Risk factors for<unk>  formation include intravenous drug use. Another possible risk factor is a prior history of disc herniation or other spinal abnormality, though this has not been proven.<unk> es are caused by bacterial infection,<unk> rasites, or foreign substances. Bacterial infection is the most common cause. Often many different types of bacteria are involved in a single infection. In many areas of the world the most common bacteria present is methicillin-resistant Staphylococcus aureus. Among spinal subdural<unk> es, methicillin-sensitive Staphylococcus aureus is the most common organism involved. Rarely<unk> rasites can cause<unk> es and this is more common in the developing world. Specific<unk> rasites known to do this include dracunculiasis and myiasis. Perianal<unk>  Surgery of the anal fistula to drain an<unk>  treats the fistula and reduces likelihood of its recurrence and the need for repeated surgery. There is no evidence that fecal incontinence is a consequence of this surgery for<unk>  drainage. Perianal<unk> es can be seen in people with, for example, inflammatory bowel disease (such as Crohn's disease) or diabetes. Often the<unk>  will start as an internal wound caused by ulceration, hard stool, or penetrative objects with insufficient lubrication. This wound typically becomes infected as a result of the normal presence of feces in the rectal area, and then develops into an<unk> . This often presents itself as a lump of tissue near the anus which grows larger and more<unk> inful with time. Like other<unk> es, perianal<unk> es may require prompt medical treatment, such as an incision and debridement or lancing. Incisional<unk>  An incisional<unk>  is one that develops as a complication secondary to a surgical incision. It presents as redness and warmth at the margins of the incision with purulent drainage from it. If the diagnosis is uncertain, the wound should be aspirated with a needle, with aspiration of pus confirming the diagnosis and availing for Gram stain and bacterial culture.
Abscess
Necrotizing fasciitis
Dilaceration
Cellulitis
Joint effusion
Sebaceous cyst
Thrombus
Phlegmon