Flattened sheet-like fornix forming a "Cobra Hood" deformity: A previously unreported variant of fornix anatomy and its implication for surgical approaches to the third ventricle.

BACKGROUND: The fornix is the main efferent tract from the hippocampus and is an important component of the memory pathways. Variations in the anatomy of the fornix are not commonly encountered. MATERIALS AND METHODS: The anatomy of the fornix was studied in 30 cadavers of normal adult healthy males who had died in road accidents. The full extent of the hippocampus was prosected up to the tail under the magnoscope. RESULTS: In 10 of the 30 brains, the crura and the body of fornix were bilaterally broad and flat like a sheet, rather than the usual compact bundle, forming a cobra-like hood over the roof of the third ventricle. The maximum width was approximately 16 mm on the right side (mean: 11.7 mm) and 11 mm on the left (mean: 8.5mm). CONCLUSION: Knowledge of this variation will be useful during the transcallosal approach to third ventricle tumors, especially while going subchoroidal, because an unexpected lateral span of the fornix in the surgical corridor can result in inadvertent injury to it, leading to memory defects.

The hippocampal commissure: a new finding at prenatal 3D ultrasound in fetuses with isolated complete agenesis of the corpus callosum.

OBJECTIVE: The aim of this research was to determine the prevalence and sonographic appearance of the hippocampal commissure in fetuses with isolated complete agenesis of the corpus callosum by three-dimensional neurosonography in the multiplanar mode. METHODS: This was a multicenter observational study. Stored volume datasets of fetuses with isolated complete agenesis of the corpus were retrospectively retrieved for analysis in three tertiary centers. The presence or absence of the hippocampal commissure was independently evaluated in the coronal and midsagittal planes by two operators. Postnatal follow-up was obtained in all cases. RESULTS: From November 2007 to February 2013, 41 cases between 19 and 30 weeks of gestation were retrieved for analysis. The hippocampal commissure was visible in the coronal and sagittal planes in 27/41 (65.8%), absent or not clearly recognizable in the remaining 14 cases. The qualitative analysis of the two operators was concordant in 100% of cases. CONCLUSIONS: In more than half of fetuses with complete callosal agenesis, the hippocampal commissure may be visualized at prenatal ultrasound. This is a residual interhemispheric connection, which in normal cases is hidden by the corpus callosum itself. Further research is needed to establish if this has an impact on postnatal outcome.

Developmental anomalies of the medial septal area: possible implication for limbic epileptogenesis.

INTRODUCTION: The maldevelopment of the midline structures is connected with neurologic disorders. The cavum septum pellucidum (CSP) exists in the fetal period, then it is re-absorbed. The presence of unfused leaflets/fornices may be considered important in the genesis of neurodevelopmental abnormalities inclunding epilepsy. The limbic system includes a group of interconnected gray and white matter structures; in this circuit, the fornix is an important white matter connection with the septum pellucidum. METHODS: Five children, 3-10 years of age, with epilepsy and an unfused septum pellucidum and fornices on MRI, were evaluated by diffusion tensor imaging-fiber tracking (DTI-FT) in order to explore the integrity of the axonal microenviroment of these structures. RESULTS: The patients had generalized tonic-clonic seizures (GTCS). The electroencephalogram (EEG) showed focal-temporal abnormalities with secondary generalization. Magnetic resonance imaging (MRI) and DTI-FT demonstrated the CSP, and the presence of the fornix's body split into two bundles with the fornices separated. CONCLUSION: The fornix appears more involved than CSP alone, as suggested by fornix atrophy observed in MTLE. Even if epilepsy is suggested to be a grey matter disorder, changes in the underlying brain connectivity have an important contribution in seizure generation and diffusion. In addition, the interconnections of medial septal area with hyppocampus, amygdala and entorhinal cortex, have led to the hypothesis of functional limbic epilepsy. In our patients, the role of DTI was not conclusive since the definition of the number of unmyelinated fibers responsible for epilepsy could not be demonstrated probably for a limited number of seizures and for a short period of drug administration.

Absence of the septum pellucidum associated with a midline fornical nodule and ventriculomegaly: a report of two cases.

We report two autopsy cases that revealed the partial absence of the septum pellucidum with ventriculomegaly. In each case, the brain showed mild dilatation of both frontal horns of the lateral ventricles, normal third and fourth ventricles and no aqueductal stenosis. The posterior portion of the septum pellucidum was absent and the fornices were fused in a single midline nodule, abnormally displaced to a caudal position and lodged in the foramina of Monro. The brain base showed no apparent abnormalities; the optic nerves were well developed. We conclude that the caudally displaced fornix in the absence of the septum pellucidum may have intermittently obstructed the foramina of Monro and induced mild ventriculomegaly.

Effects of failed commissuration on the septum pellucidum and fornix: implications for fetal imaging.

In the previous article, we considered the normal appearances of the midline stuctures of the brain as they appear on high-resolution magnetic resonance imaging. In this article, we discuss the effects of failed commissuration on the midline structures. We highlight some of the misconceptions of this process that may lead to misdiagnosis of agenesis of the corpus callosum in utero.

Imaging the corpus callosum, septum pellucidum and fornix in children: normal anatomy and variations of normality.

The midline structures of the supra-tentorial brain are important landmarks for judging if the brain has formed correctly. In this article, we consider the normal appearances of the corpus callosum, septum pellucidum and fornix as shown on MR imaging in normal and near-normal states.

Three-dimensional high-resolution diffusion tensor imaging and tractography of the developing rabbit brain.

Diffusion tensor imaging (DTI) is sensitive to structural ordering in brain tissue particularly in the white matter tracts. Diffusion anisotropy changes with disease and also with neural development. We used high-resolution DTI of fixed rabbit brains to study developmental changes in regional diffusion anisotropy and white matter fiber tract development. Imaging was performed on a 4.7-tesla Bruker Biospec Avance scanner using custom-built solenoid coils and DTI was performed at various postnatal ages. Trace apparent diffusion coefficient, fractional diffusion anisotropy maps and fiber tracts were generated and compared across the ages. The brain was highly anisotropic at birth and white matter anisotropy increased with age. Regional DTI tractography of the internal capsule showed refinement in regional tract architecture with maturation. Interestingly, brains with congenital deficiencies of the callosal commissure showed selectively strikingly different fiber architecture compared to age-matched brains. There was also some evidence of subcortical to cortical fiber connectivity. DTI tractography of the anterior and posterior limbs of the internal capsule showed reproducibly coherent fiber tracts corresponding to known corticospinal and corticobulbar tract anatomy. There was some minor interanimal tract variability, but there was remarkable similarity between the tracts in all animals. Therefore, ex vivo DTI tractography is a potentially powerful tool for neuroscience investigations and may also reveal effects (such as fiber tract pruning during development) which may be important targets for in vivo human studies.

The volumes of the fornix in schizophrenia and affective disorders: a post-mortem study.

Structural and functional pathology of limbic structures including the hippocampus are frequently replicated in schizophrenia. Although the fornix is the main afferent system of the hippocampus to the septal nuclei and the hypothalamus (especially the mammillary bodies), relatively few studies have investigated structural changes of the fornix in schizophrenia. We measured the volume of the fornix in post-mortem brains in 19 patients with schizophrenia, 9 patients with bipolar disorder, 7 patients with unipolar depression, and 14 control subjects by planimetry of serial sections. The volumes, the mean cross-sectional areas, and the anterior to posterior distances of the fornix did not differ among patients with schizophrenia, bipolar disorder, unipolar depression, and control subjects. No lateralization existed between the right and the left fornices in among patients in the diagnostic groups and the control subjects. The fornix does not show morphometrical abnormalities in patients with schizophrenia, bipolar disorder and unipolar depression compared with control subjects, which might indicate that the fornix is not a primary focus of structural changes in these diseases.

Variability of Forebrain Commissures in Callosal Agenesis: A Prenatal MR Imaging Study.

BACKGROUND AND PURPOSE: Agenesis of the corpus callosum, even when isolated, may be characterized by anatomic variability. The aim of this study was to describe the types of other forebrain commissures in a large cohort of randomly enrolled fetuses with apparently isolated agenesis of the corpus callosum at prenatal MR imaging. MATERIALS AND METHODS: All fetuses with apparent isolated agenesis of the corpus callosum undergoing prenatal MR imaging from 2004 to 2014, were evaluated for the presence of the anterior or a vestigial hippocampal commissure assessed in consensus by 2 pediatric neuroradiologists. RESULTS: Overall, 62 cases of agenesis of the corpus callosum were retrieved from our data base. In 3/62 fetuses (4.8%), no forebrain commissure was visible at prenatal MR imaging, 23/62 fetuses (37.1%) presented with only the anterior commissure, and 20/62 fetuses (32.3%) showed both the anterior commissure and a residual vestigial hippocampal commissure, whereas in the remaining 16/62 fetuses (25.8%), a hybrid structure merging a residual vestigial hippocampal commissure and a rudiment of the corpus callosum body was detectable. Postnatal MR imaging, when available, confirmed prenatal forebrain commissure findings. CONCLUSIONS: Most fetuses with apparent isolated agenesis of the corpus callosum showed at least 1 forebrain commissure at prenatal MR imaging, and approximately half of fetuses also had a second commissure: a vestigial hippocampal commissure or a hybrid made of a hippocampal commissure and a rudimentary corpus callosum body. Whether such variability is the result of different genotypes and whether it may have any impact on the long-term neurodevelopmental outcome remains to be assessed.

Columns of the fornix, not to be mistaken for the cavum septi pellucidi on prenatal sonography.

OBJECTIVE: Visualization of the cavum septi pellucidi (CSP) is considered an integral part of the prenatal second-and third-trimester sonographic evaluations of the fetal neural axis. We have noted that another anatomic structure, the columns of the fornix, can be mistaken for the CSP and result in the missed diagnosis of agenesis of the corpus callosum. METHODS: We describe a case in which the columns of the fornix were misinterpreted as representing the CSP during a sonographic evaluation at 18 weeks' gestation. After a follow-up sonogram at 35 weeks, agenesis of the corpus callosum was detected. A retrospective evaluation of the prevalence of forniceal columns was then performed in 100 consecutive sonograms of pregnancies between 18 and 24 weeks' gestation. A prospective study was then performed in 20 patients to determine the prevalence of visualization of the columns of the fornix. RESULTS: In 86 of 100 patients, the columns of the fornix were retrospectively identified as discrete and separate structures from the CSP. When additional views were obtained prospectively in the forebrain, the fornix could be identified in all 20 patients. CONCLUSIONS: The columns of the fornix may simulate the appearance of the CSP on second- and third-trimester sonograms. The distinction between these structures can be made because the columns of the fornix will show a linear reflection (3 lines) at their interface, whereas the CSP will appear as a fluid-filled triangular or rectangular fluid-filled space without a central line.

Limbic tract anomalies in pediatric myelomeningocele and Chiari II malformation: anatomic correlations with memory and learning--initial investigation.

PURPOSE: To prospectively determine anomalies of limbic tracts and to describe the relationship between these anomalies, seen on diffusion-tensor magnetic resonance (MR) and fiber tract (FT) reconstruction images, and learning and memory in children with myelomeningocele (MM) and Chiari II malformation. MATERIALS AND METHODS: The investigation was HIPAA compliant and approved by institutional review boards; informed consent was obtained. In seven male and six female patients (aged 6 months to 16 years) with MM and Chiari II malformation, diffusion-tensor imaging and FT reconstruction were performed. FT reconstruction was generated with fractional anisotropy continuous tracking algorithm and manually drawn regions of interest. Limbic tract abnormalities were assessed on FT reconstruction images by an experienced pediatric neuroradiologist blinded to results of cognitive testing. Nine patients met criteria for memory and learning testing by a trained cognitive neuroscientist blinded to MR results. Exact Wilcoxon rank sum test was used to compare performance with learning and memory tasks in two groups. RESULTS: Eleven of 13 patients had defects within fornices and/or cingulum; three patients had aberrant fibers of cingulum. In nine patients, six had deficits in general memory; four, in learning; and four, in both. Atresia or hypoplasia of crura and body of fornices was noted in six patients with memory deficits and four patients with learning deficits. Five of six patients with memory deficits and three of four with learning deficits had hypoplasia or atresia of cingulum. Exact Wilcoxon rank sum test demonstrated significantly poorer performance for nonverbal immediate recall tasks in patients with anomalies of the fornix compared with those without (P = .04, exact two-tailed test). CONCLUSION: Diffusion-tensor and FT reconstruction images revealed that limbic fiber abnormalities were common in patients with MM and Chiari II malformation. Nonverbal immediate recall task performance appeared to be related to abnormalities of the fornix.

Endoscopic third ventriculostomy through the interfornicial space.

Endoscopic third ventriculostomy (ETV) is the most common cranial endoscopic surgery being done worldwide for a variety of conditions resulting in hydrocephalus. We report ETV in a case of congenital hydrocephalus with deficient third ventricular roof and wide interfornicial space. A 6-month-old male child presented with gradual progressive head enlargement and signs of raised intracranial pressure. Computed tomography of the head showed aqueductal stenosis with enlargement of third and lateral ventricles. The patient was operated under general anesthesia with endotracheal intubation. A right coronal burr hole and free-hand entry were made into the right lateral ventricle. The anterior part of the septum and the third ventricular roof were deficient with a narrow Monro's foramen and the third ventricular floor was visible through the space between both fornices. ETV was done in standard fashion. Postoperatively the patient showed uneventful recovery clinicoradiologically. We review the literature and discuss the findings and technique of ETV in this rare entity.

A case of ring chromosome 22 with deletion of the 22q13.3 region associated with agenesis of the corpus callosum, fornix and septum pellucidum.

We report a 16-week-gestation foetus obtained by voluntary abortion after prenatal diagnosis, in which a ring chromosome 22 was observed with deletion of the 22q13.3 region. A prenatal study of the amniotic fluid by standard chromosome technique with G bands and FISH (fluorescence in situ hybridisation) was performed. After the abortion, the anatomopathological study of the obtained foetus was carried out. Morphological and histological analysis of the foetus did not reveal severe physical abnormalities, although alterations of the nervous system were observed consisting of corpus callosum, fornix and septum pellucidum agenesia. It could be that the genes in this region that were involved in the development of the central nervous system were responsible for the alterations found in the morphological study. The wide range of manifestations observed in patients with this cytogenetic alteration is probably due to size differences in the deleted region.

Malformations of the midline commissures: MRI findings in different forms of callosal dysgenesis.

Malformations of the corpus callosum (CC) may occur in many different syndromes. Various forms have been observed. We report seven cases of malformation of the CC. Special attention is directed towards the development of the fornix and hippocampus as a hippocampal commissure is a prerequisite of normal hippocampal development. The clinical disability of the patients presented here differed significantly, which may in part be due to the different extent of this cerebral malformation. The relevance of the concomitant aplasia of the limbic system has not been addressed in detail previously in the literature.

Diagnostic imaging and clinical findings in rhombencephalosynapsis: case report and literature review.

Rhombencephalosynapsis is a rare condition in which most cases are found in newborns and infants. Morphological findings are predominantly characterized by fusion of the cerebellar hemispheres and absence of the vermis with often associated supratentorial anomalies. We review the literature with emphasis on diagnostic imaging of this condition and present a case of a 2-year-old girl.