Category: Radiology

Is the 6-Hour CT for SAH Debate Over?

There has been a fair bit of back and forth about the validity of early CT in the setting of “thunderclap headache” to obviate a lumbar puncture in the search for aneurysmal subarachnoid hemorrhage.  David Newman and Kevin Klauer debated this subject a few years ago – and that was in all-comers, not simply those in the few hours following onset.

This most recent meta-analysis and systematic review gathers together all the published literature regarding early CT and the incidence of SAH on follow-up.  Including 8,907 patients from five publications, based on a few assumptions from retrospective studies, there were up to 13 missed cases of aneurysmal SAH occurring despite a negative CT within 6 hours of onset.  Worst-case sensitivity based on these data, then, was 0.987 (95% CI 0.971-0.994).

The prevalence of SAH in patients presenting with true thunderclap headache is estimated at ~10%.  The post-test odds, then, after a negative CT, are on the order of 0.1% – in line with David Newman’s posit of requiring 1000 LPs to catch one missed SAH.  The problem, then, lies in taking the next step in Bayesian reasoning – how likely is the positive LP to be true SAH?  If prevalence has dropped to 1 in 1000 after a negative CT, and the specificity of LP for SAH is only 65%, even a positive result barely budges the likelihood of disease.

How do you consent a patient for an invasive procedure in a setting in which a positive result has only the tiniest fraction of a chance of being real – and the treatments based on findings of follow-up examinations may be more likely to harm the patient than the magnitude of benefit associated with detection of a true positive?

“Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis”
http://stroke.ahajournals.org/content/early/2016/01/21/STROKEAHA.115.011386.abstract

Radiation Therapy for the Common Cold

We overuse computed tomography for many things – popular topics in the literature (and on this blog) are mostly minor head injury, renal colic, and CT pulmonary angiograms.  But, it is not simply these modalities that have increased in the preceding decades, as this research letter shows.  CT use has also increased for such apparently benign conditions as non-acute upper respiratory symptoms.

This is a National Hospital Ambulatory Medical Care Survey analysis, with all the sampling limitations inherent to such a data source, evaluating CT usage for upper and lower respiratory complaints between 2001 and 2010.  CT usage in 2001 for such complaints ranged from a 0.5% of visits for non-acute URI, to 3.1% of visits for acute LRTI symptoms.  In 2010, such usage ranged from 3.6% to 12.1%.  Despite all this added cost and extensive evaluation, management of these patients remained unchanged: both antibiotic use and admission rates were steady.

The NHAMCS is an imprecise tool to full discern the reasons for visit on a granular level, but the relative increase in advanced imaging is consistent with increases in CT usage for other indications.  Obviously, the radiation itself has no known therapeutic potential – so, therefore, the clear conclusion is simply the unfortunate presence of additional low-value care.

“Use of Computed Tomography in Emergency Departments in the United States: A Decade of Coughs and Colds”
http://www.ncbi.nlm.nih.gov/pubmed/26720289

Welcome to Yesterday, Have You Heard of PERC?

I usually like these sorts of articles regarding the yield and utilization of CT pulmonary angiograms.  They’re fun to dissect, useful to marvel at the inefficiency of our usage, and finally to feed my editorial hyperbole.  But, not this time.

This is a retrospective study from the University of Michigan comprising six months of CTPA data from 2013.  These authors reviewed charts on 602 consecutive patients and calculated modified Wells and PERC for each, and describe the appropriateness and yields of various cohorts.

Rather than detail these statistics and outcomes – other than to note their overall yield of 61 positives reported out of 602 scans – I’d rather just focus on the 108 patients scanned who were PERC negative.  PERC has been around since 2004, and it’s been percolating into various guidelines and evidence-based algorithms since.  Hello, it’s 2015: why are almost 20% of CTs at an academic medical center PERC-negative?

The authors state two PERC-negative patients had positive CT findings; given the pretest probability, I wouldn’t be surprised if one or both were ultimately false-positives.  Come on, man.

“CT Pulmonary Angiography: Using Decision Rules in the Emergency Department”
http://www.ncbi.nlm.nih.gov/pubmed/26435116

Hunting for Strokes in Vertigo

The vast majority of presentations for “dizziness” in the Emergency Department are benign diagnoses – various dysequilibrium syndromes, vestibulitis, neuritis, and other disorders of the otologic canalicular system.  But, then, some are strokes – and it’s quite challenging to balance diagnostic accuracy and MRI utilization.

This is an observational study performed at the University of Michigan evaluating patients presenting with complaint and exam findings consistent with acute dizziness – requiring either nystagmus or demonstrated gait instability.  Of these patients, all underwent a standardized neurologic examination, including HINTS examination, and subsequent MRI.  A stroke was the presumed diagnosis if an MRI was performed within 14 days and diagnostic of hemorrhage or acute infarction.

There were 320 patients enrolled, and 272 completed the clinical evaluation and an MRI.  Overall, 29 (10.7%) of patients had positive imaging – and, unfortunately, little was strongly predictive.  The few predictive features that shook out of their logistic regression model were the ABCD2 score, a positive HINTS exam, a central pattern to nystagmus, or the presence of other neurologic deficits.  Those individuals hitting all the risk factors ended up with ~20% risk of stroke, while those with none were <5%.  The remaining patients were simply in the intermediate risk group, reflecting the overall baseline level, and approximately one-third of the cohort fell into each category.

I do like their objective criteria for enrollment, based on a minimum of nystagmus or gait abnormality.  I tend to feel many patients receive MRI for similar complaints absent any of these features.  There is, unfortunately, no accounting of any general background rate of diagnosis of posterior circulation stroke at their institution, so there’s no way to estimate the miss rate or added value of their inclusion criteria.  I think their general observations are fair starting points for shared decision-making, although there’s still not quite enough information here to dramatically improve imaging yield.

“Stroke risk stratification in acute dizziness presentations: A prospective imaging-based study”
http://www.ncbi.nlm.nih.gov/pubmed/26511453

A Very Odd Look at CT In the ED

Why do we perform CTs in the Emergency Department?  It’s fair to say the primary indication is diagnostic certainty: the ruling-in or ruling-out of a disease process of substantial clinical relevance.  However, this study begs the question: have we lost touch with this concept of “substantial clinical relevance”?

This is a qualitative study evaluating physician decision-making in the context of CT ordering.  These authors provided physicians, approximately 2/3rds attending physicians, a questionnaire pre- and post-CT for 1,280 patients in the Emergency Department.  The main gist: what are you worried about?  How confident are you in the diagnosis?  And, then, after CT, how about now?

The bullet-point summary:

  • Physician confidence in their diagnosis grew after CT.  Splendid.
  • CT excluded or confirmed alternative diagnoses in 95+% of cases.  Excellent.
  • Increasing pre-CT confidence in a leading diagnosis was associated with lesser changes in leading diagnosis post-CT.  OK.
  • Many pre-CT leading diagnoses were benign, but with low physician confidence.  Except for CT head.
  • Nearly 3/4ths of CT scans performed of the head had a leading diagnosis of “Benign headache” or other, had no change in diagnosis following CT, and confidence was generally pretty high.  This is awful.
  • Finally, if you were hoping a CT would prevent bouncebacks: no.  15% of abdominal pain returned within a month for related reasons, as well as 14% of chest pain/dyspnea, and 11% of headache.

CT is an important tool.  It certainly makes the life of the risk-averse physician much, much easier.  However, the instances in which CT identified an important diagnosis in this study are certainly in the minority – most final diagnoses were either benign or could have been achieved through other means.  Unfortunately, very few specific actionable items can be taken away from this study – excepting CT for headache (ugh) – but it certainly shows there is fertile ground for a culture change to take root and decrease low-yield CT utilization.

“CT in the emergency Department: A Real-Time Study of Changes in Physician Decision Making”
http://www.ncbi.nlm.nih.gov/pubmed/26402399

The “Routine” Chest X-Ray

Many presenting complaints in the Emergency Department call for cardiothoracic imaging.  Some can be assessed by point-of-care ultrasound, but, for the most part, plain radiography is the established routine.  Whether the pretest probability of disease warrants such widespread use is one matter.  This article documents yet another – duplication of imaging.

These authors review four years of radiology from their institution and document 3,627 patients for whom both CXR and chest CT were ordered.  Their main analysis breaks down the use of radiology mostly looking at the order of which these studies were requested, and whether results from one were available prior to the completion of the other.

For the most part, the CXR was ordered first, and the images were available for review before the subsequent CT chest.  However, in 354 (9.8%) cases, the CXR images hadn’t even yet been acquired when the CT chest was ordered.  This probably generally overlaps the 134 (3.7%) cases where the CT chest was ordered simultaneously or prior to the CXR.  Regardless – if the results were clinically irrelevant, why order the test?

I think it’s fair to say many of the CXRs included in this study were pointlessly redundant – especially when the decision for CT was obviously made prior to their acquisition.  No doubt the CXR is included in most ED protocols for certain chief complaints, and is ordered reflexively without thought.

Looking for waste to target in the system?  Here you go.

“Inefficient Resource Use for Patients Who Receive Both a Chest Radiograph and Chest CT in a Single Emergency Department Visit”
http://www.ncbi.nlm.nih.gov/pubmed/26387774

The Battle for Age-Adjusted D-Dimer

Around these parts, we are fans of the age-adjusted D-dimer.  Jeff Kline proposes their use in his algorithm for the diagnosis of PE.  We embed decision-support in our EHR to encourage their use.  But, this new review from Annals of Emergency Medicine describes its test characteristics in the Kaiser Permanente population – and reports the age-adjusted D-dimer is not infallible.

These authors look retrospectively at 31,094 patients over 50, with a chest- or respiratory-related complaint, for whom a D-dimer was ordered.  14,434 of these patients had a D-dimer above the “customary” level of 500 ng/dL, and clinicians ordered 12,486 imaging studies to evaluate for PE.  Of these, 507 were diagnosed with PE.  This gives a 4.1% yield for CTPA – which, frankly, is disturbingly low – but another topic for another day.

The 500 ng/dL threshold was sensitive for 497 of the 507, while using an age-adjusted D-dimer would have reduced sensitivity to 471 of the 507.  Thus, using an age-adjusted D-dimer in this retrospective cohort may potentially have introduced an additional 26 missed PEs.  The savings, however, amount to 2,924 fewer CTPAs – or, roughly, 100 CTs per missed PE.

The contemporaneous Twitter response:

@EBMgoneWILD @ZackRepEM So age-adjusted D-dimer is dead? 26 misses to save $290K in costs = dead.

— Robert McNamara (@RobertMcNamar12) September 4, 2015

I don’t think so – but questions abound, many of which need be directly addressed by our specialty.  What is an acceptable miss rate for pulmonary embolism?  What is an acceptable miss rate of the pulmonary emboli in this age-adjusted range, just above our prior test threshold?  Does the net harm reduction from reduced testing outweigh the harms of missing those PEs?  Do those PEs convey the same level of morbidity or mortality if the diagnosis is missed or delayed?  How does the radiologic false-positive rate trend for PEs whose D-dimers are just over the test threshold?  And, finally – the age-adjusted D-dimer is not a static construct – would other age-adjustment formulas strike a better balance between sensitivity and specificity?

When all the questions are posed, I believe the summative value shows it reduces physiologic harms from testing, harms from healthcare costs, and harms from false-positives.  But, like everything we do, the age-adjusted D-dimer is still deserving of continued questioning and refinement.

“An Age-Adjusted D-dimer Threshold for Emergency Department Patients With Suspected Pulmonary Embolus: Accuracy and Clinical Implications.”
http://www.ncbi.nlm.nih.gov/pubmed/26320520

Soothing Songs and the CT Scanner

Yes, this is a trial of music therapy.  In the Emergency Department.  What fun!

This is a convenience sample of 62 children up to three years of age being referred for head CT after minor trauma, randomized to either soothing music or none.  Children were assessed for calmness by a visual analog scale of anxiety and a Modified Ramsay Sedation Scale before transport to CT.  Then, music was either present or absent while the child was being positioned on the scanner.  A second assessment of anxiety was then performed prior to CT.

The good news, as reported by the authors:

In conclusion, measured on a VAS, there was a significant decrease in agitation in children undergoing a head CT when children’s songs with integrated heart beat sounds were played before and during the procedure.

Unfortunately for their comparison, the control group was quite calm to start – with little room to improve – while the experimental group was fussier at baseline.  And, even though the CT introduced some agitation into the control group, nearly identical numbers of patients in each group successfully completed their imaging.  So, even though I think their intervention has value, the reliability of their conclusion is probably threatened by the chance baseline differences between groups.

But, it otherwise makes sense – and, it’s harmless, zero-cost intervention – so, why not?

“Randomized single-blinded clinical trial on effects of nursery songs for infants and young children’s anxiety before and during head computed tomography”
http://www.ncbi.nlm.nih.gov/pubmed/26314215

Your CTPA is Lies

There are a few moments you pat yourself on the back in Emergency Medicine.  The good save.  Shared decision-making that goes well.  And, the small victory when you’ve utilized an evidence-based pathway for pulmonary embolism, and received positive results for the leviathan of over-utilization and over-diagnosis: the CT pulmonary angiogram.

Well, it’s time to deduct about 1.25 fingers from that pat on the back you give yourself, because, unfortunately, radiology PE overcalls may be more rampant than initially thought.

This is a retrospective, single-center study reviewing a year’s worth of CTPA for pulmonary embolism, a total of 937 studies.  Of the studies included, 174 (18.6%) were initially read as positive.  Then, each positive study was reviewed by a panel of three, specially trained chest radiologists, with their consensus read used as the gold standard for diagnosis.  And so: 45 (25.9%) were subsequently judged to be incorrectly read by the original radiologist – a quarter of positive studies! – with those patients almost certainly consigned to at least short-term anticoagulation as a result.

In a light moment in the discussion, the authors helpfully contribute the following commentary:

Furthermore, many pulmonary CTA examinations in our institution are ordered by the emergency department before assessment by the admitting medical team.

My heart goes out to the poor Scottish EM physicians, for whom their radiology colleagues apparently have quite the low opinion for appropriate testing.  However, the authors’ attention may be better spent further discussing their own false-positive rate, which is double the ~11% rate of other similar reviews.  They also do not provide any accompanying data on the rate of false-negatives, although, in theory, these should be less clinically important.

So, think twice about doing your little happy dance for a positive CT – if your pretest likelihood was low, and the PE is subsegmental, there’s a substantial chance the stars have aligned in just the wrong constellation.

“Overdiagnosis of Pulmonary Embolism by Pulmonary CT Angiography”
http://www.ncbi.nlm.nih.gov/pubmed/26204274

The No-CT in Trauma Experience

In many trauma centers, the Emergency Department role is essentially: place an IV for which contrast may be delivered for CT.  Oh, yes, there’s some airway management, perhaps a FAST exam, some rolling and cutting of clothing, and the remainder of our expertise should not be diminished, but modern management has been distilled to: trauma = pan-scan.

Except in San Diego.

This fascinating paper describes 11 years of experience at a Level 1 trauma center in which the vast minority of their patients underwent automatic CT.  Between the hours of 8AM and 11PM, a resident and staff ultrasonographer were available for ultrasound examination of trauma patients.  At the discretion of the attending surgeon, the ultrasonographers performed an examination consisting of seven abdominal windows, bilateral visceral organ windows, and cardiac windows.

And, of the 19,126 trauma patients included in this study, essentially all patients presenting between 8AM and 11PM underwent this ultrasound.  Minus the 13 patients who went directly to the OR, this constitutes 12,565 patients initially screened with ultrasound.  Of these, 12,070 were judged to be negative examinations.  By the authors definition of false negative, a positive exploratory laparotomy finding, only 35 ultimately required such – a false negative rate of 0.29%.  Comparatively, CT was performed off-hours in 6,548 patients, and had a 0.1% false negative rate.

There were, of course, a mix of patients with positive ultrasound results who ultimately had negative CTs, and 1,119 negative ultrasounds who underwent CT with a 86 positive results.  So, there’s a lot of details and hidden corners to evaluate and analyze beyond their narrow definition.  But, still, impressively, their trauma protocol at a Level 1 center managed to spare half the patients the ubiquitous pan-scan.

Fascinating!

“Complete ultrasonography of trauma in screening blunt abdominal trauma patients is equivalent to computed tomographic scanning while reducing radiation exposure and cost”
http://www.ncbi.nlm.nih.gov/pubmed/26218686