Blunt Carotid Injury- CT Angiography is Adequate For Screening Kelly Knudson, M.D. UCHSC April 3, 2006
CT Angiography vs Digital Subtraction Angiography Blunt carotid injury screening is one of the very few ways we can PREVENT poor neurologic outcomes in trauma patients. Conventional angiography is the gold standard, but new multi-slice CT angiography is adequate and provides faster, safer results.
Why does this matter? Blunt cerebrovascular injury screening is a way to prevent ischemic neurologic events. In 2005 DHMC published the following data on BCVI 15, 767 Blunt Trauma Patients 727 patients met screening criteria 15,040 patients not screened 21 patients with s/s of neurologic Ischemia on presentation 244 BCVI identified on screening (34%) 187 patients anticoagulated 48 not anticoagulated
Anti-thrombotic thrombotic therapy prevents strokes in asymptomatic BCVI patients
BCVI Related Morbidity and Mortality
Screening Modalities Digital Subtraction Angiography Gold standard Expensive Invasive Difficult to get at 3 a.m. MRA Published results no better than CTA Difficulty accommodating multi-trauma trauma patients Expensive and difficult to get at 3 a.m. U/S Can t t visualize injuries in the bony canal and the vertebral arteries
CT Angiography
Multi-Slice Technology Allows for more images to be taken at the exact same moment and reduces motion artifact; preserving anatomic relationships of close structures. Less dilution of contrast bolus as images are acquired more quickly allows for the arch to the vertex to be imaged in the arterial phase. Acquired slice thickness is narrowed. Newer hardware, software and PACS systems provide better reconstructions and allow for scrolling through images on a monitor.
The Fine Print Cothren, Biffl,, et al (DHMC studies) Single slice GE Hilite with images from C-3 C 3 to the sella turcica reconstructed to 1mm and reviewed on film. Miller (Memphis) Siemens Somatom 4 (slices) with images from aortic arch to skull base. 3 mm axial slices reconstructed to 1 mm, with every 3 rd image printed and reviewed on film. Berne (East Texas) GE Lightspeed 4 and 16 imaged from arch to clinoids with reconstruction down to 0.63mm and reviewed on a PACS system. Bub (Seattle) GE single, 4 and 8 slice with reconstruction down to 0.6 mm and reviewed on PACS.
BCVI Screening with Multi-Slice CT Berne et al J Trauma 2004;57:11-18 No Patients who had a negative CTA went on to develop clinical signs or symptoms of BCVI.
16 Slice Multi-detector In 2002 when the 16 slice scanner was introduced the overall incidence of BCVI increased from 0.38% to 1.05% and the incidence in screened pts increased from 2.8% to 6.9% Specificity also averaged 99% and PPV increased to 83% (only 2 False +)
Retrospective Comparison of CTA to Angiography 32 patients identified who had undergone CTA and 4 vessel angio for blunt trauma. 8,057 admits, 178 CTAs,, 106 DSA for BCVI 37 both CTA and DSA, 5 more than a week apart 30 additional normal CTAs interspersed Blinded neuroradiologist (2) and 3 rd reviewed studies. yr res rd yr Sensitivity and specificity determined using DSA as gold standard Studies were graded for Technical quality - 1 (excellent) 5 (poor) Injury probability 1 (normal) 5 (definite injury) DSA consensus interpretation was 3 (equivocal) or higher by 2 radiologists Injury type (Biffl( scale) and location
CTA Technical Quality and Inter-observer variability Mean quality rating 2.2 (very good/good) Single detector quality 3.4 (good/fair) 4 slice detector 2.2 (very good/good) 8 slice detector 1.4 (excellent/very good) Inter-observer variability Pairwise agreement on DSA 81% (43/53) κ= = 0.54 indicating moderate agreement Pairwise agreement on CTA 89% (54/64) κ= = 0.7 indicating substantial agreement
Mean Sensitivity 88% and Specificity 94% If the positive CTA threshold is lowered to an injury probability of 2/5 (abnormal but probably no injury) then sensitivity increases to 92% for all readers on carotids. Because of the low number of vertebral injuries determining accuracy is limited
Missed Injuries 10 out of 10 patients with carotid injuries were correctly diagnosed. The 2 missed carotid injuries were in patients with bilateral injuries where the other side was correctly identified. One contralateral missed injury in a 22 month old with limited quality CTA- injury was described as equivocal on DSA Other missed injury was a grade 2 dissection missed by 2/3 reviewers 1 vertebral artery injury was missed by all reviewers because it was more proximal than the most proximal CT slice All 3 readers missed a grade 1 vert injury categorized as an equivocal (3/5) by DSA consensus. 2/3 CTA readers called it a 2/5.
Advantages of CTA CTA provides faster diagnosis of injuries allowing for early treatment to prevent stroke. 44% of patients in DHMC study became symptomatic 18 or more hours after admission. Krajewski reports 58% of patients develop symptoms 10 hours after admission. Rogers reports time to diagnosis decreased from 156 hours to 6 hours using CTA instead of angiography. CTA can be performed at the same time as the rest of the trauma workup with minimal additional time and no additional contrast bolus on new machines. CTA is more cost effective- the patient is already there and CT costs are 1/3 or less the costs of angio.
Advantages of CTA CTA is safer than angiography 1.3% of all cerebral angiograms suffer neurologic complications; 0.5% of these are permanent. Additional risks of hematoma, pseudoaneurysm,, AV fistula formation, contrast nephropathy Inherent risks of being out of ICU with critically ill trauma patients (complication rate of transport out of ICU 5.5-6.3%)
In Summary (The Clichés s Apply) You get what you pay for. CTA performed on newer generation scanners provide adequate imaging of the cerebral vessels to screen for blunt carotid injury. Speed is of the essence. CTA is more expeditious, allowing for treatment to prevent progression of BCVI to stroke and neurologic deficit First do no harm. CTA is safer because it s s an non-invasive procedure that is likely going to be performed anyway and does not require additional contrast, road trips, or new holes in the patient.
In Reality At DHMC 4 vessel angio is available most of the time and the CT scanners are not the newest generation of scanners. Level one status patients are more likely to have suffered a severe enough trauma to sustain a BCVI. Until a RTC comparing newer generation scanners to 4 vessel angio is available these patients should likely continue to undergo 4 vessel screening. In smaller hospitals with less trauma and limited access to IR, (and newer scanners) CTA is a safe and effective screening modality for blunt cerebrovascular injury. Screening should not be delayed if CTA is the only feasible modality, as prompt anticoagulation is critical to preventing stroke and permanent neurologic deficit. As CT technology continues to develop and radiologists become more familiar with the technology this question will likely be completely resolved and CTA will be proven as the modality of choice.