Low torcular Herophili position and large brainstem-tentorium angle in fetuses with open spinal dysraphism at 11-13 weeks' gestation.

OBJECTIVE: To evaluate whether in fetuses with open spina bifida (OSB) the tentorium can be seen to be displaced downwards and vertically oriented by the time of the 11-13-week scan and whether this is reflected in an alteration of the brainstem-tentorium (BST) angle. METHODS: The study population was recruited between 2015 and 2020 from three fetal medicine referral centers and comprised a control group and a study group of pregnancies with OSB. The control group was recruited prospectively and included singleton pregnancies with a normal sonographic examination after first-trimester combined screening for chromosomal abnormalities and normal outcome. The study group was selected retrospectively and included all cases with OSB between 2015 and 2020. All cases underwent detailed ultrasound assessment at 11 + 0 to 13 + 6 weeks' gestation. The position of the torcular Herophili (TH) was identified in the midsagittal view of the fetal brain with the use of color Doppler and was considered as a proxy for the insertion of the tentorium on the fetal skull. The BST angle was calculated in the same view and was compared between the two groups. RESULTS: Sixty normal fetuses were included in the control group and 22 fetuses with OSB in the study group. In both groups, the BST angle was found to be independent of gestational age or crown-rump length (P = 0.8815, R2 = 0.0003861 in the controls, and P = 0.2665, R2 = 0.00978 in the OSB group). The mean BST angle was 48.7 ± 7.8° in controls and 88.1 ± 1.18°, i.e. close to 90°, in fetuses with OSB. Comparison of BST-angle measurements between the control group and cases with OSB showed a statistically significant difference (P = 0.0153). In all fetuses with OSB, the downward displacement of the TH and tentorium was clearly visible at the 11-13-week scan. CONCLUSIONS: In fetuses with OSB, the BST angle is significantly larger than in normal controls, with the tentorium being almost perpendicular to the brainstem. This sign confirms the inferior displacement of the tentorium cerebelli with respect to its normal insertion on the occipital clivus as early as the first trimester of pregnancy and is useful in the diagnosis of Chiari-II malformation at this early stage. In fetuses with OSB, the low position of the tentorium and TH is clearly visible, even subjectively, at the 11-13-week scan. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Position of the choroid plexus of the fourth ventricle in first- and second-trimester fetuses: a novel approach to early diagnosis of cystic posterior fossa anomalies.

OBJECTIVE: To describe the sonographic appearance and position of the choroid plexus of the fourth ventricle (4V-CP) between 12 and 21 weeks' gestation in normal fetuses and in fetuses with Dandy-Walker malformation (DWM) or Blake's pouch cyst (BPC). METHODS: The study population comprised 90 prospectively recruited normal singleton pregnancies and 41 pregnancies identified retrospectively from our institutional database that had a suspected posterior fossa anomaly at 12-13 weeks' gestation based on the ultrasound finding of abnormal hindbrain spaces. In all cases the final diagnosis was confirmed by prenatal and/or postnatal magnetic resonance imaging or postmortem examination. All pregnancies underwent a detailed ultrasound assessment, including a dedicated examination of the posterior fossa, at 12-13 weeks, 15-16 weeks and 20-21 weeks of gestation. Two-dimensional ultrasound images of the midsagittal and coronal views of the brain through the posterior fontanelle and three-dimensional volume datasets were obtained. Multiplanar orthogonal image correlation with volume contrast imaging was used as the reference visualization mode. Two independent operators, blinded to the fetal outcome, were asked to classify the 4V-CP as visible or not visible in both normal and abnormal cases, and to assess if the 4V-CP was positioned inside or outside the cyst in fetuses with DWM and BPC. RESULTS: Of the 41 fetuses with apparently isolated cystic posterior fossa anomaly in the first trimester, eight were diagnosed with DWM, 29 were diagnosed with BPC and four were found to be normal in the second trimester. The position of the 4V-CP differed between DWM, BPC and normal cases in the first- and second-trimester ultrasound examinations. In particular, in normal fetuses, no cyst was present and, in the midsagittal and coronal planes of the posterior fossa, the 4V-CP appeared as an echogenic oval-shaped structure located inside the 4V apparently attached to the cerebellar vermis. In fetuses with DWM, the 4V-CP was not visible in the midsagittal view because it was displaced inferolaterally by the cyst. In contrast, in the coronal view of the posterior brain, the 4V-CP was visualized in all cases with DWM at 12-13 weeks, with a moderate decrease in the visualization rate at 15-16 weeks (87.5%) and at 20-21 weeks (75%). In the coronal view, the 4V-CP was classified as being outside the cyst in all DWM cases at 12-13 weeks and in 87.5% and 75% of cases at 15-16 and 20-21 weeks, respectively. In fetuses with BPC, the 4V-CP was visualized in all cases in both the midsagittal and coronal views at 12-13 weeks and in 100% and 96.6% of cases, respectively, at 15-16 weeks. In the coronal view, the 4V-CP was classified as being inside the cyst in 28 (96.6%), 27 (93.1%) and 25 (86.2%) cases at 12-13, 15-16 and 20-21 weeks, respectively. The medial segment of the 4V-CP was visualized near the inferior part of the vermis. CONCLUSIONS: Our study shows that longitudinal ultrasound assessment of the 4V-CP and its temporal changes from 12 to 21 weeks is feasible. The 4V-CP is located inside the cyst, just below the vermis, in BPC and outside the cyst, inferolaterally displaced and distant from the vermian margin, in DWM, consistent with the pathogenesis of the two conditions. The position of the 4V-CP is a useful sonographic marker that can help differentiate between DWM and BPC as early as in the first trimester of pregnancy. © 2021 International Society of Ultrasound in Obstetrics and Gynecology.

Prenatal visualisation of the torcular herophili by means of a Doppler technology highly sensitive for low-velocity flow in the expert assessment of the posterior fossa: a prospective study.

OBJECTIVE: To evaluate the usefulness of a Doppler technology highly sensitive for low-velocity flow in the antenatal imaging of the torcular herophili (TH) in the second trimester of pregnancy. DESIGN: Prospective study. SETTING: Referral Fetal Medicine Unit. POPULATION: Non-consecutive series of singleton pregnancies submitted to antenatal neurosonogram between 20 and 28 weeks of gestation. METHODS: A midsagittal section of the fetal brain was obtained by insonating through the anterior fontanelle, then the MV-Flow™ and LumiFlow™ presets were selected to visualise the TH as the posterior confluence of the superior sagittal sinus and the straight sinus. MAIN OUTCOME MEASURES: Evaluation of the anatomic relationship of the TH with the 'transpalatal line' joining the upper bony palate to the fetal skull. RESULTS: A total of 99 pregnant women were recruited, including one fetus with open spina bifida, one with Dandy-Walker malformation (DWM) and two with Blake's pouch cysts. In normal fetuses, the TH appeared to lie on or just below the 'transpalatal line'. In the cases of Blake's pouch cyst, the position of the TH appeared normal if compared with controls, whereas in DWM a supra-elevated position of the TH in respect of the transpalatal line was demonstrated. Finally, in the fetus with Chiari II malformation the TH was identified below the 'transpalatal plane'. CONCLUSIONS: Prenatal ultrasound visualisation of the TH by means of newly developed Doppler technologies characterised by high sensitivity for low-velocity flow is feasible and allows the indirect evaluation of the insertion of cerebellar tentorium in the second trimester. TWEETABLE ABSTRACT: Prenatal imaging of the torcular herophili using a Doppler technology highly sensitive for low-velocity flow.

Three-dimensional volumetric study with VOCAL in normal and abnormal posterior fossa fetuses.

Purpose: The aim of this study was to compare volumetric parameters in the abnormal and normal posterior fossa using the Virtual Organ Computer-aided AnaLysis (VOCAL™) technique to determine whether fetuses with an abnormal posterior fossa have different volumes.Methods: A prospective study was conducted on 17 fetuses with an abnormal posterior fossa including, Dandy Walker malformation (DWM) (n = 6), vermian hypoplasia (VH) (n = 3), mega cisterna magna (MCM) (n = 8), and 99 healthy control fetuses from 20 to 34 weeks' gestation. Measurement of the fetal cisterna magna and cerebellar volume was performed in the standard transcerebellar plane through the VOCAL™ method. To establish the correlation of volumes with gestational age, polynomial regression analysis was performed. For comparison between groups, univariate ANCOVA was performed using gestational age as a covariate. The reliability was analyzed by the intraclass correlation coefficient (ICC).Results: Cerebellar volume and cisterna magna volume were correlated with gestational age. Posterior fossa volume was significantly larger in DWM (p < .0001) and MCM (p < .0001) in comparison to the control group. In VH group, cisterna magna volume does not seem to expand (p = .298). Cerebellar volume does not seem to change in subgroups when the influence of gestational age is discarded (p = .09). The ratio of cerebellar volume to the cisterna magna volume decreases significantly in abnormal fetuses (p < .0001). Good intraobserver and interobserver reliabilities were found for both cerebellum and cisterna magna measurements.Conclusions: Volume analysis may have a role in discrimination of different posterior fossa pathologies.

A comprehensive review of the clivus: anatomy, embryology, variants, pathology, and surgical approaches.

INTRODUCTION: The clivus is a bony structure formed by the fusion of the basioccipital and basispheniod bone at the sphenooccipital synchondrosis. This downward sloping structure from the dorsum sellae to the foramen magnum is derived from mesoderm and ectoderm properties. METHODS: This comprehensive review of the clivus will discuss its basic anatomy, embryology, pathological findings, and surgical implications. The clivus is an endochondral bone, formed under two processes; first, a cartilaginous base is developed, and it is secondly reabsorbed and replaced with bone. Knowledge of its embryological structure and growth of development will clarify the pathogenesis of anatomical variants and pathological findings of the clivus. CONCLUSIONS: Understanding the anatomy including proximity to anatomical structures, adjacent neurovasculature properties, and anatomical variants will aid neurosurgeons in their surgical management when treating pathological findings around the clivus.

Post Mortem Diagnosis of Blake's Pouch Cyst: A Presentation of Distended Cyst at Necropsy.

BACKGROUND: Blake's pouch cyst forms from non-permeabilization of Blake's pouch. It is difficult to visualize at necropsy as the cyst ruptures easily into the 4th ventricle during dissection. CASE REPORT: Based upon prenatal imaging, delicate dissection allowed post-mortem confirmation of the Blake's pouch cyst. CONCLUSIONS: This highlights the importance of utilizing premortem imaging to help guide the postmortem dissection and documentation of a posterior fossa cyst.

Embryology of the craniocervical junction and posterior cranial fossa, part II: Embryogenesis of the hindbrain.

Although pathology of the hindbrain and its derivatives can have life altering effects on a patient, a comprehensive review on its embryology is difficult to find in the peer-reviewed medical literature. Therefore, this review article, using standard search engines, seemed timely. The embryology of the hindbrain is complex and relies on a unique timing of various neurovascular and bony elements. Derailment of these developmental processes can lead to a wide range of malformations such as the Chiari malformations. Therefore, a good working knowledge of this embryology as outlined in this review of the hindbrain is important for those treating patients with involvement of this region of the central nervous system. Clin. Anat. 31:488-500, 2018. © 2018 Wiley Periodicals, Inc.

Enlarged posterior fossa on prenatal imaging: differential diagnosis, associated anomalies and postnatal outcome.

INTRODUCTION: The primary aim of this study was to ascertain the prevalence of the individual conditions and of associated anomalies in fetuses with the prenatal diagnosis of enlarged posterior fossa (PF) and to explore the diagnostic accuracy of ultrasound in these anomalies. The secondary aim was to evaluate the postnatal outcome of children affected by PF anomalies. MATERIAL AND METHODS: All fetuses with enlarged PF detected by prenatal sonography at a referral center from 2001 to 2015 were analyzed retrospectively. Some were also studied by fetal magnetic resonance imaging (MRI) or volume ultrasound examinations. Fetal sonographic and MRI were compared using following classification: Dandy-Walker malformation (DWM); megacisterna magna (MCM); Blake's pouch cyst; isolated vermian hypoplasia; vermian agenesis; PF arachnoid cyst (AC); and cerebellar hypoplasia (CH). RESULTS: The ultrasound diagnoses of the 69 fetuses were as follows: MCM (n = 29; of these isolated n = 15), DWM (n = 28, isolated n = 4), vermian hypoplasia (n = 5, isolated n = 4), Blake's pouch cyst (n = 4, isolated n = 1), CH (n = 2; none isolated) and AC in the PF (n = 1, isolated). Thirteen of the 41 karyotyped fetuses were aneuploid, including seven with DWM. Associated malformations were found in 37/69 cases. There were 39 live births, including 11 with confirmed DWM, six of whom show a normal development. Twelve infants with isolated MCM show normal development. There were eight false-positive prenatal diagnoses (or resolution until birth) of "enlarged PF": three with Blake's pouch cyst, two with MCM and one with vermian hypoplasia. CONCLUSIONS: An enlarged PF requires specific diagnoses for the best possible counseling. The term "Dandy-Walker variant" should not be used anymore. Isolated MCM and Blake's pouch cyst can either resolve or be normal variants, but may also indicate the presence of a more severe anomaly or associated malformations.

Congenital basis of posterior fossa anomalies.

The classification of posterior fossa congenital anomalies has been a controversial topic. Advances in genetics and imaging have allowed a better understanding of the embryologic development of these abnormalities. A new classification schema correlates the embryologic, morphologic, and genetic bases of these anomalies in order to better distinguish and describe them. Although they provide a better understanding of the clinical aspects and genetics of these disorders, it is crucial for the radiologist to be able to diagnose the congenital posterior fossa anomalies based on their morphology, since neuroimaging is usually the initial step when these disorders are suspected. We divide the most common posterior fossa congenital anomalies into two groups: 1) hindbrain malformations, including diseases with cerebellar or vermian agenesis, aplasia or hypoplasia and cystic posterior fossa anomalies; and 2) cranial vault malformations. In addition, we will review the embryologic development of the posterior fossa and, from the perspective of embryonic development, will describe the imaging appearance of congenital posterior fossa anomalies. Knowledge of the developmental bases of these malformations facilitates detection of the morphological changes identified on imaging, allowing accurate differentiation and diagnosis of congenital posterior fossa anomalies.

Transsphenoidal meningocele: an anatomical study using human fetuses including report of a case.

An asymptomatic transsphenoidal meningoencephalocele was discovered incidentally by fiber laryngoscopic examination in a 62-year-old man suffering from hoarseness due to dysplasia of the vocal cord epithelium. To provide a better understanding of the pathogenesis of this anomaly, we performed histologic observations of paraffin-embedded specimens of 42 human fetal heads at 12-16 weeks of gestation. At these stages, ossification had started in the clivus but the sphenoid sinus was not developed. In contrast to the very low incidence of the intra- or trans-sphenoidal remnant of Rathke's pouch after birth, we found (1) the typical mid-line cleft of the sphenoid body in two specimens (2/42 or 4.8 %) and (2) a duct-like, sellar inferior protrusion ending in the sphenoid body in 12 specimens (12/42 or 28.6 %). The cyst-like structure in the protrusion (two specimens) seemed to be composed of obstructed veins. The intra- and trans-sphenoidal anomalies were observed more frequently in specimens without ossification of the sphenoid body than in those with ossification. However, irrespective of ossification, a cyst-like remnant of the most upper part of Rathke's pouch was always seen between the anterior and posterior lobes of the developing pituitary gland. In addition, the bursa pharyngea was seen in four specimens and we confirmed that the notochord was attached to the bursa in each case. The consistent remnant of the intrasellar Rathke's pouch appeared to explain the high incidence of Rathke's cleft cyst in adults. The relatively high incidence of intrasphenoidal anomalies in fetuses (14/42) suggested that the intra- or trans-sphenoidal remnant of Rathke's pouch was physiologically closed by ossification of the sphenoid body.

Brainstem-vermis and brainstem-tentorium angles allow accurate categorization of fetal upward rotation of cerebellar vermis.

OBJECTIVE: To evaluate the role of the brainstem-vermis (BV) and brainstem-tentorium (BT) angles in the differential diagnosis of upward rotation of the fetal cerebellar vermis. METHODS: The BV and BT angles were measured retrospectively on median sonographic views of the brain in 31 fetuses at 19-28 weeks' gestation with upward rotation of the cerebellar vermis due to Blake's pouch cyst (n = 12), Dandy-Walker malformation (n = 12) and cerebellar vermian hypoplasia (n = 7). Eighty normal fetuses at 20-24 weeks were included as controls. RESULTS: In the control group, BV and BT angles were 9.1 ± 3.5° (range, 4-17°) and 29.3 ± 5.8° (range, 21-44°), respectively. The BV angle was significantly increased in each of the three subgroups of anomalies: Blake's pouch cyst (23 ± 2.8°; range, 19-26°), vermian hypoplasia (34.9 ± 5.4°; range, 24-40°) and Dandy-Walker malformation (63.5 ± 17.6°; range, 45-112°), the angle increasing with increasing severity of the condition. The BT angle had a similar pattern but there was overlap among the different groups. CONCLUSION: The BV angle and, to a lesser degree, the BT angle are simple and reproducible measurements that provide valuable additional information for the categorization of upward rotation of the fetal cerebellar vermis. From mid gestation, a BV angle > 45° is strongly suggestive of a Dandy-Walker malformation, while a measurement < 30° favors the diagnosis of a Blake's pouch cyst.

Prenatal diagnosis and outcome of fetal posterior fossa fluid collections.

OBJECTIVE: To evaluate the accuracy of fetal imaging in differentiating between diagnoses involving posterior fossa fluid collections and to investigate the postnatal outcome of affected infants. METHODS: This was a retrospective study of fetuses with posterior fossa fluid collections, carried out between 2001 and 2010 in two referral centers for prenatal diagnosis. All fetuses underwent multiplanar neurosonography. Parents were also offered fetal magnetic resonance imaging (MRI) and karyotyping. Prenatal diagnosis was compared with autopsy or postnatal MRI findings and detailed follow-up was attempted by consultation of medical records and interview with parents and pediatricians. RESULTS: During the study period, 105 fetuses were examined, at a mean gestational age of 24 (range, 17-28) weeks. Sonographic diagnoses (Blake's pouch cyst, n = 32; megacisterna magna, n = 27; Dandy-Walker malformation, n = 26; vermian hypoplasia, n = 17; cerebellar hypoplasia, n = 2; arachnoid cyst, n = 1) were accurate in 88% of the 65 cases in which confirmation was possible. MRI proved more informative than ultrasound in only 1/51 cases. Anatomic anomalies and/or chromosomal aberrations were found in 43% of cases. Blake's pouch cysts and megacisterna magna underwent spontaneous resolution in utero in one third of cases and over 90% of survivors without associated anomalies had normal developmental outcome at 1-5 years. Isolated Dandy-Walker malformation and vermian hypoplasia were associated with normal developmental outcome in only 50% of cases. CONCLUSION: Prenatal neurosonography and MRI are similarly accurate in the categorization of posterior fossa fluid collections from mid gestation. Blake's pouch cyst and megacisterna magna are risk factors for associated anomalies but when isolated have an excellent prognosis, with a high probability of intrauterine resolution and normal intellectual development in almost all cases. Conversely, Dandy-Walker malformation and vermian hypoplasia, even when they appear isolated antenatally, are associated with an abnormal outcome in half of cases.

Abnormal or delayed development of the posterior membranous area of the brain: anatomy, ultrasound diagnosis, natural history and outcome of Blake's pouch cyst in the fetus.

OBJECTIVES: To review the normal and pathological development of the posterior membranous area (PMA) in the fetal brain, to define sonographic criteria with which to diagnose a Blake's pouch cyst (BPC) in the fetus and to review the ultrasound features, associations and outcome of 19 cases of BPC seen at our center over the last 5 years. METHODS: We conducted a MEDLINE search using the terms 'Blake's pouch', with or without 'fourth ventricle' or '4(th) ventricle', with or without 'roof' and identified articles describing normal and/or abnormal development of the PMA, whether or not they were cited in the limited clinical literature on BPC. A description of the normal and abnormal development of BPC was derived by collating these articles. The clinical retrospective study included 19 cases of posterior fossa anomalies with a final diagnosis of BPC seen at our institution. The following variables were assessed: referral indication, gestational age at diagnosis, ultrasound and magnetic resonance imaging (MRI) findings, associated anomalies, natural history and pregnancy and neonatal outcome. A transvaginal three-dimensional (3D) ultrasound examination was performed in all cases and 15 cases underwent MRI. To confirm the diagnosis, postnatal MRI, transfontanellar ultrasound or autopsy were available in all cases. RESULTS: Among the 19 cases reviewed, referral indications were: suspicion of vermian abnormality in 11 (58%) cases and other non-central nervous system anomaly in eight (42%) cases. Sonographically, all cases showed the following three signs: 1) normal anatomy and size of the vermis; 2) mild/moderate anti-clockwise rotation of the vermis; 3) normal size of the cisterna magna. On 3D ultrasound, the upper wall of the cyst was clearly visible in 11/19 cases, with choroid plexuses on the superolateral margin of the cyst roof. On follow-up, the BPC had disappeared by 24-26 gestational weeks in six of the 11 cases which did not undergo termination of pregnancy (TOP), and remained unaltered until birth in the other five cases. There were associated anomalies in eight (42%) cases, in five of which this consisted of or included congenital heart disease. Karyotype was available in 14 cases, two of which were abnormal (both trisomy 21). Regarding pregnancy outcome, there were eight (42%) TOPs, two (10%) neonatal deaths and nine (48%) survivors. One neonate, in whom the BPC had disappeared by the time of birth, had obstructive hydrocephaly confirmed. Another neonate was diagnosed with Down syndrome after birth. Excluding the Down syndrome baby, neurodevelopmental outcome was normal at the time of writing in all eight cases. CONCLUSIONS: Based on our analysis of ultrasound features, we propose that for BPC to be diagnosed in a fetus the following three criteria should be fulfilled: 1) normal anatomy and size of the vermis; 2) mild/moderate anti-clockwise rotation of the vermis; 3) normal size of the cisterna magna. Furthermore, we found that BPC can undergo delayed fenestration at 24-26 weeks in more than 50% of cases. Finally, it seems that BPC shows a risk of association with extracardiac anomalies (heart defects in particular) and, to a lesser extent, trisomy 21.

Three-dimensional sonography of the posterior fossa in fetuses with open spina bifida at 11-13 weeks' gestation.

OBJECTIVES: To investigate the posterior fossa of normal fetuses and fetuses with open spina bifida in stored three-dimensional (3D) volumes and to describe signs that might allow early detection of this defect. METHODS: A prospective study of 3D volumes of the fetal brain obtained from 10 normal fetuses and three fetuses with open spina bifida was undertaken. Measurements of the anteroposterior diameters of the cisterna magna and fourth ventricle were taken in the tilted axial view. In the mid-sagittal plane the brainstem (BS) diameter and the brainstem-occipital bone (BSOB) distance were measured. The BS/BSOB ratio was calculated. All measurements were expressed as Z-scores. Structural analysis of the differences in the posterior fossa between normal fetuses and fetuses with open spina bifida was undertaken. RESULTS: In normal fetuses all measurements were within ±2.5 Z-scores. In three fetuses with open spina bifida the BS Z-scores were 2.7, 2.8 and 2.8; the BSOB scores were -3.4, -2.8 and -2.9; the cisterna magna scores were -5.6, -3.7 and -4.2; and the BS/BSOB ratio scores were 4.1, 9.7 and 8.9. In normal fetuses the cisterna magna was posterior to the fourth ventricle and extended along its entire length. In fetuses with open spina bifida the cisterna magna was partially or completely obliterated. CONCLUSIONS: Assessment of the cranial posterior fossa is feasible at 11-13 weeks' gestation. There are distinct signs in fetuses with open spina bifida which can be evaluated by ultrasonography.

Posterior fossa malformations.

Understanding embryologic development of the cerebellum and the 4th ventricle is essential for understanding posterior fossa malformations. Posterior fossa malformations can be conveniently classified into those that have a large posterior fossa and those with normal or small posterior fossa. Disorders associated with a large posterior fossa include classic Dandy-Walker malformation, Blake's pouch cyst, mega cisterna magna, and posterior fossa arachnoid cyst. Disorders associated with normal or small posterior fossa include Dandy-Walker variant, Joubert syndrome, tecto-cerebellar dysraphia, rhombencephalosynapsis, the neocerebellar hypoplasias, and cerebellar atrophy. Neuro-imaging features should enable the imager to provide the referring physician a logical approach to these complex posterior fossa malformations.

Appearance of the fetal posterior fossa at 11 + 3 to 13 + 6 gestational weeks on transabdominal ultrasound examination.

OBJECTIVES: To describe the sonographic appearance of the structures of the posterior cranial fossa in fetuses at 11 + 3 to 13 + 6 weeks of pregnancy and to determine whether abnormal findings of the brain and spine can be detected by sonography at this time. METHODS: This was a prospective study including 692 fetuses whose mothers attended Innsbruck Medical University Hospital for first-trimester sonography. In 3% (n = 21) of cases, measurement was prevented by fetal position. Of the remaining 671 cases, in 604 there was either a normal anomaly scan at 20 weeks or delivery of a healthy child and in these cases the transcerebellar diameter (TCD) and the anteroposterior diameter of the cisterna magna (CM), measured at 11 + 3 to 13 + 6 weeks, were analyzed. In 502 fetuses, the anteroposterior diameter of the fourth ventricle (4V) was also measured. In 25 fetuses, intra- and interobserver repeatability was calculated. RESULTS: We observed a linear correlation between crown-rump length (CRL) and CM (CM = 0.0536 × CRL - 1.4701; R2 = 0.688), TCD (TCD = 0.1482 × CRL - 1.2083; R2 = 0.701) and 4V (4V = 0.0181 × CRL + 0.9186; R2 = 0.118). In three patients with posterior fossa cysts, measurements significantly exceeded the reference values. One fetus with spina bifida had an obliterated CM and the posterior border of the 4V could not be visualized. CONCLUSIONS: Transabdominal sonographic assessment of the posterior fossa is feasible in the first trimester. Measurements of the 4V, the CM and the TCD performed at this time are reliable. The established reference values assist in detecting fetal anomalies. However, findings must be interpreted carefully, as some supposed malformations might be merely delayed development of brain structures.

Normal and abnormal anatomy of the cerebellar vermis in midgestational human fetuses.

BACKGROUND: Evaluation of the cerebellar vermis is an important component of fetal autopsy, but lack of an established approach, inadequate normal anatomic data, and the subtle nature of some cerebellar malformations negatively affect concordance between prenatal ultrasound and autopsy diagnoses. METHODS: Gross anatomy and sagittal histologic sections of vermis from 26 midgestation fetuses with no posterior fossa anomalies detected by prenatal ultrasound or autopsy were examined to establish stage-specific norms. These were compared to data from three fetuses with prenatal ultrasound diagnoses of hypoplasia or absence of the cerebellar vermis, each of which had no or equivocal gross cerebellar malformation at autopsy. RESULTS: Two findings segregated cases from controls: (1) The ratio of the rostro-caudal length of the vermis to that of the cerebellar hemispheres was shorter for cases (<0.7), in comparison with controls (0.7-1). (2) The lobules of the vermis, particularly in the posterior lobe, were less arborized, and the nodulus (caudal-most lobule) was elongated. Prenatal sonograms from the three cases predicted more severe vermis hypoplasia than was evident at autopsy. CONCLUSIONS: Prenatal ultrasound images that suggest moderate-to-severe hypoplasia of the cerebellar vermis may reflect relatively subtle malformations, which are recognized histologically by direct comparison with stage-matched control data. The data in this series and others suggest a somewhat consistent pattern of lobular malformation, which affects the caudal cerebellum, particularly the nodulus, most severely. Rotation of the cerebellum, secondary to an enlarged fourth ventricle, may account for discordance between ultrasound and autopsy findings.

Oronasopharyngeal chordomas.

BACKGROUND: Chordomas are rare tumors derived from notochordal remnants. The authors report on a series of three cases of primary familial oronasopharyngeal chordomas treated at our institution. METHODS: A retrospective chart review was completed of the three cases of primary familial oronasopharyngeal chordoma treated at the University of Utah. FINDINGS: All three patients (100%) were neurologically intact and presented with nasal obstruction. The patients ranged in age from 5 to 65 years and were first-degree relatives. None of the patients had bony erosion of the skull base on imaging, and all of the patients' tumors connected with the skull base via a tract. All three patients were treated with a wide excision combined with drilling of the involved skull base. They all tolerated the procedure without any complications and remain tumor free with a follow-up of 12 months to 4.5 years. CONCLUSION: Primary oronasopharyngeal chordomas are rare tumors that may present without bony erosion of the skull base. A wide excision with drilling of the involved bony structures may offer an oncologic cure.