Figure 3b. Classification of sacrococcygeal teratomas. (a) Type I. Coronal US image of a fetal spine shows a small, exophytic, cystic mass (straight white arrow) emanating from the coccyx (curved arrow). No internal component was identified. Black arrow = iliac crest. (b) Type II. Longitudinal US image of a lower fetal spine shows a mixed cystic and solid sacrococcygeal teratoma (straight arrow), which extends into the presacral space (arrowhead). Curved arrow = coccyx. (c) Type III. Sagittal T2-weighted image shows a mass with a cystic external component and extension of a solid portion into the fetal abdomen (white arrow). Arrowhead = umbilical cord insertion. A type IV mass would have no external component.