A 37-year-old primigravida was referred to our prenatal diagnosis unit at 12 weeks of gestation for further examination following an abnormal ultrasound scan. She had no significant personal or family medical history. During transvaginal two-dimensional (2D) ultrasound examination, a singleton fetus with a crown–rump length of 61 mm and nuchal translucency thickness of 1.2 mm was observed. A cystic mass of 18 × 16 mm was noted within the umbilical cord, near the cord insertion. The fetal bladder appeared as a fluid-filled structure in the pelvis with apparently normal characteristics. A patent communication between the fetal bladder and the cystic mass was not identified on 2D ultrasound. No other structural abnormalities were detected. After the initial 2D scan, we proceeded to use three-dimensional (3D) ultrasound imaging (Voluson E8, GE Medical Systems, Valencia, Spain) to acquire volumetric data. Once the 3D dataset of the region of interest had been obtained, SonoAVC (Sonography-based Automated Volume Count, GE Medical Systems) software was used to further explore the cystic mass. SonoAVC allowed visualization of the cystic mass within the umbilical cord, but, more importantly, clearly showed a patent communication of the mass with the vertex of the fetal bladder (Figure 1). Furthermore, the use of SonoAVC with 3D Doppler ultrasound clearly identified the umbilical arteries running around the bladder, passing through the abdominal wall defect and surrounding laterally the cystic mass to end in the umbilical cord (Figure 2). Therefore, the diagnosis of a patent urachus with bladder prolapse was made. Follow-up ultrasonographic studies showed that the cystic mass spontaneously reduced in size until it was undetectable at 28 weeks of gestation. At 39 weeks' gestation a male infant weighing 2894 g was delivered vaginally. At initial examination an anomaly on the base of the umbilical cord with protruding mucosa was observed, from which urine was voided (Figure 3). Recovery was uneventful following excision of the patent urachus. Visualization using SonoAVC of a cystic mass (CM) (white) within the umbilical cord and a patent communication (arrow) with the vertex of the fetal bladder (B) (blue). SonoAVC with 3D Doppler ultrasound showing umbilical arteries running around the bladder (B), passing through the abdominal wall defect (yellow arrows) and surrounding laterally the cystic mass (CM) (solid green arrows) to end in the umbilical cord (dashed green arrows). UC, umbilical cord vessels. SonoAVC ultrasound image (a) and its correlation with the anomaly found at the base of the umbilical cord at birth, a prolapsed bladder with protruding mucosa (b). Persistent patent urachus is a rare congenital anomaly found in 1/100 000 births1. Urachus is the intra-abdominal remnant of embryonic allantois lying between the peritoneum and transversalis fascia, stretching from the dome of the bladder to the umbilicus2. Urachal anomalies result from failed obliteration of the urachus, creating different pathologies such as patent urachus, urachus cyst, urachal sinus or vesicourachal diverticulum2, 3. Persistent patent urachus is easily recognized at birth but is rarely diagnosed prenatally1-6. Differential diagnoses include omphalocele, bladder exstrophy, persistent omphalomesenteric duct and umbilical edema2, 3, 7. The most common sonographic finding is the presence of a cystic mass located in the base of the umbilical cord, communicating with the bladder and flanked by the umbilical arteries3, 8. Moreover, a reduction in size (or even disappearance) of the mass over the course of pregnancy is also a feature of this pathology2, 3, 5. SonoAVC is a software program that allows identification and quantification of hypoechoic regions within a 3D dataset and provides automatic estimation of their absolute dimensions, mean diameter and volume9, 10. This 3D modality transforms hypoechoic regions into color-coded structures based on their different volumes9, 10. However, 3D technology is still highly dependent on the acquisition modality, which means that the initial capture of the region of interest is essential; also, when using SonoAVC software, further manual processing of the image is needed in order to optimize the visualization obtained. In summary, this technology is still highly operator dependent. In our case, the use of 3D SonoAVC strengthened the diagnosis of a patent urachus with bladder prolapse by enabling visualization of the communication between the fetal bladder and urachal cyst through a small channel. This case suggests that this new 3D modality may facilitate early prenatal visualization of patent urachus by enhancing the appearance of cystic lesions. F. Raga*, F. Bonilla-Musoles*, J. C. Castillo*, * Department of Obstetrics and Gynecology, University of Valencia, Valencia, Spain