Carbuncle is an ineffective gangrene of the subcutaneous tissue due to Staphylococcal infection. Gram-negative bacilli and Streptococci may be found coincidentally.
Carbuncles mostly seen on the back, in the nape of the neck where the skin is coarse and vitality of the tissue is less. The shoulders, the cheek, dorsum of the hand are the other rare sites. Hirsute portions of the chest and abdomen may also be involved.
When the invading staphylococci bacteria penetrate the deeper layers of the skin and the subcutaneous fat, a carbuncle is formed.This consists of a series of communicating abscesses, which discharge by separate openings on the surface. That is why the surface is sieve-like. Individual compartments in the carbuncle are maintained through persistence of fascial attachment to the skin. Carbuncles may be more extensive than they appear. There is a central large slough, surrounded by a rosette of small areas of necrosis. In untreated cases infection may extend widely with fresh openings appear on the surface, which coalesce with those previously formed. Under treatment when the central slough is drained off, fibroblastic reactions start from the surrounding granulation tissue and carbuncle heals with a characteristic induration.


