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Imaging description Focal left ventricular hypertrophy is a variant phenotype of hypertrophic cardiomyopathy (HCM) usually described as involvement of Importance Focal HCM can have a mass-like appearance and irregular delayed enhancement that may lead to incorrect diagnosis of a cardiac tumor such as metastasis, lymphoma, fibroma, or rhabdomyoma. This can lead to patient anxiety, inappropriate biopsies, or even surgery. Typical clinical scenario HCM is the most common primary genetic disease of the heart and has a prevalence of 1:500 in the general population. In a large study of 333 individuals with HCM, 12% of patients had the focal pattern of hypertrophy. Patients with a focal pattern of HCM may be initially detected by echocardiography, which can lead to further evaluation by cardiac MRI. Patients are often asymptomatic or may have symptomatic left ventricular outflow tract obstruction due to septal wall hypertrophy and/or systolic anterior motion of the anterior mitral valve leaflets. Differential diagnosis The differential diagnosis includes metastatic and primary cardiac tumors.

Imaging description Motion artifact in coronary CT angiography (CCTA) occurs when the temporal resolution of the acquisition is inadequate to resolve moving cardiac structures. A temporal resolution of 70 beats per minute), reconstructed phases obtained in end-systole at approximately 30–40% of the R-R interval have the greatest chance of diagnostic images. For motion-degraded CCTA examinations, multiple reconstructed phases can often be used to piece together a comprehensive assessment of the coronary arteries. In this scenario, not all vessel segments will be best visualized on a single phase, but each segment is well visualized on at least one phase. Importance Motion blurring can simulate coronary artery stenosis. The motion leads to blurring of the coronary lumen and adjacent low-attenuation fat, resulting in an appearance mimicking high-grade stenosis. Reconstructed phases from different points in the cardiac cycle should be evaluated to confirm or disprove any significant coronary artery stenosis (Figure 32.2). Motion artifact is the major reason for non-diagnostic scans.

Imaging description Cor triatriatum, also known as cor triatriatum sinister, is a congenital abnormality of the left atrium in which a fibromuscular membrane separates the atrium into anterior and posterior chambers (Figure 21.1). The membrane appears as a low-attenuation structure on cardiac CT extending from the atrial septum medially to the ridge of tissue between left pulmonary vein ostia and the left atrial appendage laterally. Cor triatriatum is the result of incomplete fusion of a common pulmonary vein chamber posteriorly with the anterior mitral valve and left atrial appendage during fetal life. The result is a fibromuscular membrane within the left atrium which usually contains one or multiple openings that allow communication between anterior and posterior chambers. Depending on the size of the opening(s) of the membrane, there may be obstruction of pulmonary venous outflow, resulting in symptoms similar to mitral stenosis. Cor triatriatum with larger defects may present with symptoms late in adulthood or can be entirely asymptomatic (Figures 21.1, 21.2). Importance Cor triatriatum is an uncommon abnormality, which in adults is frequently misdiagnosed at initial presentation as mitral valve disease or pulmonary hypertension. If identified, it is important to draw attention to the abnormality and recommend further non-invasive evaluation with echocardiography to assess for any functionally significant obstruction that might require surgical treatment. Typical clinical scenario Cor triatriatum is a rare abnormality, accounting for less than 1% of all congenital cardiac malformations. The majority of patients with cor triatriatum present in infancy; however, a minority of patients will present in adulthood. Differential diagnosis Cor triatriatum should be differentiated from a complete total anomalous pulmonary venous return, in which pulmonary veins connect to a common venous chamber that drains separately into the heart. Chronic left atrial clot can sometimes have angular or web-like appearances that may simulate cor triatriatum; however, it will often be associated with a masslike thrombus or calcifications.

Imaging description Ductus diverticulum (DD) is an anatomic variant incidentally found at cardiovascular imaging characterized by a smooth bulge of the anterior wall of the aorta at the aortic isthmus, just distal to the origin of the left subclavian artery. DD is best visualized on sagittal oblique reconstructions on CT, MRI, or digital subtraction angiography (DSA) (Figures 57.1 and 57.2). DD may be difficult to appreciate on standard axial images. On reconstructions, it is recognized as an anteriorly directed bulge of the undersurface of the aortic arch that extends to the proximal descending thoracic aorta. DD has smooth, gentle margins, and obtuse shoulders. Importance DD must not be confused with traumatic aortic transection or ductus arteriosus aneurysm, both of which can occur at the same location and have a greater risk of morbidity and mortality. Typical clinical case scenario DD is typically encountered as an incidental finding on CT, MR or DSA and is of no clinical significance. It occurs in approximately 26% of adults and requires no follow-up or treatment. Differential diagnosis Traumatic aortic transection, also known as post-traumatic pseudoaneurysm, is found in patients with a history of highvelocity trauma. At cross-sectional imaging, aortic transections arise from the anterior wall of the aorta at the isthmus, similar to DD. However, aortic transections have acute angles with the aortic wall, are irregular in shape and size, and often have a visible intimal flap (Figure 57.3). There may be a narrow neck that communicates with the aorta. Associated periaortic and mediastinal hematoma are typically present with traumatic aortic transection. Aneurysm of the ductus arteriosus is a rare entity characterized by a saccular aneurysm of the undersurface of the aortic arch in the region of the ductus arteriosus (Figure 57.4). Wall calcifications and partial thrombosis are frequently present. Some believe this entity is due to incomplete obliteration of the patent ductus arteriosus during early development that results in a blind-ending stump communicating with the aortic lumen. Progressive enlargement occurs over years.

Imaging description Left atrial appendage pseudothrombus is not uncommonly encountered in patients with left atrial enlargement and poor atrial function. In this entity, stasis of blood in the left atrium results in incomplete mixing, or underfilling, of nonopacified blood in the left atrial appendage with intravenous contrast. The result is a low-attenuation region in the tip of the appendage that can be mistaken for thrombus (Figure 6.1). At transesophageal echocardiography, the gold standard for evaluation of left atrial appendage thrombus, underfilling of the left atrial appendage on CT, usually corresponds to spontaneous echo contrast, a sign of blood stasis, with or without thrombus. Importance Left atrial pseudothrombus is relatively common in patients with atrial fibrillation who undergo cardiac CT for preablation mapping. In a large study of 402 atrial fibrillation patients with 64-slice contrast enhanced CT, underfilling of the left atrial appendage was seen in 40 (10%), with nine of these patients having true thrombus detected by transesophageal echocardiography. The remaining patients had spontaneous echo contrast. Left atrial underfilling is also important to recognize in patients with a history of stroke, who may have emboli originating from the left atrium. If underfilling is recognized at the time of imaging, acquisition of additional delayed images can improve differentiation of thrombus from blood stasis (Figure 6.1). Distinction of true left atrial thrombus from pseudothrombus is critical as ablation procedures should not be performed in the presence of thrombus, due to the risk of clot dislodgement and distal embolization during the procedure. Incorrect diagnosis of thrombus can result in unnecessary delay of ablation therapy and risks of anticoagulation medications. Typical clinical scenario Left atrial pseudothrombus can be seen in any patient, but is most commonly encountered in patients with dilated, poorly functioning atria. These patients have poor mixing of blood in the left atrial appendage due to stasis. Unfortunately, these same characteristics also put the patients at high risk for true left atrial thrombus, increasing the challenge of diagnosis.