Fibrin ring granuloma/ doughnut granuloma
It is a histopathological finding that is characteristic of Q fever caused by coxiella burnetii.
On H and Estaining, the fibrin ring granuloma consists of a central lipid vacuole (usually washed-out during fixing and staining, leaving only an empty hole) surrounded by a dense red fibrin ring and epithelioid macrophages.(resembles like doughnut)
It may also be seen in Hodgkin’s Lymphoma and infectious mononucleosis.