DOI: 10.1148/radiol.2321020156
(Radiology 2004;232:244-245.)
© RSNA, 2004
The Floating Viscera Sign1
Neil Switzer, MD
1 From the Department of Radiology, St Luke’s-Roosevelt Hospital Center, New York, NY. Received February 25, 2002; revision requested April 24; final revision received February 6, 2003; accepted February 27. Address correspondence to the author, Radiology Consultants Associated, 120a, 6707 Elbow Dr SW, Calgary, AB, Canada T2V 0E3 (e-mail: neilswitzer@hotmail.com).
Index terms: Aorta, dissection, 94.4124, 94.74, 981.4124, 981.74 • Signs in Imaging
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APPEARANCE
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The floating viscera sign refers to the opacification of aortic branch vessels during aortography with the catheter placed in the aortic true lumen (1,2). Branch vessels—including the celiac axis, superior mesenteric artery, and renal arteries—seem to arise out of nowhere, with little or no antegrade opacification of the aortic true lumen (Figure).
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Figure a. (a) Aortogram in the anteroposterior projection with the catheter in the downstream aortic true lumen demonstrates the floating viscera sign. Image shows opacification of the celiac axis and the superior mesenteric and left renal arteries. (b) Aortogram in the anteroposterior projection with the catheter in the aortic false lumen. No major visceral branch vessel opacification is shown.
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Figure b. (a) Aortogram in the anteroposterior projection with the catheter in the downstream aortic true lumen demonstrates the floating viscera sign. Image shows opacification of the celiac axis and the superior mesenteric and left renal arteries. (b) Aortogram in the anteroposterior projection with the catheter in the aortic false lumen. No major visceral branch vessel opacification is shown.
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EXPLANATION
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Two mechanisms—dynamic and static narrowing—can cause branch vessel compromise in aortic dissection (1). The floating viscera sign indicates the presence of aortic dissection and associated dynamic compromise of the aortic true lumen and associated visceral branch vessels.
In dynamic narrowing, the dissection flap spares the vessel origins, but the aortic true lumen upstream to the branch vessels is compressed by an expanding false lumen. The result is diminished antegrade flow within the downstream true lumen and branch vessels, despite an adequate caliber true lumen at this level. Injecting contrast material into the downstream true lumen will opacify the branch vessels and produce the floating viscera sign. Branch vessels originating from the false lumen are not visualized unless there is a reentry tear.
Static narrowing refers to the intersection of the aortic dissection flap and the branch vessel origin. The propagating intramural hematoma causes luminal narrowing at the branch vessel origin, thereby reducing flow. With static narrowing, the floating viscera sign is not seen at angiography. Instead, the hematoma is depicted as luminal scalloping or as a linear filling defect.
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DISCUSSION
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Aortic dissection results from an intimal tear with separation of the aortic wall layers. Dissections most commonly originate in the ascending aorta (75%), followed by the descending thoracic aorta distal to the left subclavian artery (25%) (3,4). Dissections involving the ascending thoracic aorta are termed Stanford type A, regardless of their distal extent or the origin of the intimal tear. Stanford type B dissections are limited to the descending thoracic or abdominal aorta (5). Approximately 30% of patients with aortic dissection have branch vessel compromise and ischemia, resulting in extremity pulse loss, impaired renal or visceral perfusion, stroke, and paraplegia (6,7). Vascular compromise is associated with a substantially higher mortality, and therefore the floating viscera sign may be prognostically important (7).
Aortic dissections are most commonly associated with hypertension, which coexists in 70%–90% of patients in most series (3). Other predisposing factors include connective tissue disorders (such as Marfan syndrome and Ehlers-Danlos syndrome), congenital bicuspid aortic valve, aortic coarctation, and collagen vascular diseases (3).
Computed tomography (CT), CT angiography, magnetic resonance (MR) imaging, and MR angiography are safe and accurate methods to evaluate patients with aortic dissection (8,9). These modalities are excellent for depicting dissection, as well as for characterizing aortic size and branch vessel involvement. Conventional aortography is invasive and may be less effective for evaluating the extent of the false lumen. Dissections may also be missed if the false lumen is thrombosed and not opacified.
Patients with dissections involving the ascending aorta are treated with surgical repair, commonly aortic valve replacement and tube graft placement. Nonsurgical treatment with antihypertensive medications is generally advocated in patients with type B dissections. Surgical intervention may be necessary in cases of peripheral vessel compromise, progressive dissection, or rupture (3,5,6). However, patients with evidence of mesenteric or renal ischemia have been shown to have operative mortality rates of 43–87% (6,7).
Endovascular interventional techniques, such as balloon fenestration, endovascular stent placement, or a combination of the two, are safe and effective management alternatives for patients with aortic dissection and ischemic complications (10). Fenestration allows blood to flow across the dissection flap from the false lumen to the true lumen. This raises true lumen pressure and increases perfusion of the branch vessels supplied by the true lumen (1,10). Placement of a stent within the aortic true lumen may improve luminal integrity and allow antegrade flow through branch vessels. However, the false lumen usually remains patent and can become aneurysmal with time (10).
Endovascular stent-grafts have also proved to be safe and effective alternatives to surgery (2,11,12). Placement of stent-grafts across the primary entry tear within the true lumen can seal the tear and thrombose the false lumen. The endovascular stent-graft also restores normal flow within the aortic true lumen and the distal branch vessels that are compromised by dynamic narrowing.
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ACKNOWLEDGMENTS
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I acknowledge James Silberzweig, MD, for his guidance in the preparation of the manuscript.
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FOOTNOTES
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A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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REFERENCES
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- Slonim SM, Nyman UR, Semba CP, et al. True lumen obliteration in complicated aortic dissection: endovascular treatment. Radiology 1996; 201:161-166.[Abstract/Free Full Text]
- Kang SG, Lee DY, Maeda M, et al. Aortic dissection: percutaneous management with a separating stent-graft—preliminary results. Radiology 2001; 220:533-539.[Abstract/Free Full Text]
- Won JY, Lee DY, Shim WH, et al. Elective endovascular treatment of descending thoracic aortic aneurysms and chronic dissections with stent-grafts. J Vasc Interv Radiol 2001; 12:575-582.[Medline]
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