DOI: 10.1148/rg.261055033
RadioGraphics 2006;26:173-196
© RSNA, 2006
Differential Diagnosis of Intracranial Cystic Lesions at Head US: Correlation with CT and MR Imaging1
Monica Epelman, MD,
Alan Daneman, MD,
Susan I. Blaser, MD,
Clara Ortiz-Neira, MD2,
Osnat Konen, MD3,
José Jarrín, RDMS and
Oscar M. Navarro, MD
1 From the Department of Diagnostic Imaging, Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada. Recipient of a Certificate of Merit award for an education exhibit at the 2004 RSNA Annual Meeting. Received March 2, 2005; revision requested April 26; final revision received and accepted July 6. All authors have no financial relationships to disclose.
Address correspondence to M.E., Department of Radiology, Children’s Hospital of Pittsburgh, 200 Lothrop St, 3950 Children’s Main Tower, Pittsburgh, PA 15213 (e-mail: monica_epelman{at}hotmail.com).
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Abstract
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The differential diagnosis of intracranial cystic lesions at head ultrasonography (US) includes a broad spectrum of conditions: (a) normal variants, (b) developmental cystic lesions, (c) cysts due to perinatal injury, (d) vascular cystlike structures, (e) hemorrhagic cysts, and (f) infectious cysts. These lesions vary in prevalence from common (cavum of the septum pellucidum, subependymal cyst, choroid plexus cyst) to rare (vein of Galen malformation). US can provide important information about the anatomic location, size, and shape of the lesions as well as their mass effect on adjacent structures. Differential diagnosis may be difficult because there is substantial overlap of US features between many of these conditions. However, if careful attention is paid to the location and characteristics of the cyst, a more specific diagnosis may be suggested. Understanding the spectrum of appearances of the various intracranial cystic lesions at head US improves the diagnostic yield, enables one to understand their pathogenesis, and facilitates patient care.
© RSNA, 2006
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LEARNING OBJECTIVES FOR TEST 5
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After reading this article and taking the test, the reader will be able to:
- Describe the main clinical and US features of intracranial cystic lesions discovered during the neonatal period.
- List the differential diagnoses for intracranial cystic lesions seen at head US.
- Discuss the US features that allow differentiation between the various intracranial cystic lesions.
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Introduction
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Cystic lesions seen at head ultrasonography (US) may initially seem to have a nonspecific appearance; however, one may arrive at a more specific diagnosis by paying attention to the exact anatomic site and characteristics of the cyst. According to their location, cystic abnormalities at head US may be classified as (a) cystic lesions within the posterior fossa, (b) supratentorial cystic lesions in a periventricular location, and (c) non-periventricular supratentorial cystic lesions in an intra- or extraaxial location.
The conditions reviewed in this article reflect a wide variety of both common and unusual pathologies. The following categories of lesions will be reviewed: (a) normal variants, (b) developmental cystic lesions, (c) cysts due to perinatal injury, (d) vascular cystlike structures, (e) hemorrhagic cysts, and (f) infectious cysts. These lesions vary in prevalence from common (cavum of the septum pellucidum, subependymal cysts, choroid plexus cyst) to rare (vein of Galen malformation).
In this article, we will illustrate the US findings that help to discriminate these different cystic lesions and we will attempt to correlate them with computed tomographic (CT) and magnetic resonance (MR) imaging findings.
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Normal Variants: Cavum Septi Pellucidum, Cavum Vergae, and Cavum Veli Interpositi
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The septum pellucidum consists of two thin laminae of white matter surrounded by gray matter with a potential intervening space (1). The leaves are separated in utero but fuse from back to front as the fetus approaches term or in the first few weeks after birth. The septum pellucidum forms the medial walls of the lateral ventricles and extends from the corpus callosum to the columns of the fornix. The septum pellucidum is part of the limbic system; although its exact function is not completely understood, it seems to moderate behaviors such as rage and arousal (2,3).
The cavum septi pellucidi persists when the two leaves fail to fuse (Figs 1, 2). It is considered a normal variant due to its frequent appearance and because a specific clinical syndrome has not yet been identified with its occurrence. However, recent studies suggest that an enlarged cavum septi pellucidi serves as a significant marker of cerebral dysfunction (4,5) and has been described in various neuropsychiatric and posttraumatic conditions (6).
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Figure 1a. Diagram shows the midline cavities and their positions in the sagittal plane (top) and coronal plane (bottom). The shaded areas represent the fluid-filled spaces, which include the cavum septi pellucidi (CSP) (a), cavum vergae (CV) (b), and cavum veli interpositi (CVI) (c).
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Figure 1b. Diagram shows the midline cavities and their positions in the sagittal plane (top) and coronal plane (bottom). The shaded areas represent the fluid-filled spaces, which include the cavum septi pellucidi (CSP) (a), cavum vergae (CV) (b), and cavum veli interpositi (CVI) (c).
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Figure 1c. Diagram shows the midline cavities and their positions in the sagittal plane (top) and coronal plane (bottom). The shaded areas represent the fluid-filled spaces, which include the cavum septi pellucidi (CSP) (a), cavum vergae (CV) (b), and cavum veli interpositi (CVI) (c).
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Figure 2a. Cavum septi pellucidi and cavum vergae in a 28-week gestation neonate. (a) Midline sagittal US scan shows a cavum septi pellucidi (CSP) and cavum vergae (CV). (b) Coronal US scan obtained at the level of the frontal horns shows the cavum septi pellucidi (CSP). (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum vergae (CV).
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Figure 2b. Cavum septi pellucidi and cavum vergae in a 28-week gestation neonate. (a) Midline sagittal US scan shows a cavum septi pellucidi (CSP) and cavum vergae (CV). (b) Coronal US scan obtained at the level of the frontal horns shows the cavum septi pellucidi (CSP). (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum vergae (CV).
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Figure 2c. Cavum septi pellucidi and cavum vergae in a 28-week gestation neonate. (a) Midline sagittal US scan shows a cavum septi pellucidi (CSP) and cavum vergae (CV). (b) Coronal US scan obtained at the level of the frontal horns shows the cavum septi pellucidi (CSP). (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum vergae (CV).
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The cavum vergae is a fluid-filled space between the two leaves of septum pellucidum located posterior to an arbitrary vertical plane formed by the columns of the fornix (7) (Figs 1, 2). The cavum septi pellucidi and the cavum vergae usually communicate with each other and obliterate from posterior to anterior, the posterior cavum vergae obliterating first and then usually the anterior cavum septi pellucidi. A cavum vergae without a cavum septi pellucidi would thus be unexpected; however, such cases have been documented, which suggests that the embryologic events in this region may not always occur in the usual sequence (8).
The cavum veli interpositi is an anatomic variation that may appear as a cyst in the pineal region at neonatal US (Figs 1, 3). It is a potential space above the tela choroidea of the third ventricle and below the columns of the fornices. The internal cerebral veins run inferiorly (9). The cavum septi pellucidi and cavum vergae may be present concomitantly with cavum veli interpositi, but usually they do not appear to displace or deform the cavum veli interpositi. The cavum veli interpositi is separated from the cavum vergae by the crura of the fornices (9).
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Figure 3a. Cavum veli interpositi. (a) Sagittal fetal MR image, obtained at 33 weeks of gestation due to an "inter-hemispheric cyst" seen at fetal US, shows a large cavum veli interpositi (CVI). No other abnormalities were identified. (b) Magnified midline sagittal US scan obtained with a linear-array transducer shows the cavum veli interpositi (arrows). This image was obtained during the first week of life. (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum veli interpositi (arrows). (d) Sagittal postnatal MR image obtained at 8 months of age shows the large cavum veli interpositi (arrows).
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Figure 3b. Cavum veli interpositi. (a) Sagittal fetal MR image, obtained at 33 weeks of gestation due to an "inter-hemispheric cyst" seen at fetal US, shows a large cavum veli interpositi (CVI). No other abnormalities were identified. (b) Magnified midline sagittal US scan obtained with a linear-array transducer shows the cavum veli interpositi (arrows). This image was obtained during the first week of life. (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum veli interpositi (arrows). (d) Sagittal postnatal MR image obtained at 8 months of age shows the large cavum veli interpositi (arrows).
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Figure 3c. Cavum veli interpositi. (a) Sagittal fetal MR image, obtained at 33 weeks of gestation due to an "inter-hemispheric cyst" seen at fetal US, shows a large cavum veli interpositi (CVI). No other abnormalities were identified. (b) Magnified midline sagittal US scan obtained with a linear-array transducer shows the cavum veli interpositi (arrows). This image was obtained during the first week of life. (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum veli interpositi (arrows). (d) Sagittal postnatal MR image obtained at 8 months of age shows the large cavum veli interpositi (arrows).
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Figure 3d. Cavum veli interpositi. (a) Sagittal fetal MR image, obtained at 33 weeks of gestation due to an "inter-hemispheric cyst" seen at fetal US, shows a large cavum veli interpositi (CVI). No other abnormalities were identified. (b) Magnified midline sagittal US scan obtained with a linear-array transducer shows the cavum veli interpositi (arrows). This image was obtained during the first week of life. (c) Coronal US scan, obtained at the level of the bodies of the lateral ventricles, shows the cavum veli interpositi (arrows). (d) Sagittal postnatal MR image obtained at 8 months of age shows the large cavum veli interpositi (arrows).
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Development of the cavum veli interpositi is independent of the septum pellucidum, and it is believed to be the result of abnormal separation of the crura of the fornices. Associated congenital midline anomalies of the brain in the presence of cavum veli interpositi have not been reported (10).
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Posterior Fossa Cystic Lesions
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Mega Cisterna Magna
Although the term mega cisterna magna was coined by Gonsette et al (11) in 1968 to describe a series of adult patients with significantly enlarged posterior fossa cisterns attributed to cerebellar atrophy, its significance remains controversial. Since that time, the term has been loosely applied to a large retrocerebellar cerebrospinal fluid (CSF)–appearing space with a normal vermis and normal cerebellar hemispheres. More recently, Nelson et al (12) have revived the concept that a cisterna magna should enlarge only in response to volume loss of a damaged cerebellum. They believe that when such large spaces manifest with mass effect on the cerebellum, enlargement of the posterior fossa and/or splitting of the falx, and supratentorial extension, they can be attributed not to an enlarged subarachnoid cistern but to a space-occupying lesion. In their experience, careful pathologic and histologic examinations of these spaces show that they are arachnoid or Blake’s pouch cysts. Any posterior fossa cyst may simulate others in imaging studies, and thus an anatomic descriptor, such as retro-, supra-, or infracerebellar cyst, would be more appropriate than assuming a histologic diagnosis until histologic confirmation is available (12).
Mega cisterna magna occurs in approximately 1% of all brains imaged postnatally. Mega cisterna magna has been associated with infarction, inflammation, and infection, particularly cytomegalovirus, as well as with chromosomal abnormalities, especially trisomy 18. In the absence of other findings to suggest a posterior fossa lesion, a mega cisterna magna is unlikely to be clinically significant (13).
The normal cisterna magna characteristically measures 3–8 mm when measurements are taken in the midsagittal plane from the posterior lip of the foramen magnum to the caudal margin of the inferior vermis (14).
Linear echoes, usually paired, may be seen joining as they descend toward the base of the posterior fossa. These are consistent with dural folds and likely represent the inferior attachment of the tentorium (15) (Fig 4). These folds are likely to be absent in other Dandy-Walker continuum disorders (13) despite the fact that mega cisterna magna is considered to be one of the components of the Dandy-Walker continuum disorders.
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Figure 4a. Isolated mega cisterna magna in a patient with trisomy 21. (a) Sagittal US scan shows a retrocerebellar collection of CSF (arrows). (b) Transmastoid US scan of the posterior fossa shows an area of linear echogenicity consistent with a dural fold (arrow) and demonstrates the presence of a cerebellar vermis (arrowheads), which is critical for differential diagnosis from Dandy-Walker malformation. (c) US scan obtained with a linear-array transducer shows the findings in b more clearly. Arrow = dural fold, arrowhead = cerebellar vermis. (d) Unenhanced CT image shows the dural fold (arrow) and a normal cerebellum.
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Figure 4b. Isolated mega cisterna magna in a patient with trisomy 21. (a) Sagittal US scan shows a retrocerebellar collection of CSF (arrows). (b) Transmastoid US scan of the posterior fossa shows an area of linear echogenicity consistent with a dural fold (arrow) and demonstrates the presence of a cerebellar vermis (arrowheads), which is critical for differential diagnosis from Dandy-Walker malformation. (c) US scan obtained with a linear-array transducer shows the findings in b more clearly. Arrow = dural fold, arrowhead = cerebellar vermis. (d) Unenhanced CT image shows the dural fold (arrow) and a normal cerebellum.
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Figure 4c. Isolated mega cisterna magna in a patient with trisomy 21. (a) Sagittal US scan shows a retrocerebellar collection of CSF (arrows). (b) Transmastoid US scan of the posterior fossa shows an area of linear echogenicity consistent with a dural fold (arrow) and demonstrates the presence of a cerebellar vermis (arrowheads), which is critical for differential diagnosis from Dandy-Walker malformation. (c) US scan obtained with a linear-array transducer shows the findings in b more clearly. Arrow = dural fold, arrowhead = cerebellar vermis. (d) Unenhanced CT image shows the dural fold (arrow) and a normal cerebellum.
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Figure 4d. Isolated mega cisterna magna in a patient with trisomy 21. (a) Sagittal US scan shows a retrocerebellar collection of CSF (arrows). (b) Transmastoid US scan of the posterior fossa shows an area of linear echogenicity consistent with a dural fold (arrow) and demonstrates the presence of a cerebellar vermis (arrowheads), which is critical for differential diagnosis from Dandy-Walker malformation. (c) US scan obtained with a linear-array transducer shows the findings in b more clearly. Arrow = dural fold, arrowhead = cerebellar vermis. (d) Unenhanced CT image shows the dural fold (arrow) and a normal cerebellum.
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Dandy-Walker Continuum Disorders
The Dandy-Walker continuum remains poorly understood even today, more than 80 years after its original description (16). It refers to the association of a combined abnormality of the fourth ventricle and the cerebellum, most commonly severe dilatation of the fourth ventricle and cerebellar hemispheric hypoplasia.
The diagnosis of "classic" Dandy-Walker malformation includes three criteria: (a) vermian hypoplasia with cephalad rotation of the vermian remnant, (b) cystic dilatation of the posterior fossa communicating with the fourth ventricle, and (c) enlargement of the posterior fossa causing an abnormally high tentorium and torcular, the latter lying above the level of the lambdoid (ie, torcular-lambdoid inversion) (17) (Fig 5). In Dandy-Walker variant the vermis, which is usually hypoplastic, is present and the posterior fossa is not as enlarged as in the classic Dandy-Walker malformation. However, the demarcation between classic Dandy-Walker malformation and Dandy-Walker variant is vague, and thus the term Dandy-Walker continuum is more appropriate.
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Figure 5a. Dandy-Walker malformation in a full-term 1-day-old neonate. (a) Midline sagittal US scan shows a retrocerebellar collection of CSF (arrowheads). (b) Coronal US scan shows vermian agenesis and a wide communication with a "keyhole" appearance (arrowheads) between the cyst posteriorly and the fourth ventricle (4) anteriorly. The cerebellar hemispheres (C) are hypoplastic. (c) Magnified transmastoid US scan shows the findings in b more clearly. C = cerebellar hemisphere, arrowheads = communication between the cyst and fourth ventricle. (d, e) Coronal T2-weighted (d) and sagittal T1-weighted (e) MR images show the Dandy-Walker malformation.
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Figure 5b. Dandy-Walker malformation in a full-term 1-day-old neonate. (a) Midline sagittal US scan shows a retrocerebellar collection of CSF (arrowheads). (b) Coronal US scan shows vermian agenesis and a wide communication with a "keyhole" appearance (arrowheads) between the cyst posteriorly and the fourth ventricle (4) anteriorly. The cerebellar hemispheres (C) are hypoplastic. (c) Magnified transmastoid US scan shows the findings in b more clearly. C = cerebellar hemisphere, arrowheads = communication between the cyst and fourth ventricle. (d, e) Coronal T2-weighted (d) and sagittal T1-weighted (e) MR images show the Dandy-Walker malformation.
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Figure 5c. Dandy-Walker malformation in a full-term 1-day-old neonate. (a) Midline sagittal US scan shows a retrocerebellar collection of CSF (arrowheads). (b) Coronal US scan shows vermian agenesis and a wide communication with a "keyhole" appearance (arrowheads) between the cyst posteriorly and the fourth ventricle (4) anteriorly. The cerebellar hemispheres (C) are hypoplastic. (c) Magnified transmastoid US scan shows the findings in b more clearly. C = cerebellar hemisphere, arrowheads = communication between the cyst and fourth ventricle. (d, e) Coronal T2-weighted (d) and sagittal T1-weighted (e) MR images show the Dandy-Walker malformation.
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Figure 5d. Dandy-Walker malformation in a full-term 1-day-old neonate. (a) Midline sagittal US scan shows a retrocerebellar collection of CSF (arrowheads). (b) Coronal US scan shows vermian agenesis and a wide communication with a "keyhole" appearance (arrowheads) between the cyst posteriorly and the fourth ventricle (4) anteriorly. The cerebellar hemispheres (C) are hypoplastic. (c) Magnified transmastoid US scan shows the findings in b more clearly. C = cerebellar hemisphere, arrowheads = communication between the cyst and fourth ventricle. (d, e) Coronal T2-weighted (d) and sagittal T1-weighted (e) MR images show the Dandy-Walker malformation.
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Figure 5e. Dandy-Walker malformation in a full-term 1-day-old neonate. (a) Midline sagittal US scan shows a retrocerebellar collection of CSF (arrowheads). (b) Coronal US scan shows vermian agenesis and a wide communication with a "keyhole" appearance (arrowheads) between the cyst posteriorly and the fourth ventricle (4) anteriorly. The cerebellar hemispheres (C) are hypoplastic. (c) Magnified transmastoid US scan shows the findings in b more clearly. C = cerebellar hemisphere, arrowheads = communication between the cyst and fourth ventricle. (d, e) Coronal T2-weighted (d) and sagittal T1-weighted (e) MR images show the Dandy-Walker malformation.
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To further simplify these lesions, the definition of Dandy-Walker malformation has been modified and Blake’s pouch cyst has been included in the "Dandy-Walker continuum" (18–20). Persistent Blake’s pouch cyst represents an embryonic midline outpouching of a portion of the primitive fourth ventricle (superior medullary velum), which extends inferior and posterior to the vermis into the cisterna magna (18) and may push the developing tentorium into an abnormal, relatively high position. Its appearance at imaging is that of a nonspecific retrocerebellar cyst.
All the different malformations comprising the Dandy-Walker continuum disorders are characterized by overlapping embryologic disorders of the different tissues within the posterior fossa. The rationale for congregating these entities is that the processes that result in the development of the cerebellum and opening of the tentorium take place simultaneously with the transformation of the primitive meninges into the tentorium and subarachnoid spaces. As a consequence, disorders of these processes result in cystic malformations of the posterior fossa, which can be associated or not with vermian agenesis. While the origin of the Dandy-Walker malformation and Dandy-Walker variant is believed to be secondary to failure of assimilation of the area membranacea anterior, leading to anomalous development of the fourth ventricle, persistent Blake’s pouch cyst is recognized to develop secondary to failure of perforation of the foramen of Magendie (17,18).
The high insertion of the tentorium encountered in Dandy-Walker continuum disorders is considered an indicator that the malformation occurred before the end of the embryonic period (21). Even though the tentorial insertion is usually easily assessed at MR imaging due to its multiplanar capabilities, with US this may be extremely difficult. However, all other components of the spectrum are much easier to identify, particularly when dedicated images through the posterior fossa are used (15,22) (Fig 5).
The prevalence of the Dandy-Walker continuum disorders is about 1 per 25,000–35,000 live births worldwide (13). The most critical prognostic factor is the presence or absence of associated central nervous system abnormalities, such as cortical dysplasia, holoprosencephaly, or encephaloceles, since up to 18 different chromosomal abnormalities and 40 different genetic syndromes have been associated with Dandy-Walker continuum disorder (23,24). Another prognostic factor seems to be gestational age at diagnosis, with poor prognosis if diagnosed before 21 weeks of gestation and better prognosis if diagnosed postnatally (24).
Arachnoid Cyst
Arachnoid cysts are congenital lesions of the arachnoid membrane that expand with CSF secretion and comprise approximately 1% of all intracranial space-occupying lesions. One-fourth of all arachnoid cysts occur in the posterior fossa (25,26). They are usually retrocerebellar in location and less commonly may develop within the fourth ventricle or cerebellopontine cistern. Arachnoid cysts of the posterior fossa have been associated with Aicardi syndrome, glutaric acid-uria type I, and unbalanced X,9 translocation (13,27).
In cross-sectional imaging studies, these cysts appear as CSF spaces between the cerebellum and the occipital or petrous bones (Fig 6). The torcular herophili is usually in the normal position, but it may be elevated if the cyst formed early in the fetal period. The falx cerebelli is normally present. Occasionally, there is compression or absence of the inferior vermis. Other central nervous system malformations are rarely associated with arachnoid cysts (12).
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Figure 6a. Arachnoid cyst and complex posterior fossa malformations in a full-term 1-day-old neonate. (a) Left parasagittal US scan shows a CSF collection (arrowheads) anterior to the cerebellum in the cerebellopontine angle region. (b) Axial transmastoid US scan demonstrates the size of the fluid collection better (arrowheads). Arrows = bilateral internal carotid arteries. (c) Axial T2-weighted MR image corroborates the US findings and shows a small, hypoplastic cerebellum (C) on the left. (d) Left parasagittal T1-weighted MR image shows findings similar to those in a.
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Figure 6b. Arachnoid cyst and complex posterior fossa malformations in a full-term 1-day-old neonate. (a) Left parasagittal US scan shows a CSF collection (arrowheads) anterior to the cerebellum in the cerebellopontine angle region. (b) Axial transmastoid US scan demonstrates the size of the fluid collection better (arrowheads). Arrows = bilateral internal carotid arteries. (c) Axial T2-weighted MR image corroborates the US findings and shows a small, hypoplastic cerebellum (C) on the left. (d) Left parasagittal T1-weighted MR image shows findings similar to those in a.
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Figure 6c. Arachnoid cyst and complex posterior fossa malformations in a full-term 1-day-old neonate. (a) Left parasagittal US scan shows a CSF collection (arrowheads) anterior to the cerebellum in the cerebellopontine angle region. (b) Axial transmastoid US scan demonstrates the size of the fluid collection better (arrowheads). Arrows = bilateral internal carotid arteries. (c) Axial T2-weighted MR image corroborates the US findings and shows a small, hypoplastic cerebellum (C) on the left. (d) Left parasagittal T1-weighted MR image shows findings similar to those in a.
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Figure 6d. Arachnoid cyst and complex posterior fossa malformations in a full-term 1-day-old neonate. (a) Left parasagittal US scan shows a CSF collection (arrowheads) anterior to the cerebellum in the cerebellopontine angle region. (b) Axial transmastoid US scan demonstrates the size of the fluid collection better (arrowheads). Arrows = bilateral internal carotid arteries. (c) Axial T2-weighted MR image corroborates the US findings and shows a small, hypoplastic cerebellum (C) on the left. (d) Left parasagittal T1-weighted MR image shows findings similar to those in a.
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Imaging Approach to Posterior Fossa Cysts
The various posterior fossa cysts described may therefore have similar appearances at imaging, particularly at US. In an attempt to differentiate these cysts, attention must be paid to evaluating the size of the fourth ventricle, communication with the fourth ventricle, the size of the vermis and cerebellar hemispheres, and mass effect on the cerebellum (12). To improve the accuracy of diagnosis, it is also essential to take into account the clinical findings and to evaluate for hydrocephalus and the presence of other malformations. While patients with arachnoid cysts may present with cerebellar symptoms secondary to compression of the cerebellum (ataxia and dysdiadochokinesis), patients with the Dandy-Walker continuum disorders may often present with either hydrocephalus or developmental delay (26).
Vein of Galen Malformation
The vein of Galen malformation is a venous ectasia secondary to an arteriovenous shunt, draining either directly into the vein of Galen or into a tributary. The vein of Galen malformation is a form of embryonic arteriovenous shunt located in the midline, in the quadrigeminal plate cistern. It is thought to result from the development of an arteriovenous fistula between primitive choroidal vessels and the median prosencephalic vein of Markowski. Vein of Galen malformation is a misnomer; it is actually the median prosencephalic vein that is dilated. The persistent flow through the connection impedes the expected involution of this embryonic vein and precludes the development of the vein of Galen. Other venous anomalies, such as anomalous dural sinuses and sinus stenosis, are commonly present in association with vein of Galen malformation (28,29).
Vein of Galen malformation represents 1% of all vascular brain malformations. It may manifest with high-output congestive heart failure, hydrocephalus, or seizures and in older children with hemorrhage (30). Frequently, vein of Galen malformations are diagnosed during the first few weeks of life, though delivery and the first 24 hours are usually unremarkable. Larger shunts may demonstrate rapid deterioration with worsening cardiac failure leading eventually to multi-organ failure. A smaller shunt may manifest later in life with mild cardiac failure and failure to thrive (31).
At US, vein of Galen malformation is usually detected as an anechoic, tubular midline structure located superior to the cerebellum. It displays increased flow on color Doppler images (Fig 7). Variable thrombus and feeding vessels may be appreciated. The feeding arteries are difficult to analyze, but a tortuous network of dilated arteries is usually visible in the region of the malformation. The main differential diagnosis is a brain arteriovenous malformation that drains into the vein of Galen. The distinction is important as the prognosis is particularly different. Vein of Galen malformations can be treated postnatally and have a good outcome. However, a large arterio-venous malformation in this region carries a much worse prognosis. For this reason, prenatal MR imaging is useful and postnatal MR imaging and MR angiography are necessary in most cases to evaluate the exact nature of the malformation (32). The feeding vessels, nidus, and draining veins can be followed with US after embolization treatment, which may be performed shortly after birth (30).
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Figure 7a. Vein of Galen malformation. (a) Midline sagittal US scan shows an apparent cystic mass in a supracerebellar location (arrowheads). (b) Color Doppler image shows flow within the apparent mass (arrowheads). This finding indicates that the "mass" is a large vein of Galen malformation with a prominent internal carotid artery (ICA) and pericallosal branches (P). (c) Sagittal T1-weighted MR image shows the same findings as the US images. The dilated vein of Galen communicates with a persistent falcine sinus (arrow). Note the extensive phase artifact due to the malformation. (d) Lateral MR venogram shows numerous dilated arteries and drainage of the large vein of Galen malformation (arrowheads) into a prominent torcular through a persistent falcine sinus (arrows).
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Figure 7b. Vein of Galen malformation. (a) Midline sagittal US scan shows an apparent cystic mass in a supracerebellar location (arrowheads). (b) Color Doppler image shows flow within the apparent mass (arrowheads). This finding indicates that the "mass" is a large vein of Galen malformation with a prominent internal carotid artery (ICA) and pericallosal branches (P). (c) Sagittal T1-weighted MR image shows the same findings as the US images. The dilated vein of Galen communicates with a persistent falcine sinus (arrow). Note the extensive phase artifact due to the malformation. (d) Lateral MR venogram shows numerous dilated arteries and drainage of the large vein of Galen malformation (arrowheads) into a prominent torcular through a persistent falcine sinus (arrows).
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Figure 7c. Vein of Galen malformation. (a) Midline sagittal US scan shows an apparent cystic mass in a supracerebellar location (arrowheads). (b) Color Doppler image shows flow within the apparent mass (arrowheads). This finding indicates that the "mass" is a large vein of Galen malformation with a prominent internal carotid artery (ICA) and pericallosal branches (P). (c) Sagittal T1-weighted MR image shows the same findings as the US images. The dilated vein of Galen communicates with a persistent falcine sinus (arrow). Note the extensive phase artifact due to the malformation. (d) Lateral MR venogram shows numerous dilated arteries and drainage of the large vein of Galen malformation (arrowheads) into a prominent torcular through a persistent falcine sinus (arrows).
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Figure 7d. Vein of Galen malformation. (a) Midline sagittal US scan shows an apparent cystic mass in a supracerebellar location (arrowheads). (b) Color Doppler image shows flow within the apparent mass (arrowheads). This finding indicates that the "mass" is a large vein of Galen malformation with a prominent internal carotid artery (ICA) and pericallosal branches (P). (c) Sagittal T1-weighted MR image shows the same findings as the US images. The dilated vein of Galen communicates with a persistent falcine sinus (arrow). Note the extensive phase artifact due to the malformation. (d) Lateral MR venogram shows numerous dilated arteries and drainage of the large vein of Galen malformation (arrowheads) into a prominent torcular through a persistent falcine sinus (arrows).
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Supratentorial Cystic Lesions in a Periventricular Location
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Connatal Cysts
Synonyms for connatal cysts are coarctation of the lateral ventricles and frontal horn cysts. These are cystic areas adjacent to the superolateral margins of the body and frontal horns of the lateral ventricles. Though originally these lesions were believed to be the sequelae of ischemic insults (33), it is now believed that in many cases they represent a normal variant due to approximation of the walls of the frontal horns of the lateral ventricles proximal to their external angles. When the ventricular walls are close enough to touch each other, the most external portion of the ventricle acquires a rounded configuration, resulting in what sonographically appears to be a cyst (34,35).
Careful attention should be paid to the exact location of the cysts in the frontal horn area. Connatal cysts are located at or just below the superolateral angles of the frontal horns or body of the lateral ventricles and are mainly anterior to the foramina of Monro (Figs 8–10). The diagnosis of subependymal cyst is the most probable if the lesion is located below the external angle and posterior to the foramen of Monro. Periventricular leukomalacia (PVL) should be considered when it is above the angle (35,36). Connatal cysts have a reported incidence of 0.7% in low birth weight preterm infants (37). These cysts have been reported to resolve at follow-up studies (38).
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Figure 8. Differential diagnosis between the cystic lesions seen in periventricular leukomalacia (PVL), connatal cyst (CC), and subependymal cyst (SC) is facilitated by noting their distinct anatomic locations.
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Figure 9a. Connatal cysts in a 30-week gestation preterm infant. (a) Coronal US scan shows connatal cysts just inferior to the superolateral angles of the lateral ventricles (arrows). (b) Parasagittal US scan shows several small connatal cysts (arrows) lined up just lateral to the frontal horn and body of the lateral ventricle.
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Figure 9b. Connatal cysts in a 30-week gestation preterm infant. (a) Coronal US scan shows connatal cysts just inferior to the superolateral angles of the lateral ventricles (arrows). (b) Parasagittal US scan shows several small connatal cysts (arrows) lined up just lateral to the frontal horn and body of the lateral ventricle.
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Figure 10a. Bilateral connatal cysts in a 3-week-old full-term neonate who underwent a Norwood operation for hypoplastic left heart syndrome. (a) Coronal US scan shows bilateral areas of CSF echogenicity at the superolateral angles of the lateral ventricles (arrows). (b, c) Right (b) and left (c) magnified coronal US scans obtained with a linear-array transducer show the abnormalities more clearly (arrows). (d) Coronal contrast-enhanced CT image shows the left-sided connatal cyst (arrow).
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Figure 10b. Bilateral connatal cysts in a 3-week-old full-term neonate who underwent a Norwood operation for hypoplastic left heart syndrome. (a) Coronal US scan shows bilateral areas of CSF echogenicity at the superolateral angles of the lateral ventricles (arrows). (b, c) Right (b) and left (c) magnified coronal US scans obtained with a linear-array transducer show the abnormalities more clearly (arrows). (d) Coronal contrast-enhanced CT image shows the left-sided connatal cyst (arrow).
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Figure 10c. Bilateral connatal cysts in a 3-week-old full-term neonate who underwent a Norwood operation for hypoplastic left heart syndrome. (a) Coronal US scan shows bilateral areas of CSF echogenicity at the superolateral angles of the lateral ventricles (arrows). (b, c) Right (b) and left (c) magnified coronal US scans obtained with a linear-array transducer show the abnormalities more clearly (arrows). (d) Coronal contrast-enhanced CT image shows the left-sided connatal cyst (arrow).
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Figure 10d. Bilateral connatal cysts in a 3-week-old full-term neonate who underwent a Norwood operation for hypoplastic left heart syndrome. (a) Coronal US scan shows bilateral areas of CSF echogenicity at the superolateral angles of the lateral ventricles (arrows). (b, c) Right (b) and left (c) magnified coronal US scans obtained with a linear-array transducer show the abnormalities more clearly (arrows). (d) Coronal contrast-enhanced CT image shows the left-sided connatal cyst (arrow).
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Subependymal Cysts
There are two types of subependymal cysts, one of which is an acquired, posthemorrhagic cyst and the other of which is congenital and is related to germinolysis. They may be difficult to differentiate sonographically. Histologically, the cystic cavity is limited by a pseudocapsule of aggregates of germinal cells and glial tissue, but no epithelium can be found. Macrophage-like cells are found in the fluid, suggesting a vascular origin (39).
When congenital, they may be the result of hemorrhage, hypoxic-ischemic damage, or neurotropic infection. They have been reported in association with congenital viral infections (mainly cytomegalovirus and rubella) (40–42), metabolic disorders (especially Zellweger syndrome) (43), chromosomal abnormalities (40), and maternal cocaine consumption (44). However, subependymal cysts not uncommonly may be an isolated finding in otherwise healthy newborns (39,40).
The posthemorrhagic cystic lesions are most commonly detected at the caudothalamic notch, where the germinal matrix is still present late in gestation (34th–35th week) (45) (Fig 11). This may explain why they are found most frequently in preterm infants. They are often tear-shaped and measure 2–11 mm in size (46).
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Figure 11a. Acquired subependymal cyst due to an evolving subependymal hemorrhage. (a) Coronal US scan obtained with a linear-array transducer in the region of the caudothalamic groove shows a well-defined cyst (arrowheads), a finding consistent with an evolving subependymal hemorrhage. (b) Parasagittal US scan shows a multiseptate cyst (arrowheads) within the caudothalamic notch area. The linear echogenic structure (arrow) is the ipsilateral cingulate gyrus. (c) Magnified parasagittal US scan obtained with a linear-array transducer shows the multiple septa within the cyst (arrowheads) more clearly. (d) Coronal T2-weighted MR image shows the subependymal hemorrhagic cyst as an area of low signal intensity (arrow). (e) Sagittal T1-weighted MR image shows the hemorrhage as an area of high signal intensity (arrow).
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Figure 11b. Acquired subependymal cyst due to an evolving subependymal hemorrhage. (a) Coronal US scan obtained with a linear-array transducer in the region of the caudothalamic groove shows a well-defined cyst (arrowheads), a finding consistent with an evolving subependymal hemorrhage. (b) Parasagittal US scan shows a multiseptate cyst (arrowheads) within the caudothalamic notch area. The linear echogenic structure (arrow) is the ipsilateral cingulate gyrus. (c) Magnified parasagittal US scan obtained with a linear-array transducer shows the multiple septa within the cyst (arrowheads) more clearly. (d) Coronal T2-weighted MR image shows the subependymal hemorrhagic cyst as an area of low signal intensity (arrow). (e) Sagittal T1-weighted MR image shows the hemorrhage as an area of high signal intensity (arrow).
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Figure 11c. Acquired subependymal cyst due to an evolving subependymal hemorrhage. (a) Coronal US scan obtained with a linear-array transducer in the region of the caudothalamic groove shows a well-defined cyst (arrowheads), a finding consistent with an evolving subependymal hemorrhage. (b) Parasagittal US scan shows a multiseptate cyst (arrowheads) within the caudothalamic notch area. The linear echogenic structure (arrow) is the ipsilateral cingulate gyrus. (c) Magnified parasagittal US scan obtained with a linear-array transducer shows the multiple septa within the cyst (arrowheads) more clearly. (d) Coronal T2-weighted MR image shows the subependymal hemorrhagic cyst as an area of low signal intensity (arrow). (e) Sagittal T1-weighted MR image shows the hemorrhage as an area of high signal intensity (arrow).
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Figure 11d. Acquired subependymal cyst due to an evolving subependymal hemorrhage. (a) Coronal US scan obtained with a linear-array transducer in the region of the caudothalamic groove shows a well-defined cyst (arrowheads), a finding consistent with an evolving subependymal hemorrhage. (b) Parasagittal US scan shows a multiseptate cyst (arrowheads) within the caudothalamic notch area. The linear echogenic structure (arrow) is the ipsilateral cingulate gyrus. (c) Magnified parasagittal US scan obtained with a linear-array transducer shows the multiple septa within the cyst (arrowheads) more clearly. (d) Coronal T2-weighted MR image shows the subependymal hemorrhagic cyst as an area of low signal intensity (arrow). (e) Sagittal T1-weighted MR image shows the hemorrhage as an area of high signal intensity (arrow).
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Figure 11e. Acquired subependymal cyst due to an evolving subependymal hemorrhage. (a) Coronal US scan obtained with a linear-array transducer in the region of the caudothalamic groove shows a well-defined cyst (arrowheads), a finding consistent with an evolving subependymal hemorrhage. (b) Parasagittal US scan shows a multiseptate cyst (arrowheads) within the caudothalamic notch area. The linear echogenic structure (arrow) is the ipsilateral cingulate gyrus. (c) Magnified parasagittal US scan obtained with a linear-array transducer shows the multiple septa within the cyst (arrowheads) more clearly. (d) Coronal T2-weighted MR image shows the subependymal hemorrhagic cyst as an area of low signal intensity (arrow). (e) Sagittal T1-weighted MR image shows the hemorrhage as an area of high signal intensity (arrow).
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Choroid Plexus Cysts
Choroid plexus cysts are usually a few millimeters in diameter and are commonly located within the body of the plexus. Choroid plexus cysts may be limited within the body itself or may protrude into the ventricular cavity (42). Isolated choroid plexus cysts occur in about 1% of all pregnancies. These cystic lesions are a dilemma if encountered during pregnancy as they are associated with aneuploidy, particularly trisomy 18 (47). This is particularly of concern if the cysts are large (>1 cm), bilateral, and associated with structural abnormalities, when the maternal age is equal to or greater than 32 years, or if the maternal serum screening results are abnormal. Choroid plexus cysts resolve by 26–28 weeks, and in a karyotypically normal fetus, the presence of isolated second-trimester choroid plexus cysts is not associated with any neurologic sequelae, such as mental retardation or delayed development (48). When detected postnatally, choroid plexus cysts are of no clinical significance in otherwise normal neonates.
At US, their sizes are variable and they may be multiple (Fig 12). On images obtained with high-resolution transducers, they are spherical and may exhibit a double wall (49).
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Figure 12. Multiple small choroid plexus cysts in a normal infant. Parasagittal US scan shows a row of five subcentimeter (2–3-mm) choroid plexus cysts (arrowheads), which disappeared in follow-up studies.
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Periventricular Leukomalacia
Periventricular leukomalacia (PVL) refers to white matter necrosis in a characteristic distribution. The distribution pattern is dorsal and lateral to the external angles of the lateral ventricles (Fig 13) and involves particularly the centrum semiovale and the optic (trigone and occipital horns) and acoustic (temporal horn) radiations (50). PVL most frequently occurs in premature infants of less than 32 weeks gestation due to the unique anatomic features of the brain at this age. The white matter of these infants is poorly vascularized and contains oligodendrocyte progenitors, which are sensitive to the effects of ischemia and infection (51). The cortex is usually spared in preterm infants due to meningeal intra-arterial anastomoses, which involute near term (52).
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Figure 13a. Extensive cystic PVL in a 29-week gestation premature neonate. (a) Coronal US scan shows extensive multiseptate cystic areas located superiorly to the frontal horns (arrows). There is ex vacuo dilatation of the ventricles secondary to white matter loss. (b) Parasagittal US scan shows extensive cystic PVL with more cystic components anteriorly (arrows). Posteriorly, the area of ischemia is hyperechoic, which may reflect the presence of very small cysts. Note in both a and b that the cystic components are extremely irregular in outline and multiseptate. (c) Sagittal MR image obtained through the cystic areas shows the multiseptate nature of the PVL.
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Figure 13b. Extensive cystic PVL in a 29-week gestation premature neonate. (a) Coronal US scan shows extensive multiseptate cystic areas located superiorly to the frontal horns (arrows). There is ex vacuo dilatation of the ventricles secondary to white matter loss. (b) Parasagittal US scan shows extensive cystic PVL with more cystic components anteriorly (arrows). Posteriorly, the area of ischemia is hyperechoic, which may reflect the presence of very small cysts. Note in both a and b that the cystic components are extremely irregular in outline and multiseptate. (c) Sagittal MR image obtained through the cystic areas shows the multiseptate nature of the PVL.
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Abstract
LEARNING OBJECTIVES FOR TEST...
