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What is a Diplomate?
The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery.

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Dermoid Sinus

Associated Terms:

Pilonidal Sinus

The term "ACVS Diplomate" refers to a veterinarian who has been board certified in veterinary surgery. Only veterinarians who have successfully completed the certification requirements of the ACVS are Diplomates of the American College of Veterinary Surgeons and have earned the right to be called specialists in veterinary surgery.

Your ACVS board-certified veterinary surgeon completed a three-year residency program, met specific training and caseload requirements, performed research and had research published. This process was supervised by ACVS Diplomates, ensuring consistency in training and adherence to high standards. After completing the residency program, the individual passed a rigorous examination. Only then did your veterinary surgeon earn the title of ACVS Diplomate.


A dermoid sinus, also known as a pilonidal sinus, is a tubular skin defect caused by incomplete separation of the skin and the nervous system during embryonic development. The sinus can be found at any point along the back or neck, but most commonly affects the neck or upper spine. The depth of the defect varies, the tube:

  • may extend into the tissue just beneath the skin,
  • may extend deeper and connect to the membrane covering the spinal cord (dura mater) or
  • it may be a blind ended sac beneath the skin

Dermoid sinus is most common in Rhodesian ridgebacks, in which it is congenital and heritable. Therefore, affected pets should not be bred. The condition has also been reported in other breeds.

Signs and Symptoms: 

A dermoid sinus can be recognized at a young age as an opening on the midline of the back with protruding hair, often in a swirl. A tube or cord may be felt beneath the opening. Some dermoid sinuses may not be associated with any clinical signs or may be associated with mild discharge that can be controlled with gentle cleansing. However, sinuses that become plugged with keratin debris may become infected and an abscess may form. Sinuses that connect to the lining of the spinal cord can be associated with neurologic abnormalities.


Your primary care veterinarian may probe the sinus by placing a catheter into the opening. A contrast fistulogram (Figure 1) can be performed by injecting contrast material into the sinus and then taking a radiograph. Because the depth of the sinus is often filled with hair or keratin debris, probing and contrast fistulography may underestimate the depth of the sinus. In this case or when connection to the lining of the spinal cord is suspected, advanced imaging may be recommended, such as:

  • myelography (an x-ray test with contrast injected around the spinal cord)
  • magnetic resonance imaging (MRI) or
  • computed tomography (CT)

Dermoid sinuses that discharge significantly, become infected, or cause neurological signs should be treated with surgical excision by an ACVS board-certified veterinary surgeon. If the sinus connects to the vertebrae or lining of the spinal cord, more aggressive surgery may be required.

Aftercare and Outcome: 

The prognosis for dogs with dermoid sinus is very good if no neurological signs are present. Failure to remove the sinus entirely results in redevelopment of the sinus which may require a second surgery to search for remnants of the tube that were left behind. 

Content Theme: 
Also known as: 
Dermoid Sinus
Pilonidal Sinus

This Animal Health Topic was written by and reviewed by Diplomates of the American College of Veterinary Surgeons.  Any opinions stated in this article are not necessarily the official position of the American College of Veterinary Surgeons.

The American College of Veterinary Surgeons recommends contacting an ACVS board-certified veterinary surgeon or your general veterinarian for more information about this topic.

To find an ACVS Diplomate, visit www.acvs.org/find-a-surgeon.