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.