A blog for learning and discussion of Radiology Cases.
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
Sponsored Link
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.
Sponsored Links
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
Sponsored Link
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.
Sponsored Links
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
Sponsored Link
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.
Sponsored Links
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.
Sponsored Link
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.
Sponsored Links
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
Sponsored Link
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.
Sponsored Links
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
Sponsored Link
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.
Sponsored Links
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
Sponsored Link
■ 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.
Sponsored Links