Cardiac Anatomy Using CT
Typically, cardiac CT axial examinations are specifically tailored to image the heart, and therefore the imaging volume is restricted to only a portion of the thorax. Often the examination begins just below the carina, as this first plate shows. Note how the contrast bolus shows bright enhancement of the left-sided cardiovascular structures—the aorta and pulmonary veins—whereas right-sided structures (pulmonary arteries) are poorly enhanced. This is purposely accomplished by following the intravenous contrast bolus with a saline injection to “wash out” dense intravenous contrast from the right heart and thereby improve visualization of the right coronary artery.
Several millimeters inferior to Axial 1 again shows intense enhancement of left-sided cardiovascular structures—the ascending and descending thoracic aorta and pulmonary veins. A small amount of normal pericardial fluid is seen within the left pulmonic recess of the transverse sinus of the pericardium. The origin of the right middle lobe pulmonary artery is visible, marking the distal aspect of the right interlobar pulmonary artery and the beginning of the right lower lobe pulmonary artery.
The medial segment of the right middle lobe and lingular arteries are visible at this level. Usually the right middle lobe pulmonary artery arises from the distal right interlobar pulmonary artery and branches into medial and lateral segments. However, in this patient, the medial and lateral segments of the right middle lobe pulmonary artery arise directly from the right interlobar pulmonary artery.
The pericardial space is divided into the pericardium proper, consisting of a postcaval recess and right and left pulmonary vein recesses, and the transverse and oblique sinuses. The transverse sinus lies posterior to the ascending aorta and main pulmonary artery and cranial to the left atrium. The transverse sinus is further subdivided into superior and inferior aortic recesses and right and left pulmonic recesses. The oblique sinus also contains the posterior pericardial recess. Small amounts of fluid are commonly seen within some of these compartments in normal patients during thoracic and cardiovascular CT examinations.
Along the anterior aspect of the ascending aorta and main pulmonary artery, the normal pericardium is visible. A small amount of fluid immediately subjacent to the pericardium in this region, interposed between the ascending aorta and main pulmonary artery (∗), is within the anterior portion of the superior recess of the transverse sinus.
The crista terminalis is now just visible and will be readily visualized on views that follow. The crista terminalis is a vertical fibromuscular ridge that separates the smooth portion of the right atrium, which receives the superior and inferior vena cavae and coronary sinus, from the right atrial appendage and the remainder of the right atrium containing pectinate muscles. The crista terminalis extends superiorly from the anterior margin of the superior vena cava along the lateral wall of the right atrium inferiorly toward the inferior vena cava. A prominent crista terminalis can occasionally be mistaken for a right atrial mass on imaging studies.
This image shows the origin of the first septal perforator branch of the proximal left anterior descending coronary artery (also known as the anterior interventricular branch of the left coronary artery). The first septal perforator coronary artery provides blood flow to the interventricular septum and conduction system of the heart. Disruption of blood flow within the proximal segment of the left anterior descending artery and first septal perforator vessel, as may occur with significant atherosclerosis in the left main or proximal left anterior descending coronary arteries, may result in cardiac dysrhythmias and a large myocardial infarction, leading to sudden cardiac death.
The sinoatrial nodal coronary artery is visible. The sinoatrial node is the source of the cardiac impulse and is typically located at the junction of the superior vena cava and right atrium, in the superior end of the crista terminalis. The sinoatrial nodal artery usually arises as a single branch from the right coronary artery, as in this patient (see Axials 20 to 25