Feasibility and Added Value of Fetal DTI Tractography in the Evaluation of an Isolated Short Corpus Callosum: Preliminary Results

BACKGROUND AND PURPOSE

Prognosis of isolated short corpus callosum is challenging. Our aim was to assess whether fetal DTI tractography can distinguish callosal dysplasia from variants of normal callosal development in fetuses with an isolated short corpus callosum.

MATERIALS AND METHODS

This was a retrospective study of 37 cases referred for fetal DTI at 30.4 weeks (range, 25-34 weeks) because of an isolated short corpus callosum  less than the 5th percentile by sonography at 26 weeks (range, 22-31 weeks). Tractography quality, the presence of Probst bundles, dysmorphic frontal horns, callosal length (internal cranial occipitofrontal dimension/length of the corpus callosum ratio), and callosal thickness were assessed. Cytogenetic data and neurodevelopmental follow-up were systematically reviewed.

RESULTS

Thirty-three of 37 fetal DTIs distinguished the 2 groups: those with Probst bundles (Probst bundles+) in 13/33 cases (40%) and without Probst bundles (Probst bundles-) in 20/33 cases (60%). Internal cranial occipitofrontal dimension/length of the corpus callosum was significantly higher in Probst bundles+ than in Probst bundles-, with a threshold value determined at 3.75 for a sensitivity of 92% (95% CI, 77%-100%) and specificity of 85% (95% CI, 63%-100%). Callosal lipomas (4/4) were all in the Probst bundles- group. More genetic anomalies were found in the Probst bundles+ than in Probst bundles- group (23% versus 10%, P = .08).

CONCLUSIONS

Fetal DTI, combined with anatomic, cytogenetic, and clinical characteristics could suggest the possibility of classifying an isolated short corpus callosum as callosal dysplasia and a variant of normal callosal development.

Heterogeneity in defining fetal corpus callosal pathology: systematic review

OBJECTIVE

Fetal anomalies of the corpus callosum (CC) have been reported in the prenatal imaging literature since 1985, and, especially when isolated, pose challenges for both the patient and fetal medicine specialist. The purpose of this study was to review systematically the literature on prenatally diagnosed abnormalities of the CC, focusing on the terminology used to describe abnormalities other than complete agenesis of the CC, and to assess the heterogeneity of the nomenclature and definitions used.

METHODS

This study was conducted in accordance with the PRISMA statement for reporting systematic reviews. A literature search was performed to identify prospective or retrospective case series or cohort studies, published in English, French, Italian, German or Spanish, reporting fetal imaging findings and describing anomalies of the CC. Quality and risk of bias of the studies were evaluated using the Newcastle-Ottawa scale and a modification of the scale developed by Conde-Agudelo et al. for other fetal imaging studies. The data extracted included the number of patients, the number of different anomalies identified, the descriptive names of the anomalies, and, where applicable, the definitions of the anomalies, the number of cases of each type of anomaly and the biometric charts used. Secondary tests used to confirm the diagnosis, as well as the postnatal or post-termination tests used to ascertain the diagnosis, were also recorded.

RESULTS

The search identified 998 records, and, after review of titles and abstracts and full review of 45 papers, 27 studies were included initially in the review, of which 24 were included in the final analysis. These 24 studies had a broad range of quality and risk of bias and represented 1135 cases of CC anomalies, of which 49% were complete agenesis and the remainder were described using the term partial agenesis or nine other terms, of which five had more than one definition.

CONCLUSIONS

In comparison to the postnatal literature, in the prenatal literature there is much greater heterogeneity in the nomenclature and definition of CC anomalies other than complete agenesis. This heterogeneity and lack of standard definitions in the prenatal literature make it difficult to develop large multicenter pooled cohorts of patients who can be followed in order to develop a better understanding of the genetic associations and neurodevelopmental and psychological outcomes of patients with CC anomalies. As this information is important to improve counseling of these patients, a good first step towards this goal would be to develop a simpler categorization of prenatal CC anomalies that matches better the postnatal literature. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Accuracy of prenatal ultrasound screening to identify fetuses infected by cytomegalovirus which will develop severe long-term sequelae

OBJECTIVES

To compare the ability of detailed routine ultrasound examination, performed without knowledge of maternal serology and fetal status, with that of targeted prenatal imaging performed in prenatal diagnostic units in cases of known fetal infection to identify cytomegalovirus (CMV)-infected fetuses that will develop long-term sequelae.

METHODS

All prenatal imaging reports were collected for 255 children with congenital CMV in a registered cohort between 2013 and 2017 (NCT01923636). All women had undergone detailed routine fetal ultrasound examination at 20-24 and 30-34 weeks as part of routine antenatal care. All cases of known fetal CMV infection had also undergone targeted prenatal ultrasound examination. Postnatal structured follow-up for up to 48 months of age involved clinical, audiological and neurological assessment, including Brunet-Lezine scoring. Long-term sequelae (> 12 months) were considered to be mild in cases with isolated unilateral hearing loss and/or vestibular disorders, and severe in cases with bilateral hearing loss and/or neurological sequelae. All imaging reports were analyzed retrospectively with the knowledge of congenital CMV infection, searching for reference to findings that were, or could have been, related to fetal infection. Findings were analyzed in relation to whether the cases were diagnosed with CMV in utero or only postnatally.

RESULTS

There were 237 children with complete follow-up data (> 12 months), for a median of 24 (range, 12-48) months. Of these, 30% (71/237) were diagnosed with CMV prenatally and 70% (166/237) were diagnosed within 3 weeks after birth. 72.5% (29/40) of children with long-term sequelae, including 74% (14/19) with severe long-term sequelae, were not identified in the prenatal period. Among those diagnosed prenatally, the sensitivity of prenatal imaging for predicting long-term sequelae and severe long-term sequelae was 91% and 100%, respectively, while, in the group diagnosed only postnatally, non-specific infection-related ultrasound findings had been reported without raising suspicion in 48% of cases with long-term sequelae and 64% of those with severe long-term sequelae.

CONCLUSIONS

Routine detailed ultrasound examination in pregnancy is not an appropriate screening tool for congenital CMV infection that leads to long-term sequelae, in contrast with the high performance of targeted prenatal imaging in known cases of fetal infection. The non-specific nature of ultrasound features of CMV and their evolution, and a lack of awareness of caregivers about congenital CMV, are likely explanations. Awareness of the sonologist regarding congenital CMV and knowledge of the maternal serological status in the first trimester seem key to the performance of prenatal ultrasound. Copyright © 2020 ISUOG. Published by John Wiley & Sons Ltd.

Biometric and morphological features on magnetic resonance imaging of fetal bladder in lower urinary tract obstruction: new perspectives for fetal cystoscopy

OBJECTIVES

Incompatibility between currently available fetoscopes and the anatomical constraints of the distended fetal bladder, with the resulting curvature around the bladder neck, account for most technical difficulties during fetal cystoscopy in lower urinary tract obstruction (LUTO). The aim of this anatomical study was to assess by magnetic resonance imaging (MRI) the variation in three bladder angles (bladder-neck angle (BNA), vesicourethral angle (VUA) and angle between bladder dome and posterior urethra (DUA)), according to gestational age (GA), bladder volume and the presence of LUTO.

METHODS

From our fetal medicine database, we retrieved for review 46 MRI examinations of male fetuses between 2015 and 2019, including 17 with LUTO, examined at a mean GA of 28.1 (range, 17.3-35.0) weeks and 29 age-matched controls, examined at 29.9 (range, 21.9-35.0) weeks. We measured bladder volume, bladder-wall thickness and the three bladder angles, and used the Mann-Whitney U-test to compare values between groups. Variations according to GA and bladder volume were determined using analysis of variance (ANOVA). A reliability study was performed using the Bland-Altman method and Lin's correlation coefficient was calculated.

RESULTS

Both bladder volume and bladder-wall thickness were significantly greater in the LUTO group (P < 0.01). BNA was significantly larger in LUTO compared with control fetuses: the mean (range) was 127.1° (101.6-161.6°) vs 111.2° (88.5-157.3°) (P < 0.01). DUA averaged 117° and showed no difference between the groups (P = 0.92). No statistical comparison was performed on VUA since this was not measurable in most control fetuses. ANOVA showed no variation of any angle with bladder volume in both LUTO fetuses and control fetuses. BNA in LUTO fetuses was the only angle to vary with GA, being larger after, compared with at or before, 25 weeks (P = 0.04). The reliability study showed an acceptable bias for both intra- and interobserver reproducibility for all three angles.

CONCLUSION

The findings that BNA is increased by approximately 15° in fetuses with LUTO and DUA averages 117° could aid in development of a customized fetal cystoscope and help to overcome the current technical challenges of fetal cystoscopy. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Outcome of non-visualization of fetal gallbladder on second-trimester ultrasound: cohort study and systematic review of literature

OBJECTIVES

To investigate the ultrasound characteristics and outcome of fetuses with non-visualization of the fetal gallbladder (NVFGB) followed in our tertiary university hospital, and to provide a comprehensive review of the literature on prenatal findings and outcome of NVFGB.

METHODS

NVFGB was defined as non-visualization of the gallbladder on two targeted ultrasound examinations performed within a 1-week period. First, we reviewed the medical records of NVFGB cases managed in our center over a 9-year period. Then, we performed a systematic review of the literature to identify studies on NVFGB. The incidence of chromosomal anomalies, later visualization of the gallbladder, gallbladder agenesis, cystic fibrosis and biliary atresia was assessed in fetuses with isolated and non-isolated NVFGB. The role of hepatic enzyme measurements in the diagnosis of cystic fibrosis and biliary atresia in fetuses with NVFGB was also reviewed.

RESULTS

Sixteen cases of NVFGB were followed in our center, in 10 (62.5%) of which it was an isolated finding. The incidence of biliary atresia was 12.5% and that of gallbladder agenesis was 12.5%, while no case of cystic fibrosis was reported. The gallbladder was visualized later in pregnancy or postnatally in 43.8% and 25.0% of cases, respectively. A total of seven studies, including our cohort, involving a total of 280 NVFGB cases, met the inclusion criteria for the systematic review. Overall, 20.5% of fetuses had an associated ultrasound anomaly, and the incidence of chromosomal anomaly in this group was 20.4%. In cases with isolated NVFGB, the incidence of chromosomal anomaly was 1.9%. In fetuses with normal karyotype and isolated NVFGB, the gallbladder was later visualized in 70.4% of cases, while the incidence of gallbladder agenesis, cystic fibrosis and biliary atresia was 25.2%, 3.1% and 4.8%, respectively. In fetuses with non-isolated NVFGB, the incidence of cystic fibrosis and biliary atresia was 23.1% and 18.2%, respectively. The negative predictive value of amniotic fluid enzyme levels for the prediction of severe disease (including biliary atresia or cystic fibrosis) ranged between 94% and 100% when evaluated before 22 weeks' gestation, and dropped to 88% after 22 weeks.

CONCLUSIONS

In cases with persistent NVFGB, the risk of a severe postnatal condition should be considered. A detailed ultrasound scan should be offered and parents tested for cystic fibrosis gene mutation. An invasive procedure for karyotyping and measurement of liver enzyme concentrations before 22 weeks constitutes a reasonable work-up. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Refining the prognosis of fetuses infected with Cytomegalovirus in the first trimester of pregnancy by serial prenatal assessment: a single-centre retrospective study

OBJECTIVE

To define the predictive value (PV) of known prognostic factors of fetal infection with Cytomegalovirus following maternal primary infection <14 weeks of gestation, at different time points of pregnancy: the end of the second trimester; following prenatal magnetic resonance imaging (MRI) at 32 weeks of gestation; and using all ultrasound scans performed in the third trimester (US3rdT).

DESIGN

A retrospective study.

SETTING

Reference fetal medicine unit.

POPULATION

Sixty-two fetuses infected <14 weeks of gestation.

METHODS

We defined second-trimester assessment (STA) as the combination of ultrasound findings <28 weeks of gestation and fetal platelet count at cordocentesis. Three groups were defined: normal, extracerebral, and cerebral STA.

MAIN OUTCOME MEASURES

For each group, the PV of STA alone, STA + MRI, and STA + US3rdT were assessed retrospectively. Outcome at birth and at follow-up were reported.

RESULTS

The STA was normal, and with extracerebral and cerebral features, in 43.5, 42.0, and 14.5%, respectively. The negative PV of normal STA and MRI for moderate to severe sequelae was 100%. The residual risk was unilateral hearing loss in 16.7% of cases. Of pregnancies with cerebral STA, 44% were terminated. Following extracerebral STA, 48% of neonates were symptomatic and 30% had moderate to severe sequelae. In those cases, the positive and negative PV of MRI for sequelae were 33 and 73%, respectively. STA + US3rdT had a lower negative PV than MRI for symptoms at birth and for moderate to severe sequelae. Any false-positive findings at MRI were mostly the result of hypersignals of white matter.

CONCLUSIONS

Serial assessment in the second and third trimesters by ultrasound and MRI is necessary to predict the risk of sequelae occurring in 35% of pregnancies following fetal infection in the first trimester of pregnancy.

TWEETABLE ABSTRACT

Serial ultrasound prognostic assessment following fetal CMV infection in the 1st trimester is improved by MRI at 32 weeks.

Prenatally diagnosed periventricular nodular heterotopia: Further delineation of the imaging phenotype and outcome

OBJECTIVES

Periventricular nodular heterotopia (PNH) is a malformation of cortical development which presents with heterogeneous imaging, neurological phenotype and outcome. There is a paucity of comprehensive description detailing the prenatal diagnosis of PNH. The aim of this study is to report neuroimaging features and correlated outcomes in order to delineate the spectrum of prenatally diagnosed PNH.

METHODS

It was a retrospective study over 15 years in five tertiary centers. All fetuses with prenatally diagnosed PNH were collected. Fetal ultrasound and MRI were reviewed and genetic screening collected. Prenatal findings were analyzed in correlation to fetopathological analyses and post-natal follow up.

RESULTS

Thirty fetuses (22 females and 8 males) with PNH were identified. The two major ultrasound signs were ventriculomegaly associated with dysmorphic frontal horns (60%) and posterior fossa anomalies (73.3%). On MRI, two groups of PNH were identified: the contiguous and diffuse PNH (n = 15, 50%), often associated with megacisterna magna, and the non-diffuse, either anterior, posterior or unilateral PNH. FLNA mutations were found in 6/11 cases with diffuse PNH. Additional cortical malformations were exclusively observed in non diffuse PNH (9/15; 60%). Twenty-four pregnancies (80%) were terminated. Six children aged 6 months to 5 years are alive. Five have normal neurodevelopment (all had diffuse PNH) whereas one case with non diffuse PNH has developmental delay and epilepsy.

CONCLUSION

PNH is heterogeneous but patients with diffuse PNH are a common subgroup with specific findings on prenatal imaging and implications for prenatal counseling.

Vein of Galen aneurysmal malformation (VGAM) in the fetus: retrospective analysis of perinatal prognostic indicators in a two-center series of 49 cases

OBJECTIVE

Vein of Galen aneurysmal malformation (VGAM) is a rare fetal anomaly, the neurological outcome of which can be good with appropriate perinatal management. However, most fetal series are too small to allow reliable statistical assessment of potential prognostic indicators. Our aim was to assess, in a two-center series of 49 cases, the prognostic value of several prenatal variables, in order to identify possible prenatal indicators of poor outcome, in terms of mortality and cerebral disability.

METHODS

This was a retrospective study involving 49 cases of VGAM diagnosed prenatally and managed at two centers over a 17-year period (1999-2015). All cases had undergone detailed prenatal cerebral and cardiac assessment by grayscale ultrasound, color and pulsed-wave Doppler and magnetic resonance imaging (MRI). Ultrasound and MRI examination reports and images were reviewed and outcome information was obtained from medical reports. Volume of the VGAM (on ultrasound and MRI) was calculated and development of straight-sinus dilatation, ventriculomegaly and other major brain abnormalities was noted. Cardiothoracic ratio, tricuspid regurgitation and reversed blood flow across the aortic isthmus were evaluated on fetal echocardiography. Major brain lesions were considered by definition to be associated with poor outcome in all cases. Pregnancy and fetoneonatal outcome were known in all cases. Fetoneonatal outcome and brain damage were considered as dependent variables in the statistical evaluation. Poor outcome was defined as death, late termination of pregnancy due to association with related severe brain anomalies or severe neurological impairment.

RESULTS

At a mean follow-up time of 20 (range, 0-72) months, 36.7% of the whole series and 52.9% of the cases which did not undergo late termination were alive and free of adverse sequelae. Five (10.2%) cases showed progression of the lesion between diagnosis and delivery. On univariate analysis, dilatation of the straight sinus, VGAM volume ≥ 20 000 mm³ and tricuspid regurgitation were all significantly related to poor outcome. However, on logistic regression analysis, the only variables associated significantly with poor outcome were tricuspid regurgitation and, to a lesser extent, VGAM volume ≥ 20 000 mm³ . The former was also the only variable associated with brain damage.

CONCLUSIONS

Major brain lesions, tricuspid regurgitation and, to a lesser extent, VGAM volume ≥ 20 000 mm³ are the only prenatal variables associated with poor outcome in fetal VGAM. Prenatal multidisciplinary counseling should be based on these variables. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

[Prenatal discovery of Joubert syndrome associated with small bowel volvulus]

Joubert syndrome and prenatal volvulus are difficult to diagnose during pregnancy. Joubert syndrome and related diseases should be considered in case of prenatal abnormal features of the fourth ventricle. Small bowel volvulus is also a surgical emergency because of the risk of intestinal necrosis before or after delivery. This type of condition justifies the transfer of pregnant women to a specialized hospital where the newborn may receive appropriate care. We report the case of a 31-week and 4-day gestational-age fetus in whom intrauterine growth retardation and small-bowel volvulus were diagnosed. Additional imaging revealed associated Joubert syndrome. This highlights the need for regular ultrasound monitoring during pregnancy and the comanagement of obstetricians and pediatricians to provide appropriate care before and after delivery.

Prenatal prediction of pulmonary arterial hypertension in congenital diaphragmatic hernia

OBJECTIVE

To evaluate the role of prenatal prognostic markers obtained routinely by ultrasound examination and magnetic resonance imaging (MRI) in the prediction of development of postnatal pulmonary arterial hypertension (PAH) in isolated congenital diaphragmatic hernia (CDH).

METHODS

One hundred and ten cases of isolated CDH were referred to our fetal medicine unit between January 2004 and April 2013. Mortality and morbidity rates were reviewed for those presenting with postnatal PAH. The following prenatal markers were evaluated as potential predictive factors of PAH: liver position, side of the CDH defect, lung area to head circumference ratio (LHR) and observed/expected LHR (o/e-LHR), which were measured by ultrasound, and observed/expected total fetal lung volume (o/e-TFLV), which was measured by MRI. Univariable logistic regression was used to assess associations.

RESULTS

PAH was significantly associated with perinatal mortality and morbidity (P < 0.001). The occurrence of PAH decreased significantly with an increasing LHR, o/e-LHR and o/e-TFLV and was significantly increased for cases with an intrathoracic liver, but not for those with right-sided defects. Univariable regression revealed that o/e-TFLV (odds ratio (OR), 0.9 (95% CI, 0.86-0.95); P < 0.05 for percentage unit change in o/e), LHR (OR, 0.19 (95% CI, 0.09-0.40); P < 0.05 for unit change), o/e-LHR (OR, 0.95 (95% CI, 0.93-0.98); P < 0.05 for percentage unit change in o/e) and liver position (OR, 2.82 (95% CI, 1.13-7.00); P < 0.05 for intrathoracic liver) were significant predictors of subsequent PAH. No differences were found after adjusting for gestational age at delivery. The areas under the receiver-operating characteristics curve were 0.80 and 0.75 for o/e-TFLV and o/e-LHR, respectively.

CONCLUSION

In cases of CDH, PAH is associated with high rates of mortality and morbidity. Routinely obtained prenatal markers, usually used for the assessment of pulmonary hypoplasia, are also relevant for the postnatal prediction of PAH.

Standardized fetal anatomical examination using magnetic resonance imaging: a feasibility study

OBJECTIVE

To determine whether a standard complete fetal anatomical survey, as recommended for ultrasound examination guidelines, is feasible using a standardized magnetic resonance imaging (MRI) protocol.

METHODS

Based on guidelines for ultrasound examination, we created a specific MRI protocol for fetal anatomical survey. This protocol was then tested prospectively in 100 women undergoing fetal MRI examination for various specific indications at a median gestational age of 30 weeks. The feasibility of using MRI to perform the fetal anatomical survey was analyzed by two reviewers (A and B) based on 26 predefined anatomical criteria, yielding a score ranging from 0 to 26 (26 meaning successful complete anatomical study). Reproducibility was analyzed using percentage agreement and modified kappa statistics.

RESULTS

The mean score for the standardized MRI anatomical survey was 24.6 (SD, 1.4; range, 15-26) for Reviewer A and 24.2 (SD, 1.7; range, 15-26) for Reviewer B (P = 0.1). Twenty-two, two and two criteria could be assessed in > 95%, 80-95% and < 80% of cases by Reviewer A and 19, four and three criteria could be assessed in > 95%, 80-95% and < 80% of cases by Reviewer B. For both reviewers, the two most difficult criteria to evaluate were aorta and pulmonary artery. Inter-reviewer agreement was above 90% for 22 of the 26 anatomical criteria and adjusted kappa coefficients for each criterion demonstrated good, moderate and poor agreement for 22, two and two criteria, respectively.

CONCLUSION

Our data support the hypothesis that standardized fetal anatomical examination might be achieved and reproducible using MRI, although improvement is required for the cardiac part of the examination.

Three-dimensional helical computed tomography in prenatal diagnosis of fetal skeletal dysplasia

OBJECTIVES

(1) To study the use and diagnostic value, as a complement to ultrasound, of helical computed tomography (helical CT) to differentiate normal fetuses from cases of skeletal dysplasia; (2) to define the most relevant indications for helical CT; and (3) to evaluate its diagnostic performance with respect to radiological criteria considered discriminatory.

METHODS

This was a retrospective study from 2005 to 2008 in 67 pregnant women who underwent helical CT after 26 weeks of gestation for suspected fetal skeletal dysplasia due to fetal shortened long bones on ultrasound (≤ 10(th) percentile), either alone or associated with other bone abnormalities. The results were compared with pediatric examinations in 41 cases and with fetal autopsy findings after elective termination of pregnancy in the others.

RESULTS

Helical CT had a sensitivity of 82%, specificity of 91% and positive and negative predictive values of 90% and 83%, respectively, for diagnosis of fetal skeletal dysplasia. An etiological diagnosis that had not been suspected at ultrasound was specified in 15% of cases and diagnoses suspected at ultrasound were confirmed in 24% and discounted in 43% of cases. The prevalence of skeletal dysplasia was increased in cases of micromelia < 3(rd) percentile or if there was a combination of bone signs. Helical CT showed 69% sensitivity in identifying individual predefined pathological bone signs which were confirmed on fetal autopsy findings.

CONCLUSION

Helical CT is a key examination, in combination with ultrasound, in the diagnosis of fetal skeletal dysplasia from 26 weeks of gestation. It should be reserved for cases with severe micromelia below the 3(rd) percentile and for those with micromelia ≤ 10(th) percentile associated with another bone sign. A checklist of discriminatory signs is proposed.

Hidden mortality of prenatally diagnosed vein of Galen aneurysmal malformation: retrospective study and review of the literature

OBJECTIVE

To evaluate the prognosis of prenatally diagnosed vein of Galen aneurysmal malformation (VGAM) in a large cohort with this condition and to review the literature on prenatally diagnosed VGAM.

METHODS

This was a retrospective study of all cases of prenatally diagnosed VGAM managed in our referral center during a 12-year period. VGAM was categorized as being either isolated or associated with any other abnormality, based on fetal ultrasound and magnetic resonance imaging findings. Poor outcomes comprised termination of pregnancy with confirmation of antenatal findings, perinatal death and severe cardiac and/or neurological impairment in survivors. The literature was also reviewed for similar cases.

RESULTS

Twenty-one cases of prenatally diagnosed VGAM were managed in our center. Four (19.0%) cases were isolated and 17 (81.0%) were associated with other anomalies. There were nine terminations (42.9%) and six neonatal deaths (28.6%). Six children (28.6%) were still alive at last follow-up, of whom three had abnormal neurological development. VGAM associated with other anomalies was strongly associated with a poor outcome compared with isolated forms (P < 0.0001). One hundred and nine cases from the literature were also reviewed.

CONCLUSION

Fetuses with prenatally diagnosed VGAM have unexpectedly poor outcomes in the presence of cardiac or cerebral anomalies, while those with strictly isolated VGAM tend to have more favorable outcomes. Our literature review corroborates these findings.

Real-time fetal magnetic resonance imaging for the dynamic visualization of the pouch in esophageal atresia

Esophageal atresia is the principal cause of congenital esophageal obstruction. Prenatal suspicion of esophageal atresia is usually based on the presence of polyhydramnios together with an absent stomach bubble. More recently, visualization of the dilatation of the blind-ending esophagus (esophageal pouch) during fetal swallowing has been reported and proposed as the most reliable sign for predicting esophageal atresia. Improvement of radiofrequency and computer technology as well as parallel data acquisition has greatly reduced magnetic resonance (MR) scanning time, allowing visualization of the fetus in cine-mode using fast imaging employing steady-state acquisition (FIESTA). We describe the application of FIESTA sequences in fetuses with suspected esophageal atresia for visualization of the esophageal pouch using MR imaging.

Prenatal diagnosis of cardiac rhabdomyomas: incidence of associated cerebral lesions of tuberous sclerosis complex

OBJECTIVES

To determine the prevalence of specific cerebral lesions of tuberous sclerosis complex (TSC) and neurological outcome in cases diagnosed prenatally with cardiac rhabdomyomas.

METHODS

We reviewed all fetuses diagnosed prenatally with cardiac rhabdomyomas which had undergone detailed ultrasound evaluation and cerebral magnetic resonance imaging (MRI) and which were recorded in the database of a single institution covering the period January 1992 to December 2005.

RESULTS

Fifty-one fetuses were included in the study. MRI was performed at a mean +/- SD gestational age of 30 +/- 3 gestational weeks and showed specific lesions of TSC in 49% of cases. Termination of pregnancy was chosen by the parents in 26 cases. Neurological development was studied in 20 cases, follow-up lasting 4.8 +/- 2.9 years. Neurodevelopmental events occurred during the follow-up period in 45% of cases. Neurological complications occurred in 67% of patients who had cerebral lesions at MRI and in 33% of patients with normal MRI results. There was no significant difference between the two groups of patients (P = 0.2).

CONCLUSION

In fetuses with cardiac rhabdomyomas detailed ultrasound examination and third-trimester cerebral MRI are able to diagnose most TSC cerebral lesions, but fail to determine neurological outcome.

Value of prenatal magnetic resonance imaging in the prediction of postnatal outcome in fetuses with diaphragmatic hernia

OBJECTIVES

To investigate the potential value of antenatally determined total fetal lung volume (TFLV) by magnetic resonance imaging (MRI) in the prediction of the postnatal survival in congenital diaphragmatic hernia (CDH).

METHODS

We examined fetuses with isolated CDH, in which MRI was used at 22-38 weeks of gestation to measure TFLV and assess intrathoracic herniation of abdominal viscera, that were liveborn after 30 weeks of gestation and had postnatal follow-up until death or discharge from hospital. Regression analysis was used to investigate the effect on survival of gestational age at diagnosis, observed to expected (o/e) TFLV, intrathoracic herniation of the liver, side of CDH, gestational age at MRI, institution, year and gestational age at delivery. In 76 fetuses measurements of o/e TFLV and the lung area to head circumference ratio (LHR) were performed within 2 weeks of each other; in these cases o/e TFLV and o/e LHR were compared for their prediction of postnatal survival.

RESULTS

In the 148 cases that fulfilled the entry criteria, multiple regression analysis demonstrated that significant predictors of survival were the presence or absence of intrathoracic herniation of the liver and o/e TFLV. The area under the receiver-operating characteristics curves for prediction of postnatal survival from o/e TFLV was 0.786 (standard error, 0.059; P < 0.001) and that from o/e LHR was 0.743 (standard error, 0.069; P = 0.001).

CONCLUSIONS

In the assessment of fetuses with CDH, MRI-based o/e TFLV is useful in the prediction of postnatal survival.

Prenatal diagnosis of dumbbell neuroblastoma

A neuroblastoma that develops in the sympathetic nodes can infiltrate the intervertebral foramina and invade the spinal canal, leading to spinal cord and nerve root compression and neurological impairment. Dumbbell neuroblastomas are now considered to be unresectable tumors and preoperative chemotherapy is recommended. We report the prenatal diagnosis of a dumbbell neuroblastoma successfully managed through premature delivery followed by immediate chemotherapy. We suggest that delivering prematurely in such cases is only of benefit if chemotherapy can be administered under favorable conditions. Chemotherapy should proceed immediately after delivery in order to reduce the size of the tumoral mass and its effects on the spine.

Fetal magnetic resonance imaging in the antenatal diagnosis and management of hydrocolpos

Hydrocolpos should be considered systematically when an abdominopelvic cystic mass is diagnosed in a female fetus. Because the prognosis and neonatal management of isolated hydrocolpos with spontaneous resolution differs greatly from that of hydrocolpos associated with a cloacal malformation, it is important to ascertain prenatally whether there are associated anomalies. We report the prenatal characteristics of three fetuses with hydrocolpos; in two cases there was spontaneous resolution and one infant was born with digestive tract atresia. The principal ultrasound findings were an oblong anechoic pelvic mass with or without a sagittal septum, located behind a normal bladder. On magnetic resonance imaging (MRI), the cervical imprint on the vagina confirmed the diagnosis of hydrocolpos and helped to diagnose cloacal malformation by demonstrating the absence of meconium beside the bladder on T1 sequences. Our cases show that MRI is useful for differentiating isolated hydrocolpos from hydrocolpos associated with cloacal malformation.

Contribution of fetal MR imaging in the prenatal diagnosis of Zellweger syndrome

Zellweger syndrome (ZS), or cerebrohepatorenal syndrome, was the first described peroxisomal biogenesis disorder. It represents the most severe phenotype, and some of its multiple congenital anomalies can manifest prenatally. Fetal hypokinesia, renal hyperechogenicity, and cerebral ventricular enlargement are the most common reported fetal features. Single and/or late detectable manifestations account for most of the difficulties of prenatal diagnosis, as well as the limitations of ultrasonography itself. Prenatal diagnosis, however, can be achieved through (1) assays of concentrations of peroxisomal metabolites (very-long-chain fatty acids, bile acids, intermediates, plasmalogens), (2) activities of peroxisomal enzymes (dihydroacetone-phosphate acyltransferase), or (3) molecular screening techniques, if available. We report on the contribution of MR imaging to the diagnosis of ZS in 2 unrelated fetuses. MR imaging was performed in the third trimester because of cerebral ventricular enlargement diagnosed on routine sonography examinations. In both cases, MR imaging revealed ZS-characteristic abnormal cortical gyral patterns, impaired myelination, and cerebral periventricular pseudocysts. In addition, MR imaging revealed renal microcysts and hepatosplenomegaly in one case. The high level of resolution of MR imaging, which allows analysis of cerebral gyration and myelination, facilitates the prenatal diagnosis of complex polymalformative syndromes such as ZS.

Molar tooth sign and superior vermian dysplasia: a radiological, clinical, and genetic study

We have identified a group of 13 patients with a homogeneous radiological pattern at MRI consisting of the molar tooth sign (MTS) and superior vermian dysplasia. The patients represent a relatively heterogeneous clinical group with variable severity of developmental delay, ataxia, hypotonia, and apnea. Careful examination of MRI prompted us to split our series of patients into two groups, based on IVth ventricle dilatation. In 4/13 patients the IVth ventricle was judged to be dilated and those patients were less severely affected while most clinically affected patients had a normal IVth ventricle. DNA samples of blood leukocytes from 6/13 consanguineous patients were genotyped using polymorphic markers encompassing the Joubert syndrome loci. We therefore sequenced AHI1 located in 6q23 in two patients who were homozygous at the locus and in four sporadic cases. Only one homozygous nonsense mutation was identified. Clinically, the patient exhibiting the AHI1 mutation was the most severely affected child with a profound encephalopathy, major hypotonia, ataxia, Leber congenital amaurosis, and normal IVth ventricle at the MRI. The present study suggests that the syndrome associating MTS and dysplasia of the superior vermis of the cerebellum is a clinically and genetically heterogeneous entity and that Jouberin (AHI1) mutations account for a marginal fraction of patients.

Prenatal prognosis of congenital diaphragmatic hernia using magnetic resonance imaging measurement of fetal lung volume

OBJECTIVES

To investigate the correlation between fetal lung volume (FLV), measured with magnetic resonance imaging (MRI), and postnatal mortality in newborns with prenatally diagnosed isolated congenital diaphragmatic hernia (CDH).

METHODS

In a 4-year prospective multicenter study, 77 fetuses with isolated CDH diagnosed between 20 and 33 weeks' gestation underwent fast spin-echo T2-weighted lung MRI. These MRI-FLV measurements were compared with a previously published normative curve obtained in 215 fetuses without thoracoabdominal malformations and with normal ultrasound biometric findings. FLV measurements were correlated with postnatal survival. The mean gestational age at MRI was 31.3 weeks.

RESULTS

The measured/expected FLV ratio was significantly lower in the newborns with CDH who died compared with those who survived (23.6 +/- 12.2 vs. 36.1 +/- 13.0, P < 0.001). When the ratio was below 25%, there was a significant decrease in postnatal survival (19% vs. 40.3%, P = 0.008). Survival was significantly lower for neonates when one lung could not be seen by fetal MRI compared with those fetuses with two visible lungs on MRI (17.9% vs. 62.1%, P < 0.001).

CONCLUSION

In isolated CDH, FLV measurement by MRI is a good predictor of postnatal mortality due to pulmonary hypoplasia.

Fetal hemangiopericytoma with an associated cerebral anomaly

We report the first case of infantile hemangiopericytoma explored prenatally by fetal ultrasonography and magnetic resonance imaging (MRI). It was associated with a developmental cerebral anomaly identified on MRI. The largest lesions of the multifocal hemangiopericytoma were located in the soft tissue adjacent to the left temporal bone, and smaller lesions were found in the lumbar area and in the retroperitoneum. MRI showed no connection between the tumor and the fetal brain but there was anomalous cerebral gyration in the region and the Sylvian fissure beneath the tumor was enlarged. The pregnancy was terminated because of the severe brain anomalies and postmortem examination confirmed the prenatal findings. Microscopic analysis of the tumor tissue showed branching vessels which are typical of hemangiopericytoma. The lesions in our case occurred in association with macrosomia with visceromegaly detected at autopsy, suggesting a possible role of tumor suppressor genes.

A primal sketch of the cortex mean curvature: a morphogenesis based approach to study the variability of the folding patterns

In this paper, we propose a new representation of the cortical surface that may be used to study the cortex folding process and to recover some putative stable anatomical landmarks called sulcal roots usually buried in the depth of adult brains. This representation is a primal sketch derived from a scale space computed for the mean curvature of the cortical surface. This scale-space stems from a diffusion equation geodesic to the cortical surface. The primal sketch is made up of objects defined from mean curvature minima and saddle points. The resulting sketch aims first at highlighting significant elementary cortical folds, second at representing the fold merging process during brain growth. The relevance of the framework is illustrated by the study of central sulcus sulcal roots from antenatal to adult age. Some results are proposed for ten different brains. Some preliminary results are also provided for superior temporal sulcus.

Intellectual prognosis of the Dandy-Walker malformation in children: the importance of vermian lobulation

Half of patients with the Dandy-Walker malformation (DWM) have normal intellectual development. We aimed to identify feature on MRI associated with good intellectual prognosis. We reviewed 20 patients with DWM diagnosed on MRI, mean age 14.6+/-9.9 years. We assessed their intellectual development and related it to the MRI features. We found two groups with a statistically different intellectual outcome. All 14 patients with normal intellectual development had a normal lobulation of the vermis, without supratentorial anomalies. Of the six patients with mental retardation, three had an abnormal vermis, together with dysgenesis of the corpus callosum. In the other three, there were normal vermian anatomy with associated anomalies. Normal lobulation of the vermis, in the absence of any supratentorial anomaly, appears to be a good prognostic factor in DWM. Preservation of cerebrocerebellar pathways and neonatal plasticity could explain the normal intellectual development. These findings might be useful in prenatal diagnosis.

Prenatal diagnosis of hypoplasia of the corpus callosum in association with non-ketotic hyperglycinemia

Abnormalities of the corpus callosum are often associated with a poor prognosis due to the anatomical defect itself and associated anomalies that include malformations and inherited metabolic disorders. We report a case of the prenatal diagnosis of hypoplasia of the corpus callosum that was associated with non-ketotic hyperglycinemia. Metabolic disorders are a known association with corpus callosum abnormalities and carry a dismal prognosis. A diagnosis of non-ketotic hyperglycinemia should be considered when a fetus presents with an abnormality of the corpus callosum. A literature search reviews other inherited diseases associated with hypoplasia of the corpus callosum.

Arthrogryposis multiplex congenita and cerebellopontine ischemic lesions in sibs: recurrence of prenatal disruptive brain lesions with different patterns of expression?

Arthrogryposis multiplex congenita (AMC) is a heterogeneous group of disorders in which prolonged decrease or absence of fetal movements results in a series of deformational anomalies. The rate of recurrence ranges from 25% in some recessive forms of myogenic arthrogryposis or of primary anterior horn cell loss, to less than 1% in anoxic-ischaemic damage. Cerebral clastic processes are considered as sporadic. We report on a non-consanguineous family in which the first child was affected by AMC and the following pregnancy was terminated because cerebellum hypoplasia was suspected at ultrasound and confirmed by fetal magnetic resonance imaging. Post-mortem findings demonstrated pontocerebellar ischaemic-haemorrhagic injuries. The occurrence of these neurologic abnormalities in the same family suggests a common mechanism, which might correspond to a same genetic defect with different patterns of expression. This is the first prenatal report suggesting that an 'ischaemic' process, usually recognised as sporadic could in fact be due to an inherited abnormality. Careful prenatal follow-up of third-trimester fetal brain development may be required in pregnant women with a family history of AMC.

Antenatal diagnosis of spinal lipomas

OBJECT

The purpose of this study was to highlight the key prenatal diagnostic features of fetal spinal lipomas.

METHODS AND RESULTS

All fetuses in whom a spinal lipoma was suspected prenatally or diagnosed postnatally were included in the study. Lumbosacral lipoma was diagnosed in 16 fetuses (group 1), but at birth 3 of these were found to have other forms of occult dysraphism. In 2 other fetuses (group 2) a meningocele was suspected but at birth these lesions were found to be lumbosacral lipomas. The lipomas were covering large meningoceles in 13 fetuses and filling the cul-de-sac in 2 others. Three sets of parents decided on termination. Of the 13 children born with a spinal lipoma, 9 were operated on and 4 were managed conservatively. At the last follow-up, 7 were neurologically intact.

CONCLUSION

The distinction between meningomyelocele and spinal lipoma is possible antenatally. The differential diagnosis between lipoma and the other forms of occult dysraphism is more difficult.

Local and spatial factors determining HIV-1 protease substrate recognition

Insertional mutagenesis of the Escherichia coli thymidylate synthase (TS) was used to address substrate recognition of HIV-1 protease in a well characterized structural context. By modifying the TS conformation while maintaining its enzymic activity, we investigated the influence of protein folding on protease-substrate recognition. A slight destabilization of the TS structure permitted the cleavage of a target site, which was resistant in the native TS. This result supports a dynamic interpretation of HIV-1 protease specificity. Exposure time of the potential cleavage site, which depends on the stability of the global conformation, must be compatible with the cleavage kinetics, which are determined by the local sequence. Cleavage specificity has been described as the consequence of cumulative interactions, globally favourable, between at least six amino acids around the cleavage site. To investigate influence of local sequence, we introduced insertions of variable lengths in two exposed loops of the TS. In both environments, insertion of only two amino acids could determine specific cleavage. We then inserted libraries of dipeptides naturally cleaved by the HIV-1 protease in order to assess the limitations of established classifications of substrates in different conformational contexts.

Determination of the anatomical location of an antenatal intestinal occlusion by magnetic resonance imaging

Intestinal occlusion occurs in approximately 1 in 3000 births. Its diagnosis can be made in utero with ultrasound however, determination of its precise location is difficult to achieve. We report herein the feasibility of diagnosing and locating a fetal small-intestine occlusion with the use of magnetic resonance imaging.

Fetal lung volume measurement by magnetic resonance imaging in congenital diaphragmatic hernia

OBJECTIVE

To study the potential for prenatal magnetic resonance imaging to predict pulmonary hypoplasia in congenital diaphragmatic hernia.

DESIGN

Prospective observational study.

SETTING

Tertiary care centre.

PARTICIPANTS

Thirteen cases of congenital diaphragmatic hernia (11 left, 2 right) without associated anomalies and 74 controls.

METHODS

Measurements by magnetic resonance imaging of fetal lung volume were achieved. In the control fetuses, a regression analysis was performed to associate fetal lung volume with gestational age. This yielded a formula allowing calculation of the expected fetal lung volume as a function of gestational age. In the cases with congenital diaphragmatic hernia, the observed/expected fetal lung volume ratio was compared with perinatal outcome.

MAIN OUTCOME MEASURES

Neonatal mortality and pulmonary hypoplasia, which was defined as lung/body weight ratios less than 0.012.

RESULTS

The expected fetal lung volume was derived from the following formula: Fetal lung volume (mL) = exp (1.24722 + 0.08939 x gestational age in weeks). The observed/expected fetal lung volume ratio was significantly lower in congenital diaphragmatic hernia (median: 0.31, range: 0.06-0.63), than in controls (median: 0.99, range: 0.42-1.94). This ratio was significantly less in the infants with congenital diaphragmatic hernia who died (median: 0.26, range: 0.06-0.63) compared with those who survived (median: 0.46, range: 0.35-0.56). The observed: expected fetal lung volume ratio was significantly correlated with the post mortem lung: body weight ratio.

CONCLUSION

In isolated congenital diaphragmatic hernia, fetal lung volume measurement by magnetic resonance imaging is a potential predictor of pulmonary hypoplasia and postnatal outcome. Further studies are required to establish the clinical value of magnetic resonance imaging for the prenatal assessment of fetal lungs.

[Prenatal semiology of diastematomyelia]

Diastematomyelia is a rare spinal malformation characterized by a division of the spinal cord. More often, the two hemicords are separated by a midline and sagittal osseous or fibrocartilaginous spur. In this report we describe two cases of diastematomyelia detected at routine second trimester detailed sonography and further assessed by MRI and spiral CT with surface shaded 3D-reconstructions. In addition to providing diagnosis, prenatal evaluation helps differentiate between diastematomyelia with good or bad prognosis.

A mathematical model for experimental gene evolution

The purpose of this paper is to determine the optimal mutation rate for random mutagenesis procedures used to make mutant libraries for subsequent screening. When the mutation rate is low, the probability of achieving a rare beneficial mutation is low. When the mutation rate is high, the probability of producing lethal mutations which result in loss of function is also high. We demonstrate that between these two extremes, an optimal mutation rate exists for experimental gene improvement. This rate depends strongly on the number of simultaneous mutations required for a beneficial change of the gene, but only weakly on the number of possible lethal mutations. This model predicts that when mutagenesis is performed at the optimum mutation rate, at least 63% (1--e(-1)) of the cloned genes in a mutant library will be non-functional.

Prenatal diagnosis and postnatal follow-up of pericallosal lipoma: report of seven new cases

BACKGROUND AND PURPOSE

Pericallosal lipomas are rare tumors. Few reports have included their imaging characteristics. Furthermore, little is known about their evolutive course. Our purpose was to describe the imaging features of seven cases of pericallosal lipoma diagnosed in utero and followed up after birth.

METHODS

We reviewed seven cases of pericallosal lipoma diagnosed by obstetric sonography (n = 7) and examined by fetal MR imaging (n = 5). Analysis of the complementary findings provided by fetal MR imaging was conducted. All findings were correlated with the postnatal imaging and clinical findings.

RESULTS

Obstetric sonography easily showed the pericallosal lipoma in all seven patients. In one, however, it was misinterpreted as intracranial hemorrhage. The morphology and integrity of the underlying corpus callosum were less easy to assess by using sonography. Fetal MR imaging confirmed the fatty content and location of the lesion in all five cases. It showed the choroidal extension in two patients and the type of associated callosal anomaly in another patient better than did sonography. In two patients, the lipoma grew, as revealed by subsequent postnatal MR imaging. The results of the neurologic examinations remained normal for the five surviving patients at a mean follow-up of 3 years (1 month-9 years).

CONCLUSION

Obstetric sonography is able to easily show pericallosal lipoma. Fetal MR imaging may be useful to characterize the lipomatous nature and the extension of the lipoma and the status of the corpus callosum. Long-term follow-up is necessary to understand the clinical consequences of such lesions.

Fetal lung volume: estimation at MR imaging-initial results

PURPOSE

To plot normal fetal lung volume (FLV) obtained with fast spin-echo magnetic resonance (MR) images against gestational age; to investigate the correlation between lung growth and fetal presentation, sex, and ultrasonographic (US) biometric measurements; and to investigate its potential application in fetuses with thoracoabdominal malformations.

MATERIALS AND METHODS

In a prospective multicenter study, 336 fetuses suspected of having central nervous system disorders underwent fast spin-echo T2-weighted lung MR imaging. Data obtained at 21-38 weeks gestation in 215 fetuses without thoracoabdominal malformations and with normal US biometric findings were selected for an FLV normative curve. FLV measurements obtained at pathologic examination with an immersion method were compared with MR FLV measurements in 11 fetuses. MR FLV values in 16 fetuses with thoracoabdominal malformations were compared with the normative curve.

RESULTS

Normal FLV increased with gestational age as a power curve; the spread of values increased with age. Interobserver correlation was excellent (R(2) = 0.96). FLV measurements at MR imaging were 0.90 times those at pathologic examination. A constant ratio (0.78) between FLV on the left and right sides was observed. No significant difference in FLV was observed between fetal presentations. Normal FLV was observed in all fetuses with cystic adenomatoid malformations and in four of six with oligohydramnios. Lowest FLV values were observed in fetuses with diaphragmatic hernia.

CONCLUSION

In fetuses with normal lungs, FLV distribution against gestational age is easily assessed in utero with fast spin-echo T2-weighted MR imaging. These preliminary findings illustrate the potential for comparing FLV measurements in fetuses at risk of lung hypoplasia with normative values.

Prenatal diagnosis of sporadic Apert syndrome: a sequential diagnostic approach combining three-dimensional computed tomography and molecular biology

Apert syndrome is characterized by coronal craniosynostosis, midfacial hypoplasia, symmetrical syndactyly of the hands and feet described as 'mitten-like' with varying degrees of mental retardation. It results from a mutation of the fibroblast growth factor-2 (FGFR2) gene. In the absence of a family history, prenatal diagnosis may be difficult based on sonography alone. We report a case in which the prenatal diagnosis of Apert syndrome was suspected by ultrasonography, established by three-dimensional computed tomography scan (3DTS) and confirmed by the detection of a mutation on amniotic cells. This underscores the usefulness of a sequential diagnostic approach combining 3DTS and molecular biology in cases in which sonography alone is not con- clusive.

Intracranial venous anomalies associated with atretic cephalocoeles

BACKGROUND

Midline scalp lesions are frequent in children. They include soft-tissue masses and atretic meningocoeles. Their recognition is important as their treatment differs. Intracranial venous anomalies are known to be associated with atretic cephalocoeles.

MATERIALS AND METHODS

A retrospective study was undertaken to assess the frequency of intracranial venous anomalies associated with atretic meningocoeles (AT). Thirty-one patients with AT were studied by MRI. There were 13 meningocoeles and 14 encephalocoeles; 4 have not yet received surgery.

RESULTS

Venous anomalies were found when the cephalocoeles lay above the torcular. They include absence of the straight sinus and duplication of the longitudinal sinus.

CONCLUSION

Venous anomalies are frequent in atretic cephalocoeles and are part of the dysraphic state.

The contribution of prenatal diagnosis to the understanding of malformative intracranial cysts: state of the art

This review evaluates the contribution of prenatal diagnosis to the understanding of intracranial cysts. We describe the outcome of 54 fetuses in which prenatal investigations indicated the presence of such lesions. The cysts were diagnosed between 20 and 30 weeks of gestation. Most (63%) were supratentorial and interhemispheric. There was only a single sylvian cyst. In the infratentorial compartment, median retrocerebellar cysts were predominant. Incisural cysts accounted for 14.8% of the series. Nine pregnancies were interrupted because of the presence of associated brain disorders. Forty-five children are alive. Thirty-four had neuropsychological tests. Cysts rarely progressed, most frequently stabilized and often regressed postnatally. Hydrocephalus was rare. In two cases delivery was precipitated at 36 weeks to allow urgent treatment of rapidly evolving cysts. Thirteen children (28.2%) were treated postnatally, in general for developing cysts. The median follow-up for the whole series exceeds 4 years. Behavior, neurological development, and intelligence are normal in 88% of the cases, and 91% have a normal neurological status. Prognosis at the time of the prenatal consultation was correct in 89% of the cases. We emphasize the value of prenatal magnetic resonance imaging and karyotype studies to limit risks of incorrect prognosis.

The intracytoplasmic domain of the Env transmembrane protein is a locus for attenuation of simian immunodeficiency virus SIVmac in rhesus macaques

The human and simian immunodeficiency virus (HIV-1 and SIVmac) transmembrane proteins contain unusually long intracytoplasmic domains (ICD-TM). These domains are suggested to play a role in envelope fusogenicity, interaction with the viral matrix protein during assembly, viral infectivity, binding of intracellular calmodulin, disruption of membranes, and induction of apoptosis. Here we describe a novel mutant virus, SIVmac-M4, containing multiple mutations in the coding region for the ICD-TM of pathogenic molecular clone SIVmac239. Parental SIVmac239-Nef+ produces high-level persistent viremia and simian AIDS in both juvenile and newborn rhesus macaques. The ICD-TM region of SIVmac-M4 contains three stop codons, a +1 frameshift, and mutation of three highly conserved, charged residues in the conserved C-terminal alpha-helix referred to as lentivirus lytic peptide 1 (LLP-1). Overlapping reading frames for tat, rev, and nef are not affected by these changes. In this study, four juvenile macaques received SIVmac-M4 by intravenous injection. Plasma viremia, as measured by branched-DNA (bDNA) assay, reached a peak at 2 weeks postinoculation but dropped to below detectable levels by 12 weeks. At over 1.5 years postinoculation, all four juvenile macaques remain healthy and asymptomatic. In a subsequent experiment, four neonatal rhesus macaques were given SIVmac-M4 intravenously. These animals exhibited high levels of viremia in the acute phase (2 weeks postinoculation) but are showing a relatively low viral load in the chronic phase of infection, with no clinical signs of disease for 1 year. These findings demonstrated that the intracytoplasmic domain of the transmembrane Env (Env-TM) is a locus for attenuation in rhesus macaques.

[Contribution of MRI in the evaluation of fetal malformations]

MRI was first used 10 years ago for the study of fetal morphology. This non invasive technique is mainly advocated for the study of fetus brain. Principle indications for MRI are Examinations are performed at 0.5 and 1.5 Tesla. Minimal study consists of T2 sequences in the 3 dimensions and T1 in one. Maternal premedication using hydroxizyne dichlorhydrate (25mg) can be proposed to avoid fetal movements. The main advantage of MRI compared with US is to detect gyral and neuronal migration anomalies, cerebral signs, of tuberous sclerosis and recent hemorrhagic lesions.

Variable constraints on the principal immunodominant domain of the transmembrane glycoprotein of human immunodeficiency virus type 1

Lentiviruses have in their transmembrane glycoprotein (TM) a highly immunogenic structure referred to as the principal immunodominant domain (PID). The PID forms a loop of 5 to 7 amino acids between two conserved cysteines. Previous studies showed that envelope (Env) glycoprotein functions of feline immunodeficiency virus (FIV) could be retained after extensive mutation of the PID loop sequence, in spite of its high conservation. In order to compare Env function in different lentiviruses, either random mutations were introduced in the PID loop sequence of human immunodeficiency virus type 1 (HIV-1) or the entire HIV-1 PID loop was replaced by the corresponding PID loop of FIV or simian immunodeficiency virus (SIV). In the macrophage-tropic HIV-1 ADA Env, mutations impaired the processing of the gp160 Env precursor, thereby abolishing viral infectivity. However, 6 of the 108 random Env mutants that were screened retained the capacity to induce cell membrane fusion. The SIV and FIV sequences and five random mutations were then introduced in the context of T-cell-line-adapted HIV-1 LAI which, although phenotypically distant from HIV-1 ADA, has an identical PID loop sequence. In contrast to the situation for HIV-1 ADA mutants, the cleavage of the Env precursor was unaffected in most HIV-1 LAI mutants. Such mutations, however, resulted in increased shedding of the gp120 surface glycoprotein (SU) from the gp41 TM. The HIV-1 LAI Env mutants showed high fusogenic efficiency. Three Env mutants retained the capacity to mediate virus entry in target cells, although less efficiently than the wild-type Env, and allowed the reconstitution of infectious molecular clones. These results indicated that in HIV-1, like FIV, the conserved PID sequence can be changed without impairing Env function. However, functional constraints on the PID of HIV-1 vary depending on the structural context of Env, presumably in relation to the role of the PID in the interaction of the SU and TM subunits and the stability of the Env complex.

Shared usage of the chemokine receptor CXCR4 by primary and laboratory-adapted strains of feline immunodeficiency virus

Strains of the feline immunodeficiency virus (FIV) presently under investigation exhibit distinct patterns of in vitro tropism. In particular, the adaptation of FIV for propagation in Crandell feline kidney (CrFK) cells results in the selection of strains capable of forming syncytia with cell lines of diverse species origin. The infection of CrFK cells by CrFK-adapted strains appears to require the chemokine receptor CXCR4 and is inhibited by its natural ligand, stromal cell-derived factor 1alpha (SDF-1alpha). Here we found that inhibitors of CXCR4-mediated infection by human immunodeficiency virus type I (HIV-1), such as the bicyclam AMD3100 and short peptides derived from the amino-terminal region of SDF-1alpha, also blocked infection of CrFK by FIV. Nevertheless, we observed differences in the ranking order of the peptides as inhibitors of FIV and HIV-1 and showed that such differences are related to the species origin of CXCR4 and not that of the viral envelope. These results suggest that, although the envelope glycoproteins of FIV and HIV-1 are substantially divergent, FIV and HIV-1 interact with CXCR4 in a highly similar manner. We have also addressed the role of CXCR4 in the life cycle of primary isolates of FIV. Various CXCR4 ligands inhibited infection of feline peripheral blood mononuclear cells (PBMC) by primary FIV isolates in a concentration-dependent manner. These ligands also blocked the viral transduction of feline PBMC by pseudotyped viral particles when infection was mediated by the envelope glycoprotein of a primary FIV isolate but not by the G protein of vesicular stomatitis virus, indicating that they act at an envelope-mediated step and presumably at viral entry. These findings strongly suggest that primary and CrFK-adapted strains of FIV, despite disparate in vitro tropisms, share usage of CXCR4.

Structural and functional analysis of surface domains unique to bacteriophage T4 thymidylate synthase

The bacteriophage T4 genome encodes most of its own enzymes for dNTP synthesis, which form a complex in infected Escherichia coli. The T4 thymidylate synthase (TS) and the T4 deoxycytidylate deaminase (CD) catalyze sequential reactions and are physically linked within this complex [McGaughey, K. M., Wheeler, L. J., Moore, J. T., Maley, G. F. , Maley, F., and Mathews, C. K. (1996) J. Biol. Chem. 271, 23037-23042]. From the crystal structure of T4TS [Finer-Moore, J. S., Maley, G. F., Maley, F., Montfort, W. R., and Stroud, R. M. (1994) Biochemistry 33, 15459-15468], it appears that three regions corresponding to insertions relative to E. coli TS lie on one side of the enzyme surface. We have investigated the residual activity of T4TS in response to complete deletion or substitution mutagenesis of these insertions. Two deletions generated in the small domain (residues 70-103) reduced the TS activity to 0.2% and 0.7% of the wild-type activity, with the latter able to complement growth of a thyA- E. coli strain in the absence of thymidine. By insertion of exogenous sequences variable in length and in sequence into these deletion mutants, enzyme activity increased to 44% that of the wild type. Restoration of the TS activity depended mostly on the hydrophobicity of the inserted residues. The sites of insertions also displayed distinct permissiveness for accommodating the exogenous insertions. Deletions and substitutions near the C-terminus resulted in complete inactivation of the T4TS. Proteolysis experiments revealed that the modified surface loops of the small domain were still accessible and flexible for protein-protein interactions. We have used ELISA to detect a physical association between T4TS and T4CD and compared the binding affinity of WT T4TS for two purified insertion mutants of T4CD. The results obtained showed that the native sequences of the small domain inserts are not required for T4TS/T4CD complex formation.