I would like to share with you all the results of my questions regarding differences between an abscess and a cyst and how we can start getting surgeons to tell the difference.... "Re: cyst and abscess, Webster's Seventh New Collegiate: abscess n. a localized collection of pus surrounded by inflamed tissue cyst n. a closed sac having a distinct membrane and developing abnormally in a cavity or structure of the body The following picture is an abscess becoming a cyst: epidermis (skin) is growing into a chronic abscess from right to left along the bottom edge of this low power view. In high power we see the growing edge of epidermis. See the diagram of Figure 11 of Bascom 1990 where a chronic abscess becomes an epithelial tube (skin lined tube). The distinction is subtle, hard to teach and perhaps it is an unimportant "why" as long as long as readers understand the "how" of efficient pilonidal care. Pits are shallow. Epidermis of the follicle less than 1cm deep covers the walls of pits in ~95% of pilonidal pit cases. It is deeper, 1-2cm in ~4%. 2-7cm in ~1%. Epidermis can cover most of the walls of an abscess cavity, it ultimately converted the abscess into a cyst in 2-3 of my 600 cases !!! In rarest of cases the advancing epidermis becomes disordered and malignant, as the squamous cell cancer in only 1 of my 600 (highly selected. True incidence must be 1/10,000 or 100,000). As a surgeon I can se the extent of epidermal ingrowth grossly as I slit open the "tube" of the pit. Microscopic sections are not useful at the operating table. But I have to look closely at the specimen and I know what I seek. A lining that looks like a miniture white tube of macaroni announces an epithelial tube; an abscess is rough and brown-red. The distinction is important because a cyst must be removed, "excised", and an abscess can rmain in place. An abscess will heal following "drainage" or "cleft lift", once conditions improve. I have tried to be clear on the distinction but find some titles of my articles use sinus and some abscess. Routine surgery should seek simplest measures to treat the commonest abscesses and leave exceptional measures, i.e. "excision", for exceptional cysts as they are diagnosed in the course of surgery. An analogy to burns helps understand the futility of wide excision: A hot burner will blister in a pattern on a hand if one lays a hand on the burner. The solution is to turn off the burner, not cut off the hand. In pilonidal disease the solution is to correct the cleft "poisons" that break down skin of the cleft, not cut away the tissue being damaged by the "poisons", and also cutting away normal tissue that surrounds the abscess using "wide excision". When surgeons follow "...wide excision to periosteum....", which is too often given as standard instruction, they leave giant cavities or deep clefts that heal slowly or never heal. Yet the intention is good, to "remove all of the cyst wall". Except that the "cyst wall" exists only in the surgeon's mind in the vast majority of cases, planted there by textbooks and even current literature on "pilonidal CYSTS". Perhaps that explains my preference for the term, "pilonidal abscess".