What is ... ?:

Dermoid sinus is a tubular indentation of the skin in the middle of the back, that may go as deep as the spinal canal. The tracts may be single or multiple.
This condition occurs because of an abnormality early in embryonic development, in which there is incomplete separation of the tissues that will become the skin and the nervous system.

How is ... inherited?:

Various modes of inheritance have been suggested including dominant with incomplete penetrance, or recessive. It is possible that there is an inherent deficiency in the Rhodesian Ridgeback breed in the absorption or utilization of folic acid (a B vitamin), that leads to this defect.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Dermoid sinus is present from birth, although the condition is usually not noticed until later. The tracts contain debris from the skin - sebum (waxy lubricating substance), dead skin cells, and hair - and commonly become infected and painful. If the tract extends to the spinal canal, infection may cause meningitis or myelitis, resulting in various neurologic signs such as local or general spinal pain, stiffness, or weakness (depending on the location of the sinus).

How is ... diagnosed?:

You or your veterinarian may notice firm painful swellings in the middle of your dog's back, from which there may be some exudate. A cord of fibrous tissue (the tract) can usually be felt under the skin. Your veterinarian will take x-rays using a contrast dye to determine the extent of the tract.

How is ... treated?:

In an affected dog, the only successful treatment is surgical removal of the the whole tract, which may be a simple procedure or it may be fairly complicated if the tract extends into the vertebrae and spinal canal. Incomplete removal results in recurrence.
There is evidence that suggests folic acid supplementation of breeding bitches (both before and during pregnancy) can reduce the occurrence of this condition (see below).
For the veterinarian: Meningitis or myelitis are treated as appropriate. Laminectomy may be necessary to remove portions of the tract from within the spinal canal.

For the veterinarian:

Clinical signs of meningitis or myelitis may be seen. In these cases, a CSF tap is generally abnormal, consistent with bacterial infection. Fistulography using a dye non-irritating to nervous tissue (eg. metrizamide) or myelography will show whether the sinus communicates with the subarachnoid space.

Breeding advice:

Affected dogs and their close relatives should not be bred. Breeders may want to consider folic acid dietary supplementation of breeding bitches (see reference below).
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Roberts, JG and Nicholls-Grzemski, FA 1996 A role for folic acid in the prevention of dermoid sinus in the Rhodesian Ridgeback presented at the World Conference of Rhodesian Ridgebacks, Melbourne, Australia

LeCouteur, R.A., Child, G. 1995. Diseases of the spinal cord. In S.J. Ettinger and E.C. Feldman (eds.) Textbook of Veterinary Internal Medicine. p. 629-696. W.B. Saunders Co., Toronto.

pilonidal sinus/cyst

dermoid sinus