Abstract Context The cervical teratomas are rare, benign tumors, they are formed by the three embryonic layers, and they represent only 6% of teratomas. The prog- nosis depends mainly on the size and location of the lesion, on the tumor growth rate, and on the level of tracheal compression. Prenatal diagnosis is usually reached with the aid of a two-dimensional ultraso- nography (2DUS) after the 15th week of gestation, which shows a large heterogeneous mass in the cervical region, plus a polyhydramnios, on the Doppler mode which also shows the vascularization of the tumor. Case report We report a case of cervical teratoma diagnosed on the 31st week of gestation with the aid of a 2DUS and color Doppler mode. We focus on the main findings obtained with the three-dimensional ultrasonography in surface mode, and we highlight the importance of this methodology for the indirect eval- uation of the neonatal prognosis. Keywords Cervical teratoma Æ Prenatal diagnosis Æ Three-dimensional ultrasound Introduction Cervical teratomas are rare tumors, which have an incidence which varies from 1 in 20,000 to 1 in 40,000 live births, and which represent 6% of all fetal ter- atomas [1]. Histologically, they are benign tumors formed by the three germinal layers (ectoderm, mesoderm, and endoderm). The prenatal diagnosis of a cervical teratoma, reached with the aid of a two-dimensional ultraso- nography (2DUS), is extremely important to show the complications derived from this anomaly, and to allow for a safer planning of the parturition which will occur somewhere [2, 3]. As for the three-dimensional ultrasonography (3DUS), there is only one report in MEDLINE of the use of such methodology in prenatal diagnosis of cer- vical teratoma [2]. We presented a case of fetal cervical teratoma diagnosed on the 31st week of gestation. We focused on the main findings obtained with the 3DUS, and on the contribution of this methodology in helping parents and the medical team (obstetrician, neonatologist, and pediatric surgeon) to better understand this pathology. Case report A 20-year-old woman, with one previous gestation but childless with gestational age of 31 weeks and 2 days, according to the last menstruation date (LMD), was referred to our service for the assessment of a fetal cervical mass. On the complementary questioning she denied having consanguinity, family history of fetal malformations, or using teratogenic drugs. She E. Araujo Ju ´ nior (&) Æ L. M. Nardozza Æ A. F. Moron Department of Obstetrics, Sao Paulo’s Federal University (Unifesp/EPM), Napolea ˜o de Barros Street, 871 Vila Clementino, 04024-002 Sa ˜o Paulo, Brazil e-mail: araujojred@terra.com.br E. Araujo Ju ´ nior Æ H. A. Guimara ˜ es Filho Æ M. Saito Æ A. B. Pires Æ A. L. S. Pontes Conceptus-Fetal Medicine Unit of Sao Paulo, Antonio Borba Street, 192 apt. 43 Alto de Pinheiros, 05451-070 Sa ˜o Paulo, Brazil Arch Gynecol Obstet DOI 10.1007/s00404-006-0180-9 123 CASE REPORT Prenatal diagnosis of a large fetal cervical teratoma by three-dimensional ultrasonography: a case report Edward Araujo Ju ´ nior Æ He ´lio A. Guimara ˜es Filho Æ Mauricio Saito Æ Alexandra B. Pires Æ Ana Letı´cia S. Pontes Æ Luciano M. Nardozza Æ Antonio Fernandes Moron Received: 3 March 2006 / Accepted: 26 April 2006 Ó Springer-Verlag 2006