Blake's pouch cyst: an entity within the Dandy-Walker continuum

Abnormal cerebrospinal fluid (CSF) collections within the posterior fossa are defined by the Dandy-Walker complex (DWC) and by arachnoid cysts (AC). The DWC includes the Dandy-Walker malformation (DWM), the Dandy-Walker variant (DWV) and the mega-cisterna magna (MCM). In addition, Tortori-Donati et al. added persistent Blake's pouch cyst (BPC) as an independent entity within the DWC. BPC represents a posterior ballooning of the superior medullary velum into the cisterna magna. All of these malformations are overlapping developmental anomalies characterized by varying degrees of malformation of the medullary vela, the cerebellar vermis and hemispheres, the fourth ventricle choroid plexus, the posterior fossa subarachnoid cisterns and the enveloping meningeal structures. We present two cases of persistent BPC detected in two adult women without history of gestational or subsequent growth problems. They underwent neuroradiological investigation because of headache and because of recurrent episodes of loss of consciousness, respectively. The MRI findings included tetraventricular hydrocephalus, wide communication of the fourth ventricle and the cystic posterior fossa (i. e. BPC), inferior posterior fossa mass effect with or without hypoplasia of both the cerebellar vermis and the medial aspects of the cerebellar hemispheres, and absence of communication between fourth ventricle and the basal subarachnoid space in the midline posteriorly. Persistent BPC is defined by a failure of embryonic assimilation of the area membranacea anterior within the tela choroidea associated with imperforation of the foramen of Magendie. Typically this condition becomes symptomatic early in life. In the current cases the normal function of the laterally positioned foramina of Luschka probably helped to maintain some CSF flow between intraventricular and subarachnoid spaces, with the establishment of a precarious equilibrium characterized by a compensatory enlargement of the cerebral ventricular system (i. e. hydrocephalus). Received: 2 July 1999 Accepted: 13 July 1999     

The "keyhole": a sign of herniation of a trapped fourth ventricle and other posterior fossa cysts

When a cystic structure in the posterior fossa increases in size, the accompanying increase in pressure may cause it to herniate upward through the tentorial hiatus. In our experience this happens most commonly with a dilated trapped fourth ventricle secondary to infection or intraventricular hemorrhage. However, herniation of an arachnoid cyst or a Dandy-Walker malformation through the tentorium may also occur. When herniation occurs, the cystic structure assumes a "keyhole" configuration, indicating that it is trapped and that surgical intervention is necessary. Five cases are presented that illustrate this point, including two patients with dilatation of the fourth ventricle secondary to hemorrhage, two patients with Dandy-Walker malformation, and one patient with an arachnoid cyst.     

后颅窝囊肿的CT－MR影像学

目的：本文目的是对后颅窝囊肿的ＣＴ－ＭＲ影像学的诊断作用进行评价。材料与方法：１２例后颅窝囊肿的ＣＴ和ＭＲ影像表现进行了分析，探讨了其与临床表现和类型的相关性。结果：本组病例包含Ｄａｎｄｙ－Ｗａｌｋｅｒ囊肿（５例）、蛛网膜囊肿（３例）和巨枕大池（４例），ＣＴ和ＭＲ都可提供无创性检测手段。结论：ＣＴ和ＭＲ二者对后颅窝囊肿的诊断均有效，但在显示病变的性状、大小和轮廓方面，ＭＲ比ＣＴ稍胜一筹     

CSF flow studies of intracranial cysts and cyst-like lesions achieved using reversed fast imaging with steady-state precession MR sequences

BACKGROUND AND PURPOSE: Differentiating between intracranial cysts or cyst-like structures and communicating or noncommunicating cysts is often not possible with cranial CT or nonfunctional MR imaging. We evaluated a retrospective ECG-gated fast imaging with steady-state precession (PSIF) MR sequence with optional cine mode to differentiate cystic masses from enlarged CSF spaces and to determine the accuracy of detecting communication between cysts and neighboring CSF spaces. METHODS: Fourteen patients with intracranial cystic masses underwent CSF flow studies with an ungated and a retrospective ECG-gated cine-mode PSIF sequence in addition to spin-echo imaging. Findings were evaluated retrospectively by using a five-point rating scale and without knowledge of clinical or other imaging findings. Results were compared with intraoperative findings or with results of intrathecal contrast studies. RESULTS: Eighteen arachnoid cysts and one enlarged cisterna magna were diagnosed. Improved differentiation between cysts and enlarged CSF spaces was obtained with cine-mode PSIF imaging in six lesions (six patients). Increased diagnostic certainty as to communication between cysts and CSF spaces was obtained in 18 cysts (13 patients). Diagnoses were verified by membranectomy in five lesions, by CT cisternography in five lesions, and indirectly by shunting in one cystic lesion. In one case, MR diagnosis was not confirmed by CT cisternography. CONCLUSION: Cine-mode MR imaging with a retrospective ECG-gated flow-sensitive PSIF sequence contributed to the certainty of communication between arachnoid cysts and neighboring CSF spaces with an accuracy of 90%, using surgical findings or intrathecal contrast studies as reference. Differentiation between intracranial cysts and enlargement of CSF spaces and other cystic masses was improved in 25% of cases.     

Revised classification of posterior fossa cysts and cystlike malformations based on the results of multiplanar MR imaging

MR and clinical data on 31 patients with posterior fossa CSF collections were analyzed. A clear separation of these patients into classical categories was not possible because of new information obtained from the MR images. We present a new classification of these disorders. The Dandy-Walker malformation, Dandy-Walker variant, and mega-cisterna magna seem to represent a continuum of developmental anomalies of the posterior fossa. A possible embryologic basis for this continuum is suggested. Discrete posterior fossa CSF collections that are clearly separate from the fourth ventricle and vallecula are classified as posterior fossa cysts. Posterior fossa CSF collections that communicate with the fourth ventricle and are associated with cerebellar atrophy are classified as prominent cisterna magna. Both the Dandy-Walker complex and posterior fossa cysts can cause enlargement of the posterior fossa and scalloping of the inner table of the occipital bone. The Dandy-Walker complex presents with seizures, developmental delay, and enlarging head size; it requires CSF diversion when associated with hydrocephalus. Posterior fossa cysts present with symptoms of a posterior fossa mass; they generally require surgical resection. Prominent cisterna magna is a result of degenerative disorders and requires no surgical therapy. This new classification facilitates both diagnosis and therapy of these disorders. MR revealed that disorders previously referred to as the Dandy-Walker malformation, the Dandy-Walker variant, and the mega-cisterna magna actually are not separate entities, but appear to represent steps on a continuum of developmental anomalies of the posterior fossa. Because of this, we suggest a new term, the Dandy-Walker complex, be used to describe this continuum.     

MRI tight posterior fossa sign for prenatal diagnosis of Chiari type II malformation

Introduction Chiari type II malformation (CMII) is one of three hindbrain malformations that display hydrocephalus. We have observed that cerebrospinal fluid (CSF) signal in the posterior fossa, which is always apparent on normal fetal MR images, is not visible in a fetus with CMII. We use the term ‘tight posterior fossa’ for this MR imaging finding, and evaluate the diagnostic value of this finding on fetal MR images. Methods Included in the study were 21 fetuses which underwent brain MR imaging at 1.5 T using two-dimensional balanced turbo-field-echo (2-D balanced-TFE) in the axial and sagittal planes. Postnatal diagnoses were CMII (n=5), CNS abnormalities other than CMII (n=8), and no abnormality (n=8). A tight posterior fossa was defined as an absent or slit-like water signal space around the hindbrain in the posterior fossa on both sagittal and axial MR images. Results All CMII fetuses displayed a tight posterior fossa on MR images. Hydrocephalus was visualized in all CMII fetuses and myelomeningocele in four fetuses, but hindbrain herniation was visualized only in two of five fetuses. The CSF signal surrounding the hindbrain was clearly visible in all the other 16 fetuses, including five with hydrocephalus not associated with CMII, although it was slightly narrower in a fetus with a cloverleaf skull than in the normal fetuses. Conclusion Tight posterior fossa in the presence of hydrocephalus is a useful and characteristic finding of CMII on fetal MRI. Part of this paper was presented at the 35th Annual Meeting of the Japanese Society of Neuroradiology and at the 65th Annual Meeting of the Radiological Society of Japan.     

Functional analysis of third ventriculostomy patency by quantification of CSF stroke volume by using cine phase-contrast MR imaging

OBJECTIVE: Endoscopic third ventriculostomy (ETV) is increasingly used as alternative treatment for obstructive hydrocephalus. The aim of this study was to determine the utility of quantitative and qualitative examinations with cine phase-contrast MR imaging to determine the efficacy of ventriculostomy across time and whether CSF pulsation is restored after ETV. METHODS: Thirty-eight patients treated with ETV were evaluated with cine phase-contrast MR within 1 month after surgery. Follow-up studies were performed after 1 year in 25 patients and after 2 years in 12. We evaluated flow void changes in the floor of the third ventricle and quantified the stroke volume at the site of the ventriculostomy. We also recorded changes in ventricular size and clinical outcome. To determine the restoration of CSF pulsation, we compared the CSF waveform at the ventriculostomy with the CSF waveform at the aqueduct in a healthy control group. RESULTS: After ventriculostomy, restoration of pulsate motion characteristics of CSF circulation was observed. The stroke volume registered at ventriculostomy was maintained with time. There was a statistically significant relationship between clinical outcome and stroke volume. Overall flow magnitude was the most effective variable to determine which patients would improve after surgery. Values >75 mm3 showed a sensitivity of 76.7% and a specificity of 87.5% There was no relationship between ventricular size changes and clinical outcome. Patients with primary aqueduct stenosis had the best response to surgery, whereas patients with Arnold Chiari malformation or communicating hydrocephalus had the worst response. CONCLUSION: Quantitative analysis with phase-contrast MR imaging indicates that ETV is an efficient technique for restoring CSF pulsation, with efficacy being maintained during the follow-up controls. Quantification of stroke volume at ventriculostomy is a good indicator of the functional status of ETV, and a high stroke volume in the ventriculostomy appears to be a positive predictor of favorable clinical outcome.     

先天性四脑室中、侧孔闭锁(Dandy—Walker Syndrome)的CT诊断

本文报告20例先天性四脑室中侧孔闭锁的CT诊断,男性13例,女性7例,年龄45d～8岁.CT表现:第四脑室囊状扩大9例;第四脑室囊状扩大通过小脑溪与后颅窝小囊腔相通4例,或大囊腔相连3例;第四脑室与两侧小脑半球大小不等的两囊腔相连1例;扩大的第四脑室向天幕上延伸7例;枕大池、脑沟、脑裂消失20例;第三脑室及两侧侧脑室对称性重度积水扩大20例.合并右额顶区硬膜下积液1例.本病需与后颅窝蛛网膜囊肿、囊性新生物和变异的巨大枕大池以及重度小脑发育不全鉴别.     

evaluation of communication between intracranial arachnoid cysts and cisterns with phase-contrast cine MR imaging

BACKGROUND AND PURPOSE: The demonstration of communication between arachnoid cysts (ACs) and the adjacent subarachnoid space is a prerequisite for their proper management. CT cisternography (CTC) is the conventional method for functional evaluation of ACs. The sensitivity of MR imaging to CSF flow has been demonstrated, but reports of the clinical usefulness of MR CSF flow techniques in this application are limited. The purpose of our study was to prospectively evaluate the accuracy of MR CSF flow study as an alternative to CTC in this setting. METHODS: MR CSF flow study with retrospective ECG-gated 2D, fast low-angle shot, phase-contrast (PC), cine gradient-echo sequence was performed in 39 patients with an intracranial AC. Results were compared with intraoperative and CTC findings. RESULTS: PC cine MR imaging results were compatible with operative or CTC findings in 36 (92.3%) of 39 patients. Twenty-four cysts were noncommunicating, and 15 were communicating. Three cysts were evaluated as being noncommunicating on PC cine MR imaging (false-negative) but demonstrated contrast enhancement on CTC. No false-positive diagnoses occurred. All cysts regarded as being communicating on PC cine MR imaging were also found to be communicating on both confirmation methods. CONCLUSION: MR CSF flow imaging with a PC cine sequence can be incorporated in the imaging work-up of ACs. This is a reliable alternative to invasive CTC for the functional evaluation of ACs.     

应用3.0TMR电影相位对比成像定量研究颈椎管内脑脊液腹侧和后外侧运动的区别

目的应用磁共振电影相位对比方法定量研究活体颈椎管内蛛网膜下腔脑脊液腹侧和后外侧运动的区别。资料与方法无任何颅内及椎管内病变的健康志愿者80例,应用GEsigna EXCITE3.0T HD磁共振扫描仪分别于颈2～7椎间盘水平行磁共振电影相位对比法扫描,获得每一个椎间盘水平一个心动周期内不同时相的脑脊液流速与流向,分别测量腹侧、右后侧及左后侧峰值流速、峰值流量。结果颈椎管内每一个水平腹侧峰值流速、峰值流量明显大于右后侧、左后侧峰值流速、峰值流量(P<0.05)。颈椎管内不同椎间盘水平的腹侧、右后侧及左后侧峰值流速、峰值流量没有显著性差异。结论应用磁共振相位对比法测量颈椎管内蛛网膜下腔脑脊液流速发现椎管内腹侧峰值流速、峰值流量明显大于右后侧、左后侧峰值流速、峰值流量。椎管内腹侧脑脊液循环动力明显大于两后外侧脑脊液循环动力。     

MR ventriculography for the study of CSF flow

BACKGROUND AND PURPOSE: Various MR techniques have been used to assess CSF flow and to image the subarachnoid spaces and ventricles. Anecdotal reports describe the use of intrathecal and intraventricular gadolinium-based contrast agents in humans and animals. We sought to determine the clinical usefulness of gadolinium-enhanced MR ventriculography for assessing CSF flow in patients with various neurologic conditions. METHODS: Five patients (three female and two male patients aged 6 months to 65 years) were included in the study. After performing sagittal, coronal, and axial T1-weighted MR imaging of the brain, 0.02-0.04 mmol of gadodiamide was injected into the lateral ventricle. Sagittal, coronal, and axial T1-weighted imaging was repeated soon after the injection. We were specifically looking for the site of obstruction to CSF flow in those patients with hydrocephalus, communication between cysts and ventricles, elucidation of suspicious intraventricular lesions, and patency of third ventriculostomies. RESULTS: MR ventriculography showed good delineation of the ventricular system in all patients. In one patient with carcinomatosis and hydrocephalus, a block to contrast material flow was detected at the right foramen of Luschka. In another patient with hydrocephalus, partial block to the flow of contrast material was demonstrated at the right foramen of Monro. In a patient with hydrocephalus and a posterior fossa cyst, flow of contrast material was blocked between the third ventricle and the cyst, with a thin streak of contrast material in the aqueduct. As an assessment of the patency of a third ventriculostomy, MR ventriculography showed flow of contrast material into the suprasellar cisterns from the third ventricle in one patient and absence of flow in another. CONCLUSION: MR ventriculography is a safe technique for assessing CSF flow, with application in determining the site of obstruction in hydrocephalus, in assessing communication between cysts and the ventricle, and in determining the functioning status of endoscopic third ventriculostomies.     

颅内疾病对导水管脑脊液流量的影响

目的：探讨用磁共振相位对比电影(PC cine)对导水管脑脊液定量测量的临床应用价值。方法：将35例中枢神经系统不同疾病分三组，用PC cine方法进行导水管脑脊液流量测量。结果：在脑血管病组伴白质改变时导水管流量增加；梗阻性脑积水导水管流量减少，流动波形异常；交通性脑积水导水管流量增加，波形圆钝。结论：磁共振PC cine方法测量导水管脑脊液流量简单易行，可为临床提供更多的影像信息。     

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. This work was presented as an educational lecture at the 64^th Japan Radiological Society meeting (April 2005) in Yokohama.     

Cerebrospinal fluid flow imaging by using phase-contrast MR technique

Cerebrospinal fluid (CSF) spaces include ventricles and cerebral and spinal subarachnoid spaces. CSF motion is a combined effect of CSF production rate and superimposed cardiac pulsations. Knowledge of CSF dynamics has benefited considerably from the development of phase-contrast (PC) MRI. There are several disorders such as communicating and non-communicating hydrocephalus, Chiari malformation, syringomyelic cyst and arachnoid cyst that can change the CSF dynamics. The aims of this pictorial review are to outline the PC MRI technique, CSF physiology and cerebrospinal space anatomy, to describe a group of congenital and acquired disorders that can alter the CSF dynamics, and to assess the use of PC MRI in the assessment of various central nervous system abnormalities.     

磁共振相位对比电影对蛛网膜囊肿与蛛网膜下腔扩大的鉴别诊断

目的：应用磁共振相位对比法,揭示脑与脑脊液运动的相互关系,以评价此方法对鉴别蛛网膜囊肿与蛛网膜下腔扩大的诊断价值。材料与方法：运用磁共振相位对比电影和流动分析软件,对１０例健康人脑与脑脊液运动规律相关性进行研究和１０例影像学疑蛛网膜囊肿或蛛网膜下腔扩大患者的脑脊液运动进行最化分析,绘出一个心动周期不同时相脑脊液流量贡线和时间、信号强度曲线,并进行分析比较。结果：脑脊液流动是由脑运动驱动引起,而脑运     

Cerebrospinal fluid flow in foramen magnum: temporal and spatial patterns at MR imaging in volunteers and in patients with Chiari I malformation

PURPOSE: To measure spatial and temporal variations in cerebrospinal fluid (CSF) flow through the cardiac cycle and throughout the subarachnoid space at magnetic resonance (MR) imaging in volunteer subjects with no known neurologic or spinal problems and in patients with Chiari I malformation. MATERIALS AND METHODS: A cardiac-gated phase-contrast MR technique was used to acquire images at 14 time points evenly spaced through the cardiac cycle in 10 volunteers and eight patients with Chiari I malformation. Instantaneous CSF velocities were displayed as temporal and spatial plots and examined for homogeneity, differences between flow anterior and flow posterior to the spinal cord, synchronous bidirectional flow, and equivalence of the caudad flow and craniad flow in each voxel. Indexes for flow homogeneity, synchronous bidirectional flow, and preferential flow direction were calculated, and differences between the patient and volunteer groups were tested for significance with a t test of the means. RESULTS: In volunteers, diastolic velocity peaked in two regions in the anterior paramedial subarachnoid space. Patients had greater inhomogeneity of flow than volunteers. They had substantially increased flow (jets) in the anterior paramedial locations. Synchronous bidirectional flow was seen in six of the patients and in none of the volunteers. Cephalad flow in the jets or nodes (P =.05), proportion of cephalad and caudad flow in the anterior compartment (P <.005 for both), and the fraction of voxels with flow directionality (P =.03) differed significantly between patients and volunteers. CONCLUSION: CSF flow in symptomatic patients with Chiari I malformation, unlike that in volunteer subjects, is characterized by flow jets, regions with a preponderance of flow in one direction, and synchronous bidirectional flow.     

Idiopathic spinal cord herniation: value of MR phase-contrast imaging.

We report two patients with an idiopathic transdural spinal cord herniation at the thoracic level. Phase-contrast MR imaging was helpful in showing an absence of CSF flow ventral to the herniated cord and a normal CSF flow pattern dorsal to the cord, which excluded a compressive posterior arachnoid cyst.     

Analysis and classification of cerebellar malformations

BACKGROUND AND PURPOSE: Because of improved visualization of posterior fossa structures with MR imaging, cerebellar malformations are recognized with increasing frequency. Herein we attempt to describe and propose a rational classification of cerebellar malformations. METHODS: MR images obtained in 70 patients with cerebellar malformations were retrospectively reviewed. The cerebellar malformations were initially divided into those with hypoplasia and those with dysplasia. They were then divided into focal and diffuse malformations. Finally, they were separated according to other features, such as brain stem involvement and cerebral involvement. RESULTS: All patients with diffuse cerebellar dysplasia (muscular dystrophy [n = 10], cytomegalovirus [n = 6], lissencephaly [n = 3],) had abnormalities of the cerebrum. Patients with focal cerebellar dysplasia of the Joubert (n = 12) and rhombencephalosynapsis (n = 8) types had variable cerebral dysplasia. Patients with nonsyndromic focal cerebellar dysplasia (isolated focal cerebellar cortical dysplasia [n = 2], cerebellar heterotopia with cerebellar cortical dysplasia [n = 1], idiopathic diffuse cerebellar dysplasia [n = 1], Lhermitte-Duclos syndrome [n = 1]) and those with cerebellar hypoplasia (isolated cerebellar hypoplasia [n = 6], pontocerebellar hypoplasia type 1 [n = 1]) had normal cerebra. Patients with features of Dandy-Walker malformation (n = 19) had both hypoplasia and dysplasia of the cerebellum. No notable difference was found between the cerebella of patients with large fourth ventricle cysts (Dandy-Walker malformations) and those without large fourth ventricle cysts (isolated cerebellar hypoplasia). Therefore, the Dandy-Walker malformation seems to be heterogeneous. CONCLUSION: Use of this classification system helps in the segregation and understanding of the relationship among cerebellar malformations. Although it will undoubtedly require revisions, this classification is a first step in combining imaging with molecular biology to facilitate understanding of cerebellar development and maldevelopment.