Fetal Presentation of Mediastinal Immature Teratoma: Ultrasound, Autopsy and Cytogenetic Findings

Teratomas are the most common congenital tumors, occurring along the midline or paraxial sites, or uncommonly, the mediastinum. Teratomas are classified as mature, containing only differentiated tissues from the three germinal layers; and immature, which also present with neuroectodermal elements, ependymal rosettes, and immature mesenchyme. Herein, we describe a new case of fetal mediastinal immature teratoma detected at 21 weeks of gestational age (wga) + 1 day with thorough cytogenetic analysis. Ultrasound (US) showed a solid and cystic mass located in the anterior mediastinum, measuring 1.8 x 1.3 cm with no signs of hydrops. At 22 wga, US showed a mass of 2.4 cm in diameter and moderate pericardial effusions. Although the prenatal risks and available therapeutic strategies were explained to the parents, they opted for termination of pregnancy. Histology showed an immature teratoma, Norris grade 2. Karyotype on the fetus and tumor exhibited a chromosomal asset of 46,XX. The fetal outcome in the case of mediastinal teratoma relies on the development of hydrops due to mass compression of vessels and heart failure. Prenatal US diagnosis and close fetal monitoring are paramount in planning adequate treatment, such as in utero surgery, ex utero intrapartum therapy (EXIT) procedure, and surgical excision after birth.