Around the anus

20 Around the anus

The conditions that occur around the anus are very common but are very distressing for the patient.

Abscesses

Perianal abscesses are common surgical emergencies. They are acute infections of an anal gland, and present with severe perianal pain and swelling, often with a painful mass (Fig. 3.20.1A). A fistula may form after drainage. Initial treatment is with surgical incision and drainage under general anaesthesia. Large abscesses should be packed while granulation tissue fills the defect.

Fig. 3.20.1 Classification of abscesses (A) and fistulae (B); high fistulae open into the anal canal at or above the anorectal ring.

A fistula is an abnormal communication between two epithelial surfaces (Fig. 3.20.1B). It presents as a painful discharging opening onto the skin. Fistula-in-ano can be classified by site: intersphincteric (70%; low), transphincteric (25%; low or high), suprasphincteric (5%; high) and extrasphincteric (<1%; supralevator, high). The fistula may be carefully probed to identify the tract, and MRI provides detail in complicated cases. Fistulae can also be classified by type, using the ‘surgical sieve’ (p. 16):