The parotid duct, or duct of Stenson, is the vessel or canal by which saliva is conveyed from the salivary gland into the mouth. On leaving the gland the parotid duct (fig. 92, p. 259) passes along the inner surface of the lower jaw, and then winds round its lower border in front of the great muscle of the cheek in company with the inferior maxillary artery and vein, and finally opens into the mouth opposite to the junction of the second with the third molar tooth of the upper jaw. In its course round the jaw-bone and along the side of the face it becomes exposed to injury, and as the result of blows from the kicks of horses and other mishaps as well as from the ulcerating effects of calculi (stones) which sometimes form within it, an opening is made through its walls at the seat of injury by which the saliva is allowed to escape instead of passing into the mouth. The duct may be completely divided, as sometimes occurs from external violence, in which case one portion of the vessel is separated from the other, or it may only be punctured. Obviously the former condition is the more serious of the two, since the divided ends draw away from each other and are with difficulty brought together under the most favourable circumstances; and if allowed to remain apart for any length of time that portion connected with the mouth closes up, owing partly to no saliva being able to enter it, but more immediately as the result of inflammation excited in it by the accident. Fistula of the parotid duct may also result from the formation of an abscess in some part of its course giving rise to ulceration of its walls.
The existence of this disease is known when a watery fluid is found to discharge through an opening in the skin at or near the lower border of the jaw (fig. 94). The quantity will depend a good deal upon the size of the opening and also upon the act of mastication. When feeding, the secretion of saliva is most active and the flow is very considerable, but becomes comparatively slight when food ceases to be taken.
The indications here are to close the external wound promptly, and by so doing cause the saliva to flow along and keep open its proper channel and allow the rent in the vessel to heal. Success will greatly depend upon:
1. Whether the vessel is partially or completely divided.
Fig. 94. - Fistula of the Parotid Duct.
2. Upon the period of time which is allowed to elapse between the injury and recourse to treatment.
3. As to the state of the duct itself.
When the duct is cut through, or its walls are involved in an ulcerative condition, the prospects of cure are remote; when, however, the duct is simply perforated it is more favourable.
Whatever treatment is undertaken, solid food must be altogether withheld for three or four days, or more if necessary, and the patient supported on liquid aliment such as thin oatmeal and maltmeal gruel mixed with eggs, beef-tea, and milk alternately, the object being to keep the jaws at rest and the secretion of the saliva as far as possible in abeyance.
The hair must now be removed from about the wound and the part thoroughly cleansed with soap and water and afterwards freely irrigated with a solution of carbolic acid. With a small needle and catgut-thread the lips of the wound are then to be carefully and completely drawn together, in doing which a sufficient hold should be taken of the skin to guard against tearing out. The part is then to be covered by a thick dressing of styptic-colloid and covered with a thick pad of antiseptic wool or absorbent lint.
When necessary both should be renewed but not otherwise, and the animal is to be so secured that he may not rub or otherwise disturb the application.
By some, closure of the wound is attempted to be brought about by the production of a scab, and for this purpose it is freely dressed with caustic, such as nitrate of silver, nitric acid, or the hot iron.
In old-standing cases, where the wound has become callous and that part of the duct near the mouth closed up and impermeable, the salivary gland should be destroyed, and the formation and discharge of saliva from it altogether arrested. This is accomplished by injecting some irritant along the duct into the gland. For this purpose a solution of one of the following drugs is employed, viz.: - Nitrate of silver, caustic ammonia, or tincture of iodine. The immediate effect of this course is to cause inflammation and swelling of the gland, sometimes also the production of an abscess; the ultimate result, however, is that the organ is spoilt, ceases to secrete saliva, and wastes away. After this has been effected some little defect in mastication will be observed for a short time, and it may be that an attack of indigestion may follow, but with care in feeding and management this will soon cease to be a matter of concern.