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DERMOID SINUS
Overview
A dermoid sinus is a tubular skin defect caused by incomplete separation of the skin and the neural tube during embryonic development. The depth of the defect varies. The tube may extend into the tissue just beneath the skin, it 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. The sinus can be found at any point along the back or neck, but most commonly affects the cervical or cranial thoracic area.
Incidence/Risk Factors
Dermoid sinus is most common in Rhodesian ridgebacks, in which it is congenital and heritable. Therefore, affected animals 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 dorsal midline with protruding hair, often in a swirl. A tube or cord may be palpated 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 dura mater can be associated with neurologic abnormalities.
When to Seek Veterinary Surgical Advice
Dermoid sinuses that discharge moderately, become infected, or cause neurological signs should be treated with surgical excision. Find an ACVS Veterinary Surgeon.
Diagnostic Tests
The sinus can be cannulated by introducing 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, cannulation and contrast fistulography may underestimate the depth of the sinus. In this case or when connection to the dura mater is suspected, myelogragraphy, magnetic resonance imaging, or computed tomography can be performed.
Figure 1. Contrast fistulogram. Contrast material has been injected into the sinus.
Surgical Treatment
Dissection of the sinus should be performed to the base of the tube (Figure 2). Antibiotics are typically used. If the sinus connects to the vertebrae or covering of the spinal cord, a laminectomy may be indicated.
Figure 2. Surgical dissection of a dermoid sinus.
Prognosis
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 requires a second surgery to search for remnants of the tube that were left behind.
Prevention
Because this condition is hereditable in Rhodesian Ridgebacks, affected animals should not be bred.
—Brenda Salinardi, DVM, MS
Diplomate ACVS, Small Animal Surgery
Posted 8/10/2009
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