Dermoid Sinus in Cats

The malformation is most often seen in Rhodesian ridgeback dogs, but may also occur in cats. It is a very rare condition in cats, though, with only three documented cases. No breed, sex, or age predispositions have been identified, though research suggests that Burmese cats may have a higher disposition for developing dermoid sinus.

Dermoid sinus in cats is a congenital defect characterized by an opening on the back or neck. Beneath this opening is a tube, which drains and usually looks like skin with hair surrounding it. The tube may connect to tissue just beneath the skin, extend deeper to the spinal cord, or be detached completely, floating in the muscles.

Since it is a birth defect, signs of dermoid sinus will be apparent early on in a cat’s life. Dermoid sinuses may present no symptoms or may present symptoms associated with infection or neurologic abnormalities. Ensure you can recognize the signs of dermoid sinus, and seek immediate veterinary attention as soon as you notice any of the following:

• An opening on the back or neck
• A sac under the skin
• Hair around the opening, especially in a swirl pattern
• Evidence of a tube near the opening
• Discharge near the opening
• Abscesses near the opening (indicative of infection)
• Signs of neurologic abnormalities

The only known cause of dermoid sinus in cats is a congenital defect. The defect occurs when the skin and nervous system do not separate completely during the embryonic stage of development. The opening is often filled with keratin debris from the skin. When this debris builds up, it may cause abscesses and infection.

Your vet will be able to make a tentative diagnosis based on a thorough physical examination and presentation of symptoms. Your vet may ask for your cat’s complete medical history, and may also want to know where you acquired the cat.

Physical examination is usually sufficient for making the definitive diagnosis. However, your vet may choose to insert a catheter into the opening in order to see how far the tube extends. The vet will do this by injecting a contrast material and then performing an x-ray. Since it is likely there is debris in the opening, the vet may need to conduct more thorough testing to examine the full length of the tube. These tests may include a CT scan, an MRI, and a myelography, which is an x-ray of the spinal cord using contrast injection.

Treatment may not be required in mild cases that do not present any symptoms or signs of infection. Your vet will be able to advise you on a treatment plan based on your cat’s specific needs. 

Dermoid sinuses that cause infection or discharge or affect the neurological system will need to be removed with surgery. At present, there is little literature on the specifics of the surgical procedure due to the rarity of the condition. However, current literature suggests that the procedure is generally straightforward in mild cases. Analgesics for pain management and other medications are generally not required following surgery.

Dermoid sinuses which connect to the spinal cord will require more aggressive surgery, which comes with higher risk of complications. Severe injury to the spinal cord during surgery may cause sudden death. If the entire sinus is not removed, the defect may recur. This will warrant a second exploratory surgery to find the part of the sinus that was not extracted initially. Other potential complications include breakage, migration, or improper positioning of the spinal implants. This may cause pain or injury to the spinal cord.

Recovery and prognosis are generally good following surgery, particularly in cases with no signs of neurological abnormality. Always follow your vet’s post-treatment and/or post-operative instructions carefully. If your cat has had surgery, ensure they have a warm, safe place to rest. Do not allow them to irritate the surgery site. An Elizabethan collar may help with this. You should check the surgery site daily to ensure there is no swelling or discharge.

If your cat’s dermoid sinus did not require surgery and you notice discharge or abscesses forming near the opening, you will need to contact your vet immediately. Dermoid sinuses that produce discharge or become infected will require surgical removal to prevent further complication.

Your vet may schedule follow-up appointments as needed to monitor healing. The vet may also take x-rays during these appointments to ensure that no complications have arisen and the entire sinus was removed.

If you have any questions, or if you notice the sinus start to redevelop, contact your vet immediately.