Dermoid Sinus in the Rhodesian Ridgeback
by Diane Jacobsen
4561 Todd Road
Sebastopol, CA 95472-5227
The dermoid sinus (D.S.) has been known by many names, a few of which are dermoid cyst, hair cyst, and African cyst. It is a sinus, in that it is tubelike and does drain, and dermoid because it is skinlike. It may or may not contain hair follicles or be lined with hair. As the hair sheds on the outer coat of the pup, so does the hair inside this tube. The body's natural response to dead material is to flush it out and thus the serum builds up and expels the debris. Not all of the dermoid sinuses are true tubes. Some are not hollow and the serum and debris cannot drain. In these cases an abscess forms and the resulting swelling that accompanies, can rupture the skin allowing the drainage into the surrounding area. This results in a very painful situation for the pup. At its worst it is life threatening.
The D.S. is generally found on the midline of the neck, back, and tail along the spinal column. Although rarely found in the ridge there have been several cases noted. Dermoid sinuses have also been noted on ridgeless puppies. The D.S. is a congenital condition, meaning that it is present at birth. It can be palpated on the newborn pups, and the affected pups identified. The affected pups should be put to sleep or if they are to be kept, surgery to remove the D.S. should be performed before sending them to their new homes. The affected pups are pet stock only and should not be considered as breeding material.
To find the D.S. you must palpate along the midline of the spine, starting at the top of the head close to the occiput (bump) bone. To do this you may pick the pup up and hold it in the cup of your hand or palpate as the pup is sleeping. Take the other hand and envision yourself picking up a baby kitten by the scruff of the neck with your thumb and forefinger. Exert enough pressure to feel, but not enough to bruise. Use your whole hand as one unit, pulling first up toward the nose and then down toward the tail. The skin will stretch quite a bit in both directions. Do not roll the skin through your fingers. The fingers remain exactly where you placed them on the skin. The D.S., being attached on the top to the skin and at the base to the spinal cartilage, will slip through your fingers. A large D.S. will feel like a wet noodle and a finer D.S., like a small string. Reposition your fingers on the neck just below the starting spot and repeat this process. Continue to work your way down the neck and back to the tail.
At the tail it is very difficult to raise enough skin to palpate effectively. It is best to use your thumb in this area. With fingers underneath the pup supporting it, place the flat of your thumb over the spinal column at the pelvic area. Push skin first to one side and then back to the other side. Again, remember that the D.S. is attached and will slip under your thumb. This will feel like a squiggly noodle on a larger, longer D.S., or just an area that simply will not move at all on a shorter D.S. If you do not feel anything by sliding the skin from side to side, try sliding the skin toward the nose and then back to the tail, taking care to slide the skin, not your thumb.
As you palpate the area over the shoulders, you may feel connective tissue that holds the skin to the shoulder area. The tissue is heavier in this area than in the other areas of the spinal column. It will feel flat and you will not be able to trace it from the area close to the muscle all the way to the skin, whereas the D.S. is easily traced from the muscle to the top of the skin and feels round.
The D.S. can be visually detected by looking for a group of hairs that protrude straight up out of the hair coat of the pup. This is usually around 3 to 5 weeks of age. When you see this, the pup should be palpated for a D.S. The hair can also be shaved at this site and upon examination; a small dimple or hole will be revealed. By moving the skin back and forth, the dimple will become more apparent as the anchor of the D.S. will pull the skin down more in that area.
The D.S. can be surgically removed. It is advised that a vet be contacted that is familiar with this condition and has performed this operation before. This surgery should be done as early as 6 weeks and it is strongly suggested that it be preformed prior to 5 months. The D. S. grows with the dog and becomes more invasive. Success rates will go down the older the dog.
Dermoid sinuses are not alike in their makeup and it is impossible to tell which ones are easily removed or which ones go to the spine. They can wrap around or enter the area of the spinal cord, which makes them almost, if not impossible, to remove. In cases such as this some success has been achieved by folding the D.S. over and tying it off, but some have had regrowth. Since there is no way to detect which type of D.S. that the pup has, it is suggested that the instructions to the vet should include that if the D.S. is not completely removable, the pup be put to sleep. D.S. pups should not be promised to a new home until after the surgery.
The healing process can be as traumatic as the operation itself. In the simple cases that remove easily, there will be little or no serum build-up in the surgical area. In the more complicated surgeries, where the tissue damage has been more severe, the serum will start building up as soon as the surgical site heals over on the top of the skin. Usually this will be on the fourth or fifth day. It is tempting to drain this fluid or put in a surgical drain but it heals faster and better if left alone. About 5 to 8 days of a lumpy neck the body will absorb the fluid. There will be a slight lump for a while but that too will dissolve.
Pups that have had surgery must be removed from the litter to prevent damage to the surgical site. As puppies play, they grab and shake areas of skin on the other pups. If they were to grab and shake over or near the surgical site, damage occurs and the serum buildup becomes a bigger problem. A pressure bandage over the site of the surgery helps keep the swelling down but check often that it is loose enough under the neck so the puppy can eat and most important breathe.
Dermoid sinuses have been detected on other parts of the body, but are not as commonly seen as on the midline of the spine. A few have been noted on the head, attaching to the skull or the base of the ear. Another area of note is on the neck under the ear or on the front of the neck. Sometimes these can be dermoid sinuses and sometimes they are skin tabs. Do palpate to confirm. A skin tab will not have the tube that continues past the skin area.
The exact mode of the inheritance of the D.S. is not known. It is thought to be polygenic (multiple genes), rather than simple dominant or recessive. It has been noted that there can be carriers, or individuals that produce more dermoid sinuses than their littermates. Some lines are relatively D.S. free. Dogs that are subjects of D.S. are not candidates for a breeding program. The surgery removes the visual defect but not the genetic one. Pups having had surgery to remove a D.S. are eliminated from the conformation ring as per the AKC rules, which clearly state that a dog that has been surgically altered cannot compete.
The ethics of breeding require you to put the best possible representative of the breed out there. It should not only look like a Rhodesian Ridgeback, but it should be as healthy and sound as possible. As the D.S. is a very serious unsoundness, much thought should be given in your decision of the disposition of a D.S. puppy. If you decide to keep and operate on a D.S. subject, care must be taken to assure the pup of a home that will spay or neuter.
[NOTE: Because of the D.S., avoid injections in the area of the top of the neck and shoulders. Occasional reactions to vaccines can produce an inflammation that resembles a D.S.]
Dermoid Sinus - A Summary
by E. Clough, V.M.D.
1010 Daniel Webster Highway
Merrimack, New Hampshire 03054
Dermoid sinus (D.S.) was first used to describe the Rhodesian Ridgeback skin anomaly by Steyn, et al. This skin condition has also been called trichiasis spiralis, dermoid cyst, dermoid inclusion cyst and epidermal inclusion cyst. All of these terms have some applications; however, Dermoid, skin-like sinus, channel or fistula; (cyst means sac, i.e., not open to the surface) is most applicable. The Rhodesian Ridgeback Club of the U.S., Inc. prefers to use D.S. to describe the condition.
No reports have been located which substantiate the author's impression that D.S. has been found in other breeds. Dermoid sinus included in the ridge has been reported only once. They also occur in the sacral (rump) area and in this location are sometimes connected to the dura (spinal cord covering). This is not the case in the more common cervical (neck area) D.S. which connects the skin to the dorsal spinous ligament (the ligament which connects the top parts of the vertebrae). One or more D.S. may occur in the same animal. These sinuses are congenital (present at birth) and can be palpated (felt) as cords running between the skin and the spine. They form a small external opening which can be readily seen once the hair has been shaved.
Histologically (microscopically) the sinus is a thick-walled tube composed chiefly of fibrous tissue and lined with stratified squamous epithelium (skin cells). The surrounding connective tissue may or may not contain hair follicles, sebaceous glands and sweat glands which open into the lumen (hollow center) of the sinus. In uncomplicated cases the sinus is filled with sebum (oil), skin debris and hair. Once infected with bacteria the resulting inflammation and abscessation can lead to myelitis and encephalitis (swelling and infection of the spinal cord, its covering, and the brain). The reason for discrimination against animals with D.S. is the almost inevitable abscess which forms.
Although not well understood, transmission of D.S. seems to be a dominant, polygenic problem with inconstant penetration. Another geneticist thinks that D.S. is due to a single completely recessive autosomal gene. This is not likely because normal parents do produce pups affected with D.S. Because of the genetic complexity and the difficulty in arranging, coordinating and collating the breeding studies necessary to prove the heredity of D.S., it is unlikely that we will be able to substantiate the exact mechanism of genetic transmission. There is a widely held belief that breeding Ridgebacks with D.S. produces an increased prevalence of pups with D.S. The R.R. Club of the U.S., Inc. believes that this could be substantiated if breeders had accurate records which could be collated and computed. It is our belief that careful controlled breeding studies would prove the inheritance of D.S. to be not only complex but also inter-related with other characteristics. Therefore, the likelihood seems to be remote that we will ever have Ridgebacks which are entirely free of D.S.
Because selective breeding will unquestionably reduce the prevalence of D.S., but probably not eliminate its occurrence, and because the condition results in difficult to treat abscesses unless surgically removed, it is our opinion and strong recommendation that dogs which have D.S. not be acceptable as show or breeding candidates. Surgical correction can be accomplished; however, culling at birth is a more humane way to handle the affected pups.