Sonographic diagnosis and prognosis of fetal arachnoid cysts.

PURPOSE: To explore the clinical significance of sonographic (US) diagnosis of fetal arachnoid cysts and to evaluate their prognosis. METHODS: Sixty fetuses deemed to have arachnoid cysts by prenatal US were included in this study. Data from serial US, prenatal and/or postnatal MRI, or post-mortem examinations were retrospectively analyzed. For live births, the developmental quotient scores were determined using the Gesell Developmental Scale. RESULTS: Thirty fetuses were diagnosed during the second trimester and another 30 fetuses were diagnosed in the third trimester. Fifty-one lesions were located in the supratentorial compartment, and 9 were located in the posterior fossa. Twenty-four lesions were isolated, and the remaining lesions were associated with intracranial and/or extra central nervous system malformations. The evolution of the cysts included progression, stability, or spontaneous resolution. The outcomes included induced abortion, intrauterine death, live birth with either normal neurodevelopment or mental retardation, and infant mortality. Two cases were lost to follow-up. The accuracy of prenatal US diagnosis was 86.2% (50/58). CONCLUSION: Prenatal US is the modality of choice for the diagnosis of fetal arachnoid cysts. Serial US examinations are critical to monitor the lesions. Moreover, prenatal MRI is a valuable complementary tool. For live births, the prognosis appears to be good.

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.

Quistes aracnoideos: embriología y anatomía patológica / Arachnoid cysts: Embriology and pathology

Existe en la actualidad todavía mucha controversia en cuanto al origen de los quistes aracnoideos. En el caso de los quistes aracnoideos congénitos, la teoría más aceptada es aquella que explica cómo se forman a partir del desarrollo anómalo de la membrana aracnoidea, la cual se desdobla facilitando la acumulación de líquido cefalorraquídeo en su interior, dando lugar a un quiste. Esta teoría parece explicar el origen de los quistes aracnoideos de convexidad y silvianos, mientras que aquellos en otras localizaciones podrían ser debidos a otras causas. En el estudio anatomopatológico se aprecia que la pared de los quistes aracnoideos difiere poco de la membrana aracnoidea normal, pudiendo estar engrosada debido a un aumento de depósito de material colágeno. Exponemos el desarrollo embriológico normal de la aracnoides, las alteraciones que se producen en dicho desarrollo y que condicionan la formación de los quistes aracnoideos describiendo sus hallazgos anatomopatológicos más característicos

There is still great controversy surrounding the origin of the arachnoid cyst. The most accepted theory in the case of congenital cysts explains how they are formed from an anomalous development of the arachnoid membrane, which is unfolded allowing the accumulation of cerebrospinal fluid inside and creating a cyst. This theory seems to explain the origin of convexity and sylvian cistern arachnoid cysts, whereas those in other locations might be due to other mechanisms. In the anatomopathological analysis, the arachnoid cyst wall can be seen as having few differences from normal, although thickened due to an increase quantity of collagenous material

[Arachnoid cysts: Embriology and pathology]. / Quistes aracnoideos: embriología y anatomía patológica.

There is still great controversy surrounding the origin of the arachnoid cyst. The most accepted theory in the case of congenital cysts explains how they are formed from an anomalous development of the arachnoid membrane, which is unfolded allowing the accumulation of cerebrospinal fluid inside and creating a cyst. This theory seems to explain the origin of convexity and sylvian cistern arachnoid cysts, whereas those in other locations might be due to other mechanisms. In the anatomopathological analysis, the arachnoid cyst wall can be seen as having few differences from normal, although thickened due to an increase quantity of collagenous material. A description of the embryological development of the arachnoid layer and cyst formation is presented, describing the main anatomopathological findings.

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.

Midline cystic malformations of the brain: imaging diagnosis and classification based on embryologic analysis.

This article describes a classification and imaging diagnosis of intracranial midline cystic malformations based on neuroembryologic analysis. Midline cystic malformations are classified into two categories from an embryologic point of view. In one category, the cyst represents expansion of the roof plate of the brain vesicle, and in the other the cyst consists of extraaxial structures such as an arachnoid membrane or migrating ependymal cells. Infratentorial cysts, such as the Dandy-Walker cyst or Blake's pouch cyst, and supratentorial cysts, such as a communicating interhemispheric cyst with callosal agenesis or a dorsal cyst with holoprosencephaly, are included in the first category. Infratentorial arachnoid cavities, such as the arachnoid cyst, arachnoid pouch, and mega cisterna magna, are in the second category. Noncommunicating interhemispheric cysts, such as interhemispheric arachnoid cyst or ependymal cyst, with callosal agenesis are also in the second category. A careful review of embryologic development is essential for understanding these midline cysts and for making a more accurate radiologic diagnosis.

First-trimester diagnosis of fetal arachnoid cyst: prenatal implication.

We report a case of the early diagnosis of an arachnoid cyst. Transvaginal ultrasound examination of the fetal brain at 13 weeks' gestation revealed the presence of an anechoic mass above the posterior fossa. After extensive counseling and because of the uncertain prognosis of a first-trimester diagnosis of an arachnoid cyst, the parents opted for termination of pregnancy. The diagnosis was confirmed by postmortem examination.

[Arachnoid cysts: histologic, embryologic and physiopathologic review]. / Les kystes arachnoïdiens : mise au point histologique, embryologique et physio-pathologique.

Arachnoid cysts form a cavity containing a cerebrospinal-like fluid, the wall of which is composed of arachnoidal cells. Other types of intracranial cysts have been described, they differ from arachnoid cysts by the histological characteristics of their wall. To analyze homogeneous series, it is thus necessary to differentiate arachnoid cysts from the other types of cysts. Several localizations of these lesions have been described: the most frequent being the temporo-sylvian area. Arachnoid cysts are considered as resulting from congenital malformations that can change during postnatal life. They can no longer be considered as resulting from cerebral atrophy. This arachnoid malformation could be the primary event or be explained by an impairment of the cerebrospinal fluid drainage generated by venous agenesis. Several mechanisms could account for the inflation of these cysts: secretion by the cells forming the cyst walls, unidirectional valve, liquid movements secondary to pulsations of the veins.