Panniculitis, i.e. a nodular inflammatory reaction of the subcutaneous fat. The protuberance is reddened, tender and feels solid when palpated. Erythema nodosum is the most common form of panniculitis. In the depicted patient, the panniculitis is caused by pancreatitis and the secretion of enzymes associated with it. A biopsy specimen must contain fat tissue in order to establish the diagnosis.