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 (Fig. 12.18). Sinuses and fistulas may be congenital
or acquired. Forms which have a congenital origin include
preauricular sinuses (Chapter 37), branchial fistulas (Chapter 43), tracheo-oesophageal
fistulas (Chapter 50) and arteriovenous fistulas (Chapter 15). 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
(Chapter 61). Acquired arteriovenous fistulas are caused by trauma or operation
(for renal dialysis).
•
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
•
ischaemia;
•
drugs, e.g. steroids, cytotoxics;
•
malnutrition;
•
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.
Treatment
.