Granulomas

Granulomas are nodular, nonulcerative, and not usually pruritic. Some are mineralized. Granulomas form when the immune system walls off a foreign substance. Generally this is because the immune system can’t eliminate it. Complexes of immune cells surround an infectious agent (bacteria, fungus, parasite) or material such as keratin or suture. Granulomas are typically composed of macrophages, often fusing to form multinucleated giant cells. The other cell types in the granuloma can be hints as to the originating problem (eg eosinophils with parasites or immune complexes). Granulomas develop as solid structures but loss of blood supply may lead to necrotic centers that appear caseated or cheesy.

The entire mass may be removed and submitted for histopathology, particularly if it is in a problematic area or is enlarging. Many respond well to intralesional or systemic steroids but it is important to biopsy first to ensure there isn’t an ongoing infection. Finding and removing the irritant is important for recurrent or persistent granulomas. Many of these are due to insect bites so protection from insects can help mitigate the problem.

“Fungal” granulomas are found in warm, tropical climates, including SE USA. Generally these are aggressive, ulcerated lesions on the ventrum and limbs of horses where the animals come in contact with swampy water. Small, hard coral-like masses called “kunkers” are commonly found in these lesions and help with diagnosis. Many are caused by the organism Pythium insidiosum and are referred to as pythiosis. [Note: Pythium is not a true fungus.] Treatment is challenging. Early aggressive surgical debridement and immunotherapy may help. In Minnesota,  blastomycosis has been identified as a cause of granulomas in horses as well as dogs.

Equine glanders is not currently seen in the US but is an important differential for pythiosis (at least for NAVLE).

Lumpy jaw (cattle) –