PMC6159241_01
Consecutive 2.5 mm axial slices through the right upper lobe anterior segmental artery (arrows) reviewed on lung windows. Gradual antidependent fading of contrast is demonstrated peripherally (a and b), with replacement of contrast with air, in keeping with peripheral pulmonary arterial air embolus. Distally (c) the completely air-filled artery resembles a bronchus, running parallel to another bronchus: the "double bronchus sign". This appearance was replicated in multiple antidependent segmental and subsegmental pulmonary arteries, involving all lobes.
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f1
Review on lung windows elicited that these vessels were not truncated but that intraluminal contrast within these vessels gradually faded peripherally and was replaced with air (Figure 1).
Further examples of the "double bronchus" sign (arrows) in axial section through right apex (a) and oblique reformats through left upper lobe subsegmental (b) and right upper lobe segmental (c) pulmonary arteries. Peripheral pulmonary arterial air emboli running alongside their paired bronchi give the false impression of twinned bronchi running parallel alongside each other.
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f2
We propose this appearance as the "double bronchus sign" (Figure 2), which has not been previously described.
Oblique reformats through the right upper lobe anterior segmental pulmonary artery on the first acquisition (a) demonstrate no pulmonary embolus and on the second acquisition (b) clearly demonstrate peripheral pulmonary air embolus. The two acquisitions were performed in quick succession, using the same peripheral cannula, and the patient remained on the scanner between the two attempts.
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f3
Crucially, direct comparison of the two scans revealed that air embolus was only present on the second acquisition (Figure 3), confirming that the aetiology was iatrogenic and directly related to contrast injection.