The relationship of Arnold-Chiari and Dandy-Walker malformations

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.

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.

Pathophysiology of tethered cord syndrome and similar complex disorders

✓Tethered cord syndrome (TCS) is a stretch-induced functional disorder of the spinal cord due to the fact that its caudal portion is anchored by an inelastic structure. The functional lesion of TCS is generally situated in the lumbosacral cord, and many authors have shown that the syndrome is reversible via surgery to untether the cord. To clarify the expressions relevant to TCS, such as “cord tethering” and “tethered cord,” the authors have formulated three categories. These categories include cases that show the anatomical appearance of spinal cord stretching. Among them, Category 1 is isolated to represent the “true TCS.”

The authors focus their discussion of the pathophysiology of TCS on Category 1 to explain the impaired oxidative metabolism and electrophysiological derangements within the tethered spinal cord, which is the primary intrinsic cause of the dysfunction. Furthermore, they extend the discussion to the extrinsic (outside the spinal cord) factors and other complex conditions that mimic TCS.

Dorcas Hager Padget: neuroembryologist and neurosurgical illustrator trained at Johns Hopkins

✓ Dorcas Hager Padget was a pioneer in the fields of neurosurgical illustration and neuroembryology who practiced during the early 20th century at The Johns Hopkins University. Without a college degree, she trained as a medical illustrator in the Johns Hopkins School of Medicine's Department of Art as Applied to Medicine under Max Brödel. She began her career working for Walter Dandy as his medical artist, gaining worldwide recognition for her neurosurgical illustrations. With Dandy's encouragement, Hager Padget undertook her own scientific research, studying neurodevelopment and aneurysm formation in the circle of Willis by using human embryos from the world-renowned Carnegie Collection. She made lasting contributions to the field of neuroembryology, publishing the first major work on neurodevelopment of the cerebral arterial and venous systems. Following Dandy's death in 1946, Hager Padget began a full-time career as a scientific researcher, first at the Department of Embryology at the Carnegie Institution of Washington in Baltimore and later at the University of Maryland School of Medicine. She continued to make contributions to the field of congenital malformations of the brain and spine, coining the term “neuroschisis” to describe a possible mechanism of neural tube damage leading to the creation of a myelomeningocele. The authors describe Dorcas Hager Padget's contributions to neurosurgical illustration and neuroembryology, as well as her remarkable career.

Dorcas Hager Padget: artist and embryologist

Dorcas Hager Padget (1906-1973), a largely self-taught illustrator, became a more polished artist under Max Brödel at Johns Hopkins Hospital, before going to work for neurosurgeon Walter Dandy. In search of more information on vascular anatomy, she became an expert neuroembryologist, first in the development of arteries and veins and later chiefly involved with anomalies of neural tube development. She was able to clarify the development of the Arnold-Chiari and Dandy-Walker syndromes.

Subtorcular occipital encephaloceles. Anatomical considerations relevant to operative management

Three cases of occipital encephalocele, one with associated myelomeningocele, are presented. All received preoperative evaluation with magnetic resonance imaging. Such studies provide optimal demonstration of the cerebral and hindbrain anatomy to guide operative treatment and formulate prognosis. Review of available radiographic, operative, and pathological information suggests that most, if not all, occipital encephaloceles are associated with an anomaly of the hindbrain, and the usual anomaly is a rhombic roof encephalocele. In such cases, the site of cranial herniation is caudal to the torcula, regardless of the presence or absence of occipital lobe tissue within the sac. Experimental and clinical analysis suggests that occipital encephaloceles most likely arise from abnormalities in the development of the skull base.

Diagnosis of brain neuropathology in utero

The fetal brain can be evaluated very effectively with high-resolution real-time ultrasound equipment. This paper reviews normal fetal brain anatomy with specific emphasis on artifacts of ultrasound scanning of the brain. A review of the developmental abnormalities seen in utero include ventriculomegaly, anencephaly, encephalocele, meningomyelocele, Dandy-Walker syndrome, holoprosencephaly, craniosynostosis, microcephaly, and agenesis of the corpus callosum. The destructive lesions reviewed include hydranencephaly, infection, intracranial hemorrhage, and mass lesion. Identification of these abnormalities can be extremely helpful in providing the patients with management options and providing the obstetrician with information which can help in obstetric and neonatal therapy.

The Dandy-Walker malformation. A review of 40 cases

Forty cases of Dandy-Walker malformation referred to the Hôpital Necker Enfants-Malades between 1969 and 1982 have been reviewed. The incidence of the malformation in hydrocephalus was 2.4%. There was a slight, statistically insignificant, female prevalence. Hydrocephalus should not be included in the definition of the syndrome. In 80% of the cases, it was actually a post-natal complication of the malformation and most often developed within 3 months after birth. In 80% of the cases, a communication, although insufficient, was found between the dilated 4th ventricle and the subarachnoid space. Since this communication is probably established through the foramina of Luschka, the definition of the Dandy-Walker malformation should only include atresia of the foramen of Magendie. Associated brain and systemic malformations were numerous. Among facial anomalies, facial angiomas were found in 10% of our cases. The association of facial and cardiovascular anomalies favors the hypothesis that the onset of the malformation occurs between the formation and the migration of the cells of the neural crest (that is, between the 3rd and the 4th post-ovulatory week, earlier than previously thought). Except in selected patients, membrane excision has a high rate of failure and should be abandoned. Cyst-peritoneal shunting avoids the risk of an entrapped fourth ventricle and is presently the best surgical procedure. The overall mortality in this series was 12.5%. Intelligence quotients were over 80 in 60% of the patients. Other studies will be necessary to understand why the communication between the fourth ventricle and the subarachnoid spaces, sufficient in utero, usually becomes insufficient for a normal cerebrospinal fluid (CSF) circulation in the first months following birth. Two hypotheses are discussed: a change in CSF circulation, or bleeding in the dilated fourth ventricle during delivery.

Dandy-Walker syndrome. Clinical analysis of 23 cases

A clinical analysis of 23 patients with Dandy-Walker malformation indicates that more than 85% of them were diagnosed at or before 1 year of age, and that the incidence of associated anomalies is approximately 50%, with a 17% incidence for agenesis of the corpus callosum. The significance of the presence of these anomalies is substantiated by the fact that of the seven deaths recorded, six were related to this disease and five were affected by associated anomalies. The high mortality rate (26%) is comparable to that of other series. The differential diagnosis with posterior fossa extra-axial cysts is discussed. Ten patients were primarily treated with excision of the cyst membrane; all of them required subsequent shunting to control the intracranial pressure, demonstrating the futility of this approach. None of the patients treated with lateral ventricle shunting suffered an upward herniation of the posterior fossa contents, suggesting that combined shunting of the lateral and fourth ventricles is rarely necessary. The technical advantages of posterior fossa shunting alone are outlined. Of the 16 survivors, 14 were assessed for their mental development by means of standard psychometric testing. The results of the intelligence quotient (IQ) scoring have indicated that 71% of the patients have subnormal mental development (IQ less than 83). There was no significant relationship between retardation and associated anomalies, although agenesis of the corpus callosum was related to poor intellectual development in the two patients so affected (IQ's of 50 and 73).

Dandy-Walker syndrome: analysis of 21 cases

During the years 1950 to 1978, a total of 21 cases of Dandy-Walker syndrome were seen at the Vancouver General Hospital. Apart from hydrocephalus, the associated brain anomalies included agenesis of the corpus callosum in four cases, occipital meningocele in two and aqueductal stenosis in one patient. Systemic malformations were present in four patients and included two cases of cleft palate, one of polycystic kidneys and one of congenital rubella syndrome. The over-all mortality was 48 per cent, but has declined since 1965. Of the 12 cases treated surgically, only four have died. The number of shunt revisions was high (about two per patient). Of the 11 survivors, three have normal intelligence, four show mild mental retardation, and four are moderately to severely retarded. The differential diagnosis, clinical course and surgical therapy are discussed. It is recommended that double shunting of a lateral ventricle and of the enlarged fourth ventricle should be the primary procedure in cases associated with aqueductal stenosis or occlusion, and should be the secondary procedure in patients who exhibit recurrence of increased pressure in the posterior fossa after simple shunting of a lateral ventricle.

Computed tomography in hydrocephalus

Computed tomography has changed the direction of the investigation of hydrocephalus. Alone or with ventriculography and radionuclide CSF flow studies the types and causes of hydrocephalus can usually be diagnosed. Atrophy with large ventricles, subdural hygromas and mild hydrocephalus may still be difficult to separate. Many of the complications of treatment, such as subdural hematoma, shunt blocks and ventricular isolation, are now visible with the use of computed tomography.

Vermian agenesis and unsegmented midbrain tectum. Case report

A male infant had spells of tachypnea leading to apnea. He had vermian agenesis and and unsegmented midbrain tectum. This identifies the time of teratogenesis at about embryonic stage XVII to XVII (40 days gestation).

Transitional forms of Arnold-Chiari and Dandy-Walker malformations

The morphological findings in 12 cases of Arnold-Chiari and 3 cases of Dandy-Walker malformations are described and compared to those in 2 cases of congenital hydrocephalus of unknown origin, 1 case of isolated meningo-myelocele and 2 cases of normal newborn brains. Lesions common to both types of malformation indicate a same time-related embryogenetic defect of the roofplate of the rhombencephalon, that does not allow the inferior vermis and the choroid plexus to turn inward into the fourth ventricle.