Abdominal aortic aneurysms revisited: MDCT with multiplanar reconstructions for identifying indicators of instability in the pre- and postoperative patient

Status of diagnosis and therapy of abdominal aortic aneurysms

Abdominal aortic aneurysms (AAAs) are characterized by localized dilation of the abdominal aorta. They are associated with several serious consequences, including compression of adjacent abdominal organs, pain, treatment-related financial expenditure. The main complication of AAA is aortic rupture, which is responsible for about 200,000 deaths per year worldwide. An increasing number of researchers are dedicating their efforts to study AAA, resulting in significant progress in this field. Despite the commendable progress made thus far, there remains a lack of established methods to effectively decelerate the dilation of aneurysms. Therefore, further studies are imperative to expand our understanding and enhance our knowledge concerning AAAs. Although numerous factors are known to be associated with the occurrence and progression of AAA, the exact pathway of development remains unclear. While asymptomatic at most times, AAA features a highly unpredictable disease course, which could culminate in the highly deadly rupture of the aneurysmal aorta. Current guidelines recommend watchful waiting and lifestyle adjustment for smaller, slow-growing aneurysms, while elective/prophylactic surgical repairs including open repair and endovascular aneurysm repair are recommended for larger aneurysms that have grown beyond certain thresholds (55 mm for males and 50 mm for females). The latter is a minimally invasive procedure and is widely believed to be suited for patients with a poor general condition. However, several concerns have recently been raised regarding the postoperative complications and possible loss of associated survival benefits on it. In this review, we aimed to highlight the current status of diagnosis and treatment of AAA by an in-depth analysis of the findings from literatures.

Abdominal Aortic Aneurysms (Etiology, Epidemiology, and Natural History)

Abdominal aortic aneurysm is a potentially lethal condition that is decreasing in frequency as tobacco use declines. The exact etiology remains unknown, but smoking and other perturbations seem to trigger an inflammatory state in the tunica media. Male sex and advanced age are clear demographic risk factors for the development of abdominal aortic aneurysms. The natural history of this disease varies, but screening remains vital as it is rarely diagnosed on physical examination, and elective repair (most commonly done endovascularly) offers significant morbidity and mortality advantages over emergent intervention for aortic rupture.

Computed Tomography Attenuation Values of the High-Attenuating Crescent Sign Can Discriminate Between Rupture, Impending Rupture, and Non-Rupture of Aortic Aneurysms

BACKGROUND

Although the high-attenuating crescent (HAC) sign can indicate aortic aneurysm (AA) impending rupture, the relation of its computed tomography (CT) value to the aneurysmal status remains unclear. This study compared the HAC sign CT-attenuation values among rupture, impending rupture, and non-rupture AA cases.

METHODS AND RESULTS

This included 76 patients (mean age: 77.0 years) diagnosed with HAC sign-associated AA between January 2005 and July 2015. The CT-attenuation values of the HAC sign (H) and aortic lumen (A) using region-of-interest methodology were measured and the H/A ratio was calculated. The study classified patients into the rupture group (R-G, n=36), impending rupture group (IR-G, n=16), and non-rupture group (NR-G, n=24); the H and the H/A ratio were compared among them. Additionally, the H and the H/A ratio cut-offs between the IR-G and NR-G groups were evaluated. The H and the H/A ratio were significantly higher in the R-G and IR-G than in the NR-G (both P<0.001); the H/A ratio was significantly higher in the R-G than in the IR-G (P=0.038). The optimal cut-off for H between the IR-G and NR-G was 50.3 Hounsfield units (area under the curve [AUC]=0.875; sensitivity=87.5%; specificity=87.5%), and that for the H/A ratio was 1.3 (AUC=0.909; sensitivity=91.7%; specificity=87.5%).

CONCLUSIONS

Among patients with AA, the H and the H/A ratio were significantly higher in cases of rupture and impending rupture than in those of non-rupture.

Stress Analysis in AAA does not Predict Rupture Location Correctly in Patients with Intraluminal Thrombus

BACKGROUND

A biomechanical approach to the rupture risk of an abdominal aortic aneurysm could be a solution to ensure a personalized estimate of this risk. It is still difficult to know in what conditions, the assumptions made by biomechanics, are valid. The objective of this work was to determine the individual biomechanical rupture threshold and to assess the correlation between their rupture sites and the locations of their maximum stress comparing two computed tomography scan (CT) before and at time of rupture.

METHODS

We included 5 patients who had undergone two CT; one within the last 6 months period before rupture and a second CT scan just before the surgical procedure for the rupture. All DICOM data, both pre- and rupture, were processed following the same following steps: generation of a 3D geometry of the abdominal aortic aneurysm, meshing and computational stress analysis using the finite element method. We used two different modelling scenarios to study the distribution of the stresses, a "wall" model without intraluminal thrombus (ILT) and a "thrombus" model with ILT.

RESULTS

The average time between the pre-rupture and rupture CT scans was 44 days (22-97). The median of the maximum stresses applied to the wall between the pre-rupture and rupture states were 0.817 MPa (0.555-1.295) and 1.160 MPa (0.633-1.625) for the "wall" model; and 0.365 MPa (0.291-0.753) and 0.390 MPa (0.343-0.819) for the "thrombus" model. There was an agreement between the site of rupture and the location of maximum stress for only 1 patient, who was the only patient without ILT.

CONCLUSIONS

We observed a large variability of stress values at rupture sites between patients. The rupture threshold strongly varied between individuals depending on the intraluminal thrombus. The site of rupture did not correlate with the maximum stress except for 1 patient.

Chronic Contained Rupture of the Abdominal Aortic Aneurysm

Background

The most lethal complication of the abdominal aortic aneurysm (AAA) is rupture (rAAA). A triad of abdominal or back pain, a pulsating mass in the abdomen, and decrease in blood pressure is mostly diagnostic. However, this presentation may not be complete due to either an impalpable aneurysm or atypical symptoms which leads to difficulties in diagnosis and delayed management. Chronic contained rupture of AAA (CCR-AAA) is a rare but well-recognized condition. Its diagnosis may be difficult because of the atypical and chronic nature of the symptoms. The aim of this study is to investigate the incidence and to highlight the importance of this less common presentation of rAAA.

Methods

Patients who presented to King Abdullah University Hospital (KAUH) with infra-renal AAAs (elective and emergency) from January 2014 to April 2021 were prospectively collected. Patients with CCR-AAA were identified and evaluated in terms of demographic data, associated comorbidities, presentation, treatments, and outcomes.

Results

A total number of 85 patients were admitted with an infra-renal AAA. Seventeen patients (20.0%) had rAAA, of them only 5 patients (29.4%) were diagnosed with CCR-AAA. CCR-AAAs represent 5.9% of cases with AAA. CCR-AAAs were all in men, with a mean age ± SD of 73.1±8.3. Two patients (40.0%) had abdominal pain, 2 patients (40.0%) had back pain and one patient (10.0%) had no symptoms at the time of diagnosis.

Conclusion

CCR-AAA represents 5.9% of all AAA and 29.4% of rAAA. To prevent this potentially fatal condition, awareness is required especially in old males with abdominal or back pain.

Signs of impending rupture in abdominal aortic and iliac artery aneurysms by computed tomography: Outcomes in 41 patients

OBJECTIVES

This study aimed to determine the prevalence of signs of impending rupture (SIR) in asymptomatic patients with abdominal aortic and iliac artery aneurysms, and to evaluate whether these signs were associated with rupture in asymptomatic patients.

METHODS

This was a retrospective study of patients with abdominal aortic and iliac artery aneurysms identified on computed tomography (CT) over a 10-year period in a single center. The CT scans were reviewed by two reviewers, and patients with SIR were assigned to one of three groups: (1) early symptomatic (ES), (2) late symptomatic (LS), and (3) always asymptomatic (AA). The four main SIR described in the literature were investigated: 1) crescent sign, 2) focal wall discontinuity of circumferential calcifications, 3) aortic bulges or blebs, and 4) aortic draping.

RESULTS

From a total of 759 aortic and iliac aneurysm reports on 2226 CT scans, we identified 41 patients with at least one SIR, and a prevalence of 4.14% in asymptomatic patients. Focal wall discontinuity of circumferential calcifications was the most common sign, and it was present in 46.3% of these patients (19/41); among these, 26 were repaired (ES: 9, LS: 2, AA: 15). Eleven asymptomatic patients underwent follow-up CT. The aneurysm increased in size in 6 of the 11 (54.5%) patients, and three ruptured (all with discontinuity of calcifications), one of which had no increase in diameter.

CONCLUSIONS

The presence of focal wall discontinuity of circumferential calcifications was the most common SIR. There was a prevalence of all signs in less than 5% of asymptomatic patients. In unrepaired patients, the signs could be observed on follow-up CT scans with an increase in aneurysm size, indicating that the presence of SIR alone in the absence of other clinical factors or aneurysm characteristics is an insufficient indication for surgery.

Scannographic Study of Risk Factors of Abdominal Aortic Aneurysm Rupture

BACKGROUND

Current decision about when to operate abdominal aortic aneurysms (AAAs) is based only on the maximum aneurysm diameter (MAD). However, small aneurysms still rupture and we can observe very large AAA without any symptom. A simple morphologic analysis could be a tool to assess the risk of rupture. The main objective of this study was to assess the relevance of ratios between MAD and healthy aorta on computed tomography (CT) as a risk factor of AAA rupture. The secondary objective was to evaluate CT signs as risk factors of AAA rupture.

METHODS

Retrospective observational bicentric study comparing CT scans of a ruptured AAA group and a control group treated electively was conducted. Appariement 1:1 based on MAD was applied. Ratios between healthy aorta diameters at several levels, celiac trunk (CTR), superior mesenteric artery (SMA), highest renal artery (RA), and the MAD were calculated. The presence of blebs, crescent signs, ruptures of calcifications of the aneurysm sack, and draped aorta were notified.

RESULTS

From 2010 to 2016, 38 ruptured AAA and 38 controls were included. Ratios were superior in the rupture group, respectively: MAD/CTR [2.77 (±0.5) versus 2.58 (±0.4) P < 0.095], MAD/SMA [2.92 (±0.7) versus 2.74 (±0.5) P < 0.194], and MAD/RA [3.02 (±0.70) versus 2.76 (±0.5) P < 0.054] but not significatively. Receiver operating characteristic curve analysis demonstrated optimal threshold to detect rupture at 2.8 for the ratio MAD/CTR (area under the curve (AUC) 0.593, sensitivity 47.4%, specificity 78.9%), at 3.3 for the ratio MAD/SMA (AUC 0.564, sensitivity 31.6%, specificity 92.1%), and at 3.3 for the ratio MAD/RA (AUC 0.591, sensitivity 31.6%, specificity 94.7%). Bivariate analysis for rupture risk factor showed significance for the three ratios (MAD/CTR > 2.8 [OR = 11 (1.42; 85.20) P < 0.0217], MAD/SMA > 3.3 [OR = 10 (1.28; 78.12) P < 0.0281], and MAD/RA >3.3 [OR = 11.00 (1.42; 85.20) P < 0.0217]). One scannographic sign was more present in the rupture group: crescent sign 36.8% versus 5.3%, P = 0.0007, as well in bivariate analysis [OR = 7 (1.59; 30.80) P < 0.0326].

CONCLUSIONS

In our experience, specific ratios when they exceed calculated threshold, seem to be more prone to rupture. We could consider that these measures, easy to apply in clinical practice, would be complementary keys for rupture risk individual assessment.

Multidetector Computed Tomography in Traumatic and Nontraumatic Aortic Emergencies: Emphasis on Acute Aortic Syndromes

Aortic emergencies comprise of a list of conditions which are uncommon but are potentially fatal. Prognosis is usually determined by emergent diagnosis and treatment and hence radiology plays a key role in patient management. In this article, we aim to review the various causes of aortic emergencies and the relevant imaging findings placing special emphasis on acute aortic syndromes.

Incidental findings in lumbar spine MRI: their prevalence and potential impact on patient management

Background

To document the prevalence of extra spinal findings in lumbar MRI

Results

Among the scanned 400 patients, 90 cases had incidental non-spinal findings, and in 30 out of these 90 patients, the finding was the only reason for their complaint.

Conclusions

Radiologists should give attention to the non-spinal findings in lumbar spine MRI, as the detected pathology could be the source of pain or could potential life-threatening conditions.

Abdominal aortic aneurysms that have ruptured or are at imminent risk of rupture

The rupture of an abdominal aortic aneurysm (AAA) is considered a high-risk surgical emergency, given the catastrophic consequences and high mortality rate. The objective of this pictorial essay is to illustrate the radiological signs that indicate rupture or imminent rupture. To that end, we describe cases treated at our facility and present a brief review of the literature on the topic. The clinical diagnosis of imminent AAA rupture can be difficult, because patients are usually asymptomatic or have nonspecific pain complaints. In the subsequent follow-up, it is possible to identify radiological signs that indicate instability or rupture itself and thus change the prognosis. Computed tomography is the modality of choice for evaluating an AAA and abdominal pain in the emergency setting. It is therefore essential that the radiologist immediately identify the imaging findings that indicate AAA rupture or the imminent risk of such rupture.

Abdominal aortic aneurysm: pictorial review of common appearances and complications

Abdominal aortic aneurysms (AAAs) are defined as focal dilatations of the abdominal aorta that are 50% greater than the proximal normal segment or when it is more than 3 cm in maximum diameter. The early diagnosis and treatment is very important to prevent catastrophic complications. Due to its ability to assess the peri-aortic soft tissue and the exact extension of aneurysm, as well as its excellent vascular opacification and multiplanar reconstruction capabilities, computed tomography angiography (CTA) has become an integral part of the evaluation of AAA and has virtually replaced conventional angiography for the evaluation of AAA. Knowledge of the characteristic imaging features of AAA is essential for the prompt diagnosis of life-threatening complications. In this pictorial essay, we will discuss the CTA findings in AAA and its complications including rupture, infection, aorto-enteric fistula and aorto-caval fistula.

Spectrum of Abdominal Aortic Disease in a Tertiary Health Care Setup: MDCT Based Observational Study

INTRODUCTION

Abdominal aortic disease is an important cause of clinical disability that requires early detection by imaging methods for prompt and effective management. Understanding regional disease pattern and prevalence has a bearing on healthcare management and resource planning. Non-invasive, conclusive imaging strategy plays an important role in the detection of disease. Multi-Detector Computed Tomography (MDCT) with its technological developments provides affordable, accurate and comprehensive imaging solution.

AIM

To evaluate regional demography of abdominal aortic disease spectrum detected using MDCT imaging data in a tertiary hospital.

MATERIALS AND METHODS

A descriptive study was conducted based on MDCT imaging data of patients who were investigated with clinical diagnosis of abdominal aortic disease, from March 2008-2010, over a period of 24 months. Patients were examined with the contrast-enhanced MDCT examination. Morphological diagnosis of the aortic disease was based on changes in relative aortic caliber, luminal irregularity, presence of wall calcification, dissection or thrombus and evidence of major branch occlusion. Patients were categorized into four groups based on imaging findings. MDCT information and associated clinical parameters were examined and correlated to management of patient. Descriptive statistical data, namely mean, standard deviation and frequency of disease were evaluated.

RESULTS

A total of 90 out of 210 patients (43%) were detected with the abdominal aortic abnormality defined by imaging criteria. Group I, comprising of patients with atherosclerosis -including those with complications, constituted 65.5% of the patients. Group II represented patients with aneurysms (45.5%). Group III, consisting of 32.2% of the patients, contained those with dissections. The rest of the patients, including patients with aorto-arteritis, were classified as group IV. Eight patients with aneurysm and one patient with aorto-arteritis were considered for surgical treatment. Ten patients with dissection underwent endovascular procedure. Rest of the patients was managed conservatively.

CONCLUSION

Aortic disease was observed in 43% of investigated patients. Atherosclerosis with and without aortic aneurysm constituted the largest group. MDCT provided comprehensive information about the lesion and associated complications. In view of the wider availability and desired imaging qualities, MDCT provided optimal information for diagnosis and management of aortic pathology. Majority of our patients (90%) were treated conservatively.

Impending aortic aneurysm rupture - a case report and review of the warning signs

Abdominal aortic aneurysm (AAA) may present with subtle clinical findings. Recognition of the imaging features of an impending rupture is key for timely diagnosis. This report reviews the classic computed tomography findings of impending AAA rupture and presents a recent case which illustrates the key features.

Unstable abdominal aortic aneurysms: a review of MDCT imaging features

Abdominal aortic aneurysms are commonly encountered during abdominal CT imaging, and size-based parameters for surgical or endovascular repair are well established. Aneurysms greater than 5 cm in diameter are recognized as representing an increased rupture risk and meriting intervention. Increasingly, additional interest has been generated in recognizing imaging features which may herald instability and portend a higher chance for potentially catastrophic rupture. This article will review and illustrate such signs, including hyperattenuation of mural thrombus, rapid expansion, low thrombus to lumen ratio, intimal calcification disruption, posterior mural draping, and saccular outpouching. Other features of complicated abdominal aneurysms including perianeurysmal inflammation, aortocaval and aortoenteric fistula formation will also be addressed. Heightened awareness of these features and their prognostic implications, as well as timely communication with the clinical service, is critical for the interpreting radiologist.