DOI:10.2214/AJR.08.1121
AJR 2008; 191:W77
© American Roentgen Ray Society
Reply
Stephan Meckel and
Stephan G. Wetzel
University Hospital Basel Basel, Switzerland
WEB—This is a Web exclusive article.
With interest we read the letter to the editor, "Cause of
False-Positive When Using Arterialization of Cerebral Veins as a Diagnostic
Feature of Dural Arteriovenous Fistula"
[1]. The observation of
unilateral high contrast enhancement inside a left dural venous sinus
exceeding that of the intracranial arteries on CT angiography (CTA) is very
interesting. In addition, a high intensity of the extracranial posterior veins
was noted, also greater than the arterial system. It is true that these
observations exclude the possibility of a dural arteriovenous fistula (DAVF)
being related to this type of venous contrast enhancement. Thus we agree with
the recommendation of the authors to thoroughly analyze the intensity of
venous contrast enhancement relative to cerebral arteries.
However, the termed "alternative mechanism" of this apparent
left-sided venous reflux into extracranial and intracranial veins has already
been described. On conventional digital subtraction angiography and
venography, a physiologic compression of the left brachiocephalic vein passing
between the aortic arch and the sternum has been reported to cause hemostasis
or even retrograde flow within the left internal jugular vein and left sigmoid
sinus that is reversible during full inspiration
[2,
3]. Its incidence appears to
increase with patient age, and on correlation with contrast-enhanced thoracic
CT, the external compression is relieved at full inspiration because of the
increased distance between the aortic arch and the sternum. Moreover, this
left-sided cranial venous outflow obstruction can cause signal abnormalities
of the affected veins on conventional T1-weighted and T2-weighted MR images
and changes of venous blood flow detectable on phase-contrast MR venography
[2,
3]. Acquiring MR angiograms
during deep inspiratory breath-holding is a simple and quick method to reduce
false-positive interpretations in patients suspected of having venous sinus
thrombosis [3]. On 3D
time-of-flight MR angiography, Uchino et al.
[4] reported an incidence of
6.2% for the finding of retrograde flow in the left dural sinuses.
In our original report [5],
we described the arterialization of a cerebral vein on CTA images consisting
of a unilateral higher contrast enhancement of a vein, in the majority of
cases being a dural venous sinus. Thereby the intensity of the enhancement
exceeded that of the contralateral venous structures and was similar to that
of the depicted cerebral arteries. This sign was found diagnostic for DAVF in
a small series of five cases. However, because we did not analyze the
sensitivity and specificity of this sign, we could not form conclusions on
possible differential diagnoses or other possible mechanisms related to this
finding.
We conclude that the observation of unilateral high contrast enhancement in
the left-sided lateral venous sinuses and extracranial cervical veins
exceeding that of the cerebral arteries on CTA is very important. It may favor
the diagnosis of venous outflow obstruction or even retrograde flow in the
left internal jugular vein caused by an underlying physiologic left
brachiocephalic vein compression rather than by an arteriovenous shunt due to
a DAVF. Yet, we do not believe that invasive cerebral digital subtraction
angiography should be the primary examination of choice to prove or rule out a
DAVF. Instead, we propose that in addition to measuring the intensity of
venous contrast enhancement, the anatomic extent of such high intensities
within the intracranial venous system should be well analyzed on CTA source
images. In accordance with our own daily observations in a large tertiary
center of clinical neuroscience, left-sided retrograde venous flow or
physiologic stasis has never been reported to extend retrogradely to the
intracranial venous system beyond the level of the transverse–sigmoid
sinus junction and the inferior petrosal sinus, respectively
[2–4].
This distribution also appears suggestive on Figures 1A and 1B in the present
letter by Simpson and Teasdale
[1].
On the other hand, signs that may favor the diagnosis of a DAVF on CTA
images are indicators for arterial feeders, such as tiny transosseous vessels
or prominent branches of the external carotid arteries, as well as
arterialized cortical veins [5,
6]. If findings are still
equivocal on CTA, we would primarily recommend proceeding to MRI with MR
angiography. The MR examination should include a fast, time-resolved
contrast-enhanced MR angiography series that enables a better diagnostic
differentiation of a DAVF and can also be acquired during deep inspiratory
breath-holding to relieve possible left-sided physiologic venous stasis or
retrograde flow [7].
References
- Simpson GC, Teasdale E. Cause of false-positive when using
arterialization of cerebral veins as a diagnostic feature of dural
arteriovenous fistula. (letter) AJR 2008;191
:[web] W76[Free Full Text]
- Tanaka T, Uemura K, Takahashi M, et al. Compression of the left
brachiocephalic vein: cause of high signal intensity of the left sigmoid sinus
and internal jugular vein on MR images. Radiology1993; 188:355
-361[Abstract/Free Full Text]
- Kudo K, Terae S, Ishii A, et al. Physiologic change in flow
velocity and direction of dural venous sinuses with respiration: MR venography
and flow analysis. Am J Neuroradiol 2004;25
: 551-557[Abstract/Free Full Text]
- Uchino A, Nomiyama K, Takase Y, et al. Retrograde flow in the dural
sinuses detected by three-dimensional time-of-flight MR angiography.
Neuroradiology 2007;49
: 211-215[CrossRef][Medline]
- Meckel S, Lovblad KO, Abdo G, et al. Arterialization of cerebral
veins on dynamic MDCT angiography: a possible sign of a dural arteriovenous
fistula. AJR 2005;184
: 1313-1316[Abstract/Free Full Text]
- Alatakis S, Koulouris G, Stuckey S. CT demonstrated transcalvarial
channels diagnostic of dural arteriovenous fistula. Am J
Neuroradiol 2005; 26:2393
-2396[Abstract/Free Full Text]
- Meckel S, Maier M, Ruiz DS, et al. MR angiography (MRA) of dural
arteriovenous fistulas: diagnosis and follow-up after treatment using a
time-resolved 3D contrast-enhanced MRA technique. Am J
Neuroradiol 2007; 28:877
-888[Abstract/Free Full Text]
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