FALSE-POSITIVE DIAGNOSIS OF SPINA-BIFIDA IN A FETUS WITH TRIPLOIDY

Background: Neural tube defects can be difficult to diagnose using ult rasound. Cranial markers, such as the lemon and banana signs, are usef ul sonographic findings that alert the ultrasonographer to examine the spine more carefully. The false-positive rate for the banana sign has been reported previously as zero. Case: A patient with elevated mater nal serum alphafetoprotein presented for a fetal ultrasound examinatio n. Findings on the scan included a lemon sign, a banana sign, an effac ed cisterna magna, and splayed lumbar vertebrae. After pregnancy termi nation, no spinal abnormality was detected on autopsy. X-rays of the f etal spine demonstrated narrowing in the thoracic spine. The karyotype of the fetus was 69,XXY. Conclusion: The sonographic cranial findings suggestive of a neural tube defect were misleading in this case. (C) 1997 by The American College of Obstetricians and Gynecologists.