Intracranial vascular imaging: Pearls and pitfalls by ProQuest

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The entire duration of 64-slice CTA, from start of contrast injection to conclusion of scanning, is approximately 20 to 25 sec. Because image acquisition only requires 3 to 4 sec, most of this time is due to the delay between when contrast is injected and when scanning is begun.

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									Intracranial vascular imaging:
Pearls and pitfalls

Jane J. Kim, MD, and Max Wintermark, MD




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       here has been increasing reliance     diplopia, diffuse weakness and vomit-          after the initial CTA, to reevaluate his
       on computed tomography angi-          ing. Given the concern for posterior-          vasculature (Figure 3). Again, there
       ography (CTA) and magnetic            circulation ischemia, a CT/CTA was             was no neurologic deterioration at the
resonance angiography (MRA) for eval-        requested and performed within the first       time of the study. DSA demonstrated
uation of the intracranial vasculature in    hour of symptom onset (Figure 1). Our          occlusion of the right vertebral artery,
patients suspected of acute stroke. Digi-    standard CT stroke protocol included           occlusion of the left vertebral artery
tal subtraction angiography (DSA),           64-slice CTA from the base of the heart        proximal to the posterior inferior cere-
while traditionally the gold standard, is    through the cerebral vertex, as well as        bellar artery (PICA), reconstitution of
invasive and associated with potential       delayed contrast-enhanced head CT              the vertebrobasilar confluence distal to
complications. Further, DSA is not read-     obtained approximately 1 min after CTA         the PICA, and occlusion of the remain-
ily accessible anytime day or night. In      (without the need for additional contrast      der of the basilar artery with filling of
the acute stroke setting, DSA is typically   material because contrast has already          the basilar tip via the posterior commu-
reserved for patients undergoing thera-      been injected for CTA). In this patient,       nicating artery.
peutic intervention with intra-arterial      the initial CTA demonstrated lack of              The important point about this case is
thrombolysis or embolectomy.                 opacification of the bilateral distal verte-   that CTA, contrast-enhanced CT, MRA
   The purpose of this article is to com-    bral arteries and proximal basilar artery,     and DSA obtained within 24 hours of
pare the diagnostic accuracy of CTA,         while the delayed contrast-enhanced            each other, and without any change in
MRA and DSA for evaluation of the            images demonstrated normal opacifica-          the patient’s clinical status, demon-
intracranial circulation in patients with    tion of the left distal vertebral artery and   strated very different findings. Both
stroke. We will discuss the technical        proximal basilar artery.                       MRA and DSA appeared to demon-
parameters and potential artifacts that         Based on the clinical and imaging           strate occlusion of the basilar artery, as
must be understood so that an accurate       findings, the patient received IV tissue       well as occlusion of the bilateral distal
interpretation of each modality can be       plasminogen activator (tPA) and                vertebral arteries. However, most of the
made. We will structure our discussion       underwent 3-dimensional time of flight         basilar artery appeared patent on CTA,
around an illustrative clinical case of a    (TOF) intracranial MRA approxi-                which showed occlusion limited to the
patient who underwent CTA, MRA and           mately 4 hours following CTA to                bilateral distal vertebral arteries and
DSA within a 24 hour time frame.             reassess his vasculature after throm-          only the most proximal aspect of the
                                             bolysis (Figure 2). The MRA demon-             basilar artery. Delayed contrast-
Clinical case                                strated absence of flow-related                enhanced CT, in turn, appeared to
  A 62-year-old man presented to the         enhancement in the bilateral distal ver-       demonstrate patency of the distal left
emergency room with acute onset              tebral and entire basilar artery, which        vertebral and entire basilar artery.
                                             was discrepant with the initial CTA,              One explanation for the discrepancy
  Dr. Kim is Assistant Professor of Clini-
                                             especially considering that there was          is that the patient’s basilar artery
 cal Radiology, Neuroradiology Section,
 San Francisco General Hospital, Uni-        no change in the patient’s clinical            thrombosed between the time of CTA
 versity of California, San Francisco, CA;   examination and no evidence of neuro-          and MRA/DSA. However, the absence
 and Dr. Wintermark is Chief of the Divi-    logic deterioration between initial CTA        of any neurological changes between
 sion of Neuroradiology, University of       and follow-up MRA.                             examinations, as would be expected
 Virginia Health System, Charlottesville,
                                                The patient then underwent DSA the          with a typically devastating basilar
 VA.
                                             following day, approximately 24 hours          artery occlusion, weighs against this


28   ■     APPLIED RADIOLOGY     ©
                                     www.appliedradiology.com                                                               April 2010
INTRACRANIAL VASCULAR IMAGING


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