A blog for learning and discussion of Radiology Cases.
Dandy Walker Malformation
Definition/Background
Dandy-Walker malformation is a congenital abnormality
characterized by an enlarged posterior fossa, high position of the tentorium
and torcula herophili, partial or complete absence of the cerebellar vermis,
and a cystic dilation of the fourth ventricle.
Characteristic
Clinical Features
Developmental delay and the signs and symptoms of
hydrocephalus are known presenting features.
Characteristic
Radiologic Findings
Imaging shows partial or complete hypoplasia of the
cerebellar vermis, a large fourth ventricle, a large posterior fossa, and
highly placed tentorium and torcula herophili.
Less Common
Radiologic Manifestations
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Associated central nervous system anomalies include
hydrocephalus, corpus callosum agenesis, heterotopias, schizencephaly, and
cephaloceles.
Primary Differential
Diagnoses
1-Dandy-Walker Variant
2-Mega Cisterna Magna
3-Arachnoid Cyst
Discussion of
Differential Diagnoses
Dandy-Walker Variant:
Consists of vermian hypoplasia and cystic dilation of the fourth ventricle without
enlargement of the posterior fossa.
Mega Cisterna Magna:
Consists of an enlarged cisterna magna that can result in an enlarged posterior
fossa. However, the cerebellar vermis and fourth ventricle are normal.
Arachnoid Cysts:
Sometimes can be large and result in an enlarged posterior fossa. However, the
fourth ventricle and vermis are normally formed and often displaced by the
cyst.
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Chiari II malformation
Definition/Background
The Chiari II malformation is a complex anomaly with skull,
dural, brain, spine, and spinal cord manifestations. This disorder is almost
invariably associated with myelomeningocele.
Characteristic
Clinical Features
Two distinct age-dependent syndromes are identified in Chiari II malformations. One syndrome
involves infants, and the other involves older children. Signs and symptoms
during infancy include respiratory distress, difficulty swallowing, inspiratory
stridor, apnea, weakness or spasticity of the upper or lower extremities, and scoliosis.
Signs and symptoms during childhood include syncopal episodes, spastic
quadriparesis, nystagmus, weakness in upper extremities with increased tone,
and exaggerated deep-tendon reflexes.
Characteristic
Radiologic Findings
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CT and MR can both evaluate for Chiari II malformation. The
bony changes can be much better appreciated on CT scans.
Bony changes:
Small posterior fossa, concave clivus, and
petrous ridges, gaping foramen magnum, calvarial defects (Lacunar skull).
Dural changes:
Fenestrated falx.
Brain: Inferiorly
displaced, peg-shaped tonsils, towering cerebellum, cerebellum creeping around
the brain stem, beaked tectum, interdigitating gyri.
Ventricles:
Hydrocephalus, colpocephaly, and elongated and inferiorly displaced fourth
ventricle.
Spine and spinal
cord: Spina bifida, segmentation anomalies, diastomatomyelia, and
myelomeningocele.
Less Common
Radiologic Manifestations
Corpus callosal agenesis, heterotopia, and poly- microgyria.
The patient is an 8-year-old girl with spastic quadri-
paresis and exaggerated deep-tendon reflexes.
Sagittal T1WI demonstrates a relatively small posterior fossa with inferiorly displaced peg-shaped cerebellar tonsils. Also noted is concave clivus (arrow).
Axial T2WI demonstrates beaked tectum. Also noted is cerebellum creeping around the brain stem.
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Chiari 1 Malformation
Definition/Background
Chiari I malformation is defined as downward displacement of
the peg-shaped cerebellar tonsils, and sometimes the inferior vermis, through
the foramen magnum into the upper dorsal cervical canal.
Characteristic
Clinical Features
Headaches (often worsened by physical stress), ocular disturbances,
dizziness, and tremors are common presenting features. When associated with
syringohydromyelia, a sensory level can be elicited. Other associated findings
include abnormal reflexes and weakness of the extremities.
Characteristic
Radiologic Findings
Inferiorly displaced (≥5 mm), peg-shaped cerebellar tonsils,
Compression of the cerebellar cisterns. Anterior displacement of the cerebellum.
Reduced length of the clivus.
Less Common
Radiologic Manifestations
Hydrocephalus, Syringohydromyelia, Basilar invagination, Klippel-Feil
anomaly
Primary Differential
Diagnoses
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o
Downward Displacement of the Tonsils
o
Mass Lesion
o
Syringohydromyelia (Possible Etiologies)
o
Chiari I Malformation
o
Chiari II Malformation
o
Trauma
o
Intramedullary Tumors
o
Idiopathic
o
Infective Lesions, Including Arachnoiditis
o
Compressive Lesions of the Cord
o
Multiple Sclerosis
o
Communicating Hydrocephalus
Discussion of
Differential Diagnoses
Mass Lesion: The
intracranial mass lesion responsible for the downward displacement of the
tonsils will be easily identified. Also, the downward displacement of the
tonsils will not demonstrate the typical peg-shape seen in Chiari malformation.
Syringohydromyelia:
It is critical to evaluate the underlying etiology of the syrinx. The
associated findings with each of the above processes help in determining the
cause of the syrinx.
The patient is a 22-year-old man with weakness of the extremities.
Sagittal T1WI demonstrates a syrinx extending from the craniocervical junction up to the upper thoracic spine.
Sagittal T2WI demonstrates downward displacement of peg-shaped tonsils. The classic haustral pattern of the syrinx can be appreciated. Diagnosis: Chiari I malformation with syringohydromyelia.
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Schizencephaly
Definition/Background
Schizencephaly is a gray matter-lined, cerebrospinal fluid-filled
cleft that extends from the ependymal lining of the ventricle to the pia of the
overlying cerebral cortex. The clefts can be unilateral or bilateral, and can
occur anywhere in the brain. There are two types of schizen-cephaly: type I, or
closed-lip schizencephaly, in which the cleft walls are in apposition; and type
II, or open-lip schizencephaly, in which the walls are separated.
Characteristic
Clinical Features
Clinical features of schizencephaly are highly variable. Patients
with unilateral clefts with fused lips may have mild hemiparesis and seizures
but otherwise have normal development. When the cleft is open, patients present
with mild-to-moderate developmental delay and hemiparesis; severity is related
to the extent of cortex involved in the defect. Patients with bilateral clefts
present with severe mental deficits and severe motor anomalies, including
spastic quadriparesis.
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Characteristic
Radiologic Findings
CT and MR can be used to evaluate for schizencephaly. Multiplanar
capability of MR and its inherently better soft-tissue resolution makes it a
better imaging modality to evaluate for shizencephaly.
A gray matter–lined cerebrospinal fluid-filled cleft is seen
to extend from the ependymal lining of the ventricle to the pial surface of the
brain. A characteristic feature of such clefts is a slight outpouching or
“nipple” along the ependymal surface of the cleft. This is most often seen with
closed lip, or minimally open lip, schizencephaly. The gray matter lining the
cleft is always abnormal, and frequently demonstrates a nodular gyral pattern.
Less Common
Radiologic Manifestations
A large percentage of patients with schizophrenia present with
an absent septum pellucidum. Almost half of such patients exhibit optic nerve
hypoplasia. The neuroradiologist should therefore evaluate for septo-optic
dysplasia in patients with schizencephaly.Mild hypoplasia of the corpus
callosum is commonly seen.
Primary Differential
Diagnosis
1-Porencephalic Cyst
Discussion of
Differential Diagnosis
Porencephalic Cyst:
Cerebrospinal fluid-filled cyst lined by gliotic white matter and not gray
matter.
The patient is a 16-year-old boy with seizures.
Axial CT scan demonstrates a deep gray matter–lined (arrowheads) cleft extending from the pia of the overlying cerebral cortex to the ependymal lining of the ventricle.
At a slightly caudal level, axial CT scan demonstrates a slight outpouching or “nipple” (arrow) along the ependymal surface of the cleft. Diagnosis: Closed-lip schizencephaly.
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Polymicrogyria
Definition/Background
Polymicrogyria is a cerebral cortical malformation characterized
by interruption of the normal cortical development during the late stages of
neuronal migration and cortical organization. This results in abnormal development
of the deeper layers of the cortex, with multiple small gyri and shallow
cortical sulci.
Characteristic
Clinical Features
Clinical features
include developmental delay, and seizures.
Associations:
Congenital cytomegalovirus infection, in utero ischemia, and chromosomal
mutations (mutations of Xq28, 16q12.2-21).
Syndromic
associations: Congenital bilateral perisylvian syndrome and Aicardi
syndrome.
Characteristic
Radiologic Findings
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MR imaging is the gold standard to evaluate for polymicrogyria.
3DFT spoiled gradient acquisition (T1W) analyzed
in at least two imaging planes is essential. The typical imaging appearance is
of small irregular cortical gyri with shallow or absent sulci. Occasionally, a
thick, bumpy cortex is seen. Perisylvian cortex is the most common location,
although any area of the cerebral cortex can be involved. Usually focal,
unilateral; multifo-cal; bilateral, asymmetrical; or bilateral, symmetrical forms
have been described. Bilateral involvement is often syndromic.
Primary Differential
Diagnosis
1-Pachygyria
Discussion of
Differential Diagnosis
Pachygyria: Characterized by a broad thick gyrus and does
not demonstrate the typical irregular, bumpy
cortical surface noted in polymicrogyria. However, sometimes it can be
difficult to distinguish the two entities.
The patient is a 14-year-old boy with developmental delay.
Coronal 3DFT SPGR sequence demonstrates shallow, absent cortical sulci in the left perisylvian region.
Axial 3DFT SPGR sequence demonstrates a bumpy left perisylvian cortex.
Sagittal 3DFT SPGR sequence demonstrates a thickened cortex with small irregular cortical gyri and absent sulci involving predominantly the frontal operculum in the left perisylvian region. Diagnosis: Polymicrogyria.
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Cavum Septum Pellucidum
Definition/Background
Cavum septi pellucidi (CSP) and cavum vergae (CV) represent
collections of cerebrospinal fluid (CSF) between the leaves of septum
pellucidum and have been mis-named as the fifth and sixth ventricles. CSP is a
constant feature in the human fetus and usually gets obliterated toward term.
However, persistence is relatively common, and has been reported in 20% of
brain autopsies. CV is a posterior extension of CSP and is never described alone.
Characteristic
Clinical Features
CSP and CV are usually asymptomatic.
Characteristic
Radiologic Findings
Both CT and MR demonstrate nonenhancing CSF-filled midline
cavities bounded superiorly by the corpus
callosum and laterally by the leaves of the septum pellucidum and the
fornices. There is no communication with the lateral ventricles.
Primary Differential
Diagnoses
1. Cavum
Velum Interpositum (CVI)
2.
Arachnoid Cyst
3.
Epidermoid Cyst
Discussion of
Differential Diagnoses
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Cavum Velum
Interpositum (CVI): Typically triangular, nonenhancing CSF-filled midline
cavity will be seen within the cistern of velum interpositum at the level of
the bodies of the lateral ventricles. CVI does not extend anteriorly into the
region of the frontal horns of the lateral ventricles.
Arachnoid Cyst:
Based on imaging alone, it can be difficult to distinguish an arachnoid cyst
from CSP or CV. Presence of hydrocephalus should favor arachnoid cyst; also, it
should be noted that midline CSF-containing cysts should favor CSP, CV, or CVI,
or, less likely, an arachnoid cyst.
Epidermoid Cyst:
Diffusion restriction will be seen.
The patient is a 42-year-old man with change in mental status.
Axial T2WI at the level of the frontal horns demonstrates cerebrospinal fluid (CSF)between the leaves of the septum pellucidum suggestive of cavum septi pellucidi.
Axial T2WI at the level of the body of the lateral ventricle demonstrates cerebrospinal fluid (CSF) between the leaves of the septum pellucidum suggestive of cavum septi vergae.
Sagittal T1WI in a different patient demonstrates upward bowing of the fornix (arrowhead) and downward displacement of the internal cerebral vein (arrow). Diagnosis: Cavum septi pellucidi and vergae.
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Agenesis of Corpus Collosum
Definition/Background
Agenesis of the corpus callosum is a rare congenital disorder
in which there is partial or complete absence of the corpus callosum. It is
usually a sporadic occurrence, but is known to be associated with trisomy 18,
trisomy 13, and trisomy 8.
Characteristic
Clinical Features
Signs and symptoms of agenesis of corpus callosum vary greatly
among individuals. Some common characteristics include vision impairment,
delayed milestones, and hypotonia.
Characteristic
Radiologic Findings
Though the diagnosis of agenesis of the corpus callosum can
be easily established on CT studies, MR with its multiplanar capability and
inherently superior soft-tissue resolution is better at demonstrating the
imaging features of agenesis of the corpus callosum.
■ Parallel, nonconverging lateral ventricles, best appreciated
on axial scans
■ High-riding third ventricle, which may be open superiorly to
an inter-hemispheric cyst, best appre-
ciated on coronal images
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■ Indentation on the medial aspect of the frontal horns by
Probst bundles (longitudinally oriented fiber tracts) resulting in the “Viking
horns” or “bull’s horns” appearance, best appreciated on coronal images
■ Dilated occipital horns (Colpocephaly), best appre-ciated on
axial or coronal images
■ Radial, spokelike orientation of the gyri, best appre-ciated
on sagittal T1WI
Associated findings:
■ Lipoma of the corpus callosum (midline)
■ Azygous anterior cerebral artery
■ Chiai II malformation
■ Migration disorders
■ Cephaloceles (usually midline)
■ Dandy-Walker malformation
■ Holoprosencephaly
■ Median cleft syndrome
Note: Diagnosis of agenesis of corpus callosum can be established
on prenatal sonogram or MRI studies.
The patient is a 42-year-old, with change in mental status.
Axial CT scan demonstrates parallel, nonconverging lateral ventricles. Also noted are dilated occipital horns suggestive of colpocephaly.
Axial CT scan demonstrates high-riding third ventricle.
Reformatted coronal CT scan demonstrates indentation on the medial aspect of the frontal horns by Probst bundles, resulting in “bull’s horns” appearance.
Reformatted mid-sagittal CT scan demonstrates absent corpus callosum. This results in radial, spoke-wheel-like orientation of the gyri. Diagnosis: Agenesis of corpus callosum.
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Lobar Holoprosencephaly
The patient is a 5-month-old infant with hypotelorism, a
cleft palate, and delayed milestones.
Definition/Background
Holoprosencephaly (HPE) is a complex group of malformation
disorders characterized by a failure of differentiation and cleavage of the
prosencephalon, occurring between the 18th and the 28th day of gestation, and affecting
both the forebrain and the face. HPE has been associated with both teratogenic
(such as maternal diabetes) and genetic causes. Sonic hedgehog (SHH), ZIC2,
SIX3, TGIF, PTCH, GLI2, and TDGF1 genes have been positively implicated in HPE.
This disorder can also be due to chromosomal abnormalities, with a higher
prevalence observed in trisomy 13 (Patau’s syndrome), and less commonly in
trisomy 18 (Edward’s syndrome) and triploidy. Classically, three levels of increasing
severity are described: lobar, semilobar, and alobar. Another milder subtype of
HPE, the middle inter-hemispheric variant (MIH), or syntelencephaly, has also been
recognized.
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Characteristic
Clinical Features
HPE is generally associated with craniofacial anomalies, such
as hypotelorism, midline cleft lip and/or palate, cebocephaly (flattened nose
with single nostril), single maxillary central incisor and microcephaly. In
severe cases, anophthalmia, cyclopia, or proboscis (ethmocephaly), can be
present. The most common neurologic sign is developmental delay. Other commonly
seen signs include mental retardation, epilepsy, weakness, spasticity,
dystonia, and choreoathetosis. Endocrine disorders (diabetes insipidus or growth
hormone deficiency), oro-motor dysfunction (feeding and swallowing
difficulties) and autonomic dysfunction (instability of temperature, heart,
and/or breath rate) may also be seen. Usually the degree of craniofacial and
neurologic abnormalities cor-relates with the severity of the brain
malformation.
Characteristic
Radiologic Findings
Alobar Holoprosencephaly: Presents a pancake-like cerebrum,
without interhemispheric division; large monoventricle that can communicate
with a dorsal cyst; absence of olfactory bulbs and tracts (arrhinen-cephaly);
absence of corpus callosum; and fusion of deep gray nuclei.
Semilobar Holoprosencephaly: Shows rudimentary cerebral lobes,
with incomplete interhemispheric division (IHF and falx present posteriorly
only); presence of posterior ventricle horns with small third ventricle; absence
or hypoplasia of olfactory bulbs and tracts; presence of splenium of corpus
callosum; partial fusion of thalami and basal ganglia; and dorsal cyst.Lobar
Holoprosencephaly: Presents with almost normal lobar differentiation and
separation of the hemispheres, with the exception of midline continuity of the
basal frontal cortex; IHF and falx hypoplastic anteriorly and presenting
posteriorly; rudimentary anterior horns of the ventricles; presence of splenium
of corpus callosum, and variable presence of anterior body with hypoplasia of
the genu of corpus callosum; usually fully separated thalami; and variable
degree of fusion of the basal ganglia.
Middle Interhemispheric Variant of Holoprosencephaly (MIH):
Shows failure of separation of the posterior frontal and parietal lobes; normal
or hypoplasic ante-rior horns; presence of genu and splenium of corpus callosum
with absence of callosal body; fully separated hypothalamus and basal ganglia;
and variable fusion of thalami. Cortical dysplasia and heterotopic gray matter
are also common findings.
Primary Differential
Diagnosis
1-Septo-Optic Dysplasia
Discussion of
Differential Diagnosis
Septo-Optic Dysplasia (SOD): Consists of hypoplasia of the
optic nerves and hypoplasia or absence of the septum pellucidum. Schizencephaly
and gray matter heterotopias may be present. However, some authors consider
that some patients with SOD have a mild form of holoprosencephaly.
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Cephalocele
DEMOGRAPHICS/CLINICAL
HISTORY
The patient is an 18-month-old boy with developmental delay.
DISCUSSION
Definition and Background
Cephaloceles (encephaloceles) encompass all neural tube defects
that result in abnormal herniation of intracranial structures through mesodermal
defects. They can be divided into meningoceles and meningoencephaloceles, depending
on whether there is a neural component within the herniation. The herniating
brain is often abnormal.Encephaloceles can be divided into the anterior (sincipital),
basal, and posterior (occipital) types. Sincipital (also called frontoethmoidal
type) encephaloceles represent herniation towards the soft tissues of the
forehead, external nose, and orbit. These are particularly common in Southeast
Asia, and are further classified as nasofrontal, nasoethmoidal, and nasoorbital
(anterior and posterior orbital), named according to the bones at the superior
and inferior margins of the defect.Basal encephaloceles protrude through
defects in the basal skull bones (anterior and central skull base) and can be
subdivided into the transethmoidal, sphenoethmoidal, sphenomaxillary,
spheno-orbital, and transsphenoidal subtypes.Posterior encephaloceles are
occipital or craniocervical in location, with defects located in the occipital
bone, and posterior arch of atlas. These are often associated with a hindbrain
abnormality.Rare varieties include the convexity encephaloceles, including the
atretic cephaloceles.
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Characteristic
Clinical Features:
Most anterior (frontoethmoidal) and posterior (occipital)
encephaloceles are usually diagnosed at birth, if not diagnosed antenatally. These often
present as a skin-covered mass, although some atretic cephaloceles over the
convexity may not be diagnosed till much later in life. If the encephalocele is
not skin-covered, it is treated as a neurosurgical emergency at birth.Basal
cephaloceles may present as an intranasal or nasopharyngeal mass with nasal obstruction,
or with symptoms of complications such
as CSF leaks (CSF rhinorrhea) or recurrent
meningitis, or epilepsy. Nasal meningoencephaloceles may change in size in response
to the Valsalva maneuver and will transillumi-nate. Hydrocephalus may occur.Posterior
encephaloceles are associated with higher risk of hydrocephalus and seizures,
the determinants of overall prognosis.
Characteristic
Radiologic Findings
In general, encephaloceles are associated with defects in the
cranium or the skull base that may be best defined by CT, further enhanced with
3D rendering. Evaluation of the contents of the herniation and the brain parenchyma,
and any associated anomalies, is best performed with MRI.
It is useful to remember that the structures of the anterior
skull base including the cribriform plate may be partially or incompletely
ossified till about 2 years of age.Posterior encephaloceles may be associated
with Chiari and Dandy-Walker malformations.
Primary Differential
Diagnoses
1-Nasal Dermoid
2-Nasal Glioma
Discussion of
Differential Diagnoses
Nasal Dermoid: The most common nasal abnormalities, presenting
as a midline mass without or with a sinus tract. External opening may show a
tuft of hair.
Nasal Glioma: Midline, firm, nasal or nasopharyngeal mass
consisting of glial tissue that could be considered a variant of an
encephalocele, although no skull base defect may be demonstrable.
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