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
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
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
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
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
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
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.
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