Examination of the Aorta

Because atherosclerosis is the most common lesion affecting the aorta, the aorta should be opened longitudinally along its posterior or dorsal aspect from the ascending aorta through the bifurcation and into both common iliac arteries. The extent of disease and the types of lesions may then be described. While this method enables inspection of the complete intimal surface, it may not be optimal for certain types of pathology, such as aortic aneurysms, which may best be demonstrated by cross-sectional slices 1 to 1.5 cm apart in the perfusion-fixed, distended specimen (Figure 2.2.1.9). Aortic dissections may be examined by a longitudinal cut (long-axis cut) with the aorta cut into anterior and posterior halves (Figure 2.2.1.10) or by transverse cut at 1- to 1.5-cm intervals after the aorta has been allowed to fix for 24 hours in a distended state or free floating in anatomic position in formaldehyde.

Figure 2.2.1.9 (A) External view of the abdominal aorta with an infrarenal aneurysm (arrows). Note the size, which is best expressed as the largest diameter. In this case, it is 7 cm. (B) Same aneurysm cut transversely at 1.0 to 1.5 cm apart. Note the extent of luminal (L) narrowing secondary to an organizing thrombus. (From Virmani, R., Ursell, P.C., and Fenoglio, J.J., Examination of the heart, in Virmani, R., Atkinson, J.B., and Fenoglio, J.J., Eds., Cardiovascular Pathology, W.B. Saunders, Philadelphia, 1991, pp 1-20. With permission.)

Figure 2.2.1.9 (A) External view of the abdominal aorta with an infrarenal aneurysm (arrows). Note the size, which is best expressed as the largest diameter. In this case, it is 7 cm. (B) Same aneurysm cut transversely at 1.0 to 1.5 cm apart. Note the extent of luminal (L) narrowing secondary to an organizing thrombus. (From Virmani, R., Ursell, P.C., and Fenoglio, J.J., Examination of the heart, in Virmani, R., Atkinson, J.B., and Fenoglio, J.J., Eds., Cardiovascular Pathology, W.B. Saunders, Philadelphia, 1991, pp 1-20. With permission.)

Figure 2.2.1.10 The heart has been cut in the long-axis plane, exposing the right and left ventricles and the aortic root and valve. In this plane, the anterior wall of the aorta has been removed. Note the dissecting aneurysm that starts just distal to the subclavian artery and extends along the greater curvature of the aorta to just below the left renal artery (arrowhead). Within the false lumen there are fibrous strands (arrows) connecting the outer media and adventitia to the inner media and intima. Note also the organizing thrombus within a fusiform aneurysm distal to the subclavian and within the abdominal aorta of the false lumen. (From Virmani, R., Ursell, P.C., and Fenoglio, J.J., Examination of the heart, in Virmani, R., Atkinson, J.B., and Fenoglio, J.J., Eds., Cardiovascular Pathology, W.B. Saunders, Philadelphia, 1991, pp 1-20. With permission.)

Eustach

Triant

Eustach

Triant

Medial papillary muscle

AV node

Figure 2.2.1.11 Diagram of location of the atrioventricular (AV) and sinoatrial (SA) nodes along with the landmarks that help in locating their positions during sectioning of the heart. (Modified from Davies, M.J., Anderson, R.H., and Becker, A.E., The Conduction System of the Heart, Butterworth & Co, London, 1983. From Virmani, R., Ursell, P.C., and Fenoglio, J.J., Examination of the heart, in Virmani, R., Atkinson, J.B., and Fenoglio, J.J., Eds., Cardiovascular Pathology, W.B. Saunders, Philadelphia, 1991, pp 1-20. With permission.)

Annulus of tricuspid vaĆ­ve

Membranous septum

Medial papillary muscle

AV node

Figure 2.2.1.11 Diagram of location of the atrioventricular (AV) and sinoatrial (SA) nodes along with the landmarks that help in locating their positions during sectioning of the heart. (Modified from Davies, M.J., Anderson, R.H., and Becker, A.E., The Conduction System of the Heart, Butterworth & Co, London, 1983. From Virmani, R., Ursell, P.C., and Fenoglio, J.J., Examination of the heart, in Virmani, R., Atkinson, J.B., and Fenoglio, J.J., Eds., Cardiovascular Pathology, W.B. Saunders, Philadelphia, 1991, pp 1-20. With permission.)

For cases in which conduction disturbances were suspected clinically, histologic examination of the cardiac conduction tissues is often rewarding in terms of documenting a structural basis for the problem. Many pathologists are intimidated by the prospect of doing conduction system studies because the pertinent tissue cannot be visualized grossly. Yet, with practice and careful attention to anatomic landmarks, this part of the examination of the heart is really not so difficult.18'19

In most humans, the sinus node is a spindle-shaped structure located in the sulcus terminalis on the lateral aspect of the superior vena cava and the right atrium (Figure 2.2.1. 11). In some patients, it is a horseshoe-shaped structure wrapped across the superior aspect of this cavoatrial junction. Histologically, the sinus node consists of relatively small-diameter, haphazardly oriented atrial muscle cells admixed with connective tissue, collagen, and elastic fibers (Figure 2.2.1.12). Often, the artery to the sinus node can be identified in or around the nodal tissue. Because the sinus node is not visible grossly, the entire block of tissue from the suspected area should be taken and serially sectioned, either in the plane perpendicular to the sulcus terminalis (parallel to the long axis of the superior vena cave) or in the plane containing the sulcus (perpendicular to the vessel). In small infants, serial sectioning of the entire cavoatrial junction is preferred.

There are no anatomically distinct muscle tracts for conduction through the atria. The impulse is collected in the atrioventricular node, which is located within the triangle of Koch in the floor of the right atrium. In the heart dissected in the traditional manner along the lines of blood flow, this region is delineated by the following landmarks: the tricuspid valve annulus inferiorly, the coronary sinus posteriorly, and the continuation of the valve guarding the coronary sinus (tendon of Todaro) superiorly (Figure 2.2.1.11). The atrioventricular node lies within Koch's triangle (Figure 2.2.1.11), and the apex of the triangle anteriorly denotes the point at which the common bundle of His penetrates the fibrous annulus to reach the left

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