Category: Radiology

Still Not Choosing Wisely in Trauma Imaging

We can all agree the advent of CT has improved our diagnostic capabilities, particularly in multi-system trauma.  Few would challenge an assumption that outcomes are positively impacted by timely, accurate identification of clinically important pathology.

Unfortunately, the pendulum has swung so far in favor of CT in trauma, any intelligent reliance on clinical exam skills has been deprecated to obsolete.  As such, the expected fallout includes increases in costs, radiation, and length-of-stay as the zero-miss culture creeps from multi-system trauma into the lightly injured.  This has become such an issue the American College of Surgeons devoted one of five slots in their first Choosing Wisely Guidelines to reducing the use of the trauma “pan-scan”.

Hopefully, the culture change will happen none-to-soon, as this NHAMCS data review indicates – showing steady increases in CT use for both head and body over the 2007 to 2010 review period.  Head CT increased from 9.6% to 11.6% of all injury-related encounters, while body CT increased from 5.5% to 8.1% – without any corresponding increase in positive findings.  Yield for severe injury dropped from 4.9% to 3.4% on Head CT, along with a drop for body CT from 6.4% to 3.3%.

This is the NHAMCS probabilistic sample, of course, and it’s simply a coarse observational cohort without detailed clinical factors.  However, I think the likelihood these observations accurately reflect reality is rather high.

Choose more wisely, please.

“Trends in Advanced Computed Tomography Use for Injured Patients in United States Emergency Departments: 2007–2010”
http://www.ncbi.nlm.nih.gov/pubmed/25996245

The Very Young Pediatric C-Spine Rarely Needs Radiologic Clearance

It is usually reasonable to exercise an abundance of caution with trauma patients suspected of having cervical spine injuries.  However, an abundance of caution sometimes means an abundance of radiation – and the costs and harms associated with such testing can be immense, regardless of technical difficulty in a young pediatric population.

This is a retrospective evaluation of 2,972 trauma patients aged less than 5 years, reviewing specifically the overall incidence of diagnosed cervical spine injury.  In this 12 year cohort, a grand total of 22 had confirmed CSI.  Most importantly, however, nearly all cases of CSI were associated with other serious injuries – a cohort with a median ISS of 33.  Twelve of 22 arrived intubated, 13 were in extremis, and overall mortality was 50%.  All evaluable patients had either neurologic deficits, severe neck pain, or were unable to range their neck.

These authors do not further describe their cohort for evaluation with regard to developing a predictive instrument for cervical spine injury, but these data do support a very reasonable conclusion regarding the rarity of pediatric injuries – and the near impossibility of isolated cervical spine injuries.  I tend to agree with the authors’ stated management strategy for such patients:

“Pediatric patients with abnormal neurologic examination result, decreased mental status, neck pain, or torticollis are evaluated with cervical spine CT; however if the child is asymptomatic defined by a normal neurologic examination result, appropriate mental status, with absence of neck pain or torticollis, our first step is to remove the cervical collar. We examine the patient for cervical tenderness if they are able to communicate and observe the child for normal range of motion of the neck. In preverbal patients, we simply observe neck range of motion with the collar removed. If the child seems to move his or her neck without discomfort and full range of motion, then we do not pursue any further radiologic evaluation.”

“Absence of clinical findings reliably excludes unstable cervical spine injuries in children 5 years or younger”
http://www.ncbi.nlm.nih.gov/pubmed/25909413

Back to IMS-III: It’s the Collaterals

The year 2012 was dark times for endovascular treatment for acute ischemic stroke.  MR-RESCUE, IMS-3, and SYNTHESIS were all decidedly negative, and their failures trotted out in the New England Journal of Medicine.

This current year has been much better – a trove of trials following the initial positive result of MR-CLEAN, the key features of which were:

  • Improved time from onset to endovascular intervention.
  • Effective recanalization, far exceeding that of tPA.
  • Narrowly selected patients guided by imaging criteria.

Of those three key features, it appears the universally critical items are primarily the last two – recanalization and salvageable tissue.

This is a reanalysis of IMS-3, looking retrospectively at 78 patients from the trial for whom cerebral angiograms were available.  They looked specifically a the “capillary index score”, essentially, an imaging-based classification of the collateral circulation near a lesion.  In an outcomes-blinded fashion, the authors calculated the CIS for each, and then correlated the results with functional outcomes.  The numbers are small, but the numbers achieving good outcomes are consistent and logical:

  • Poor CIS, unsuccessful recanalization: 1/15 (7%)
  • Poor CIS, successful recanalization: 2/15 (13%)
  • Good CIS, unsuccessful recanalization: 5/24 (25%)
  • Good CIS, successful recanalization: 17/24 (71%)

Essentially another brick in the small wall of evidence favoring the necessity of an imaging-based strategy to narrowly select patients for endovascular intervention, rather than a non-selected time-based strategy.

“Relative Influence of Capillary Index Score, Revascularization, and Time on Stroke Outcomes From the Interventional Management of Stroke III Trial”
http://www.ncbi.nlm.nih.gov/pubmed/25953374

Using CTA to Predict tPA Failures

tPA, the “proven” therapy foisted inappropriately on Emergency Medicine and our patients, doesn’t work.

Rather – as I’ve said before – it simply doesn’t work the way we’ve been taught.

The core concepts of the theoretical utility of tPA for ischemic stroke are demonstrated nicely in the new endovascular trials.  Patients do well, better than the natural course of their disease if:

  • There is significant viable brain distal to the vascular occlusion as a result of collateral circulation.
  • The vessel is rapidly and reliably opened.

Both these criteria were met in the new endovascular trials, requiring imaging evidence of a small infarct core and use of modern retrieval devices.  However, the broad population being pushed as candidates for tPA are not as fortunate – the key feature being the abysmal recanalization rate of tPA, only 46% in a meta-analysis of tiny case series from mostly the ‘90s.  Comparatively, in the same report, early spontaneous recanalization was present in 24%.  So, obviously, there’s only even a 1 in 5 chance a patient will receive an additive benefit from tPA for recanalization – which, with some heterogeneity, means our NNT has a maximum upper bound if we treat an unselected population of all-comers.

This study is a small case series from the ongoing PRove-IT study, looking specifically at, essentially, the permeability of intracranial thrombi.  These authors hypothesized this might be an important predictor of recanalization because, after all, if there’s no flow through an impermeable occlusion, tPA can never fully contact the substrate of interest.  These authors used CT angiography to estimate occult anterograde flow versus retrograde flow, and followed-up recanalization following tPA.

There are only 66 patients in this small observational study, but the results are rather compelling.  They estimated 17 (25.8%) of patients had some minimal anterograde flow through the occluded vessel.  These patients, with some detectable flow, had a 66.7% recanalization rate.  Conversely, the 49 patients without any residual anterograde flow had a recanalization rate of only 29.7% – a rate not dissimilar to spontaneous.  And, outcomes followed recanalization – logically, considering detectable anterograde flow and effective destruction of the occlusion are highly favorable features.

The moral of the story?  It’s quite clear there are promising venues for determining which patients have the best chance to benefit from tPA – and those for whom the harms exceed those chances.  The perpetual “tPA for all!” call being added to guidelines and quality measures is a product of conflict-of-interest and corporate sponsorship, not good medicine – and we can do better, if we simply cared to investigate.

“Occult Anterograde Flow Is an Under-Recognized But Crucial Predictor of Early Recanalization With Intravenous Tissue-Type Plasminogen Activator”
http://www.ncbi.nlm.nih.gov/pubmed/25700286

The Case of the Bloody Lumbar Punctures

Modern evaluation for aneurysmal subarachnoid hermorrhage, with some debate, may include definitive non-contrast CT performed within six hours of symptom onset.  The traditional evaluation, and still recommended beyond six hours, involves a lumbar puncture, looking for red blood cells or xanthrochromia.

This latest tale of woe from Jeff Perry’s SAH data details the pragmatic effectiveness of the traditional pathway, focusing on the primary confounder: traumatic taps.  They report on 1,739 patients undergoing lumbar puncture as part of this evaluation, and, unfortunately, the numbers are grim:  641 (36.8%) samples were abnormal in the final tube of CSF collected.  However, it isn’t so bad – 476 of those had fewer than 100 RBCs x 10^6/L, with many having only a handful of cells.  But, still, that leaves 165 patients with fairly substantial numbers of RBCs in their CSF.

Because, all told, only 15 received a final diagnosis of aneurysmal SAH.

Why is this so grim?  Because 419 of these 626 patients with RBCs on their LP subsequently were subjected to angiography – with 404 of them negative.

And xanthrochromia?  Some predictive value – 7 of 15 patients diagnosed with SAH displayed xanthrochromia, but, obviously there were 8 patients with SAH who did not, along with 16 instances of xanthrochromia in patients without SAH.

The final gist of the paper is to generate a 100% sensitive cut-off to exclude SAH – for which the authors choose 2000 x 10^6 and absent xanthrochromia.  This results in a specificity of 91.2% and a positive LR or 11.4.  This is a pretty good positive LR, but, unfortunately, given such a vanishingly rare disease, the PPV was only 21.4% in their cohort.

However, one major flaw in this study is it doesn’t usefully describe the population of true interest to Emergency Physicians – the test characteristics of those with a negative CT and a positive LP.  There were 77 patients who did not undergo CT prior to LP, but, more importantly, 10 of the patients included in this cohort had visible SAH on CT recognized by the staff radiologist, but not the Emergency Physician.  Therefore, if you practice in a setting without neuroradiology coverage, this is generalizable.  Otherwise, we can exclude those 10 cases and boggle at the massive resource utilization in terms of LPs and angiography in order to pick up just 5 cases of occult aneurysmal SAH.

In patient-oriented terms – based on these data – the risk of SAH after a negative CT performed greater than 6 hours after onset is about 1 in 330.  Using their cut-off of 2000 x10^6, the chance of a true positive LP is about 1 in 12.  A vast improvement, to be sure, but probably still not a pathway very many patients are going to choose when presented with these odds.

“Differentiation between traumatic tap and aneurysmal subarachnoid hemorrhage: prospective cohort study”
http://www.ncbi.nlm.nih.gov/pubmed/25694274 (free fulltext)

FFR(CT) Is Back! And Better Than Ever!

Invasive coronary angiography is problematic – specifically, it’s invasive.  Radial artery approaches have reduced the incidence of bleeding complications, but it remains a costly and non-risk-free procedure.  In lieu of ICA, CT coronary angiography has become increasingly popular.  However, CCTA is problematic – specifically, it’s inaccurate.

A few years ago, DeFACTO was published in JAMA and covered on this blog, a study evaluating a non-invasive model of fractional flow reserve added on to CCTA in an attempt to improve accuracy at identifying true culprit lesions.  DeFACTO was negative – specifically, the per-vessel performance at predicting flow-limiting lesions compared to the traditional 50% stenosis cut-off of CCTA was nearly identical.

Two years have passed, however, and we have a new study – NXT – using the next iteration of the HeartFlow software, and, of course, performed by authors with robust conflicts-of-interest.  Now, improvements in image quality and luminal modeling – as well as refined exclusion criteria to prevent troublesome images confounding their software – have improved performance to the point where, yes, it now seems to out-perform baseline CCTA.

The catch, of course, is the CCTA criterion standard is abysmal.  Compared with the ACRIN-PA or ROMICAT studies with their pro-CCTA COI, in which CCTA is the best thing since sliced bread, these folks are unconcerned with the collateral damage of degrading CCTA.  In this study, as performed on patients with suspected CAD, of 237 vessels read as “positive” by CCTA (>50% stenosis), only 83 (35.0%) were actually judged to be flow-limiting lesions on ICA – which is to say, false positives doubled the true positives.  Likewise – in contrast to the ROMICAT and ACRIN studies purveying CCTA as a bulletproof mechanism for discharge – 17 of 247 (6.8%) patients read as negative by CCTA (<50% stenosis) actually had flow-limiting disease.

False positives more two-thirds of the time?  And then a 7% miss rate of clinically important stenosis?  Basic, anatomic CCTA as previously described – not as fantastic as you’ve been led to believe.

The HeartFlow software?  Perhaps.  Effectiveness evaluations absent pervasive COI will be necessary to truly describe its value.

“Diagnostic Performance of Noninvasive Fractional Flow Reserve Derived From Coronary Computed Tomography Angiography in Suspected Coronary Artery Disease”
http://www.ncbi.nlm.nih.gov/pubmed/24486266

The Trauma Pan-Scan Saves Lives

… and redeems them for valuable prizes.

Such is the message of this systematic review and meta-analysis, evaluating the published literature comparing “whole body CT”, arbitrary complete scanning, with “selective imaging”, scanning as indicated by physical examination.

Identifying seven studies, comprising 23,172 patients, these authors found a 20% reduction in mortality – 20.3% versus 16.9% – associated with the use of WBCT, despite a higher mean Injury Severity Score in the WBCT cohort.  The implication: choosing a selective scanning strategy was harmful, even in the face of a less-injured cohort.  Thus, the authors conclude the mortality advantage far exceeds any risks from radiation, and WBCT should be considered the standard method of evaluation.

Except, all but 2,610 of the patients in these pooled studies are from retrospective cohorts fraught with selection bias.  There are many reasons why trauma patients with lower ISS might yet have higher mortality, and otherwise aggressive diagnostic evaluation not indicated.  And, when those retrospective patients are tossed out, the comparison is a wash in the prospectively studied cohort.

If you’re a fan of selective imaging, this study probably changes little in your mind.  If you’re a fan of WBCT, it’s another citation to add to your quiver.  The authors of this study are hoping REACT-2 gives us the definitive answer – but with only 1,000 patients, I doubt that will be the case, either.

“Whole-body computed tomographic scanning leads to better survival as opposed to selective scanning in trauma patients: A systematic review and meta-analysis”
http://www.ncbi.nlm.nih.gov/pubmed/25250591

More CT Coronary Angiography Dreaming

CT coronary angiography has been touted as a lovely test for the acute setting – a relatively fast, non-invasive method of obtaining information on the coronary vasculature with reasonable-sounding diagnostic characteristics.  However – despite what these authors seem to be trying to convey – it’s simply a test, not a protective intervention.

This is a prospective longitudinal cohort study of 585 individuals at a single institution undergoing CT coronary angiography for suspected ischemic chest pain.  Patients with negative troponins were enrolled during weekday, daytime hours, had TIMI 0-4 (mostly 0-2), and absent the usual contraindications to CTCA.  Patients were followed for nearly two years – and, of 506 patients with zero or insubstantial plaque seen on CTCA, all were still alive, and none had suffered an acute coronary syndrome.  Thus, the fantastic protective effect of a negative CTCA.

The only issue – all those patients would have achieved such event-free survival whether they underwent CTCA or not.

Of the 79 admitted for invasive angiography with severe stenosis, only 34 received PCI or CABG, and 10 were found to have less than 40% stenosis.  So – ultimately – 585 CTCAs to identify the 6% of patients who may potentially have benefited, harming just as many with invasive procedures and the remainder with radiation.  There is a reasonable, ultimate question regarding whether those with negative evaluations are obviated from additional chest pain work-up over the long run – but that has yet to be demonstrated in practice, and the costs associated with the initial false positives subtract from those future potential savings.

Rather than demonstrate the utility of CTCA in the Emergency Department, these authors better demonstrate the unfortunate characteristics of its overuse.

“Long-term Outcome after CT angiography in Patients with Possible acute coronary syndrome”
http://www.ncbi.nlm.nih.gov/pubmed/24738614

ED Hocus POCUS … or Just a Hoax?

A guest post by Rory Spiegel (@EMNerd_) who blogs on nihilism and the art of doing nothing at emnerd.com.

A landmark paper recently published in Lancet Respiratory Medicine is certainly destined to send the ED Ultrasound world into a tizzy. This is the first RCT examining the utility of Emergency Department based Point of Care ultrasound (POCUS) for patients presenting with undifferentiated respiratory complaints. Authors randomized patients presenting to the ED with signs or symptoms concerning for a respiratory etiology to either a standard work up as determined by the treating physician or the addition of POCUS performed by a single experienced operator. The US protocol consisted of sonographic examination of the heart, lungs and lower extremity deep veins to identify possible causes of patients’ symptoms. The authors’ primary outcome was the percentage of patients with a correct presumptive diagnosis 4 hours after presentation to the Emergency Department as determined by two physicians blinded to ED POCUS findings, but with access to the records of the entire hospital stay.

Using this POCUS protocol the authors found stunning success in their primary endpoint. Specifically, the rate of correct diagnoses made at 4-hours in the POCUS group was 88% compared to 63.7% in the standard work up group. Furthermore 78% of the patients in the POCUS group received “appropriate” treatment in the Emergency Department compared to 56.7% in the standard work up group.

Though promising, these benefits did not translate into improvements in true patient oriented benefits. Though not statistically significant, the observed in-hospital and 30-day mortality trended towards harm in the POCUS arm ( 8.2% vs 5.1% and 12% vs 7% respectively). Nor was there any meaningful difference in length of stay or hospital-free days between those in the POCUS group and those in the control group. Even more concerning, was the significant increase in downstream testing that occurred in patients randomized to the POCUS group. Specifically the amount of chest CTs (8.2% vs 1.9%), echocardiograms (10.1% vs 3.8%) and diagnostic thoracocenthesis (5.7% vs 0%). This, of course, may be statistical whimsy, but these findings are concerning for a certain degree of overdiagnosis. Unless detected pathology results in improved patient outcomes secondary to treatment, are we truly helping, or just piling on potential costs of increased vigilance?

I’m sure we all have experienced firsthand the utility of bedside US and this is by no means a call to abandon our probes, but rather an acknowledgement of the possibility of subtle harms. We must keep in mind, all testing comes at a price no matter how non-invasive and radiation-free it appears. The cost in this case is information and how we choose to act on it. This would certainly not be the first time increased access to medical technology has lead to such unintended consequences.

“Point-of-Care Ultrasonography in Patients Admitted With Respiratory Symptoms: a Single-Blind, Randomised Controlled Trial”
http://www.ncbi.nlm.nih.gov/pubmed/24998674

Stroke MRI in 6-Minutes or Your Money Back

Despite the advances of modern medicine, the non-contrast CT of the brain is a crude tool.  It is especially poor in the setting of acute stroke – infrequently providing helpful diagnostic information, while serving primarily to rule out intracranial hemorrhage.

These authors, however, offer us a glimpse of the MRI of the future – a useful diagnostic test without long delays of image acquisition time.  These authors report on a single-center, convenience sample of patients with acute neurologic deficits who were able to undergo MRI.  They use a 3.0T MRI to acquire DWI, FLAIR, GRE, perfusion, and MRA sequences using a 6-minute protocol on 62 patients, and two radiologists rated image quality as moderate or good 94% or greater for each modality.

The authors also provide two sample cases, one of which being an acutely altered, profoundly disabled patient within the 3-hour window for tPA.  The 6-minute MRI, however, showed heterogeneous perfusion abnormalities more suggestive of seizure, rather than stroke.  After treatment with anti-eplipetics, the patient made a full neurologic recovery.

This series is small enough it’s clearly just a technology pilot.  Additional study regarding diagnostic accuracy and feasbility in the acute setting is necessary, but it would certainly be a vast improvement over the current state of the art.  Considering the present rush to judgement for tPA and the likelihood of overtreatment of stroke mimics, a diagnostic modality that adds to clinical assessment is sorely needed.a

“Six-Minute Magnetic Resonance Imaging Protocol for Evaluation of Acute Ischemic Stroke: Pushing the Boundaries”
http://www.ncbi.nlm.nih.gov/pubmed/24916906