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Autopsy Examination of the Coronary Arteries
The method used to examine coronary artery depend on how comprehensive an answer is required.
The position of the coronary artery orifices should always be checked.
A malleable blunt-ended probe 2-3 mm in diameter can be used to find the orifices even when the aortic valve has not been opened.
If the probe slips in easily there is no ostial stenosis.
At this stage the simplest way to proceed is to cut cross-sections across the coronary arteries at 3mm intervals starting close to the aorta.
The presence of high-grade stenosis is indicated to the naked eye by a pinpoint lumen.
This corresponds to about 70% diameter stenosis.
With the high backround level of atherosclerosis, it is always difficult to know the significance of single areas of high-grade stenosis or of multiple segments of less severe stenosis.
The problem becomes particularly difficult if an autopsy report records "moderate atherosclerosis" and legal questions on life expectancy emerge.
It is advisable always to record the number of vessels with high grade stenosis and the anatomical points at which stenosis occurs.
Naked-eye examination of multiple cross-sections will show the presence or absence of thrombus and failure to find thrombus in regional infarction is more related to a failure to cut cross-sections of the relevant artery than failure to recognise thrombus with the naked eye.
This approach is often limited by calcification.
If cross-sections cannot be cut with a scalpel the pathologist has two options.
(i) A heavy pair of scissors can be used to cut the sections, but the ragged ends make the naked-eye assessment of stenosis even more difficult.
(ii) The second option is to dissect the coronary arteries from the heart and decalcify the tissue.
Which technique is adopted depends on the circumstances.
Opening the coronary arteries longitudinally has limited applications. It does show the presence or absence of atherosclerosis ; the percentage of the intimal area occupied by plaques is a classic epidemiological tool used to compare populations.
The technique of slitting the artery open is easy and quick but ensures that the exact degree of stenosis at any particular point will never be known.
More specialised methods of assessing coronary artery disease at autopsy exist.
Post-mortem angiography produces pictures directly comparable to those obtained in life.
Another method of examining coronary arteries is by perfusion fixation of the aorta with formal saline at a pressure of 100 mmHg.
The aortic valve closes and the coronary arteries are perfused.
After perfusion for 24 hours, the coronary arteries are dissected free from the heart, decalcified and then examined in serial cross-cuts at 3mm intervals.
This method, while time consuming, allows very accurate measurements of the lumen cross-sectional area along the whole length of the artery, free from interference by calcium or collapse of the vessel to produce non-circular lumens.
Examination of the cross-sections under a dissection microscope gives very striking visual images of the different type of plaque and of plaque disruption with thrombosis.
Correlation of Clinical and Pathological Estimation of Coronary Stenosis:
Clinicians measure the diameter of the lumen at a segment of stenosis and compare it with the diameter of a normal adjacent segment of artery.
Pathologists, particularly when measuring stenosis from histological sections, compare the lumen diameter with the diameter of the vessel at that point.
This introduces major discrepancy because it ignores the remodelling and increase in vessel diameter that occurs with atherosclerosis.
For the pathologist perhaps the single most important observation is that if the lumen appears as a pinpoint, it is significant stenosis.
Pathologists can be less certain of the significance of plaques which appear to occupy half the cross-section of the artery.
Specimens from coronary artery bypass procedures:
These include native coronary arteries, internal mammary artery (internal thoracic artery) and vein grafts.
The internal mammary artery may have a segment trimmed from adjacent to the area of anastomosis and sent for histological assessment to confirm that it has no intrinsic disease which might compromise the graft.
The clinical information needed is essentially the same as for the other conditions listed above.
Pathologist should comment on the following features in histopathology report:
Atheroma : Degree of occlusion ;
Thrombus : Age, assessed by the presence of recanalization , fibrosis etc. ;
Underlying vascular pathology other than atheroma, such as arteritis or phlebitis ;
Intimal thickening :Purely fibroblastic or lipid-rich as in atheroma.
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