Also can occur secondary to a vasculopathy. Must rule out infectious disease and the above listed systemic disorders before deciding it is idiopathic. Must distinguish from lesions where the panniculus is just secondarily involved from extensive dermal lesions. Necrosis of the subcutaneous fat accompanied by granulomatous to pyogranulomatous inflammation and variable degrees of fibrosis. Palpable nodules in the subcutis that may ulcerate and drain.
Microscopic example is of a cat with a subcutaneous atypical mycobacterium sp.
The bacteria most likely entered via traumatic implantation from a bite or other wound. Higher magnification reveals fat lobules surrounded by pyogranulomatous inflammation. This is characteristic of atypical mycobacteriosis. A culture would provide a definitive identification of the organism. Gross Lesion example of a cat with a subcutaneous atypical mycobacterium sp.