note.
CTA completion to recorded IRRI:
-in EMR:
Median time 13 minutes
Mean time 21 minutes
Range minutes
-recorded on the index card
Median time 5 minutes
Mean time 6 minutes
Range minutes

13. Results
The IRRI reported the presence of LVO in 47 of the 100 examinations.
In comparison to the final reports, there were 0 major changes and 7 minor discrepancies.
These minor discrepancies included nuanced report wording changes, new reportable findings such as an old lacunar infarct, identification and description of atherosclerotic disease burden, and an attending downgrade of a 2 mm aneurysm to a normal vessel infundibulum.

14. Results
-24 of these 47 patients with CTA documented LVO underwent cerebral catheter angiography.
-18 received EVT during the angiography
-6 did not receive EVT during the angiography
In our series in the cases where angiography was performed there were …
ICA occlusion 7
M1 occlusion 12
M2 occlusion 3
Basilar artery occlusion 2
Some of these cases had more than one vessel occluded; often there was a distal ICA and proximal M1 occlusion.

15. Results
The IRRI reported absence of LVO in 53 out of the 100 examinations. In cases with preliminary negative findings there were 3 major and 7 minor discrepancies between the IRRI and final report after review with the neuroradiology attending.
The major changes to these IRRI negative exams included 3 missed proximal M2 occlusions .
The minor changes again included wording changes or additional findings that would not alter immediate patient management.
For the overall cohort strength of agreement between the IRRI and final report for the absence or presence of LVO was excellent (kappa=.94; CI 95% ; p<0.005 ).

16. Major Discrepancy 1
Initial negative verbal result but then later found to have an abrupt cutoff in the anterior branch of the right M2 artery with associated decreased distal vascularity consistent with an acute thrombus.

17. Major Discrepancy 1
This finding was discovered by the on-call resident and neuroradiology fellow after the initial at the scanner resident review but before the preliminary report dictation. These CTA findings were confirmed on catheter angiography and the clot was retrieved in this case after 2 passes with a Solitaire retrievable stent system resulting in complete recanalization (TICI 3).

18. Major Discrepancy 2
Case read by the resident as negative at the scanner but then after review by the neuroradiology fellow a proximal M2 occlusion was found.

19. Major Discrepancy 2
This patient did not undergo any catheter angiogram but did receive IV TPA prior to the fellow reviewing the case. At the final read out, the attending agreed with the results of a proximal M2 occlusion.

20. Major Discrepancy 3
Initially read as negative by the resident and the fellow but the during attending read out the next day a small partially occluding thrombus of the proximal aspect of a left M2 branch was noted.

21. Major Discrepancy 3
This patient did not undergo a catheter angiogram or receive IV TPA but was managed medically by the neurology team.

22. Conclusion
Our data demonstrates that for detection of LVO, preliminary interpretation by an on-call radiology resident is timely and highly, though not perfectly, accurate.
When an LVO was detected by the radiology resident at the scanner, the attending agreed in all cases allowing the patient to subsequently undergo EVT as appropriate.
On the other hand, an M2 LVO was missed in 3 of 53 cases initially reported as negative. Another series also found that false negative interpretations of CTA are the most common cause of interrater discrepancies.12
Our process currently accounts for this small but important miss rate by a second rapid review of the CTA from a diagnostic neuroradiology fellow. Though this second review might occur as much as minutes later, it provides a safety check that limits the harm caused by a missed LVO.

23. Conclusion
Many hyperacute stroke CTAs outside of our institution will initially and ultimately be read by radiologists who have not undergone dedicated neuroradiology fellowships, including the vast majority of our residents.
Thus, giving radiology residents the initial responsibility of arriving at an accurate diagnosis is critical to maximize their training and the efficacy and safety of hyperacute stroke CTA interpretation for the patients that they will serve in the future.
Although not specifically evaluated in our analysis it has been shown before that as resident gains experience and completes more formal training the rate of errors and discrepancies will statistically decrease. 14,15

24. Conclusion
In this study major discrepancies occurred in patients with M2 branch occlusions.
The efficacy of endovascular thrombectomy for M2 occlusions also remains uncertain; thus, missing an M2 occlusion may not have a significant effect on clinical outcome in most cases.11  
Differentiation between occlusion and absence or hypoplasia of a variant M2 branch has previously been identified as a common pitfall in CTA intrepataion.13
The routine use of coronal and sagittal reformatted maximum intensity projections (MIP) can be helpful in identifying and accurately interpreting the CTA.
During the time period of this study MIPs were not available in the CT scanner control room but were available on the full PACS workstation in the reading room.
Identification of acute thrombus as evident by abrupt vessel cutoff is more clearly seen on several of the MIP images in our example cases.

25. Limitations
Limitations of this study include that it was obtained at a single institution and thus may not be generalizable to other hospitals with radiology residency programs.
In the routinely busy emergency department at our institution the radiology resident were asked to record their initial interpretation and communication to the stroke team on index cards.
Only a fraction of the residents filled out this index card; however, the EMR and radiology report provided sufficient redundancy to allow us to carry out this analysis.

26. Summary
Radiology residents can provide an accurate and fast interpretation of hyperacute stroke CTAs with regards to the presence or absence of LVOs, though will miss an LVO occasionally as is expected for a training program.
Rapid oversight of CTAs initially deemed to be negative by a neuroradiology fellow or radiology attending might help to mitigate this very small fraction of misses, but is not necessary when an LVO is initially identified.

27. References
1. Berkhemer O, Fransen P, Beumer D, et al. A Randomized Trial of Intraarterial Treatment for Acute Ischemic Stroke. New Engl J Med. 2014;372(1): doi: /NEJMoa
2. Campbell BCV, Mitchell PJ, Kleinig TJ, et al. Endovascular Therapy for Ischemic Stroke with Perfusion-Imaging Selection. N Engl J Med. 2015;372(11): doi: /NEJMoa
3. Goyal M, Demchuk AM, Menon BK, et al. Randomized assessment of rapid endovascular treatment of ischemic stroke. N Engl J Med. 2015;372(11): doi: /NEJMoa
4. Jovin TG, Chamorro A, Cobo E, et al. Thrombectomy within 8 Hours after Symptom Onset in Ischemic Stroke. N Engl J Med. 2015;372(24):1-11. doi: /NEJMoa
5. Saver JL, Goyal M, Bonafe A, et al. Stent-Retriever Thrombectomy after Intravenous t-PA vs. t-PA Alone in Stroke. N Engl J Med. 2015;372(24): doi: /NEJMoa
6. Powers WJ, Derdeyn CP, Biller J, et al AHA/ASA Focused Update of the 2013 Guidelines for the Early Management of Patients With Acute Ischemic Stroke Regarding Endovascular Treatment. Stroke. 2015:STR doi: /STR
7. Wildermuth S, Knauth M, Brandt T, Winter R, Sartor K, Hacke W. Role of CT Angiography in Patient Selection for Thrombolytic Therapy in Acute Hemispheric Stroke. Stroke. 1998;29(5): doi: /01.STR
8. Lev MH, Farkas J, Rodriguez VR, et al. CT angiography in the rapid triage of patients with hyperacute stroke to intraarterial thrombolysis: accuracy in the detection of large vessel thrombus. J Comput Assist Tomogr. 2001;25(4): doi: /

28. References
9. Josephson S a, Bryant SO, Mak HK, Johnston SC, Dillon WP, Smith WS. Evaluation of carotid stenosis using CT angiography in the initial evaluation of stroke and TIA. Neurology. 2004;63(3): doi: /01.WNL C. 10. Nguyen-Huynh MN, Wintermark M, English J, et al. How accurate is CT angiography in evaluating intracranial atherosclerotic disease? Stroke. 2008;39(4): doi: /STROKEAHA Goyal M, Menon BK, Zwam WH Van, et al. Endovascular thrombectomy after large-vessel ischaemic stroke : a meta-analysis of individual patient data from five randomised trials. 2016: doi: /S (16)00163-X. 12. Strub WM, Vagal AA, Tomsick T, Moulton JS. Overnight resident preliminary interpretations on CT Examinations: Should the process continue? Emerg Radiol. 2006;13(1): doi: /s Power S, McEvoy SH, Cunningham J, et al. Value of CT angiography in anterior circulation large vessel occlusive stroke: Imaging findings, pearls, and pitfalls. Eur J Radiol. 2014;84(7): doi: /j.ejrad Erly WK, Berger WG, Krupinski E, Seeger JF, Guisto JA. Radiology resident evaluation of head CT scan orders in the emergency department. Am J Neuroradiol. 2002;23(1): Cooper VF, Goodhartz LA, Nemcek AA, Ryu RK. Radiology Resident Interpretations of On-call Imaging Studies. The Incidence of Major Discrepancies. Acad Radiol. 2008;15(9): doi: /j.acra

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