Discussion:
Yolk sac tumors are germ cell tumors that most commonly arise from the gonads(4). Extragonadal germ cell tumors are rare and primary yolk sac tumors of the liver are extremely rare with only few case reports being described(5). Primary yolk sac tumors of the liver arise in young adults and the prognosis is variable with several case reports showing successful treatment with chemotherapy.
These tumors can pose a significant diagnostic challenge as multiple liver lesions in young adults have a broad differential diagnosis. Multifocal liver lesions in young adults and children can be of benign or malignant origin. Common benign causes include focal nodular hyperplasia, liver abscesses, and hepatic adenomas. While causes of malignant multifocal liver lesions in adults include Infantile hepatoblastoma, lymphoma, hepatocellular carcinoma, hepatic epithelioid hemangioendotheliomas, and metastases (6, 7). MRI abdomen with a histologic diagnosis is key to establishing a definite diagnosis. In our case, there was a high probability of primary liver tumor with a second likely differential of liver metastases from colon until the biopsy results revealed the histology of yolk sac tumor from liver lesion as well as from sigmoid colon. Correct diagnosis is essential for early recognition and early initiation of appropriate therapy.
Histologically, yolk sac tumors display marked heterogeneity, with numerous architectural patterns described. A combination of patterns is common, in varying proportions. The various histological patterns include microcystic/reticular, macrocystic, papillary, solid, sarcomatoid, glandular, hepatoid, myxomatous, perivascular, and polyvesicular vitelline patterns. Schillar-Duval bodies are another characteristic finding but are not required for diagnosis. Hyaline globules are usually noted in the hepatoid pattern, which are usually AFP positive.
Primary hepatic yolk sac tumors are rare and to date, several case reports have been reported(8–14). There are no specific radiologic diagnostic features of yolk sac tumors and hence their ability to masquerade other liver lesions(10). Several treatment modalities have been reported. The treatment depends on whether the tumor is resectable or not, the presence of metastasis, and the initial response to chemotherapy. Successful treatment with surgical resection has also been achieved (5). Treatment by embolization for liver yolk sac tumor has been reported. (14) While Liver transplant as a treatment option has also been reported successfully (11,12). Despite these options, the mainstay treatment modality in the extragonadal yolk sac tumors is chemotherapy as these tumors are highly sensitive to chemotherapy. The main chemotherapy is Bleomycin etoposide and cisplatin-based. Other regimens have also been used.
Yolk sac histology and the presence of metastasis are predictors of poor survival in germ cell tumors(3). Other established predictors of poor prognosis include mediastinal primary origin, non-pulmonary metastases and elevated markers (AFP > 10,000 ng/ml, LDH > 10x upper limit of normal, beta-HCG > 50,000 IU/l(15). Our patient was classified as a poor prognosis group due to the presence of poor prognostic markers including Yolk sac histology and colonic metastasis.