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Bone - Cyst

Image of cyst in the bone from a female B6C3F1/N mouse in a chronic study
Bone - Cyst in a female B6C3F1/N mouse from a chronic study. The cyst is expansile and has a thin wall of cortical bone.
Figure 1 of 4
Image of cyst in the bone from a female B6C3F1/N mouse in a chronic study
Bone - Cyst in a female B6C3F1/N mouse from a chronic study (higher magnification of Figure 1). The bone directly surrounding the cyst has been replaced by fibrous connective tissue.
Figure 2 of 4
Image of cyst in the bone from a male F344/N rat in a chronic study
Bone - Cyst in a male F344/N rat from a chronic study. The cyst contains large amounts of hemorrhage.
Figure 3 of 4
Image of cyst in the bone from a male F344/N rat in a chronic study
Bone - Cyst in a male F344/N rat from a chronic study. The multilocular bone cyst contains variable amounts of erythrocytes and proteinic material.
Figure 4 of 4
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comment:

Cortical bone cysts (aneurysms) are characterized by expansion of the cortex and/or marrow cavity by an expansile cystic space composed of a thin wall of cortical bone ( Figure 1image opens in a pop-up window ). The expansile nature of these lesions may induce pressure atrophy of the surrounding bone, with loss of bony trabeculae or cortical bone and replacement by connective tissue ( Figure 2image opens in a pop-up window ). Bone cysts may be unilocular ( Figure 3image opens in a pop-up window ) or multilocular and may contain variable amounts of erythrocytes, fibrin, or proteinic material ( Figure 4image opens in a pop-up window ). Solitary bone cysts are rarely observed in the F344 rat, and their significance and pathogenesis are not known. These lesions may occur anywhere along the diaphysis; however, cysts may occur within the subchondral bone as a component of joint degeneration or osteochondrosis in the rat.

recommendation:

Solitary bone cysts should be diagnosed when observed. However, when a cyst occurs as a component of a primary lesion of osteochondrosis (seen as a developmental defect in Sprague-Dawley rats) or degeneration of the joint, it should not be diagnosed. These lesions represent sporadic background processes in the B6C3F1 mouse and F344 rat; increases in bone cysts have not been associated with chemical exposures. Secondary lesions, such as atrophy, should not be diagnosed separately unless warranted by severity.

references:

Leininger JR, Riley MGI. 1990. Bones, joints, and synovia. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman G, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, 209-226.

Long PH, Leininger JR. 1999. Bones, joints, and synovia. In: Pathology of the Mouse (Maronpot R, Boorman G, Gaul BW, eds). Cache River Press, St Louis, 645-678.