Teratoma (teratoma adultum) are a relatively rare, benign but locally invasive neoplasia of dogs characterized by germ-cell tumors containing skin, connective tissue and sometimes bone.
Teratomas originate from the embryonic notochord, which are normally located in germinal tissue such as the ovary or testis, but can arise in the retroperitneal space, spinal column or cervical region.
These tumors, which can vary in size from 1 - 30 cm in diameter, are composed of ectoderm, mesoderm and/or endoderm. Tumors may contain hair, keratin, squamous epithelium, nerve cells, bone, cartilage, adipose tissue, smooth or striated muscle and sometimes teeth. Intestinal, thyroid, respiratory epithelial and pancreatic endocrine parenchyma may also be involved.
Metastasis to the abdominal viscera, lymph nodes, bone and lungs occurs in around 33 – 50% of malignant teratomas.
Teratomas are classified according to their histological appearance as either mature (benign), immature (malignant) or monodermal. Mature and immature teratomas are derived from more than one germ layer and monodermal teratomas arise from the predominant embryonic cell line within the tumor. In dogs, monodermal teratomas usually present as thyroid parenchyma within ovarian stroma.
Clinically-affected dogs are usually young entire females up to 6 years of age with symptoms referable to an ovarian mass. Abdominal distension and pain, peritoneal effusion and weight loss are common.
Blood tests and peritoneal cystocentesis are usually unrewarding, but ultrasonography usually reveals a large multilobulated caudal abdominal associated with peritoneal effusion.
Radiographs may indicated calcification of the mass.
A definitive diagnosis usually requires histological analysis of fine needle biopsy or excised tissue samples.
Surgical extirpation is usually curative.
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