Dermoid Sinus in Dogs

A dermoid sinus is a cyst-like structure that lies below the skin along the back and is sometimes connected to the spine. As the puppy embryo develops during pregnancy, the neural tube that forms the spine should separate completely from the skin. When this separation fails to take place, a dermoid sinus develops. Once the puppy is born, the sinus may remain connected to the spinal canal or may end in a blind sac.

Dermoid sinuses occur as inherited, autosomal recessive traits in Rhodesian ridgebacks or ridgeback-crosses, and they are occasionally seen in other breeds of dogs, such as the Shih tzu and the boxer. With recessive genetic traits the condition only becomes apparent when the puppy receives one defective gene from both parents. A dermoid sinus develops when two defective genes are present together. When only one defective gene occurs, the dog is a carrier of the condition, but does not show any signs of a dermoid sinus.

Young animals are most commonly affected. Affected individuals may be asymptomatic (have no clinical signs) early in the disease process. Signs resulting from a dermoid sinus depend on its location.

What to Watch For

Draining tracts on the skin of the back

Single or multiple openings or holes on the back, sometimes with protruding hair

Cyst-like swellings on the back 

Additionally, clinical signs of meningitis (inflammation of the covering of the brain and spinal cord) or myelitis (inflammation of the spinal cord) including spinal pain, rigidity, and fever may be seen as a result of extension of a deep infection.

Diagnosis

Your veterinarian may recommend the following tests: 

Baseline tests, including a complete blood count (CBC), biochemical profile, and urinalysis to look for signs of infection and other problems

Radiographs (X-rays) of the spine and soft tissues of the back

Fistulogram, an injection of a dye that shows up white on X-rays into one or more of the holes in the skin, to determine how deep the sinus cavity goes

Myelogram, a dye X-ray study of the spinal cord, to determine whether the sinus is still connected to the spinal canal. If a myelogram is performed, the spinal fluid retrieved is usually submitted for analysis.

Surgical exploration of the site with possible removal of all abnormal tissue and closure of any connections to the spinal canal 

Computed tomography (CT) or magnetic resonance imaging (MRI) if the dog is showing neurologic signs

Treatment

If there are no clinical signs associated with the lesion and the site is not draining or connected to the spinal canal, then your veterinarian may recommend the site just be observed. If any clinical signs are present or the lesion has an open connection to the spinal canal, then surgical excision is the treatment of choice. If neurologic signs are present by the time of diagnosis, the dog may be left with permanent changes despite corrective surgery.

Antibiotic therapy may be indicated, especially in cases associated with meningitis or myelitis. Dermoid sinuses complicated by infections of the spinal canal or spinal cord carry a very poor prognosis.

Home Care

Administer all medications as directed by your veterinarian. If any change is noted in your pet's condition, notify your veterinarian immediately. 

There is no prevention available for a dermoid sinus. Affected animals should be neutered, and the parents and littermates of affected animals should not be used for breeding.