Ovary, Bursa - Cyst
Bursal cysts ( Figure 1 and Figure 2 ) are characterized by dilation of the ovarian capsule, or bursa. Bursal cysts are frequently found in aged mice and rats at necropsy. These cysts are lined by a simple squamous epithelium ( Figure 3 ). Bursal cysts should be distinguished from true ovarian or paraovarian cysts. Bursal cysts envelop the ovary and may cause compression but are not present within the ovary. Typically, a distended bursa collapses at dissection, disclosing an intact ovary within it, whereas a true ovarian cyst is found within the ovarian parenchyma and may generally be dissected intact at necropsy. Paraovarian cysts are present within and/or adjacent to the ovary and are lined by flattened, cuboidal or columnar epithelium; the epithelium may be ciliated, and a connection to paraovarian structures in the mesovarium may be seen. The pathogenesis of bursal cysts has not been elucidated.
Ovarian bursal cysts should be diagnosed, but cysts occurring as background lesions need not be graded. In the case of a bursal cyst, the diagnosis should include the type of cyst/location as a modifier (i.e., Ovary, Bursa - Cyst). If the cysts are thought to be treatment related, they may be graded to fully characterize the treatment effect. If applicable, the terms "bilateral" and "multiple" may be included in the diagnosis.
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