Adrenal Gland - Amyloid

The term "amyloid" classically denotes various insoluble, fibrillar proteins that share a similar configuration (β-pleated sheets). These abnormally folded proteins form and accumulate intra- and extracellularly in many tissues due to many causes, such as genetic predisposition and local and systemic inflammation of various etiologies. In rats, focal or generalized amyloid deposition rarely occurs in any tissue, including the adrenal gland. In mice, amyloid deposition in the adrenal gland and other tissues is overall far more common. There are genetically related differences in incidence, with very low incidences in some strains, such as the B6C3F1/N mouse, and much higher incidences in other strains, such as (Swiss) CD-1 and Swiss Webster mice. In mice, amyloidosis is usually a spontaneous, age-related systemic disease, with the adrenal gland one of the more commonly affected tissues. Severity (amount of amyloid/tissue) also tends to increase with age in all tissues, including the adrenal gland. In mice, adrenal amyloid deposition usually first appears as small clumps between cells of the inner cortex, with progressive centripetal extension into the outer cortex (zona fasciculata) (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, and Figure 6). The amyloid proteins can form large, expansile aggregates (Figure 1 and Figure 2), which distort the normal architecture and can eventually coalesce into thick circumferential bands that surround the medulla (Figure 3 and Figure 4). The amyloid may extend into the medulla or zona glomerulosa, but these regions are generally unaffected.

With hematoxylin and eosin (H&E) stain, amyloid deposits appear as homogeneous, amorphous, pale eosinophilic material (Figure 1, Figure 2, Figure 3, and Figure 4). Special histochemical stains are often used to distinguish amyloid from fibrous connective tissue, fibrin, and other substances. One of the most widely used stains is Congo red. Amyloid stained with Congo red appears pale to dull red under nonpolarized light (Figure 5) but exhibits brilliant birefringence (usually "apple green") under polarized light (Figure 6). Other methods for amyloid detection include fluorescent or metachromatic stains and immunohistochemistry.