Amyloid deposition (amyloidosis) is a systemic disease that is rare in B6C3F1, BALB/c, and C3H/HeJ mice and in rats but is common in CD-1, A, Swiss Webster, SJL, and C57BL/6 mice. In B6C3F1 mice, vascular deposits can be limited to a single tissue (e.g., jejunum, pancreas, testis). Amyloid appears as an amorphous, eosinophilic, extracellular substance that expands the tunica media and tunica adventitia of small to midsize arteries and, less frequently, veins. Congo red stains amyloid orange to orange-red and under polarized light imparts a light green, so-called apple green fluorescence.
Deposition of amyloid damages the tunica media and adventitia of affected vessels, resulting in stenosis of the vascular lumen and fragmentation of the internal elastic lamina. These changes may result in fibrinoid necrosis and microaneurysm formation, predisposing to hemorrhage and infarction.
Amyloid should be recorded and graded based on the extent of deposition. Amyloid should be recorded in the organ affected; the type of blood vessel affected should be specified as a site modifier (artery or vein). If the type of blood vessel cannot be determined, the site modifier "blood vessel" may be used. Amyloid in protocol-required blood great vessels, such as aorta, should be recorded with the blood vessel as the site (e.g., Aorta - Amyloid).
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