Gender: Female (spayed today)
Mature dog with ovarian asymmetry found at ovariohysterectomy. No abnormalities in hormones noted clinically except for an episode of pseudopregnancy one year ago, right ovary and left ovary submitted.
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Left ovary: Within the ovarian parenchyma there is an encapsulated region of proliferative adipocytes and fibrous connective tissue. Adjacent to this is a follicular structure lined by stratified squamous epithelium that exhibits abrupt keratinization. The cyst is filled with keratin. Mature sebaceous and apocrine glands are noted in the cyst wall.
- Right ovary: Within normal limits
- Left ovary: Dermoid cyst
Dermoid cysts are rarely observed in dogs and cats but are identical to the human lesion with the same name. These cysts are developmental anomalies manifested by mature dermal and epidermal elements within the ovary. Interestingly, the left ovary is more frequently affected than the right ovary. Dogs may be asymptomatic. Excision should be curative and should prevent possible future complications such as ovarian torsion, rupture, malignant transformation (very rare <1%) or superimposed infection.
Many times, the term “dermoid cyst” is used interchangeably with “teratoma” and although the two conditions may appear similar they are different entities:
Dermoid cysts arise from only epidermal (ectoderm origin) and dermal (mesoderm) components.
Mature teratomas arise from at least 2 of the 3 germ layers – mesoderm, ectoderm and/or endoderm. Generally, these will contain mature skin, hair, blood, fat, bone, nails, teeth, eyes, cartilage, neural tissue and/or thyroid tissue.
Tumors that contain mature components from at least 2 germ lines as well as embryologic elements are termed “Immature teratomas”. These are much less common than the mature teratoma and they are much more aggressive behaviorally often displaying malignant behavior
Jubb, Kennedy and Palmer. Pathology of domestic animals.5th ed. 2007. pp592-592.
Nicole Kraipowich, DVM, MS
Diplomate, American College of Veterinary Pathologists