Basics of Microscopic Autopsy Examination

Question 1

General principles for tissue fixation and handling

Answer 1

1. Avoid excessive handling and force
2. Do not allow tissue to dry out
3. Use adequate fixative (10 vol fixative : 1 vol tissue)
4. Gently remove large collections of blood from external tissue surfaces (eg, circle of Willis in case of vessel rupture) before fixation

Question 2

Bloody fixatives fix. . .

Answer 2

poorly

Question 3

Alcohol solutions as fixatives

Answer 3

Compared to PFA, alcohol-based fixatives are less toxic, but cause increased tissue shrinkage and brittleness.

Question 4

Microwave fixation

Answer 4

Microwave light may be utilized to speed alcohol or formaldehyde fixation, with optimal fixation between 45C and 55C.

However, there is the possibility of overheating artifact.

Question 5

Overheating artifact

Answer 5

Characterized by tissue vacuoles, pyknotic nuclei, and overstained cytoplasm.

Question 6

Decalcifying solution “classes”

Answer 6

Strong acids (5%-10% nitric acid or hydrochloric acid): Best for thick bony specimens.
Weak acids (5-25% formic acid, sometimes picric acid or trichloroacetic acid): Best for thin bony specimens (ribs, calcified vessels)
Chelators (EDTA): Best for trace calcification.

Question 7

When a coronary artery is significantly narrowed (>50% stenosis) but there is no gross evidence of infarct. . .

Answer 7

. . . sample the myocardium adjacent to and distant to the arterial lesion.

Question 8

Examination of coronary arteries

Answer 8

1. Transect perpendicularly to the path of the vessel in regular, ~3mm intervals.
2. Note the extent of plaque along the vessel
3. Note the degree of stenosis of the vessel
4. Select the narrowest sections and any area containing candidate thrombi for microscopic evaluation

Question 9

LAD grafts are typically added. . .

Answer 9

. . . end-to-side from the aortic arch

Question 10

RCA grafts are typically added. . .

Answer 10

. . . side-to-side from the aortic arch

Question 11

Anatomic position of the SA node on gross heart dissection

Answer 11

Identify the terminal sulcus between the takeoff of the SVC and the right atrium. This may be obscured by adipose tissue and require careful blunt dissection.

This groove will contain the SA node. It should be removed whole in a 2cm-wide block, including 0.5cm of SVC and 0.5 cm of atrium.

Question 12

Principals of polarized light microscopy

Answer 12

Polarized light is shined through the sample and onto an analyzer.

Compensators are efficient birefringent materials that retard one of the colors of the visible spectrum.

Microscopes for clinical applications are equipped with red compensators, which turn the microscopic field red and causes birefringent material in the visible field to become blue (positive elongation) or yellow (negative elongation).

Question 13

Bone marrow imprint

Answer 13

A 0.5cm to 1cm cubic sample of marrow is squeezed out of a rib and placed on a piece of cardboard.

A clean microscope slide is then lightly applied to the marrow, allowing for a small touch prep.

Next, the slide is applied to another slide in order to spread the marrow out under pressure. The slides are lifted apart, air dried, and stained.

Question 14

Fixative for electron microscopy

Answer 14

2.5% Buffered glutaraldehyde