A sinus in Latin stands for a hollow or a bay or gulf. A sinus is a blind track leading from an epithelial surface into the surrounding tissues. The track is oftgen covered with granulation tissue.
Frontal and nasal sinuses are normal anatomical sinuses. Different pathologies may cause sinuses.
Sinus usually represents the path by which the discharge escapes from an abscess cavity that has not closed yer.
A sinus will persist until the obstacle to closure of the original abscess is removed.
It could be a foreign body [sequestrum, an infected ligature, or a bullet etc]. The removal of the foreign body causes healing of sinus.
The presence of a foreign body is often suggested by a mass of redundant granulations at the mouth of the sinus.
A sinus that passes over a muscle is prevented from healing by the repeated contractions. The muscles need to be rested by splinting/resection.
Fistula in Latin stands for a pipe or tube. It is an abnormal communication between lumen or surface of one organ and lumen or surface of other organ.
Thus a fistula connects mucous surface to the skin or to another mucous surface.
Fistulae can result following suppuration, which normally occurs near the natural openings of mucous canals. Fistula from salivary gland on the cheek, lachrymal fistula besides the inner angle of the eye, a mstoid fistula near the ear etc.
Intestinal fistulae may occur in intestinal obstruction, after the strangulated hernia, tuberculous peritonitis, and other conditions.
Stricture of the urethra may lead to perineal fistula
Congenital fistulæ, such as occur in the neck from imperfect closure of branchial clefts, or in the abdomen from unobliterated fœtal ducts such as the urachus or Meckel’s
Both sinuses and fistulas can be may be congenital or acquired.
Preauricular sinuses, branchial fistulas, tracheo-oesophageal fistulas and arteriovenous fistulas are example of congenital conditions.
Acquired forms often follow inadequate drainage of an abscess. Thus, a perianal abscess may burst on the surface and lead to a sinus. 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).
Causes of Persistence of a sinus or fistula
A persistent sinus or fistula could be caused by many reasons. These causes are discussed below.
A foreign body or necrotic tissue like a suture, hairs, a sequestrum, a faecolith or even a worm can cause persistent of sinus or fistula.
Long, narrow, tortuous track predisposes to inefficient drainage. So does the non dependent drainage.
In some cases, the fistula develops because the lumen is closed distal to the fistula. This leads to persistence drainage. In such cases, it is essential that the distal obstruction must be removed. In most of the cases, the fistula closes spontaneously.
In fistula-in-ano due to the normal contractions of the sphincter force fecal material through the fistula. This leads to persistence of fistula.
Changes in Lining
Epithelial or endothelial lining of the fistula/sinus prevents the closure. Dense fibrosis prevents contraction and healing.
Some infections are known to be associated with sinuses. For example tuberculosis or actinomycosis. In cases of osteomyelitis, an active sinus indicates an ongoing infection.
A malignant disease may also cause persistence sinuses.
Similarly ischemia of the tissue, drugs like steroids, cytotoxic drugs, malnutrition or radiotherapy may contribute.
Guinea worm is the parasite responsible for the disease causing a persisting sinus on the lower leg.
Sinuses in the body
These are normal sinuses present in body [not the pathological]
Dural venous sinuses
- Anterior midline – Cavernous, Superior petrosal, Inferior petrosal
- Central sulcus – Inferior sagittal, Superior sagittal, Straight
- Confluence of sinuses
- Lateral- Transverse, Sigmoid
- Inferior – Occipital
- Carotid sinus
Renal sinus (drains renal medulla)
Coronary sinus (subdivisions of the pericardium)
- Subcapsular sinus (space between the lymph node and capsule)
- Trabecular sinuses (space around the invaginations of the lymphatic capsule)
- Medullary sinuses (space between the lymphatic cortex and efferent lymphatic drainage)