Evaluation Of The Vasculature

Examination of coronary arteries was described earlier in this chapter. For the study of vessels in other organs, see the appropriate chapter. Microscopic evaluation of vascular diseases should include a Verhoff-van Gieson stain.

AORTA AND OTHER MAJOR ARTERIES In general, the thoracic and abdominal portions of the aorta are opened posteriorly, between the origins of the right and left intercostal and lumbar arteries. In cases of congenital heart disease, the thoracic aorta is left attached to the heart. If an acute aortic dissection is suspected, the heart and the entire aorta should be removed intact; transsection of the ascending aorta may distort or destroy the intimal tear. For the evaluation of renovascular disease, the kidneys and renal arteries are best kept together with the abdominal aorta.

Measure all aneurysms in length and diameter. They may be dissected either longitudinally or by cross-section, noting the amount of mural thrombus and the size of the residual lumen. Rupture sites should be studied microscopically for any underlying disease processes. Most forms of obstructive arterial disease are best evaluated by cross-section, but in fibromuscular dysplasia, longitudinal sections are recommended both grossly and microscopically.

Although the mesenteric arterial system can be more rapidly examined by opening the vessels longitudinally, cross-sections are better for the documentation of obstructions. If vasculitis is suspected, multiple cross-sections from the distal portion of the mesentery will reveal many small arteries for microscopic evaluation. The celiac arterial system is best demonstrated by arte-riography (see Chapter 5), followed by dissection of the major branches.

Atherosclerosis of the longitudinally opened aorta is graded according to the percentage of intimal surface area that contains plaques. Four grades of disease exist, based on 25% increments of involvement. Grade 4 implies that more than 75% of the surface area is involved by plaques. Grade 0 indicates an absence of lesions. Mural thrombus, ulceration, calcification, and aneurysm do not affect the grade but are described individually. Usually, the grade is stated separately for the thoracic and abdominal regions (or for the suprarenal and infrarenal regions), because infrarenal disease is often more severe.

Atherosclerosis of aortic branches (such as coronary, renal, and mesenteric arteries) is graded according to the percentage of obstruction in cross-sectional area. Thus, a four-point grading system is applied to cross sections of these vessels, based on 25% increments of involvement. Grade-4 disease indicates a region of stenosis in which more than 75% of the expected cross-sectional area has been obstructed; this often leads to ischemic injury. Total occlusion (100% obstruction) should be specified; it is generally the result of old or acute plaque rupture and thrombosis.

Older methods of evaluating atherosclerosis require longitudinally opened vessels. The intima is stained with Sudan IV solution (68) to facilitate grading, or the vessels are compared with a panel of photographs prepared by the American Heart Association (69). These methods still may be used for research studies.

The patency of grafts and anastomoses should be recorded. Arterial and venous anastomoses in transplanted organs should be inspected for obstruction, including internal thrombosis and external compression or stricture. Synthetic vascular grafts may also compress or erode into adjacent structures. Infected grafts or aneurysm can be cultured, as described in Chapter 9.

POSTMORTEM ANGIOGRAPHY Arteriographic methods are described in Chapter 12.

OBTAINING VESSELS AFTER EMBALMING In general, the vessels of the neck, face, arms, and legs are inaccessible to the prosector until after embalming. For removal of the neck vessels, see Chapter 6. Temporal arteries may be resected from the subcutaneous aspect of the skin flap made during removal of the brain. The femoral and popliteal vessels can be removed without having to make skin incisions along the legs (70). For this method, an aluminum tube is used, which measures approx 1.5 cm in internal diameter and 75 cm in length and which has been sharpened distally to form a cutting edge (Fig. 3-12). A string is tied around the femoral artery and vein, just proximal to the inguinal ligament, and passed through the metal tube. By pulling on the string, a constant pressure is placed on the vessel, while the tubing is pushed down the thigh, with a twisting motion, toward the popliteal fossa. Then the tension on the string is released, and the vessels are cut distally by twisting the sharpened edge of the tube. Femoral and popliteal vessels are removed intact with the tube. Veins can be opened longitudinally and inspected for thrombus, particularly in the pockets of the venous valves, but arteries should be cut in cross section.

EVALUATION OF AIR AND FAT EMBOLISM Diagnostic autopsy methods are described in Part II of this book (see "Embolism, air" and "Embolism, fat").

EVALUATION OF LYMPHATIC VESSELS Under normal circumstances, only the thoracic duct and its main tributaries can be evaluated. Distended small lymphatic vessels can be identified in conditions such as lymphatic carcinomatosis, congestive heart failure, and cirrhosis of the liver.

The thoracic duct lies in the adipose tissue behind the descending aorta and is best dissected from the left side. It usually travels

Fig. 3-12. Aluminum tube for the removal of the femoral and popliteal vessels. (A) Extracted femoral-popliteal vessels, with metal tube (to the right). (B) Bilateral venous thrombosis, in opened femoral and popliteal veins. (C) Cutting edge of the metal tube.

medial to the azygos vein and crosses over to the left side of the vertebral column at the level of the aortic arch. For exposure, the left lung is either lifted upward (and held there by an assistant) or removed from the chest cavity. The intercostal arteries are transsected close to the aorta, and the descending thoracic aorta is pulled rightward so that the thoracic duct can be dissected from the surrounding fat tissue (Fig. 3-13). Care must be taken not to lacerate it, particularly near the aortic arch, to which it is closely related. Dissection is facilitated by injecting saline or gelatin solution, with or without dye. Contrast medium may be injected for lymphangiography (see Chapter 12).

Some pathologists prefer to dissect the thoracic duct after the chest organs have been removed from the body. To avoid laceration of the duct, the mediastinal tissues must be separated from the spine immediately above the vertebral periosteum. If injection of the duct and its tributaries is planned, this must be done before the thoracic organs are removed.

Peripheral lymphatics can be demonstrated at autopsy by lymphangiography. Because retrograde injection is rarely successful, a peripheral lymphatic channel must be identified. It is then cannulated with a 27-gauge needle. For contrast medium, one can use Ethiodol, stained with a few drops of oil paint, or a dilute barium sulfate mixture (71). Owing to the thick medium and small needle caliber, the required injection pressure may be quite high (500-600 mm Hg).

Lymphatic channels can also be demonstrated by applying a 3% solution of hydrogen peroxide onto the surface of an organ or tissue, which will cause after a short time the spontaneous inflation of lymphatics with oxygen. The results may be unimpressive but can be improved if the tissues are first aged for 12-24 h and then soaked for 4-8 h in a 1:10 dilution of a stock solution of 10 gallons of water, 20 lb of crystalline phenol, 5 lb of potassium nitrate, 1.5 lb of sodium arsenite, 1.5 gallons of glycerin, 1.5 gallons of ethanol, and 0.5 gallon of formalin. After this, the samples are immersed for several minutes in 1% hydrogen peroxide (72).

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