Sinuses and fistulas
A sinus (Latin a hollow; a bay or gulf) is a blind track (usually lined with granulation tissue) leading from an epithelial surface into the surrounding tissues. Pathological sinuses must be distinguished from normal anatomical sinuses (e.g. the frontal and nasal sinuses). A fistula (Latin = a pipe or tube) is an abnormal communication between the lumen or surface of one organ and the lumen or surface of another, or between vessels. Most fistulas connect epitheliallined surfaces. Sinuses and fistulas may be congenitalor acquired. Forms which have a congenital origin include preauricular sinuses, branchial fistulas , tracheo-oesophageal fistulas and arteriovenous fistulas. The acquired forms often follow inadequate drainage of an abscess. Thus, a perianal abscess may burst on the surface and lead to a sinus (erroneously termed a blind external ‘fistula’). In other cases, the abscess opens both into the anal canal and on to the surface of the perineal stem resulting in a true fistula-in-ano. Acquired arteriovenous fistulas are caused by trauma or operation (for renal dialysis).
Persistence of a sinus or fistula
The reason for this will be found among the following:
• a foreign body or necrotic tissue is present, e.g. a suture, hairs, a sequestrum, a faecolith or even a worm (see below);
• inefficient or nondependent drainage: long, narrow, tortuous track predisposes to inefficient drainage;
• unrelieved obstruction of the lumen of a viscus or tube distal to the fistula;
• high pressure, such as occurs in fistula-in-ano due to the normal contractions of the sphincter which force faecal material through the fistula;
• the walls have become lined with epithelium or endothelium (arteriovenous fistula);
• dense fibrosis prevents contraction and healing;
• type of infection, e.g. tuberculosis or actinomycosis;
• the presence of malignant disease
• drugs, e.g. steroids, cytotoxics;
• interference, e.g. artefacta;
• irradiation, e.g. rectovaginal fistula after treatment for a carcinoma of the cervix;
• Crohn’s disease;
•high-output fistula, e.g. duodenocutaneous fistula.
The remedy depends upon e removal or specific treatment of the cause (see appropriate pages).
Guinea worm (syn. dragon worm, Dracunculusmedinensis)
This is a cause of a persisting sinus on the lower leg. The larval form enters through the wall of the stomach or duodenum in drinking water contaminated by a tiny cyclops crustacean which has consumed the larvae. Settling in the abdominal connective tissue, the male and female mate, the pregnancy lasting about a year, and the female wanders in the subcutaneous tissues to select for egg laying a part of the anatomy likely to be submerged in water (containing the cyclops), usually the lower leg. Cellulitis, abscesses, ulcers and sinuses follow, through which the embryos are discharged, hopefully to be eaten by the cyclops. Baid travelled the interior of India and in 500 cases discerned a syndrome of the infestation, presenting with conjunctivitis (allergic) in 11 per cent, fibrous contracture of joints in 19 per cent, periostitis with osteomyelitis in 21 per cent and acute arthritis in 65per cent.
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