Fetal choroid plexus cysts: prevalence, clinical significance, and sonographic appearance

To determine the prevalence, sonographic appearance, and clinical significance of fetal choroid plexus cysts, we analyzed the sonograms and clinical records of 17 fetuses with cysts. Fetal and maternal age, sonographic indication, cyst size and multiplicity, and evolution on serial studies were recorded. Fetal outcome was available in 16 cases by genetic amniocentesis (n = 5) or neonatal clinical records (n = 11). The prevalence of fetal choroid plexus cysts was 0.8% (17/2084) during a 40-month period. All cysts were initially identified on sonograms performed between 14 and 21 weeks. Cysts ranged from 3 to 11 mm in size and were bilateral in four (36%) of 11 cases in which both lateral ventricles were visualized. In nine of 10 cases with serial sonograms 2-21 weeks after the initial study, the cysts were no longer present. One fetus had a small cyst persisting at term. All five cases with genetic amniocentesis had normal chromosomes. The only phenotypic abnormality in the 11 cases with clinical follow-up was a small hemangioma of the chest wall. We conclude that most fetuses with isolated choroid plexus cysts have a normal outcome and that serial sonography for cyst evaluation is not useful in determining fetal prognosis.     

Severe polyhydramnios: incidence of anomalies

The sonograms of 195 singleton pregnancies complicated by polyhydramnios were reviewed, and follow-up information was obtained on 191 patients. A grading system was developed that differentiated mild from severe polyhydramnios using real-time or static sonographic equipment. Mild polyhydramnios was present in 138 (71%), and severe polyhydramnios was present in 57 (29%). Previously it has been reported that 60% of cases of polyhydramnios are idiopathic and the pregnancies have a normal outcome. Twenty percent are associated with maternal abnormalities and 20% are associated with fetal anomalies. In this study, pregnancies with severe polyhydramnios had a much greater prevalence of fetal anomalies (75%) than pregnancies with mild polyhydramnios (29%). The 57 singleton pregnancies with severe polyhydramnios were analyzed in depth. Fourteen (25%) of the fetuses were normal; 43 (75%) had significant congenital abnormalities that predominantly involved the CNS, gastrointestinal tract, heart, and genitourinary tract. In all fetuses with primary CNS abnormalities, polyhydramnios was diagnosed at or before 30 weeks of gestation, while in most of the fetuses (83%) with gastrointestinal abnormalities it was diagnosed after 30 weeks. Sonographic findings correlated closely with the findings noted at birth or autopsy. In patients with severe polyhydramnios, normal sonograms were sensitive in excluding major congenital anomalies and, thus, were helpful in providing the parents with favorable prognoses. Sonograms should be performed in patients with polyhydramnios to identify congenital anomalies and to provide information regarding prognosis for fetal outcome.     

Clinical course of fetal hydrocephalus: 40 cases

The clinical course and outcome of hydrocephalus diagnosed in utero is not well understood. To approach this problem 40 cases were reviewed of intrauterine fetal hydrocephalus diagnosed with sonography, and follow-up information was obtained regarding them. Sonograms were evaluated for cerebral dimensions, biparietal diameter, brain mantle size, ventricular ratio, amount of amniotic fluid, and associated abnormalities. Neonatal brain sonograms and computed tomographic (CT) scans were reviewed also. Clinical charts were reviewed for maternal age and parity, referral source, family history, fetal age at diagnosis and delivery, mode of delivery, physical examination and/or autopsy findings, karyotype, amniotic alpha 1 fetoprotein level, cause of death, shunt placement after birth, and status of live infants. The observations indicate that the prognosis for fetal hydrocephalus is poor. Only six infants (15%) were alive after an average follow-up of 13 months. Three children were normal and the other three had neurologic abnormalities ranging from severe (paralysis and incontinence) to minimal (2-3 months delayed motor development). Thirty-four fetuses or neonates died. Nine families elected to terminate pregnancy. Ten opted for decompression at delivery for progressive hydrocephalus. Neural tube defects were present in 12 of 23 infants at delivery. Fourteen other infants had additional significant congenital abnormalities. Other abnormal sonographic findings included polyhydramnios (13 of 38), oligohydramnios or decreased fluid (nine of 38), neural tube defect (nine of 40), and other congenital abnormalities (nine of 40). These findings indicate that hydrocephalus diagnosed in utero by sonography is caused by a heterogeneous group of disorders. In general, the prognosis for normal development is poor. Individual prognoses, however, depend on the specific malformations and the interventions used.     

Twin embolization syndrome: prenatal sonographic detection and significance

Twin embolization syndrome (TES) is a complication of monozygotic twinning following in utero demise of the co-twin. Passage of thromboplastic material into the circulation of the surviving twin results in ischemic structural defects of the central nervous system, gastrointestinal tract, and genitourinary system. In six cases of this rare abnormality, sonographically normal fetuses subsequently demonstrated ventriculomegaly, porencephaly, cerebral atrophy, or microcephaly following demise of the co-twin. Extracranial abnormalities included small bowel atresia (two cases) and renal cortical necrosis (one case). Surviving twins all had neurodevelopmental delay at follow-up. Two fetuses were aborted because of sonographically apparent, progressively severe brain abnormality. The lone survivor of a dizygotic triplet gestation was normal, despite sonographic findings of TES in the co-triplets. Because of poor outcome, prenatal sonographic diagnosis of TES may influence antenatal or neonatal management of the surviving monozygous twin. Recognition of TES may permit accurate postnatal counseling of prognosis and recurrence risks.     

Anorectal atresia: prenatal sonographic diagnosis

To determine the prenatal sonographic findings of anorectal atresia (ARA), we retrospectively reviewed 12 proven cases. Sonography showed abnormally dilated bowel segments in five cases (42%), four of which were identified prospectively; at autopsy, two other cases showed mild colon dilatation not evident on sonograms. Bowel dilatation was not associated with the location of atresia or the presence of a fistula, but was possibly related to menstrual age. Eleven fetuses (92%) had significant other anomalies primarily related to the VACTERL syndrome (vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, radial and renal dysplasia, and limb malformations) and/or the caudal regression syndrome; of these, sonography identified one or more concurrent anomalies in seven cases. In two cases, bowel dilatation was the primary sonographic finding. Death in nine cases resulted from termination of pregnancy (four cases) or perinatal demise (five cases); three patients are still alive. We conclude that some cases of ARA can be suspected on prenatal sonograms by demonstration of dilated colon, and that the sensitivity of this finding may be related to menstrual age at the time of the examination. Distinguishing ARA from other causes of fetal-bowel dilatation is important because of the frequency of concurrent anomalies associated with ARA.     

Infection in utero: US findings in 19 cases.

The results of antenatal sonographic studies of 19 fetuses with congenital infections were retrospectively reviewed by the authors. Recognizing the significance of these antenatal sonographic findings is important because in utero infections can have devastating effects on the developing fetus. An infectious viral agent was isolated in laboratory tests at birth in 11 patients, and the effects of a viral agent were proved clinically in eight. Antenatal sonography demonstrated abnormalities in 18 fetuses: Multiple organ systems were affected in 47%; intracranial abnormalities, cardiac abnormalities, and parenchymal calcifications occurred in 42%, 37%, and 32%, respectively; large placentas were seen in 32%; and the volume of amniotic fluid was decreased in 37% and increased in 37%. Sixty-three percent of fetuses were either aborted or died at birth; the 37% that lived were all developmentally impaired. On the basis of these sonographic, laboratory, and clinical findings, the authors conclude that when multiple organ system abnormalities are found at antenatal ultrasound, the presence of an in utero infection should be considered. The parents should be informed that there is a poor prognosis for any fetus demonstrating such abnormalities.     

Gallbladder and bile duct abnormalities in AIDS: sonographic findings in eight patients

Gallbladder and biliary tract abnormalities were observed on sonography in eight patients with AIDS. The studies were obtained to evaluate right upper quadrant pain (two patients), tenderness (three patients), and abnormal liver function tests (eight patients). The two major sonographic findings were gallbladder wall thickening (eight patients), which often was marked, and bile duct dilatation (two patients). Gallbladder wall thickness varied from 4 to 15 mm and was greater than 1 cm in four patients. Follow-up sonograms in five patients showed increasing wall thickness in four and decreasing thickness in one, but these findings did not correlate well with the clinical status of the patient. Pericholecystic fluid was shown in three cases. None of the patients had gallstones. Common bile duct dilatation varied from 12 to 15 mm; no specific cause for dilatation was found by cholangiography. Mycobacterium avium intracellulare was recovered from the gallbladder in one patient, and Cryptosporidium was recovered from the duodenum in two patients. AIDS should be considered in the differential diagnosis of gallbladder wall thickening or bile duct dilatation in the appropriate clinical setting. These findings may indicate opportunistic infection of the biliary tract. A disparity may exist between the mild symptoms and signs (or lack of symptoms and signs) related to the gallbladder and bile ducts and the sometimes marked sonographic abnormalities.     

Sonography of facial features of alobar and semilobar holoprosencephaly

Twenty-seven cases of alobar/semilobar holoprosencephaly were reviewed to determine and classify the associated facial abnormalities detected with prenatal sonography. All but one case were diagnosed prospectively with sonography. Facial abnormalities were present in 24 of 27 cases and were detected in 14 (58%) of 24 fetuses on prenatal sonography. Prenatal abnormalities detected by sonography included cyclopia (four of five), ethmocephaly (two of three), cebocephaly (one of three), midline cleft lip (four of eight), lateral cleft lip (two of two), and mild hypotelorism (one of three). One or more extrafacial anomalies were present in 14 (52%) of 27 fetuses. Other major structural anomalies detected prenatally by sonography included meningomyelocele (two of two), renal dysplasia (five of six), omphalocele (three of four), esophageal atresia (zero of three), and cardiac defects (one of seven). Chromosomal analysis revealed abnormal karyotype in 13 (50%) of the 26 fetuses in which it was performed; the most common abnormality was trisomy 13 (seven cases). The perinatal mortality rate was 89% (24 of 27); three neonates with holoprosencephaly were alive when discharged from the hospital. It is concluded that when a major cystic abnormality of the fetal brain is detected, prenatal sonographic analysis of midline facial defect may allow more definitive diagnosis of alobar or semilobar holoprosencephaly; affected fetuses often have other major structural abnormalities, and the outcome is nearly always fatal.     

Sonographic findings in infants with macrocrania

This study compares the sonographic and CT findings in a group of infants with macrocrania and correlates those findings with neurologic outcome to determine the diagnostic accuracy and prognostic value of sonography. Sonographic findings in 255 infants with macrocrania are described. Of the 195 term infants examined, 130 had normal sonograms, 11 (5.6%) had significant abnormalities, and 54 had increased intra- and/or extraaxial fluid spaces. Of the 60 former preterm infants, 33 had normal sonograms, four (6.7%) had significant abnormalities, and 23 had increased fluid spaces or small resolving germinal matrix hemorrhages. The patients with significant abnormalities usually had head circumferences greater than the 95th percentile and had neurologic abnormalities. There was good correlation between sonography and CT in 30 of the 36 patients evaluated by both. In six there was mild discrepancy in the volume of the extraaxial fluid. No significant abnormality was missed by sonography. CT did not contribute any additional information. Neurologic follow-up was available for 202 patients. Nineteen percent of the term infants and 24% of the former preterm infants were abnormal on neurologic follow-up. Most patients with normal sonograms were normal on follow-up. Twelve of the term and four of the preterm infants with normal sonograms were developmentally delayed on follow-up. Increased CSF in the ventricles and/or extraaxial spaces was a common abnormality, but it usually is associated with a normal neurologic outcome and represents "benign macrocrania." We conclude that an infant with an enlarged or enlarging head should have a neurologic examination and head circumference measurement. If the patient has a head circumference greater than the 95th percentile, particularly if there are abnormal neurologic findings, further evaluation is indicated. Sonography is the initial procedure recommended since it accurately evaluates ventricular size, extraaxial fluid, and congenital malformations. If sonography is normal or shows mildly increased fluid spaces, then follow-up head circumference measurement and clinical evaluation will probably suffice. CT is indicated if there is a significant abnormality on sonography that requires further clarification.     

Fetal urethral obstruction: US evaluation

To further elucidate antenatal sonographic features of fetal urethral obstruction and attempt to determine which features might predict subsequent outcome, 40 in utero cases were reviewed. All fetuses had dilated urinary bladders and/or thickened bladder walls; in 47.5% of fetuses a dilated posterior urethra was seen. Only 15 fetuses (37.5%) survived the neonatal period. Survivors tended to present later in gestation than nonsurvivors. Poor prognostic indicators included oligohydramnios (20 of 21 subsequently died), absence of caliectasis (20 of 24 died), a large amount of urine ascites (five of six died), and dystrophic bladder wall or peritoneal calcification (five of five subsequently died). Conversely, 14 of 19 (74%) fetuses without definite oligohydramnios survived the neonatal period.     

Mild lateral cerebral ventricular dilatation in utero: clinical significance and prognosis

The medical records of 55 fetuses with sonographically diagnosed mild ventriculomegaly (MVM) were reviewed to assess prognosis. Fetuses were divided into two groups based on the presence or absence of sonographically detected associated fetal anomalies: 13 had no other anomalies detected (isolated MVM), and 42 had concomitant neural axis and visceral anomalies (nonisolated MVM). Mortality was 83% among fetuses with nonisolated MVM and 38% among fetuses with isolated MVM (P less than .005). If terminated pregnancies are excluded, only one of nine (11%) fetuses with isolated MVM died, compared with nine of 16 (56%) fetuses with nonisolated MVM (P less than .005). There are 15 living children: Nine (60%) are developmentally normal at 6-30 months of follow-up (six had isolated MVM), three (20%) are or are likely to be abnormal, and we were unable to follow up three (20%). Fetal anomalies were missed in 11 of 30 (37%) fetuses with detailed follow-up. However, this would have changed the classification from isolated to nonisolated MVM in only one case. Thus, in 54 of 55 cases (or 29 of 30 cases with detailed follow-up), fetuses were accurately classified as having isolated or nonisolated MVM. The authors conclude that sonographically isolated MVM is associated with a significantly better prognosis than nonisolated MVM, and fetuses can be classified accurately based on prenatal sonograms.     

Prenatal diagnosis of anencephaly: spectrum of sonographic appearances and distinction from the amniotic band syndrome

To document the characteristic sonographic abnormalities of anencephaly and to identify potentially confusing sonographic features, we reviewed 20 cases of anencephaly. All of these cases were diagnosed prenatally with sonography after 14 menstrual weeks in patients who were seen at our institution between 1984 and 1988. In all cases, the correct diagnosis was made on the prenatal sonograms and was confirmed pathologically. The sonographic diagnosis was primarily based on the absence of brain and calvarium superior to the orbits on coronal views of the fetal head. This typical appearance was altered by the presence of echogenic tissue superior to the orbits in nine (45%) of 20 cases. Pathologically, the tissue corresponded to angiomatous stroma (area cerebrovasculosa) and appeared quite sizable on sonograms in four fetuses (20%). It may appear solid or mixed solid and cystic. In one fetus, it appeared brainlike. Despite this appearance, the sonologist should not be dissuaded from the diagnosis of classic anencephaly. Hydramnios occurred in seven (35%) of 20 patients, and oligohydramnios occurred in none of the patients. Anencephaly may be distinguished from the cranial defects associated with the amniotic band syndrome (amputation defects that occur as the sequelae of amniotic disruption) on the basis of the symmetry of the cranial defects (100% of anencephalic fetuses in this series) and the absence of limb, body wall, and spinal abnormalities that typically accompany the amniotic band syndrome. Although there may be minor variations in the sonographic appearance of the cranial defect of anencephalic fetuses (i.e., much or little angiomatous stroma), we conclude that this anomaly can be accurately detected and diagnosed on fetal sonograms obtained after 14 weeks menstrual age and distinguished from the amniotic band syndrome.     

Osteogenesis imperfecta type II: prenatal sonographic diagnosis

Sonograms of fetuses at risk for congenital lethal osteogenesis imperfecta (osteogenesis imperfecta type II) were retrospectively reviewed blindly and correlated with pregnancy outcomes. Six of eight cases of type II osteogenesis imperfecta were correctly diagnosed with use of the proposed criteria of multiple fractures, demineralization of the calvaria, and femoral length more than 3 standard deviations below the mean for gestational age. The two cases not diagnosed had sonographic abnormalities but did not meet all three criteria. Among 18 pregnancies genetically at risk for the disease but with normal outcomes, all sonograms were normal, meeting none of the proposed criteria. Among an additional 25 fetuses with osteochondrodysplasias, no case satisfied all three of the proposed diagnostic criteria. With use of strict standards for the diagnosis of type II osteogenesis imperfecta, this disease can be distinguished from other fetal skeletal abnormalities. In a pregnancy at risk for recurrence of osteogenesis imperfecta, a normal sonogram after 17 weeks excludes this lethal condition.     

Early MR features of hypoxic-ischemic brain injury in neonates with periventricular densities on sonograms

BACKGROUND AND PURPOSE: In the early 1980s, diagnosing periventricular leukomalacia (PVL) in neonates by using cranial sonography was possible for the first time. Our purpose was to investigate the possibility of diagnosing PVL in the acute stage by using MR imaging. We evaluated early MR features of hypoxic-ischemic brain injury in neonates with periventricular densities (flares) on cranial sonograms to determine the added value of MR imaging over sonography alone for early diagnosis of brain damage. METHODS: In a prospective study, infants who showed flares and/or cysts on sonograms underwent MR imaging during the (sub)acute stage. RESULTS: Fifty infants were classified according to the highest sonographic grade up to the day of MR imaging: 23 infants had sonographic grade 1 (flares < 1 week), 15 had sonographic grade 2 (flares > or = 1 week), four had sonographic grade 3 (small localized cysts), and eight had sonographic grade 4 (extensive periventricular cysts); none had sonographic grade 5 (multicystic leukomalacia) on the day of MR imaging. Overall, the additional information provided by MR imaging (over sonography alone) consisted of the depiction of hemorrhagic lesions in 64% of the infants. Extent and severity of the hemorrhages varied from isolated punctate lesions to extensive hemorrhages throughout the white matter; the latter were followed by cystic degeneration at autopsy in two infants. In nine of the 12 infants with cystic PVL, MR images showed more numerous or more extensive cysts. In addition, in two infants, MR images showed cysts not present on sonograms. In 32% of the infants, MR imaging provided no additional information; in these children, all but one had flares on sonograms whereas MR images showed no abnormalities or a zone of mild periventricular signal change. CONCLUSION: MR imaging can depict the precise site and extent of hypoxic-ischemic brain injury at an earlier stage and allows a wider differentiation of lesions as compared with sonography alone. Hemorrhagic PVL is considered to be rare, but was present in 64% of our study population.     

Increased renal parenchymal echogenicity in the fetus: importance and clinical outcome

Pre- and postnatal ultrasound (US) findings and clinical course in 19 fetuses (16-40 menstrual weeks) with hyperechoic kidneys (renal echogenicity greater than that of liver) and no other abnormalities detected with US were evaluated to determine whether increased renal parenchymal echogenicity in the fetus indicates renal disease. Four infants (21%) were healthy at birth and had normal postnatal sonograms. Another 10 infants (53%) survived, but abnormalities were found at neonatal US. Postnatal diagnoses in these 10 neonates included unilateral renal dysplasia (n = 3), unilateral multicystic dysplastic kidney and a contralateral hyperechoic kidney (n = 2), hydronephrosis (n = 2), and renal abnormalities of unknown type (n = 3). Five fetuses with either infantile polycystic kidney disease (n = 4) or bilateral multicystic dysplasia (n = 1) did not survive. Oligohydramnios was predictive of a poor prognosis. Hyperechoic renal parenchyma in the fetus was associated with sonographic or functional abnormalities in 15 of 19 cases (79%) and a 74% survival rate.     

Value of sonography in monitoring the therapeutic response of mediastinal lymphoma: comparison with chest radiography and CT

The aim of this retrospective study was to assess the diagnostic value of mediastinal sonography, compared with that of chest radiographs and CT, in the follow-up of patients with mediastinal lymphomas and in the prediction of clinical outcome. The sonograms, chest radiographs, and CT scans of 40 consecutive patients with Hodgkin (n = 29) and non-Hodgkin (n = 11) lymphoma obtained before and after completion of therapy were analyzed blindly and independently by three radiologists and compared with clinical outcome. Nine patients were treated with radiotherapy, 12 with chemotherapy, and 19 with combined therapy. Therapeutic response was assessed from all available clinical and biochemical findings as well as from the combined results of all imaging studies performed on further follow-up. The sonograms showed obvious changes in the size and echogenicity of the mediastinal lymphomas that corresponded closely with the response to therapy. Sonography showed complete regression of the lymphomas in 30 patients who had complete remission. In five patients with incomplete remission, sonographic diagnoses were correct. All lymph nodes, irrespective of size, detected with sonography after a phase of complete remission indicated recurrence (five patients). Sonographic findings corresponded with those of CT in 25 (81%) of 31 cases. Clinical outcome suggested that the sonographic findings were more reliable in the five cases in which CT and sonographic findings conflicted. Chest radiographs were inadequate for monitoring the response of mediastinal lymphomas to therapy; in 17 (43%) of 40 cases, a false impression was obtained of the extent and therapeutic response of mediastinal lymphomas. The results of this study indicate that sonography is clearly superior to chest radiographs and comparable to CT for monitoring patients with mediastinal lymphomas.     

Unilateral hydrocephalus: prenatal sonographic diagnosis

We studied six cases of unilateral hydrocephalus detected prenatally to analyze the sonographic features of the abnormality and to determine the cause and clinical outcome. In all cases, third-trimester sonograms showed marked unilateral lateral ventriculomegaly (mean atrial width, 4.4 cm) and normal contralateral lateral, third, and fourth ventricles. Five of the six cases had marked thinning of the cortical mantle on the affected side and shift of midline structures to the contralateral side. The causes of unilateral hydrocephalus were agenesis or stenosis of the foramen of Monro in three cases, transient obstruction of the foramen in one fetus with an intraventricular hematoma, underlying brain dysplasia in one fetus with a variant of holoprosencephaly, and undetermined in one case. All six neonates had placement of a ventriculoperitoneal shunt catheter; four of these have had normal cognitive development at follow-up. The remaining two infants have moderate to severe developmental impairment. Unilateral hydrocephalus is a rare anomaly that can be recognized by prenatal sonography. Even though unilateral ventriculomegaly may be marked, early diagnosis and treatment may result in a favorable clinical outcome.     

Correlation between omphalocele contents and karyotypic abnormalities: sonographic study in 37 cases.

To evaluate the observation that fetuses with omphaloceles containing only bowel have an especially high prevalence of karyotypic abnormalities, we retrospectively reviewed the sonograms and case records of 37 fetuses with omphaloceles detected sonographically between 1984 and 1990. Nine fetuses had concomitant morphologic abnormalities characteristic of the amniotic band syndrome. Of the remaining 28 fetuses, karyotypic correlation was available in 22, and the karyotype was abnormal in five of these (23%). The omphaloceles contained liver in 22 fetuses and only bowel in six fetuses. Among fetuses with exteriorized liver, karyotypes were abnormal in one (6%) of 16 tested. In contrast, four (67%) of the six fetuses whose omphaloceles contained only bowel had abnormal karyotypes; for each of these four, sonograms showed morphologic abnormalities in addition to the omphalocele. In the two fetuses with bowel-only omphaloceles and normal karyotypes, the omphalocele was the only abnormality seen on sonograms, and these children are well after surgical repair. When fetuses with the amniotic band syndrome were excluded, sonograms showed concomitant anomalies in 15 fetuses with liver-containing omphaloceles, and the karyotype was abnormal in only one of these 15. The results of this study support previous observations that karyotypic abnormalities are more common in association with omphaloceles that contain only bowel compared with those that contain only liver. If we combine our data with data from three other studies that address this issue, 87% of fetuses with omphaloceles containing only bowel had an abnormal karyotype, a significantly higher rate than in those fetuses whose omphaloceles contained liver also (9%).     

Detection of fetal central nervous system anomalies: a practical level of effort for a routine sonogram

To evaluate the efficacy of examining the lateral ventricular atrium, cisterna magna, and cavum septi pellucidi as a means of ascertaining that the development of the fetal central nervous system (CNS) is normal, a retrospective evaluation of the sonograms of 112 fetuses (15-39 weeks gestational age) with sonographically diagnosed CNS anomalies was performed. Malformations included in the study were diverse. The lateral ventricular atrium was enlarged (greater than 10 mm) in 99 (88%) fetuses. Of the remaining 13 fetuses, seven had an abnormal-sized cisterna magna (less than 2 mm or greater than 11 mm). These two measurements alone could be used to identify the presence of a CNS abnormality in 95%. Three of the six remaining fetuses exhibited gross abnormalities easily seen on the standard axial images obtained for biparietal diameter measurement. Although the cavum septi pellucidi was absent in a number of cases, its absence did not enhance sensitivity in the cohort examined. Prospective examination of 130 consecutive normal fetuses (15-40 weeks gestational age) was also performed. When specifically sought, the ventricular atrium was identifiable and measurable 99% of the time; the cisterna magna, 90% of the time; and the cavum septi pellucidi, 95% of the time. Because major CNS anomalies are uncommon and these measurements afford high sensitivity, an extremely low probability (0.005%) of abnormal brain or spinal cord development can be predicted if a normal-sized lateral ventricular atrium and cisterna magna are present. These results should not be construed as a license to underexamine fetuses for malformations. Rather, these measurements should serve as simple positive steps to assist in a difficult task.