Fetal bifid sacrum artifact: normal developmental anatomy simulating malformation.

PURPOSE: To determine the clinical importance and origin of a bifid configuration of the fetal sacrum seen during routine fetal sonography. MATERIALS AND METHODS: An apparent bifid malformation of the sacral spine was seen in 24 fetuses at antenatal sonography. An attempt was made to recreate this configuration prospectively in 111 consecutive second- and third-trimester fetuses. Three cadavers were also imaged to determine the origin of this configuration. RESULTS: Outcome information was available for 22 of the 24 fetuses; all fetuses were normal. In the prospective study, the bifid sacrum configuration was recreated in 75 of the 111 fetuses studied. The configuration could never be produced earlier than 20 weeks gestational age, was seen in some fetuses at 20-25 weeks, and could always be seen after 25 weeks. Findings from imaging studies of the three cadavers revealed that this configuration was dependent on the demonstration of the alar ossification centers of the sacral vertebra. CONCLUSION: The bifid sacrum artifact is a skewed representation of normal anatomy and should not be interpreted as a true anomaly.

Optimizing transperineal sonographic imaging of the cervix: the hip elevation technique.

Although transperineal ultrasonography is a valuable technique for imaging the cervix in pregnancy, transperineal imaging can be compromised when bowel gas obscures the external portion of the cervix. To determine if a hip elevation technique could improve visualization of a partially obscured cervix, transperineal scanning was performed with the hips and buttocks elevated on a thick cushion in 23 patients with suboptimal routine transperineal views. The "hips up" maneuver was tolerated by all patients and improved cervical visualization in 19 of 23 cases. We conclude that the simple maneuver of elevating the patient's hips and buttocks on a thick cushion is a useful adjunctive technique to improve transperineal imaging of the cervix when routine transperineal views are compromised by adjacent bowel gas.

Fetal fourth ventricle: US appearance and frequency of depiction.

PURPOSE: To define the normal appearance of the fetal fourth ventricle throughout gestation and ascertain an expected frequency of depiction at different gestational ages. MATERIALS AND METHODS: Three hundred ten consecutive second- and third-trimester fetuses were studied with ultrasound. The posterior fossa was examined to document the size and appearance of the fourth ventricle. RESULTS: The fourth ventricle was seen in 221 of the 310 fetuses (71.3%) and was most consistently demonstrated in the middle of the second trimester. At this stage of gestation, the fourth ventricle was almost always seen when the anatomic features of the posterior fossa were identified. The mean anteroposterior dimension of the fourth ventricle was 3.5 mm +/- 1.3 (standard deviation), and the mean width was 3.9 mm +/- 1.7. CONCLUSION: The fetal fourth ventricle can be seen in most fetuses beginning in the middle of the second trimester and increases in size with advancing gestation. It can be difficult to depict before the middle of the second trimester and late in the third trimester.