Dentigerous Cyst Dentigerous cysts are commonly called “ear fistula”, “ear tooth” or “temporal cyst”. A dentigerous cyst is a rare, congenital cyst that forms around misplaced germinal dental tissue.
Malpositioning of dental tissue in the
region may occur during foetal
development resulting in the formation of a draining cyst once the foal is born.
As this condition is congenital it is present from the time of birth and is most often diagnosed in individuals less than two years of age.
Clinically a dentigerous cyst is seen as a unilateral swelling at the base of the ear and the dorsolateral aspect of the cranium. Occasionally there is swelling along the ventral aspect of the jaw line. Dentigerous cysts present with a drainage tract that most commonly discharges at the base or midway up the medial aspect of the external pinna. The discharge material is a clear or greyish, thick mucus that causes crust and alopecia or matting of the hair in the ear area.
Diagnosis can be made through signs and symptoms as well as through the visualisation of dental materials in the temporal region by .
Treatment is the surgical removal of dental materials and of the cyst capsule if possible.
Miscellaneous Skin Diseases
Nodular Necrobiosis (Equine Eosinophilic Collagenolytic Granuloma) Nodular necrobiosis is the most common nodular skin disease of the horse. It is also known as Equine Eosinophilic Collagenolytic Granuloma.
The cause of nodular necrobiosis is idiopathic, though there is thought to be some link to insect bites, trauma or high diets.
It is a hypersensitivity reaction against metabolites in the skin. When skin is damaged, the components of the skin are broken down by phagocytes. These phagocytes release the digested components into the extracellular fluid where they remain until they diffuse into the bloodstream. In some individuals the digested remnants of collagen trigger and immune mediated inflammatory reaction in the skin.
Nodular necrobiosis is seen in horses older than six years of age. Lesions are less apparent in winter months, though they persist year-round.
Lesions are commonly found on the dorsal trunk and the sides of the neck. Lesions are round circumscribed, , rounded nodules. Nodules may be isolated or may occur in multiples. Nodules are not associated with pain or pruritus, and they are covered with normal hair.
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