A solid mature teratoma of a feline ovary

Abstract

A 17-year-old female crossbred cat developed a mass on the left ovary. The mass was solid, firm, 5.5×3.5×4.5 cm. The mass contained ectodermal components (skin and appendages), mesodermal components (osseous, cartilaginous and adipose structures), and endodermal components (glandular structures lined by columnar epithelium). The tumor was diagnosed as a solid, mature teratoma of the ovary.

A17-year-old crossbred cat was presented to a private animal hospital for ovariohysterectomy. The cat had given birth to two kittens at 14 years of age and had not been in oestrus since then. On physical examination, a firm mass was palpated in the anterior dorsal abdomen. On surgical exploration, the mass was attached to the left uterine horn and was excised in toto. The mass was submitted for gross and histopathological examination. It was fixed in 10% neutral buffered formalin. On examination, calcification was noted. The sample was placed in 10% neutral buffered formalin–formic acid for 21 days for decalcification. Paraffin sections were stained with hematoxylin and eosin (H&E). Immunohistochemical stains were performed to assess the undifferentiated cells by the streptavidin–biotin method (Histofine SAB-PO kit, NICHIREI Co, Tokyo) using rabbit polyclonal anti-human cytokeratin, rabbit polyclonal anti-human S-100 protein, rabbit polyclonal anti-human glial fibrillary acidic protein (GFAP), and mouse monoclonal anti-human neurofilament antibody (NICHIREI Co, Tokyo).

The tumor was 5.5×3.5×4.5 cm, kidney shaped, grayish-white to brown, and extremely hard. The surface was smooth and glossy. On cross-section, the tumor was solid, in layers of brown, yellowish, and red-brown tissues, and covered by thick capsule (Fig 1). There was no ovarian stroma at the tip of left uterine horn.

Fig 1.

Cross section of formalin-fixed mass from the left ovary. The tumor is solid and is filled with heterogeneous tissues.

Histologically, the tumor mass was encapsulated by a thick, vascular fibrous tissue. Well-differentiated tissues were haphazardly located throughout the mass. These included ectodermal components: skin and appendages including hair follicles (Fig 2A) and sebaceous glands; mesodermal components: bone and cartilaginous matrices, adipose tissue, and the bundles of smooth muscle; and endodermal components: glandular structures lined by columnar epithelium (Fig 2B). Structures resembling pulmonary bronchi surrounded by cartilaginous rings were seen, but these lacked ciliated epithelium (Fig 2C). Mineralized woven bone was present; it resembled a long bone with epiphysis. The medullary cavities of the bone contained hematopoietic tissue and cell debris (Fig 2D).

Fig 2.

Histological features of feline teratoma of a left ovary (H&E). (A) A nest of hairs (×50), (B) glandular structures lined by columnar epithelium (×50), (C) structures resembling pulmonary bronchi surrounded by cartilaginous rings (×10), and (D) mineralized woven bone resembled long bone whose edges indicated epiphysial cartilage (arrowhead) transforming toward ossification (×10).

In immunohistochemical studies, the keratinized epithelium, hair follicles, and sebaceous glands showed positive staining with polyclonal anti-cytokeratin antibody. All tissues in the tumor showed negative staining with neurofilament, GFAP, and S-100 antibodies.

Conclusions

A teratoma arises from pluripotential germ cells and is composed of tissues derived from more than one of the embryonic layers (Kennedy 1998). A common site for these tumors is the ovary. Ovarian teratomas in humans are thought to arise from haploid germ cells, which autofertilize and develop to diploid tumor cells having the karyotype 46, XX (Robboy et al 1998). While frequently encountered in humans (Scully 1979), only four cases have been reported in cats (Dehner et al 1970, Gruys and van Dijk 1976, Gelberg and McEntee 1985, Basaraba et al 1998). According to these reports, feline teratomas show no age or breed predisposition. The present case is unusual in that it occurred in a geriatric cat. Tumorsreported have varied in size from 1.5 to 15 cm. Most teratomas occur in the left ovary; some of them are cystic and covered by haired skin (Norris et al 1969, Basaraba et al 1998).

Histologically, three embryonic components with a variety of tissues were present. The location of tissue components in the mass was heterogeneous, but ectodermal and mesodermal components predominated. These findings were similar to the general histological features of teratomas (Scully 1977, 1979, Toyosawa et al 2000). Nervous tissue is frequently observed in dog, cat, and human teratomas (Norris et al 1969, Nagashima et al 2000), but could not be identified in this case. Decalcification may interfere with immunohistochemical staining but H&E preparation was adequate to determine the lack of nervous tissue. It should be noted that the presence of nervous tissue is not necessary for the diagnosis of teratoma.

Based on the degree of maturity, human teratomas are classified into immature (usually solid and malignant) and mature (usually cystic and benign) types (Scully 1977, 1979). This case was unique because the tumor was apparently solid yet composed of well-differentiated tissues. In addition, the tumor had a benign nature pathologically and clinically, and the cat was completely well after oophorectomy.

To the best of our knowledge, there is only one report of a feline teratoma of solid type mentioned in the literature, a mixed dysgerminoma–teratoma (Dehner et al 1970). Thus, the present case is probably the first report of a mature, solid, pure teratoma in an old cat.