ACR Appropriateness Criteria ® Pulsatile Abdominal Mass Suspected Abdominal Aortic Aneurysm

The Challenge of Endoleaks in Endovascular Aneurysm Repair (EVAR): A Review of Their Types and Management

An abdominal aortic aneurysm (AAA) is a dilatation of the abdominal aorta above 3 cm or 50% greater than the segment above. It is a dangerous condition accounting for a substantial number of deaths per year and increasing at an alarming rate. Various factors come into play in the development of AAAs, which this study has elaborated on, including smoking and old age, demographics, and comorbid conditions. Endovascular aneurysm repair (EVAR) is a newer treatment modality used for AAAs in which an endograft device is placed into the aorta, thereby creating a bypass tract from the aneurysm and generating flow mimicking that of the natural aorta. It is minimally invasive and associated with less postoperative mortality and reduced hospital stay. However, EVAR is also associated with significant postoperative complications, including endoleaks, which were reviewed in depth. Endoleaks are postprocedural leaks into the aneurysm sac that are usually identified immediately after graft placement and indicate treatment failure. They are of five subtypes, categorized according to their mechanism of development. The most common type is type II endoleaks, and the most dangerous is type I endoleaks. Each subtype has multiple management options with varying rates of success. Prompt identification along with appropriate treatment of endoleaks can lead to better postoperative outcomes and improved quality of life for patients.

Ultra-low-dose non-contrast CT and CT angiography can be used interchangeably for assessing maximal abdominal aortic diameter

Background

Routine CT scans may increasingly be used to document normal aortic size and to detect incidental abdominal aortic aneurysms.

Purpose

To determine whether ultra-low-dose non-contrast CT (ULDNC-CT) can be used instead of the gold standard CT angiography (CTA) for assessment of maximal abdominal aortic diameter.

Materials and Methods

This retrospective study included 50 patients who underwent CTA and a normal-dose non-contrast CT for suspected renal artery stenosis. ULDNC-CT datasets were generated from the normal-dose non-contrast CT datasets using a simulation technique. Using the centerline technique, radiology consultants (n = 4) and residents (n = 3) determined maximal abdominal aortic diameter. The limits of agreement with the mean (LOAM) was used to access observer agreement. LOAM represents how much a measurement by a single observer may plausibly deviate from the mean of all observers on the specific subject.

Results

Observers completed 1400 measurements encompassing repeated CTA and ULDNC-CT measurements. The mean diameter was 24.0 and 25.0 mm for CTA and ULDNC-CT, respectively, yielding a significant but minor mean difference of 1.0 mm. The 95% LOAM reproducibility was similar for CTA and ULDNC-CT (2.3 vs 2.3 mm). In addition, the 95% LOAM and mean diameters were similar for CTA and ULDNC-CT when observers were grouped as consultants and residents.

Conclusions

Ultra-low-dose non-contrast CT exhibited similar accuracy and reproducibility of measurements compared with CTA for assessing maximal abdominal aortic diameter supporting that ULDNC-CT can be used interchangeably with CTA in the lower range of aortic sizes.

Role of MRI in the Evaluation of Thoracoabdominal Emergencies

Thoracic and abdominal pathology are common in the emergency setting. Although computed tomography is preferred in many clinical situations, magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) have emerged as powerful techniques that often play a complementary role to computed tomography or may have a primary role in selected patient populations in which radiation is of specific concern or intravenous iodinated contrast is contraindicated. This review will highlight the role of MRI and MRA in the emergent imaging of thoracoabdominal pathology, specifically covering acute aortic pathology (acute aortic syndrome, aortic aneurysm, and aortitis), pulmonary embolism, gastrointestinal conditions such as appendicitis and Crohn disease, pancreatic and hepatobiliary disease (pancreatitis, choledocholithiasis, cholecystitis, and liver abscess), and genitourinary pathology (urolithiasis and pyelonephritis). In each section, we will highlight the specific role for MRI, discuss basic imaging protocols, and illustrate the MRI features of commonly encountered thoracoabdominal pathology.

ACR Appropriateness Criteria® Nontraumatic Aortic Disease

Nontraumatic aortic disease can be caused by a wide variety of disorders including congenital, inflammatory, infectious, metabolic, neoplastic, and degenerative processes. Imaging examinations such as radiography, ultrasound, echocardiography, catheter-based angiography, CT, MRI, and nuclear medicine examinations are essential for diagnosis, treatment planning, and assessment of therapeutic response. Depending upon the clinical scenario, each of these modalities has strengths and weaknesses. Whenever possible, the selection of a diagnostic imaging examination should be based upon the best available evidence. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment. The purpose of this document is to assist physicians select the most appropriate diagnostic imaging examination for nontraumatic aortic diseases.

MR Imaging of the Mesenteric Vasculature

MR angiography is a flexible imaging technique enabling morphologic assessment of mesenteric arterial and venous vasculature. Conventional gadolinium-based contrast media and ferumoxytol are used as contrast agents. Ferumoxytol, an intravenous iron replacement therapy approved by the US Food and Drug Administration for iron deficiency anemia, is an effective and well tolerated blood pool contrast agent. The addition of 4D flow MR imaging enables a functional assessment of the arterial and venous vasculature; when coupled with a meal challenge, the severity of mesenteric arterial stenosis is well appreciated. Noncontrast MR angiographic techniques are useful for evaluating suspected mesenteric ischemia.

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.

Principles of three-dimensional printing and clinical applications within the abdomen and pelvis

Improvements in technology and reduction in costs have led to widespread interest in three-dimensional (3D) printing. 3D-printed anatomical models contribute to personalized medicine, surgical planning, and education across medical specialties, and these models are rapidly changing the landscape of clinical practice. A physical object that can be held in one's hands allows for significant advantages over standard two-dimensional (2D) or even 3D computer-based virtual models. Radiologists have the potential to play a significant role as consultants and educators across all specialties by providing 3D-printed models that enhance clinical care. This article reviews the basics of 3D printing, including how models are created from imaging data, clinical applications of 3D printing within the abdomen and pelvis, implications for education and training, limitations, and future directions.