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Original Report |
1 All authors: Department of Radiology, S. Maria delle Grazie Hospital, Via Domitiani, Pozzuoli 80078, Italy.
Received November 5, 2003;
accepted after revision May 14, 2004.
Address correspondence to O. Catalano.
Abstract
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CONCLUSION. We used contrast-specific sonography to assess eight patients with ruptured abdominal aortic aneurysm. Five of these cases were correlated with CT findings. We found that contrast-enhanced sonography can reveal features specific for ruptured aortic aneurysm without causing a significant delay in surgery. This technique may be as effective as CT but may allow a more rapid and noninvasive diagnosis, especially when sonography can be performed bedside.
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Contrast-specific sonography is a new, accurate, time-effective, and minimally invasive tool in the detection of ruptured aortic aneurysm. It overcomes most limitations of conventional sonography and shows good correlation with CT, although larger series are needed. Because the time intervening between rupture and diagnosis and repair significantly affects patient outcome, contrast-enhanced sonography may be preferred to CT in common clinical practice.
Low-mechanical-index contrast-specific sonography is a new imaging technique based on the capability of second-generation sonographic contrast agents to produce real-time contrast-enhanced gray-scale images [1, 2]. Contrast-specific techniques use a low applied acoustic pressure to produce images based on nonlinear acoustic interaction between the ultrasound beam and stabilized microbubbles containing gases other than air ("second-generation" contrast media). Microbubbles oscillate and subsequently resound, with continuous display of contrast enhancement on gray-scale images [1, 2].
Researchers have studied the use of sonography contrast agents for endoleak detection after aortic stent-graft repair [3]. We describe the contrast-specific sonography findings in patients with a ruptured abdominal aortic aneurysm. This entity currently is investigated using conventional sonography or CT [4–12]. Contrast-enhanced sonography findings of aneurysm rupture have not been reported yet, to our knowledge.
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The correct diagnosis was suggested by clinical findings in five cases. Admission diagnosis in the remaining three was acute abdomen, suspected myocardial infarct, and suspected aortic thrombosis. During the same period, seven other subjects underwent emergency sonography because of suspected abdominal aortic aneurysm rupture, but these patients did not undergo contrast-enhanced sonography because aneurysm was ruled out at the initial screening. Moreover, during the same period, four patients with ruptured aneurysm underwent only CT because of the referring clinician's preference for the standard reference tool.
Sonographic studies were performed by experienced radiologists 10–120 min (mean, 15 min) after the arrival of the outpatients. The inpatient was imaged 2 hr after symptoms arose. Four studies were performed in the emergency department and four in the radiology department.
A quick baseline sonography examination was performed in all patients. We rapidly explored the right upper quadrant, left upper quadrant, paracolic gutters, and pelvis to search for free peritoneal fluid. We then moved the probe to the umbilical area, and we evaluated the aorta and periaortic area to assess for aneurysm and detect potential contiguous hematoma. The superior mesenteric artery was used to define the infrarenal or suprarenal proximal extent of aortic aneurysm [7]. Finally, we moved the probe anterolateral to identify possible pararenal and perirenal fat blurring and renal displacement.
Thereafter, the contrast-enhanced study was obtained. A contrast-devoted mobile unit (EsaTune, Esaote) was used to examine six of the eight patients, and a multipurpose nontransportable unit (Technos, Esaote) was used for two. We used a 3.5-MHz convex transducer with the contrast-specific technology named "contrast tuned imaging."
A sulfur-hexafluoride microbubble contrast agent (SonoVue, Bracco) was rapidly injected IV through a 20-gauge needle. A 4.8-mL volume was administered, followed by 5–10 mL of normal saline (three-way stopcock). Continuous scanning started immediately and lasted 1–3 min. A low acoustic power setting (mechanical index, 0.06–0.07) was used. The ultrasound beam was focused at the deeper aspect of the aneurysm. Periodically, the radiologist could choose, if necessary, to add a high-power flash to the continuous acquisition to briefly break microbubbles within the insonation volume and, hence, allow a kind of opacification resetting (reperfusion). This flash proved useful in revealing contrast extravasation in a specific previously unfocused or poorly focused area around an aneurysm. All examinations were stored on the scanner as video clips.
One patient underwent unenhanced CT immediately after sonography, and four underwent contrast-enhanced CT.
One patient died during transfer to operating room. Surgery was performed in seven patients, and a bleeding aneurysm was found in all seven. The rupture site proved to be lateral in four patients, posterior in one, and anterior in two. Five patients had operative evidence of ongoing hemorrhage, and two showed a stable retroperitoneal hematoma. Four patients survived, two died during surgery, and the other died 3 days after surgery.
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Contrast-specific sonography allowed a more defined depiction of hematoma in four of six patients with visualization of periaortic collection on baseline sonography. Moreover, this tool depicted delayed opacification of the aortic lumen in eight cases (i.e., lumen enhanced later than commonly seen in normal cases), protracted opacification of the aortic lumen in five (i.e., lumen enhanced longer than commonly seen in normal cases), focal nonenhancing area within the enhanced aortic wall in two, contrast leakage within thrombus in seven, extravascular contrast leakage in seven, and extravascular dependent contrast pooling in four (Table 1 and Figs. 1A, 1B, 2A, 2B, 3A, 3B, 4).
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All five patients who underwent CT had evidence of retroperitoneal fluid with blood attenuation. In three of the four subjects who received iodized contrast medium, CT scans showed an active leak.
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Most authors agree that subjects with typical symptoms should not undergo prolonged investigation and that urgent sonography should be the initial diagnostic step [4, 5, 7, 8]. Sonography is used with increasing worldwide popularity for rapid screening for abdominal aortic aneurysm [11, 12] and blunt abdominal trauma [13]. Stable patients with questionable, possibly contained rupture are imaged with contrast-enhanced CT [4, 8].
With the currently available equipment, even if performed bedside and in the less-experienced hands of emergency physicians, sonography has been proven to be accurate and to consistently allow clinicians to rule out aneurysm (95–98% sensitivity) [5, 9–11]. This technique also can show most of the alternative causes of symptomatology. Nevertheless, conventional sonography has some limitations in imaging patients with a ruptured aneurysm because retroperitoneal hematoma is not always visible and there is no direct feature of rupture itself [11].
In some articles, researchers have suggested that, in the proper clinical stetting (hypotension, back or abdominal pain, and pulsatile mass), the detection of an aneurysm is enough to drive a patient to the operating room [4, 7, 11]. In one series [11], a 1-min sonography examination in the emergency department allowed recognition of the aneurysm in 97% of the patients imaged. Sonography had a 4% sensitivity in showing retroperitoneal hematoma, but combining the presence of aneurysm with relevant symptomatology led to the appropriate surgical decision in 21 of 22 patients; one subject had unnecessary laparotomy [11].
If possible, the rupture itself should be detected on presurgical imaging by recognizing retroperitoneal hematoma or, even better, contrast leakage. Either finding proves aneurysm to be the cause of symptoms. Abdominal aortic aneurysms are not rare in elderly patients. Moreover, in clinical practice it happens frequently that a patient with known aneurysm arrives to the emergency department without typical symptoms of rupture: In these cases, the referring clinician wants to know if the aneurysm is bleeding.
Low-mechanical-index technologies allow the nondestructive stimulation of second-generation contrast medium with the unique possibility of continuous scanning [1, 2]. Contrast tuned imaging software (CnTI module, Esaote) is based on selective tuning of a sonography scanner with contrast medium–generated return signal. A specific transmitting and receiving resonance frequency is used to avoid interference from tissue signals, which are lowered to minimum.
The contrast agent SonoVue can be prepared in a few seconds and can be administered immediately. The time needed for baseline and contrast-enhanced sonography in our series was a maximum of 6 min, which is less than the overall room time for contrast-enhanced abdominal CT in our institution.
In our series, contrast-enhanced sonography detected several signs of rupture. The aneurysm showed delayed lumen wash-in and washout (defined in comparison with opacification and deopacification times, though not specifically quantified). The aneurysmal wall enhanced normally (i.e., a thin echoic rim developed a few seconds after lumen opacification and persisted over time), but in two cases it clearly showed a focal nonenhancing area due to parietal necrosis. A leak of sonographic contrast medium was seen through mural thrombosis and an outside aneurysm. Contrast extravasation was recognized as a pulsatile hyperechoic jet splashing through the aortic wall and dissecting the periaortic planes. This jet appeared immediately after luminal opacification, but its snakelike pattern allowed confident differentiation from the aortic branches. After a high-power ultrasound flash, contrast extravasation, just as the opacification of the aneurysm lumen itself, could be seen disappearing and immediately reforming, which allowed definitive differentiation from parietal calcifications. In four cases with baseline evidence of a small hypoechoic area immediately adjacent to the aneurysm, contrast leakage was clearly seen at the same point.
The findings illustrated resemble well-known (static) CT features of aneurysm rupture [4, 8]. In our series, five cases had CT correlation and the images obtained were very similar. CT gives more information about both the aneurysm and the aorta [8], but some researchers have argued [7] that how these detailed data affect emergency treatment and prognosis has not been shown.
We also must note that patients with fluid "third-spacing" within the abdomen are at increased risk of prerenal failure and that iodinated contrast medium may theoretically precipitate this impairment [14]. In fact, renal failure, mainly due to hemoglobin accumulation and to retroperitoneal absorption of blood and necrosis catabolites, is a leading cause of postoperative death in these subjects [6]. Moreover, a patient may be too unstable to be moved from the emergency department. In our hospital, the CT scanner is not located in proximity to the emergency department, whereas sonography can be performed in the emergency department without interfering with the work of a resuscitation team.
Our study has the obvious limitation of being based on a small number of patients. In addition, some cases lack CT correlation. At the beginning of our experience, we tried to obtain a confirmatory CT scan; subsequently, we believed that performing the contrast-enhanced sonography studies in the emergency department without a following CT examination shortened the presurgical time. Progressively we obtained the surgeons' trust in basing diagnosis on sonography findings without confirmatory CT.
Contrast-enhanced sonography can identify features specific for ruptured aortic aneurysm without causing a significant delay in surgery. This technique may be as effective as CT but may allow a more rapid and noninvasive diagnosis, especially when sonography can be performed bedside. Larger series, possibly including smaller aneurysms, are needed.
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