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1 Department of Radiology, University of Virginia Health Systems Charlottesville, Virginia
Two excellent articles in this issue of RadioGraphics describe in detail the pathophysiology of cerebral venous thrombosis, the protean clinical ramifications of this disease, and how best to image it. Rodallec and colleagues (1) have chosen CT as their tool, and Leach and colleagues (2) describe both CT and MR imaging, with some preference for MR imaging. Their descriptions, in pictorial and text form, are essential reading for radiologists.
Intracranial venous thrombosis is not the most common disease state that a radiologist in practice evaluating central nervous system imaging studies will see. In fact, it is not uncommonly overlooked. In my experience, with referred cases to my institution, delays in diagnosis are not uncommon, and occasionally the disease is noted only as it progresses and results in significant secondary intracranial parenchymal findings, such as focal cerebral edema and hemorrhagic infarction. The advent of powerful, noninvasive imaging tools to evaluate the cerebral venous system (MR venography and CT venography) has increased our ability to diagnose cerebral venous thrombosis but not necessarily increased our willingness to apply the technology.
Knowledge of the intracranial venous system anatomy and its many normal anatomic variants is paramount to our understanding of the pathologic states affecting them, most notably and importantly venous thrombosis. Training in the era that I did, conventional catheter cerebral angiography was much more liberally applied, and our knowledge of the cerebral arterial and venous anatomy was arguably more thorough. Woe to the fellow who did not continue the run well into the venous phase to evaluate for venous disease! These articles should aid us all in improving our knowledge of the cerebral venous system, both normal and pathologic. They should prove to be very useful teaching tools for our trainees and a detailed refresher for those of us already interpreting results of these examinations. Knowledge of the disease states associated with venous disease also makes us all more useful resources to our clinical colleagues in evaluating problematic patients. Of particular use in this regard is the excellent discussion on clinical findings in patients with cerebral venous thrombosis and the spectrum of underlying causes resulting in this condition presented by Leach et al (2).
When do we choose to perform noninvasive venography? The short answer—when requested—falls short of our expectations of ourselves as clinical consultants. Within the guidelines of the myriad rules for independent diagnostic testing facilities and hospital inpatients and outpatients, I tend to err on the side of doing what is right for the patient and using a reasonable and modest degree of suspicion in the following scenarios: (a) the patient with an intracranial hemorrhage without an obvious cause that does not seem among the group of "usual suspect" hemorrhages, namely intracranial hemorrhage in the convexity regions, in the posterior temporal lobe, and adjacent to a dural venous sinus, with a healthy dose of skepticism as to whether the sinus is "normal" on the images I have; (b) the patient with a plainly abnormal or suspicious-appearing dural venous sinus (high attenuation at CT, unusual pattern of flow phenomena at MR imaging, etc); (c) patients with any hypercoagulable state with altered mental status, white matter changes, infarctions, or hemorrhages; and (d) pathologic conditions contiguous to a dural sinus that may result in venous thrombosis, such as meningiomas, otomastoiditis, or fractures. This is not an all-inclusive listing, by any means.
So, which technique do you choose? CT has the utility of commonly being the first stop for these patients in their evaluation, and the addition of a vascular study to the head CT examination in progress results in the always hoped for "one-stop shopping." Iodinated contrast material and the cumulative radiation dose are minor but important considerations. MR imaging has the bonus of increased sensitivity in the evaluation or detection of subtle cerebral complications of cerebral venous thrombosis such as hemorrhage, as well as the lack of bone artifact and obvious absence of iodinated contrast material or radiation. Diffusion-weighted imaging may be a requested examination, and the ease of the MR venography study at the same sitting may be a decision maker. The occasional diagnostic dilemma that these patients present is also in the mix. Often, the differential diagnostic considerations may include arterial disease as well, and the request may be made for an arterial and venous study. MR angiography and MR venography are reasonably easy to combine. CT angiography and CT venography are also easy to combine but result in the obvious additional radiation dosage.
These are complex decisions, and additional factors may also interplay in your ultimate choice. Maybe you are very comfortable with CT venography. Perhaps it is a trauma patient and the depiction of fractures is important. Perhaps the patient has renal disease and avoiding iodinated contrast material is critical. I will completely avoid discussing in this forum which MR imaging technique you choose. I would leave it at this—cerebral venous thrombosis is often recognized late, with the opportunity for progressive neurologic deficits. It can be a difficult diagnosis to make. Know all you can about your tools at hand, so you can intelligently apply them. These articles are excellent resources in that regard.
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2 Department of Radiology, Fondation Hôpital Saint-Joseph, Paris, France
3 Department of Radiology B, Hôpital Cochin, Paris, France
We greatly appreciate Dr Phillips’ complimentary comments regarding the use of multi–detector row CT for diagnosis of cerebral venous thrombosis. The essence of our article is the presentation of CT venography principles based on current state-of-the-art techniques. CT venography is a rapid and useful method that consistently yields detailed and high-quality images of intracranial venous circulation. CT venography is useful in many acute situations to confirm or exclude cerebral venous thrombosis and can be performed without delay in patients with unenhanced CT findings suggestive of venous thrombosis. The speed and simplicity of the multidetector CT technique mean that CT venography can be performed even in acutely ill restless patients.
We make no claim of the superiority of MR imaging over CT for detection of the associated parenchymal changes in cerebral venous thrombosis, but detection of microhemorrhage on its own will seldom suffice to confirm the venous origin. Obviously, MR imaging has the potential advantage of excluding other differential diagnoses, for example by using diffusion-weighted imaging. However, when MR imaging resources are not available, CT can play an important front-line role in diagnosis of cerebral venous thrombosis. CT venography performed with accurate parameters and careful analysis of the source images is a simple method of diagnosing cerebral venous thrombosis. We hope results of CT venography will be read even by nonspecialist radiologists in the future. It will increase the likelihood of diagnosing cerebral venous thrombosis in the acute stage, at a time when treatment is most likely to be effective for the benefit of most patients.
Related Articles
RadioGraphics 2006 26: S19-S41.
RadioGraphics 2006 26: S5-S18.
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