Computed Tomography Angiography of the Head Is a Reasonable Next Test After a Negative Noncontrast Head Computed Tomography Result in the Emergency Department Evaluation of Subarachnoid Hemorrhage

Abstract

CLINICAL CONTROVERSIES CT Angiography for Subarachnoid Hemorrhage Opposing authors provide succinct, authoritative discussions of controversial issues in emergency medi- cine. Authors are provided the opportunity to review and comment on opposing presentations. Each topic is accompanied by an Editor’s Note that summarizes important concepts. Participation as at authoritative discussant is by invitation only, but suggestions for topics and potential authors can be submitted to the section editors. Editor’s Note: Physicians often encounter resistance in performing lumbar puncture on patients presenting with suspected subarachnoid hemorrhage and normal noncontrast head computed tomography (CT). Despite an absence of supporting literature, an increasing number of clinicians are advocating using CT angiography, with its ability to identify vascular sources of subarachnoid hemorrhage, as the initial study in suspected subarachnoid hemorrhage, thereby eliminating the need for lumbar puncture in most patients. Although this approach is likely to decrease the need for lumbar puncture, it carries its own set of complications and challenges. In this installment of Clinical Controversies, pro and con advocates discuss opposing perspectives and present the available evidence and arguments that must be considered in deciding whether to adhere to the conventional CT–lumbar puncture diagnostic strategy or embrace CT angiography as an alternative strategy in evaluating patients with suspected subarachnoid hemorrhage. COMPUTED TOMOGRAPHY ANGIOGRAPHY OF THE HEAD IS A REASONABLE NEXT TEST AFTER A NEGATIVE NONCONTRAST HEAD COMPUTED TOMOGRAPHY RESULT IN THE EMERGENCY DEPARTMENT EVALUATION OF SUBARACHNOID HEMORRHAGE Marc A. Probst, MD, MS; Jerome R. Hoffman, MD, MA UCLA Emergency Medicine Center, School of Medicine, University of California, Los Angeles, Los Angeles, CA Although subarachnoid hemorrhage is rare, identifying a sentinel bleeding event is one of the most beneficial things an emergency physician can accomplish. For this discussion, we assume that a negative noncontrast computed tomography (CT) scan of the head is inadequate to rule out a sentinel subarachnoid hemorrhage and must be followed by another test; traditionally, a lumbar puncture. We argue that after a nondiagnostic CT result, CT angiography is an acceptable alternative in patients with a reasonable previous probability of subarachnoid hemorrhage. Volume 67, no. 6 : June 2016 Although the sensitivity of lumbar puncture for subarachnoid hemorrhage approaches 100%, it has other suboptimal characteristics. It is invasive and painful, and it often causes considerable patient anxiety such that some patients will leave against medical advice if given no other choice. Not infrequently, lumbar puncture causes a significant postdural puncture headache, the incidence of which is estimated to range from 10% to 40%. 1 This complication can require medical therapy, epidural blood patch, and even admission. (The literature is unfortunately not helpful about the frequency of any of these.) Lumbar puncture results are often inconclusive, mostly because of traumatic taps (in 15% to 20% of patients); and arbitrary cutoffs for RBC count, change in counts between tubes, or evaluation of xanthochromia cannot resolve this problem. 2 Last, lumbar puncture can be technically difficult, depending on patient body habitus, and is time consuming for the emergency physician, which can interfere with the care of other acutely ill patients. Substituting CT angiography for lumbar puncture has several advantages. It is painless and noninvasive, and can be performed rapidly; from the emergency physician standpoint, it requires little time. Diagnostically, it can identify other important causes of worrisome headache (eg, venous sinus thrombosis, ischemic stroke, arteriovenous malformation), even if subarachnoid hemorrhage is not present, albeit while forgoing cerebrospinal fluid analysis. 3 A recently published mathematical probability model suggests that this strategy would have a sensitivity of 99.5% for aneurysmal subarachnoid hemorrhage and is eminently reasonable for most such patients. 4 There are important disadvantages of CT angiography. First, the reported prevalence of incidental cerebral aneurysms in the general population is between 0.5% and 6%, depending on study design, and is likely to be at least 2%. 5 The majority of these will never cause a clinical problem. Thus, approximately 1 in 50 patients being evaluated for possible subarachnoid hemorrhage, in whom subarachnoid hemorrhage is not present, will have an incidental aneurysm identified. It is not currently possible to distinguish these from a truly dangerous aneurysm that is causing the index headache, Annals of Emergency Medicine 773