Early diagnosis of spina bifida: the value of cranial ultrasound markers

Article Abstract:

Spina bifida is a congenital abnormality involving the incomplete development of the neural tube, which surrounds the nerves from the brain to the spinal column, of the fetus. A high level of alpha-fetoprotein in the blood of the mother is highly suggestive of a neural tube defect. Although high resolution ultrasound imaging can help diagnose spina bifida, small defects can still be missed. Some researchers have found that there are markers in the brain that are indicative of open spina bifida (exposed spinal cord). To see if these cranial markers facilitate diagnosis of spina bifida, 44 fetuses were examined. Open spina bifida was diagnosed in 24 fetuses. Cranial ultrasound features included the lemon sign, scalloping of the frontal bones; the biparietal diameter (BPD), a measurement of the parietal bones of the skull; the location of the cerebellum; the size of the brain and the size of the spaces within the brain (ventricles). The lemon sign and cerebellar abnormalities were present in all of the 16 fetuses diagnosed with spina bifida during the 16th to 24th week of pregnancy. In four of the seven fetuses diagnosed in the 16th to 18th week of pregnancy, the lemon sign and cerebellar abnormalities pointed towards spina bifida even though the ultrasound results did not detect the defect. The diagnosis was confirmed when follow-up scans were performed one to two weeks later. Small head size and enlarged ventricles were present in 69 percent and 63 percent of the cases respectively. The lemon sign was detected in only 25 percent of the cases diagnosed after the 24th week of pregnancy. As the fetus advanced in age, the presence of enlarged ventricles increased, in 75 percent of the cases. Cranial markers such as the lemon sign, and cerebellar abnormalities detected by fetal ultrasound can be useful in diagnosing spina bifida early in pregnancy. The presence of these brain markers should alert the sonographer to the possibility of open spina bifida. (Consumer Summary produced by Reliance Medical Information, Inc.)

Spinal cord, Fetal brain, Ultrasonic encephalography

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Ultrasound detection of neural tube defects in patients with elevated maternal serum alpha-fetoprotein

Article Abstract:

There are a number of diagnostic techniques available for detecting fetal neural tube defects such as spina bifida. For screening purposes, measurement of the maternal serum alpha-fetoprotein (MSAFP) level is normally used. It is only an indicator of a possible neural tube defect and further evaluation with either ultrasound (US) imaging or amniocentesis is required. These latter two procedures can not be used for screening because costs or risks are prohibitive. When elevated MSAFP levels are shown, either amniocentesis or US must be performed. Amniocentesis is highly accurate for detecting neural tube defects, but is invasive and poses a risk to the fetus. US is noninvasive, but its accuracy has been questioned. This study examined the reliability of US in detecting neural tube defects in women with elevated MSAFP levels. A total of 925 cases of elevated MSAFP were evaluated using US. Amniocentesis was also performed in a few cases. Results were compared with fetal outcome. US scanning was able to detect a neural tube defect in 49 cases. US scanning detected non-neural tube defects in 43 other cases. Of the 703 patients examined solely with US, in only one positive case was a neural tube defect not diagnosed. Ultrasound had a sensitivity of 98 percent and a specificity of 100 percent in detecting neural tube defects, that is, US was able to identify neural tube defects in 98 percent of cases and this diagnosis was correct in 100 percent of cases. These result demonstrate that ultrasound is a reliable method for evaluating neural tube defects in cases of elevated MSAFP levels. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Abnormalities, Ultrasound imaging, Fetus, Neural tube, Neural tube defects, Alpha fetoproteins

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Prediction of the small for gestational age twin fetus by Doppler umbilical artery waveform analysis

Article Abstract:

It is difficult to assess the age of the fetus (gestational age) in twin pregnancies, which are often complicated by premature delivery. A fetus whose weight and size at birth are in the 10th percentile, meaning that it is smaller than 90 percent of all fetuses, is termed small for gestational age (SGA). Current techniques of assessing gestational age in twin pregnancies, such as ultrasonography (the use of high frequency sound to visualize the fetus), are not rapid and require expert analysis. Doppler ultrasound uses high frequency sound to monitor the behavior of moving structures such as flowing blood and a beating heart. To see if the flow of blood through the umbilical artery of each twin fetus, performed throughout pregnancy, is a helpful measurement for assessing fetal well-being, 178 fetuses in 89 pregnancies were studied. A total of 453 Doppler ultrasound evaluations was performed on the fetuses. There were 32 SGA infants, but only 24 abnormal results of the 82 Doppler evaluations. The sensitivity (29 percent) and positive predictability (34 percent) of Doppler waveform analysis in detecting SGA fetuses was never above 50 percent in any age group. Of the four fetuses with absent end-diastolic frequencies (a type of waveform pattern), three were SGA. Six out of seven fetuses with normal end-diastolic frequencies that became grossly abnormal later were SGA. It is concluded that the measurement of blood flow through the umbilical artery was not useful in predicting SGA fetuses in twin pregnancies. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, Evaluation, Twins, Gestational age, Duplex ultrasonography

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