Sacrococcygeal yolk sac carcinoma: imaging findings during treatment.

Sacrococcygeal teratomas and their malignant counterparts (germ cell tumors) are the most common solid tumors in neonates. Prompt diagnosis is essential because the frequency of malignant transformation increases from 10-20 % in neonates to 67 % in patients over 2 months of age. Cross-sectional imaging has largely replaced surgical exploration for staging these tumors and assessing their response to chemotherapy. Radiologists must be familiar with changes in the imaging findings of these tumors during and after treatment so that they can advise clinicians regarding the efficacy of therapy and the presence or absence of recurrent disease. From our study, magnetic resonance imaging appears to be a better modality for assessing sacral invasion and metastases and distinguishing fibrotic masses from recurrent tumor.