Diencephalic cysts

Characterization of an Inherited Neurologic Syndrome in Toyger Cats with Forebrain Commissural Malformations, Ventriculomegaly and Interhemispheric Cysts

BACKGROUND

In children, frequent congenital malformations with concomitant agenesis of the corpus callosum are diagnosed by neuroimaging in association with other cerebral malformations, including interhemispheric cysts and ventriculomegaly. Similar studies providing full characterization of brain defects by in vivo magnetic resonance imaging (MRI), and correlations with the pertinent anatomic pathologic examinations are absent in veterinary medicine.

HYPOTHESIS/OBJECTIVES

Congenital brain defects underlie the neurologic signs observed in Toyger cats selectively bred for a short ear phenotype.

ANIMALS

Using proper pedigree analysis and genetic evaluations, 20 related Oriental-derived crossbred Toyger cats were evaluated. Seven clinically healthy (carrier) cats and 13 clinically affected cats that had neurologic signs, short ear phenotype and concomitant complex brain anomalies were studied.

METHODS

Complete physical and neurologic examinations and MRI were performed in all clinically healthy and affected cats. Postmortem and histopathologic examinations were performed in 8 affected cats and 5 healthy cats.

RESULTS

Neurologic and MRI investigations confirmed 13 clinically affected cats with structural brain abnormalities. Ventriculomegaly with frequent concomitant supratentorial interhemispheric, communicating ventricular type-1b cysts and multiple midline and callosal malformations were detected in all cats displaying neurologic signs. Genetic analysis confirmed autosomal recessive mode of inheritance with no chromosomal abnormalities.

CONCLUSIONS AND CLINICAL IMPORTANCE

Neuroanatomic dissections and histopathology were helpful for evaluation of abnormalities in midline brain structures, and for the full characterization of cysts. However, MRI was more sensitive for detection of small cysts. In this feline model, MRI diagnosis had extremely good correlation with pathologic abnormalities noted in the subset of animals that were examined by both modalities.

Dorsal third ventricular cysts revisited

INTRODUCTION

We have previously argued that the clinical entity of dorsal third ventricular cyst in association with agenesis of the corpus callosum is a developmentally, radiologically, and clinically distinct and separate entity from the dorsal cyst of alobar holoprosencephaly.

PATIENTS AND METHODS

Herein, we describe seven patients who underwent treatment of their dorsal third ventricular cyst with fluid diversion and shunting and report their long-term follow-up. The authors reviewed the literature and discrepancies identified in differentiating dorsal third ventricular cysts and holoprosencephaly.

RESULTS

Postoperative scans showed evidence of cyst decompression and stabilization of head circumference. Two patients required shunt revision surgery for delayed malfunction while the remainder has had no revision surgery since initial placement.

CONCLUSIONS

Given the good clinical outcome in comparison to alobar holoprosencephaly patients, we recommend fluid diversion in this population of patients.

Supratentorial interhemispheric cysts associated with callosal agenesis: surgical treatment and outcome in 16 children

Cerebrospinal-fluid-filled interhemispheric cysts associated with callosal agenesis are relatively rare lesions, and have been subject to a varied and confusing terminology. From a pragmatic surgical point of view, we believe that the dorsal III ventricular cyst [35] and the giant interhemispheric cyst [23], although of different embryological origin, can be classified as one group. The most important condition that must be distinguished from interhemispheric cysts is the alobar form of holoprosencephaly. We describe the clinical symptomatology in 16 children who were surgically treated with a cysto-peritoneal shunt. The outcome, both neurologically and developmentally, was good in the large majority of cases, and compared favorably to similar cases in the older literature. It therefore seems reasonable, at the present state of knowledge and until further studies clarify the origin and natural history of these cysts, to treat them as early as possible in order to prevent gross developmental deficits.

Single forebrain ventricle without prosencephaly: agenesis of the corpus callosum with dehiscent fornices

Coalescence of the cerebral ventricles with formation of a single forebrain ventricle is described in an unusual case of agenesis of the corpus callosum with dehiscent fornices and severe hydrocephalus. The cerebral hemispheres were fully cleaved. The detached fornices were widely separated from the thalami. The membrana tectoria was retroverted over the midbrain and cerebellum, where it joined the fornices and merged with a curved membranous ependymal dome which, at a great distance, circumvented the thalami as it extended toward the anterior commissure. Other anomalies included arhinencephaly, multiple subependymal heterotopias, and Dandy-Walker malformation. Similar malformations have been described as interhemispheric cysts, as (holo)prosencephaly, or as "midline telencephalic dysgenesis." The basic features of prosencephaly and agenesis of the corpus callosum are reviewed and compared to the present case.

Dorsal third ventricular cyst: an entity distinct from holoprosencephaly

The treatment and subsequent developmental progress of six children with dorsal third ventricular cysts are described. This cystic malformation has a radiological appearance which is superficially similar to that of the dorsal cyst of alobar holoprosencephaly, especially when the third ventricular cyst is large. Indeed, previous reports have identified this abnormality as a form of holoprosencephaly. However, careful study reveals that the dorsal third ventricular cyst is a distinct entity both developmentally and clinically. The six patients in this series were effectively treated with shunts, and their subsequent developmental progress was assessed by means of the Prescreening Developmental Questionnaire-Revised as well as the Bayley Scales of Infant Development. The nomenclature and differences between this entity and the holoprosencephalies are reviewed. The authors conclude that dorsal third ventricular cysts have a developmental and clinical course more similar to that of arachnoid cysts than to that of the holoprosencephalies.

Giant interhemispheric cysts associated with agenesis of the corpus callosum

Interhemispheric cysts, often associated with agenesis of the corpus callosum, are rare lesions demonstrating little uniformity of pathogenesis. Four large interhemispheric cystic lesions with several unique features are reviewed. Magnetic resonance imaging clearly showed agenesis of the corpus callosum and was useful in the diagnosis of interhemispheric cysts. The differential diagnosis of these lesions is discussed, along with therapeutic considerations.

Primary intracranial arachnoidal cysts. A study of 67 childhood cases

Sixty-seven cases (41 males and 26 females) of arachnoidal cysts in children under 11 years are reported. About 53% of cases were diagnosed before 1 year of life. Thirty-one (42.2%) were supratentorial (interhemispheric 9, temporal fossa 10, convexity 5, sylvian fissure 3, supra- and/or retrosellar 4); 31 (46.2%) infratentorial (supra- and/or retrocerebellar 22, foramen of Magendie 3, quadrigeminal cistern 5, pontocerebellar 1); 5 (7.5%) supra- and infratentorial. Macrocephaly was the presenting symptom in 48 cases (71.5%). Associated features were frequent: cranial asymmetry in 24; aqueductal stenosis in 10; agenesis of corpus callosum in 8; deficient cerebellar lobullation in 4; Chiari I malformation in 2; neurofibromatosis type 1 with dysgenetic zones of the brain in 1; arteriovenous malformation in 1. Diagnosis was made at autopsy in six cases in the days before computed tomography and magnetic resonance: three patients had a cyst in the supra- and retrocerebellar midline; two had a cyst in the quadrigeminal cistern and the sixth was a rare case with the cyst passing from the posterior fossa to the left lateral ventricle through a hole in the basal surface of the brain. Small and some middle-sized cysts were not treated. Big and some middle-sized cysts were usually treated by cysto- and/or ventriculoperitoneal shunts. Arachnoidal cysts of the quadrigeminal cistern usually present with aqueductal stenosis and have to be treated with ventriculoperitoneal shunt. Craniotomy and fenestration of the cysts were performed in some cases with good results. The average mental level of these children is usually moderately low.

Parietal cephalocele: clinical importance of its atretic form and associated malformations

In this study of atretic cephaloceles, the authors have considered the pedunculated or sessile type of cephalocele and also small nonpedunculated scalp defects developing in the vertex midline. Parietal cephaloceles were found in 15 infants (10 boys and five girls), and accounted for 37.5% of all cephaloceles. They consisted of four encephaloceles, six meningoceles, and five atretic cephaloceles. The clinical and morphological characteristics of parietal cephaloceles were investigated and compared with those arising at other locations. Parietal cephaloceles carried a much less favorable prognosis than those in the occipital region, regardless of the type of cephalocele; they were associated with cerebral malformations more frequently and were more severe than occipital cephaloceles. Grave congenital anomalies were found in 87% of patients with parietal cephalocele, and only two patients (neither of whom had any other malformation) attained normal development. Brain malformations were closely related to the site from which the cephalocele issued, and dorsal cyst malformation was found in eight patients with parietal cephalocele. Two types of atretic cephaloceles were found, each in a different location. The first type was an alopecic lesion occurring in the parietal midline; all five patients with this type had dorsal cyst malformations and none developed normally. The second type was a nodular lesion developing at the occipital midline, not associated with cerebral anomalies; all five patients with this type showed normal development. The pathogenesis of atretic cephaloceles and their associated intracranial malformations are discussed.

Benign intraparenchymal brain cysts without an epithelial lining

Three patients are presented who had benign intraparenchymal cysts of the brain. The wall of each cyst was biopsied and had no epithelial lining or other microscopic feature to indicate the etiology of the cyst. The authors review published information about benign brain cysts and speculate about the origin of those having a wall composed solely of neuroglial tissue.

A suprasellar subarachnoid pouch; aetiological considerations

A child with hydrocephalus treated by a valved shunt was reinvestigated after developing a shunt infection. A pouch was discovered invaginating the floor of the third ventricle and filling slowly with CSF from the region of the interpeduncular cistern. Histology and mechanisms of this pouch formation are discussed.

Dysgenesis of the corpus callosum

The embryology of the corpus callosum is briefly reviewed in relation to dysgenesis and associated malformations. The morphology, etiology, clinical and radiological features of such malformations are discussed and illustrated.

Destructive lesions of the brain

The congenital destructive lesions of the brain include focal lesions (porencephaly) and diffuse lesions (micrencephaly, hydranencephaly). According to the time the injury occurred and following the assumption of Yakovlev and Wadworth (1946), they are classified as agenetic porencephalies, either - bilateral (schizencephaly) or unilateral, when the injury occurs early enough in gestation (before 6 months) to disturb the growth of the cerebral mantle: abnormal sulcal pattern and heterotopic gray matter are then observed. They are classified as encephaloclastic when the destruction affects an otherwise normal cerebrum (last trimester). The porencephalies should be differenciated from post natal lesions (multicystic encephalomalacia, focal cavitations). By showing the fluid cavity and the cortical distortion, neuroradiology permits precise diagnosis of the defect itself and the associated cortical disorder, as well as an evaluation when they occurred.

Pathology of an arachnoid cyst. Case report

Accidental death brought to autopsy a 19-year-old girl with asymptomatic arachnoid cyst which had expanded from the region of the interpeduncular cistern so as to replace the third ventricle and extend into both alteral ventricles. Associated with this expansion was a significant degree of hydrocephalus, compression of the walls of the lateral ventricle, and obliteration of the normal structures of the floor of the third ventricle. The histological structure of the cyst wall and its relationship to the normal arachnoid are defined and found to consist of a reduplication of the normal arachnoid membrane resulting in a space within the arachnoid tissue. It is suspected but not proven that the cyst was congenital, resulting from an abnormality in development. Some suggestions are offered regarding the mechanism for its enlargement.

Holoprosencephaly in neurosurgical practice

The clinical, angiographic, and pneumoencephalographic features of seven cases with holoprosencephaly are reported. Three of the alobar type in this series revealed the facial dysmorphia characteristic of the anomaly. In the other four cases (one alobar, one semilobar, and two lobar), such facial anomaly was absent, and the diagnosis was achieved only after contrast studies. An azygous anterior cerebral artery running over the cerebral surface due to a defective interhemispheric fissure is pathognomonic for alobar and semilobar holoprosencephaly. Dysgenesis of the deep venous system was found in alobar, semilobar, and lobar holoprosencephaly, a finding helpful in diagnosis, especially of the lobar type. Air study and computerized tomography scan revealed incomplete separation of the ventricular system. The basic nature of holoprosencephalization and its differentiation from non-holoprosencephalic malformation are discussed. Six of the seven patients reported had hydrocephalus.

Structures and development of the venous system in congenital malformations of the brain

Cerebral venograms of 21 clinical cases of midline anomalies of the brain and of 80 human fetuses between 3 and 8 months old were examined. The diagnostic value of the venogram was fully proven, particularly for the midline cerebral anomalies, where deep cerebral structures and configuration of the tentorium cerebelli were not well visualized by other neuroradiologic maneuvers. Abnormal structures of the deep cerebral veins as well as the dural sinuses in these malformations were proved to retain the venous structures in the early fetal period. The time of formation of these malformations was also inferred from the viewpoint of the venous development. Study of the fetal venous system was found quite useful for embryologic analysis and classification of congenital malformations of the brain.

Dysgenesis of the deep venous system as a diagnostic criterion for holoprosencephaly

The angiographic features of three cases with holoprosencephaly are reported. In all of them, the galenic venous system seemed to be deficient and the basal ganglia were drained by peculiar veins which coursed laterally and drained directly into the lateral sinus. These peculiar veins are considered to be remnants of the embryonic diencephalic veins, suggesting that these patients retain their early embryonic pattern of venous drainage. The diagnosis of alobar holoprosencephaly is established by the demonstration of the azygos anterior cerebral artery coursing along the frontal bone with excessive undulations. But with lobar holoprosencephaly, this characteristic feature is not present, and dysgenesis of the deep venous system is important for the diagnosis of holoprosencephaly.

[Unilateral hydrocephalus due to membranous occlusions of the foramen of Monro (author's transl)]

A case of dilatation of the right lateral ventricle due to membranous occlusion of the foramen of Monro is reported. A child aged two and a half years developed raised intracranial pressure together with disturbed consciousness, but other neurological defect, two months after after an attack of bilateral broncopneumonia. The preoperative diagnosis of occlusion of the right foramen of Monro by infiltrating tumour was made angiographically. At operation the obstruction was found to be due to a membrane. The septum lucidum was fenestrated and a ventriculoatrial shunt was inserted. After a year the shunt was removed. Twenty eight cases of unilateral hydrocephalus due to nontumorous occlusion of the foramen of Monro have been reviewed, and the aetiologies have been discussed. Clinical picture and diagnostic procedures are reviewed. The authors discuss surgical treatment, and lay stress on fenestration of the septum lucidum.