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Letters |
University of Parma
Department of Clinical Sciences
Institute
of Radiology
Parma, Italy
We read with great interest the article by Yeh et al. [1] published in the November 2004 AJR, regarding the clinical relevance of the retrograde opacification of the inferior vena cava and hepatic veins during a contrast-enhanced CT study. In particular, we appreciated the detailed discussion.
However, a few points need to be further explained about the study technique:
In our opinion, on the basis of a large experience, when the CT scan is performed at end-inspiratory breath-hold, the deep inspiration itself may be responsible for a significant attraction of the not-yet-opacified blood from the inferior vena cava to the right atrium, sometimes interrupting or preventing the reflux of contrast material.
Moreover, if the exam is performed with a very short time delay from the injection start, as can frequently happen in the study of a patient with suspected pulmonary embolism, the above-mentioned phenomenon can completely obscure inferior vena cava regurgitation.
This event also can be responsible for other flow-related artifacts [2, 3] sometimes observed during the CT study of the pulmonary arteries, such as transitory interruption of the contrast bolus flow, mimicking a nonexisting pulmonary embolus. In our experience, this type of flow-related artifact is present only if the patient is able and instructed to take a deep breath and to hold it.
In all the cases in which the artifacts were present, the inferior vena cava was not opacified. A second CT scan, of course, performed without delay with an MDCT device, can clear up the situation.
In conclusion, the reflux of unenhanced blood from the inferior vena cava to the right atrium during the end-inspiratory breath-hold could mask, at least in some cases, the opacification of the inferior vena cava.
We would be glad if the authors will share their experience regarding these problems and observations.
References
Department of Radiology
University of California-San
Francisco
San Francisco, CA
Department of Radiology
University of Chicago
Hospitals
Chicago, IL
We want to thank Drs. Cobelli, Zompatori, Lombardo, and Sverzellati for raising this important point regarding the assessment of retrograde contrast opacification of the inferior vena cava or hepatic veins. The effect of respiration on flow in the inferior vena cava has not been extensively studied in normal patients [1] but has been shown to influence blood flow in the inferior vena cava and hepatic veins in animal models [2], and end-inspiration breath-hold has been shown to be associated with an influx of unopacified blood from the inferior vena cava into the right atrium at pulmonary CT angiography [3]. Regarding our own observations of inspiratory effort and the frequency of finding retrograde inferior vena cava or hepatic vein opacification, we can only make inferences because all of the patients in our study were imaged during end-inspiratory breath-hold.
In our patient series, we noted that seven of our total 127 patients (6%) demonstrated retrograde opacification of the hepatic veins without opacification of the inferior vena cava. We suspect that this discontinuous appearance of the opacified blood column was likely due to the patient's inspiratory effort, which caused antegrade flow of unopacified blood from the inferior vena cava to drive the opacified inferior vena caval blood back into the right atrium while the opacified blood in the hepatic vein was left behind. All seven patients were scanned with high (> 3 mL/sec) IV contrast injection rate and four of these patients were scanned for possible pulmonary embolus. Two of these patients had right heart disease at echocardiography; five did not.
We also noted several patients who had alternating bands of opacified and unopacified blood, (at times, up to four alternating bands) in the inferior vena cava, and we believe this appearance was due to voluntary hyperventilation just prior to scanning. We dubbed this appearance the "rugger jersey inferior vena cava" and surmise that it was caused by alternating cycles of retrograde flow of opacified blood into the inferior vena cava or hepatic veins during exhalation then antegrade flow of unopacified blood from the hepatic veins or inferior vena cava during inspiration prior to scanning. In our analyses, a distinction was not drawn between these different patterns of retrograde flow into the inferior vena cava or hepatic veins. Further work will be needed to assess whether the pattern of retrograde flow or inspiratory effort influences the clinical significance of finding retrograde opacification of the inferior vena cava or hepatic veins in the diagnosis of possible right heart disease.
In answer to Drs. Cobelli, Zompatori, Lombardo, and Sverzellati's specific queries, since our study included all clinical CT examinations performed within 2 weeks of clinical echocardiography, a broad range of scan delays was represented in our patient sample. In brief, 56 of our 127 patients underwent CT imaging with high rates (> 3 mL/sec) of IV contrast material injection. Of these patients, CT imaging was obtained with 20-second scan delay in 46 patients, and, of these, 37 were imaged for suspected pulmonary embolism. Retrograde opacification of the inferior vena cava or hepatic veins occurred in 26 (46%), 23 (50%), and 20 (54%) of these patients, respectively.
References
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