Cyst of the filum terminale: two cases detected on prenatal ultrasound.

We herein report two cases of cyst of the filum terminale, diagnosed by prenatal ultrasound in the second and third trimesters, respectively. The first case, a 32-year-old primigravida, was referred to our center at 20weeks for a detailed anomaly scan because of a suspected periconceptional toxoplasmosis infection. Her medical and family histories were unremarkable except for obesity, with a body mass index of 35.3 kg/m2. Transabdominal ultrasound did not detect major fetal anomalies, but because of a persistent breech presentation sonographic assessment of the spine was completed with the aid of a transvaginal approach (Figure 1; Videoclip S1). At the level of L4, just caudal to the lower end of the conus medullaris and within the filum terminale, a fusiform anechoic unilocular cyst measuring 3×2mm was visualized. The cyst showed neither septations nor solid components, and was nonvascularized on high-definition color Doppler imaging (Videoclip S1). Using the three-dimensional multiplanar technique, the cyst was simultaneously visualized in sagittal (Figure 2a), coronal (Figure 2b) and transverse (Figure 2c) views. The patient was scheduled for a followup visit at our center with the aim of reassessing the unusual spine findings. At 30 weeks, no relevant anomaly was detected, but the fetus was in cephalic presentation and the filum terminale could not be properly assessed by the transabdominal approach. The patient vaginally delivered a 3460-g healthy male at term. At the time of writing, the infant was 6months old and was thriving.