Diagnostic exercise: ascites, abdominal masses, and diffuse peritoneal nodules in a rat.

A 1.4-year-old virgin female brown-hooded fancy rat presented for abdominal distention, jaundice, and dyspnea. At physical examination, a firm mass was palpable in the caudoventral abdomen as well as multiple small nodular masses associated with the abdominal viscera. At necropsy, in addition to a large mass replacing the left ovary and myriad nodules studding the peritoneal surface, there was 31 ml of abdominal effusion. By cytology, the abdominal fluid contained numerous pleomorphic vacuolated tumor cells surrounding globular pale eosinophilic to amphophilic acellular material that was strongly periodic acid-Schiff positive. Histologically, the tumor was biphasic with abundant acellular hyaline matrix that was also periodic acid-Schiff positive.

Yolk sac carcinoma derived from the rat epiblast as a renal isograft.

We report the novel observation that a biphasic, parieto-visceral (PYS/VYS) yolk sac carcinoma can develop from the isolated epiblast of the pre-primitive streak rat embryo in a prolonged cultivation in vivo as a renal isograft. Late 7-day rat egg cylinders were dissected free of the ectoplacental cone and the Reichert's membrane. The middle segment of the cylinder, in which the embryonic and the extraembryonic cell layers partly overlap, were also removed. From the rest of the cylinder the 4 cell layers were isolated and transplanted separately under the kidney capsule of isogenic adult males. After 4 weeks the hypoblast was resorbed, the extraembryonic ectoderm gave rise to hemorrhagic cysts and trophoblastic giant cells, the extraembryonic (visceral yolk sac) endoderm formed benign cystic PYS/VYS tumors, and the epiblast developed into a benign teratoma. After prolonged (7-30 weeks) development of these teratomas as isografts, a malignant yolk sac carcinoma (YSC) developed in 45% of them. It destroyed the teratoma and the recipient's kidney, metastasized to peritoneum and other sites, and caused abundant ascites containing clustered tumor cells. The primary tumor was retransplantable subcutaneously as well as intraperitoneally, and displayed the characteristics of the mixed or biphasic PVYS carcinoma, with a progressive loss of the VYS component with time. Several data are apparently in favor of its origin by transdifferentiation rather than from undifferentiated cells.

Testicular yolk sac tumor and impaired spermatogenesis in a Holstein Friesian calf.

Yolk sac tumors are testicular germ-cell tumors of the non-seminoma type. In cattle, this neoplasm is very rare and to date has only been described three times. In human males, it usually occurs in infants and children. Immunohistochemistry provides solid criteria for diagnostics. Especially present pathognomonic Schiller-Duval bodies are helpful for identification. In this report, a 32-day-old Holstein Friesian calf presented with a highly enlarged right testis. Sonographic examination was performed and blood samples were taken to measure testosterone and estrogen levels. Furthermore, the testis was surgically removed and macroscopically, histologically, and immunohistochemically examined which lead to the diagnosis of testicular yolk sac tumor. The second testis was descended until the age of nine months and histology revealed impaired spermatogenesis. This report provides the first sonographic images of bovine testicular yolk sac tumor as well as the first information about hormone levels in calves with this neoplasm. It also shows the importance to combine anamnesis, histomorphological, and immunohistochemical findings in order to diagnose yolk sac tumors when pathognomonic structures are not present.

Ovarian mixed germ cell tumor with yolk sac and teratomatous components in a dog.

Mixed germ cell tumors of the ovary have rarely been reported in veterinary species. A 3-year-old intact female Labrador Retriever dog was presented for lethargy, abdominal distention, and a midabdominal mass. An exploratory laparotomy revealed a large (23 cm in diameter) left ovarian tumor and multiple small (2-3 cm in diameter) pale tan masses on the peritoneum and abdominal surface of the diaphragm. Histological examination of the left ovary revealed a mixed germ cell tumor with a yolk sac component with rare Schiller-Duval bodies and a teratomatous component comprised primarily of neural differentiation. The abdominal metastases were solely comprised of the yolk sac component. The yolk sac component was diffusely immunopositive for cytokeratin with scattered cells reactive for α-fetoprotein and placental alkaline phosphatase. Within the teratomatous component, the neuropil was diffusely immunopositive for S100, neuron-specific enolase, and neurofilaments with a few glial fibrillary acidic protein immunopositive cells. Ovarian germ cell tumors may be pure and consist of only 1 germ cell element or may be mixed and include more than 1 germ cell element, such as teratoma and yolk sac tumor.

Testicular yolk sac tumor of myxomatous, reticular, and polyvesicular vitelline type in a newborn calf.

Yolk sac tumors (YSTs) are rare neoplasms of germ cell origin. In humans, the tumors primarily occur in the testes or ovaries, but occasionally develop at other sites. The neoplastic cells of YSTs form many histological patterns resembling embryonal structures, and the World Health Organization classification lists 11 such patterns: reticular, macrocystic, endodermal sinus, papillary, solid, glandular-alveolar, myxomatous, sarcomatoid, polyvesicular vitelline, hepatoid, and parietal. Among domestic animals, only 2 cases of YST, which were of testicular and abdominal cavity origin, have been reported in calves. In both cases, neoplastic cells had epithelial properties and disseminated metastases in the abdomen. In the present study, the enlarged testis of a newborn calf, which was subsequently diagnosed as YST and exhibited myxomatous, reticular, and polyvesicular vitelline histological patterns, is described. There was no metastasis in this case, and histological and immunohistochemical features varied from previous cases of YST.

Perforating abomasal ulcer caused by yolk sac tumor in a Holstein calf.

A 2-month-old male Holstein calf showed clinical signs of abdominal bloating, melena, and pain and was suspected of having a perforating abomasal ulcer. Necropsy revealed a large mass located preferentially around the abomasum and a large perforating abomasal ulcer on the pyloric antrum. Milky white masses of various sizes were also found in the abdominal cavity that consisted of agglutinated nodules ranging in size from a pinhead to a golf ball and were distributed on the surfaces of the liver, reticulum, omasum, abomasum, and diaphragm. Microscopic examination revealed that the masses were composed primarily of hyaline matrices, epithelioid tumor cells, and large atypical cells with hyaline droplets and/or vacuoles. Stromal hyaline matrices and hyaline droplets of the large tumor cells stained positive with periodic acid-Schiff stain. Tumor cells showed a positive reaction to anti-human alpha-fetoprotein, which is a marker of yolk sac tumors. These findings strongly suggested that the masses found in the abdominal cavity were yolk sac tumor, a rare germ cell tumor in cattle.

Mixed germ cell tumor in the eye of a dog.

A 3-year-old female neutered Staffordshire Bull Terrier presented with a mixed germ cell tumor involving the base of the iris and the ciliary body of the right eye. The tumor mass was composed primarily of packeted vacuolated, polygonal (hepatoid) cells and small round cells; epithelial cells lining tubuloacinar structures were a less prominent component. The hepatoid and round cells stained positively for alpha-fetoprotein and cytokeratin. The epithelial cells stained positively for cytokeratin only, and some contained cytoplasmic mucin droplets. The polygonal cells were interpreted as a hepatoid variant of yolk sac tumor, and the epithelial cells were considered a teratomatous component. Trabeculae of bone were observed within the mass and may have been metaplastic or a teratomatous element. Extragonadal germ cell tumors are rare in dogs and have previously been reported only in the suprasellar region. This is the first report of this tumor type in the eye of a nonhuman species.

Testicular yolk sac carcinoma in a calf.

A testicular yolk sac carcinoma (YSCA) was diagnosed in a 28-day-old male Japanese black calf. Macroscopically, the abdominal cavity was filled with reddish gelatinous masses of various sizes. There were no testes in the scrotum or pelvic cavity. Histologically, the masses consisted of the tissues showing a variety of patterns; loose reticular network, pseudopapillary arrangement, festoon, solid nest, and labyrinthine pattern. Tumor cells were round to oval, with single central or polar nuclei with sharply defined nuclear borders and deeply basophilic chromatin. Tumor cells sometimes had glycogen granules, periodic acid-Schiff (PAS)-positive inclusions, or sudanophilic droplets in their cytoplasm. Hyaline matrices were found in extracellular areas and were intensely PAS positive. Immunohistochemically, most of the tumor cells and hyaline matrices had positive reactivity to anti-alpha-fetoprotein and anti-placental-alkaline-phosphatase antibodies. Positive reaction to anti-laminin antibody appeared only in hyaline matrices. This is the first case of a tumor in a domestic animal with histologic and immunohistochemical features analogous to those of human YSCA, endodermal sinus type.