History: Presented for a routine examination. The last heat cycle was 35 days ago and was shorter than normal with no vulvar enlargement. There was no reported mating. The physical examination was normal except for the presence of a large, tubular, mass in the midabdomen. Routine hematology and clinical chemistry values were normal.
There is a large mass in the ventral abdomen. The mass is slightly lobular and causes dorsal displacement of the small intestine and descending colon. The mass contains multiple regions of amorphous mineralization. There is no evidence of enlargement of the uterine body between the descending colon and urinary bladder, but there is a focal, small, triangular soft tissue opacity between the colon, urinary bladder and caudal aspect of the mass. The proximal aspect of the spleen is visible in the ventrodorsal view, but the distal extremity is not seen in the lateral view. There is no evidence of abdominal fluid or sublumbar lymph node enlargement. There is mild to moderate spondylosis and several thoracic vertebral malformations, typical of the breed. No other abnormalities are identified.
The major considerations for the origin of the mass include uterus, spleen and ovary. The pattern of mineralization is not typical of fetal mineralization; thus if the mass is of uterine origin a pathologic mass with dystrophic mineralization would be a consideration. A malignant uterine mass would be unusual at this age. The mass could be arising from the spleen however mineralization of splenic masses is also very unusual. Given the intact nature of the patient and the characteristics of the mineralization within the mass, a primary consideration is ovarian teratoma.
Ultrasound or CT imaging could be used for more accurate staging, but a laparotomy will likely be needed. This was performed and a large ovarian mass was found. The histologic diagnosis was ovarian teratoma.
•Teratomas are complex tumors composed of multiple germ layers in various stages of maturation and may consist of tissue that is foreign to the area in which it arises1. Teratomas are thought to originate in utero.
•Teratomas are derived from 2 or 3 different germ layers. Therefore ectodermal structures such as hair, keratin, squamous epithelium, and nerve cells, and mesodermal structures such as bone, cartilage, fat, muscle and sometimes teeth can be found in the tumor.2-5 In animals, teratomas are generally benign.6
•Common signs of ovarian teratoma include abdominal distension and a palpable mass. Rarely is there evidence of hormonal activity. Surgical removal is often curative.
•Although ovarian teratomas are rare in dogs and cats, the amorphous mineralization pattern is considered to be characteristic. The following figure is another young dog with an ovarian teratoma. Note the similar mineralization pattern to the patient described above.
•The terminology associated with teratomas and other similar lesions can be confusing. As already noted, a teratoma is a tumor made up of several different types of tissue and they commonly contain tissue not normally found at that site.
•A hamartoma is a mass characterized by normal tissue proliferation in a normal location, such as adenoma, hemangioma, and lymphangioma. Some consider these to be benign neoplasms
•A choristoma is normal tissue proliferation in an abnormal location. Examples include pancreatic choristoma in a canine gallbladder7, cartilaginous choristoma in the lip of a dog8, and intestinal choristoma in the subcutis of a dog9.
1.Valenciano AC and Cowell RL. Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. Elsevier/Mosby, 2020.
2.Jergens AE et al: Ovarian teratoma in a bitch. J Am Vet Med Assoc, 1987; 191:81-83.
3.Wilson RB et al: Ovarian teratoma in two dogs. J Am Anim Hosp Assoc, 1984; 21:249-253.
4.Yamaguchi Y et al: Ovarian teratoma with a formed lens and nonsuppurative inflammation in an old dog. J Vet Med Sci, 2004;66:861-864.
5.Gulcubuk A et al: Ovarian teratoma in a dog. Turk J Vet Anim Sci, 2012;36:573-576.
6.Headley SA et al: Ovarian teratoma in a bitch. Vet Rec, 2006;158:879-885.
7.Abou Monsef Y et al: Pancreatic choristoma in a canine gallbladder. J Comp Pathol 2019; 166:17-19.
8.Lee SH at al. Cartilaginous choristoma of the lip in a dog. J Vet Med Sci 2017;79:68-70.
9.Whitten KA et al. Intestinal choristoma in the subcutis of a dog. Vet Pathol 2006;43:356-357.
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