Congenital Cranial and Spinal Disorders Flashcards
Which one of the following is most likely
based on the radiograph shown below?
a. Achondroplasia
b. Klippel-Feil
c. Osteogenesis imperfecta
d. Posterior spina bifida
e. Segmental spinal dysgenesis
b. Klippel-Feil
KFS is a congenital anomaly that is caused by the
failure of the spine to segment properly during
embryonic development, resulting in fusion of
two or more cervical vertebrae. Incidence is 1 in
40,000 with a slight female predominance (3:2).
Clinically patients may have a shortened neck, a
low posterior neckline, and limited neck mobility
(less than half possess all three). Associated findings that may provide diagnostic clues include
other skeletal abnormalities, orofacial anomalies,
and visceral defects. Congenital fusions can occur
at any level of the cervical spine, although 75%
occur in the region of the first three cervical vertebrae. The most prevalent fusion is between C2
and C3. KFS is classified into three types: Type
I—fusion of many cervical and upper thoracic vertebrae, Type II—fusion of 2-3 vertebrae with associated hemivertebrae/occipito-atlantal fusion/
other abnormality, Type III—cervical fusion with
lower thoracic/lumbar vertebral fusion. Fetal cervical vertebrae should be evaluated with ultrasound (US) for cervical fusions, blocking, and
hemivertebrae. MRI can also be useful to determine whether the cervical malformation is causing
compression of the brain, brainstem, or spinal
cord. Treatment varies depending on the severity
of the fusions, adjacent segment degenerative
disease, degree of instability present and the
underlying diagnosis. Isolated KFS is generally
well tolerated. Initial treatment strategies include
modification of activities, bracing, and traction,
all of which may delay surgery and prevent neurologic compromise. Indications for surgical
stabilization are symptomatic instability or neurologic compromise.
A young child with an FGFR-3 mutation is shown in the picture below. Which one of the following disorders is he NOT at increased risk of?
a. Cervicomedullary compression
b. Hydrocephalus
c. Posterior circulation aneurysms
d. Spinal canal stenosis
e. Thoracolumbar kyphosis
c. Posterior circulation aneurysms
Achondroplasia is the most common form of
human short-limbed dwarfism and is one of a
spectrum of diseases caused by mutations in the
FGFR3 gene. Occurs in 1 in 10,000-30,000 live
births. The disease is autosomal dominant, but
80% of patients have new mutations. Classic features include a long, narrow trunk with short
limbs, macrocephaly with frontal bossing/prominence and facial hypoplasia. Other features
include hypotonia in infancy (motor delay),
hyperextensible joints, short and broad trident
hands, and thoracolumbar kyphosis. Abnormal
compression at a number of levels along the neuraxis may result in hydrocephalus, cervicomedullary compression, spinal canal stenosis (both
cervical and lumbar), syringomyelia, and spinal
instability. Diminished growth of the skull base
in achondroplasia results in cranial foraminal stenosis and intracranial venous hypertension resulting in impaired CSF absorption, macrocephaly;
additionally, obstructive hydrocephalus may
result from cervicomedullary compression. Monitoring of head growth should be performed at
regular intervals and compared with control
charts for children with achondroplasia to avoid
unnecessary CSF shunting. If raised ICP is suspected, US can show ventricular size, but MRI
will detect transependymal spread of CSF, assess
craniocervical junction and venous stenosis.
Despite mild-moderate ventriculomegaly, the
majority of patients with macrocephaly stabilize
spontaneously, and thus insertion of a VP shunt
should be avoided if possible. Stress on the craniocervical junction by a large head with weak
cervical musculature can produce cervicomedullary compression. Patients may present with neck
pain, apneic episodes, bulbar dysfunction, bladder
dysfunction, paresis, hyperreflexia, and hypertonia with clonus. Indeed, “normal” reflexes may
reflect spasticity in normally hypotonic children
with achondroplasia. Acute deterioration may
occur after minor trauma and there is an
increased incidence of sudden death at <4 years
of age. Investigations include MR imaging and
formal polysomnography. MRI may show tight
foramen magnum, flexion/extension sequences
may demonstrate transient cervicomedullary
compression or CSF flow obstruction, and
MRV may show a persistent occipital venous
sinus preoperatively. The use of polysomnography to assess patients for the presence of
central and/or obstructive sleep apnea has been
reported to identify central/mixed apnea in up
to 60% of unselected children with achondroplasia. Indications for surgery include myelopathy
with upper motor neuron signs such as clonus
and hyperreflexia, and/or central apnea as documented on polysomnography, or the presence
of a syrinx, with evidence of a narrow foramen
magnum and/or T2 signal change in the spinal
cord on MR imaging
Which one of the following is most likely based on the MRI
a. Basilar invagination
b. Corpus callosum agenesis
c. Hydrocephalus
d. Lissencephaly
e. Type II Chiari malformationshown?
b. Corpus callosum agenesis
Complete corpus callosum agenesis is the most
common type of commissural agenesis, and may
be associated with absence of the hippocampal
commissure; in partial agenesis, the genu and
anterior body are formed, whereas portions that
develop later like the posterior body, isthmus,
and splenium are absent. Mid-sagittal MR images
are diagnostic, and also show an everted cingulate
gyrus and longitudinal Probst bundles containing
non-crossing callosal axons, lateral ventricles are
shifted laterally and closed medially by rolled up
white matter lamina (which should be forming
the leaf of the septum pellucidum). The inner
walls of the lateral ventricles are concave medially
as a result of encroachment of the Probst bundles
on the ventricular lumen. In addition, the roof of
the thirdventricle bulges upward.The frontal horns
of the lateral ventricles might be underdeveloped,
whereas the dilated temporal horns invaginate into
the core of the parahippocampal gyri because of
decreased white matter. The lateral ventricles run
parallel to each other, with marked dilation of the
trigone and occipital horns (colpocephaly). Development of the cerebrum and cerebellar hemispheres occurs at the same time, hence associated
Chiari malformation, Dandy-Walker malformation, neuronal migration anomalies, and midline
facial anomalies (facial cleft, encephalocele). Periventricular or subcortical heterotopia may also
be seen.
MRI shows the appearances below, and the lesion is bright on T2WI and dark on fat suppression sequences and does not show any contrast enhancement. Which one of the following is most likely?
a. Colloid cyst
b. Craniopharyngioma
c. Intracranial lipoma
d. Intraventricular hemorrhage
e. Pericallosal aneurysm
c. Intracranial lipoma
Intracranial lipomas are thought to be maldifferentiations of the meninx primitive (undifferentiated) mesenchyme that surrounds the developing brain. Evolution of the inner meninx primitiva leads to formation of the subarachnoid spaces, the pre-pontomedullary cistern is the first to
develop, followed by cisterns around the brainstem and cerebral hemispheres, the quadrigeminal plate, and finally the suprasellar system.
Meninx primitiva surrounding the dorsum of
the lamina terminalis is the last to become
evolved. The most common locations of an
intracranial lipoma are in the deep interhemispheric fissure (40-50%), quadrigeminal plate
cistern (30%), suprasellar/interpedicular cistern
(10-20%), cerebellopontine angle cistern (10%),
and sylvian fissures (5%). Because by embryologic definition lipomas occupy the subarachnoid
space, blood vessels and cranial nerves course
through them. Most intracranial lipomas are
asymptomatic, so they are diagnosed incidentally. On CT scan, a lipoma is a well-defined,
fat density mass within a cistern. MR appearances show T1 hyperintensity, T2 hyperintensity, fat suppression and no enhancement.
Chemical shift artifact seen around the hyperintensity confirms the fatty origin of the mass as opposed to hemorrhage. Interhemispheric lipomas are invariably associated with hypogenesis
of the corpus callosum. A pericallosal lipoma
might also show multiple signal voids because
of a combination of traversing vessels and calcification. Small lipomas might not demonstrate
chemical shift artifact. In such cases, fat saturation can be very helpful in differentiating this
lesion from other T1 bright lesions.
Which one of the following is likely based on the MRI shown?
a. Closed-lip schizencephaly
b. Cobblestone cortex
c. Septo-optic dysplasia
d. Subcortical heterotopia
e. Tuberous sclerosis
c. Septo-optic dysplasia
Coronal T2-weighted MRI shows an absent septum pellucidum, right optic nerve hypoplasia,
and “point-down” appearance of the frontal horns
of the lateral ventricles. The main features of
septo-optic-pituitary dysplasia include hypoplasia
or absence of the septum pellucidum, optic nerve
hypoplasia, and hypothalamic-pituitary dysplasia
or dysfunction. SOPD is sporadic in most of the
cases, with no etiologic factor identified although
seen with maternal diabetes and intrauterine
CMV infection. Clinical presentation is mainly
related to seizures (50%), pituitary dysfunction
or visual symptoms such as nystagmus or
decreased visual acuity. Ophthalmoscopic examination shows optic nerve hypoplasia, a pale optic nerve head, and isolated tortuosity of the retinal vein. Fifty percent of patients might present
with seizures. MRI may show corpus callosum agenesis lead to a box-like shape of the frontal
horns in coronal planes, low-lying fornix (due to
absent septum), pituitary hypoplasia/empty
sella/ectopic posterior pituitary gland, hypothalamic hypoplasia, optic nerve and/or optic
chiasm hypoplasia (visualization difficult as mild
form—ophthalmological findings more reliable).
In addition, the remainder of the brain parenchyma might have a variety of other congenital
anomalies like malformations of cortical development (schizencephaly and gray matter
heterotopia), olfactory hypoplasia (arrhinencephaly), hypoplasia of white matter, and/or ventriculomegaly.
Which one of the following is most likely based on the MRI shown?
a. Blake’s pouch cyst
b. Chiari III malformation
c. Dandy-Walker Malformation
d. Joubert’s syndrome
e. Mega cysterna magna
c. Dandy-Walker Malformation
The classic triad of the full-blown Dandy-Walker
malformation is complete or partial agenesis of
the vermis, cystic dilation of the 4th ventricle,
and an enlarged posterior fossa with upward displacement of the transverse sinuses, tentorium,
and torcula. Hydrocephalus seen in 80% of cases
but is not a part of the essential criteria. The presence of vermian agenesis and cystic dilatation
of the fourth ventricle without an enlarged posterior fossa is termed Dandy-Walker variant, and
remains in the Dandy-Walker spectrum of
rhombencephalon roof development disorders
(though hydrocephalus is less common). Failure
of incorporation of the anterior membranous area
(AMA) into the choroid plexus leads to its persistence between the caudal edge of the developing vermis and the cranial edge of developing choroid plexus. CSF pulsations cause the AMA to balloon out into a cyst that displaces the hypoplastic vermis superiorly so that it appears to be rotated in a counterclockwise fashion. The posterior membranous area can persist unopened or become patent, accounting for the reportedly variable patency of the foramen of Magendie and association of hydrocephalus. Global enlargement of the PF may result from arrested development of the tentorium, straight sinus and torcula, with failure of migration of the straight sinus from the vertex to the lambda, possibly because of the abnormal distention of the 4th ventricle. Imaging in the Dandy-Walker spectrum aims to distinguish a
dilated 4th ventricle from extra ventricular cysts
and assess hydrocephalus (the foramen of Magendie is usually not patent, whereas the foramina of Luschka generally are).
Which one of the following is most likely based on the MRI shown?
a. Arachnoid cyst
b. Dandy-Walker variant
c. Epidermoid cyst
d. Medulloblastoma
e. Type II Chiari malformation
a. Arachnoid cyst
An arachnoid cyst usually is evident as a CSF isointense, non-enhancing, space-occupying cyst with
walls that normally are too thin to visualize. It results
from splitting of arachnoid membrane with inner
and outer leaflet surrounding a cyst cavity which
can undergo progressive expansion due to a ballvalve mechanism, fluid secretion by the cyst wall,
or a small osmotic gradient. Arachnoid cysts are
filled with CSF and do not communicate with the
surrounding subarachnoid space and ventricular
system; they usually are not associated with brain
maldevelopment and may be present anywhere in
the posterior fossa.When the arachnoid cyst is present inferior to the vermis, it may compress the inferiorvermis,butidentificationofwhitematter toeach
vermian lobule suggests compression rather than
vermian hypoplasia seen in Dandy-Walker spectrum. Confusion may arise when they are large
andlocated posterior andinferior to the cerebellum.
Imaging features suggestive of arachnoid cyst are
similar intensity to CSF, mass effect, large cyst with
obstructive hydrocephalus and scalloping of the
occipital bone. The only definitive diagnosis of
arachnoid cyst can be made with CT cisternography: arachnoid cysts should not demonstrate
enhancement (or only after a delay), while cysts that
fill with contrast immediately are regarded as diverticula of the subarachnoid space. Mega cisterna
magna usually does not demonstrate mass effect
on the cerebellum and vermis even if large, and
hydrocephalus is generally absent. Arachnoid cysts
are not associated with an enlarged 4th ventricle,
whereas a persistent Blake’s pouch is. It is essential
to differentiate arachnoid cyst from epidermoid cyst
which can be easily done with the use of FLAIR
images and DWI (epidermoid cysts are diffusion
restricting). Most arachnoid cysts are an incidental
finding and patients are usually asymptomatic, but
symptoms due to mass effect or hydrocephalus can
be managed with fenestration or cystoperitoneal
shunt
A 31-year-old undergoes MRI for headache. On axial views the 4th ventricle is enlarged and on certain sequences choroid plexus can be seen under and posterior to the vermis entering the superior aspect of the lesion. There is no restricted diffusion. Which one of the following is most likely?
a. Arachnoid cyst
b. Blake’s pouch cyst
c. Cystic metastasis
d. Epidermoid
e. Type II Chiari malformation
b. Blake’s pouch cyst
Blake’s pouch is an embryologic midline evagination of the embryonic fourth ventricular roof
lined by ependyma, glia, and choroid plexus. In
normal early fetal development, this evagination
along the inferior surface of the vermis ruptures
and forms the foramen of Magendie that opens
into the subarachnoid space. If the evagination
fails to rupture, the diverticulum continues to
expand and eventually forms an uncommon midline posterior fossa cyst (Blake pouch cyst) which looks virtually identical to an arachnoid cyst posterior and inferior to the vermis. However, the
choroid plexus in a Blake pouch cyst at times
may be identified as being displaced into the cyst
along its superior wall (under and posterior to the
vermis), though this can be mimicked by a prominent inferior vermian vein. No MRI sequence
allows clear differentiation of a mega cisterna
magna from a Blake pouch cyst, but generally it
appears as a CSF collection with normal nonrotated cerebellar vermis, enlarged 4th ventricle
(though may be normal at times) and brainstem
compression, without other brain abnormalities.
A child undergoes MRI scan as part of epilepsy evaluation after two seizures unrelated to febrile episodes. There are no symptoms of hydrocephalus. MRI appearances are shown, and there is no diffusion restriction. Which one of the following is most likely?
a. Arachnoid cyst
b. Dandy-Walker malformation
c. Epidermoid cyst
d. Mega cisterna magna
e. Type III Chiari malformation
d. Mega cisterna magna
The cisterna magna is a normal subarachnoid cistern located below the cerebellum and behind the
medulla. Embryologically, it originates from the
permeabilization of theBlake’s pouch,which allows
CSF flow out of the 4th ventricle via the foramen of
Magendie. As such, it is in communication superiorly with the 4th ventricle and inferiorly with the peri-medullary subarachnoid spaces. The normal size limit is debated, but a mega cisterna magna refers to a cystic posterior fossa malformation that is characterized by large cisterna magna, an intact vermis, and absence of hydrocephalus. It is most likely the result of cerebellar volume loss and associated with cerebellar insults such as infection,
infarction, and inflammation, as well as chromosomal abnormalities. The appearance is similar to a persistent Blake’s pouch except for the consistent absence of hydrocephalus. The cerebellum and brainstem are typically normal. The vermis is intact, and there is usually no distortion of the cerebellum (unlike arachnoid cysts) though occipital scalloping may be seen when very large. Patients with mega cisterna magna do not usually have any neurological signs of involvement of PF. By
itself mega cisterna magna is asymptomatic, and
is usually discovered incidentally. The incidence
is high and represents approximately 50% of all cystic PF malformations. The CSF in the enlarged cisterna magna freely communicates with the
surrounding CSF spaces and does not obstruct
CSF circulation and hence hydrocephalus is absent.
If there is presence of hydrocephalus mega cisterna
magna is not the correct diagnosis and it should
then steer towards the diagnosis of a persistent
Blake’s pouch. There is no role for shunt surgery
even if the cisterna magna is extremely large.
Which one of the following is most likely based on the imaging shown?
a. Band heterotopia
b. Marginal glioneuronal heterotopia
c. Subcortical heterotopia
d. Subependymal heterotopia
e. Type II lissencephaly
d. Subependymal heterotopia
Heterotopias are focal collections of morphologically normal neurons in abnormal locations secondary to interrupted neuronal migration from
the ependyma of lateral ventricles to cortex.
The most common clinical presentation is seizure
disorder in the second or third decade. They are
classified by location: 1. Subependymal heterotopia (commonest):
unilateral or bilateral periventricular nodular
heterotopia, the latter is X-linked dominant
disorder only seen in females (lethal inmales).
2. Subcortical heterotopia: no longer includes
band heterotopia, which is included with
lissencephaly due to common genetic
background.
3. Marginal glioneuronal heterotopia—
overmigration of neurons and glial cells
into the leptomeninges but microscopic
and not visible on imaging.
Imaging shows focal ovoid lesions which match
the gray matter in signal intensity on all the
sequences, lack edema and do not enhance with
contrast. Differential diagnosis is subependymal
hamartomas of tuberous sclerosis (irregular, isoto hypointense to white matter, may enhance,
associated tubers) and subependymal metastases
A 45-year-old woman with intractable structural epilepsy who had experienced partial complex and secondarily generalized seizures from the age of 8 years. Coronal FLAIR MRI is shown. Which one of the following is most likely?
a. Abscess
b. Focal cortical dysplasia
c. Lissencephaly
d. Mesial temporal sclerosis
e. Tuberous sclerosis
b. Focal cortical dysplasia
FCD is the most commonly found malformation
of cortical development in the surgical series and
accounts for approximately 20-50% of all cases
that have undergone epilepsy surgery. Attempts
at classifying FCD have been incomplete and
unsatisfactory because of the absence of a scientifically proven etiology. The latest classification system uses a multimodality approach which includes a combination of histopathological examination, imaging, and genetic findings. The most common clinical presentation is partial seizures with an otherwise normal neurological examination. The classical imaging features of FCD seen on T2 or FLAIR images is focal cortical thinning
with hyperintensity and volume loss of the underlying white matter. High resolution thin section images may show focal blurring of the gray-white matter junction. Rarely, FCD may be associated with neuroglial tumors, such as dysembryoplastic neuroepithelial tumor and ganglioglioma and may also be seen in association with mesial temporal sclerosis.
Which one of the following is most likely
based on the imaging shown below?
a. Cobblestone cortex
b. Focal cortical dysplasia
c. Hemimegalencephaly
d. Lissencephaly with band heterotopia
e. Periventricular nodular heterotopia
d. Lissencephaly with band heterotopia
As progenitor cells begin to proliferate, they normally migrate outward from the germinal matrix
to form the cortex. Lissencephaly is a severe form
of abnormal neuronal migration characterized by
an absence of gyri with a thickened cortex (agyria)
or the presence of few broad fat gyri with a
thickened cortex (pachygyria), bothleading to a relatively smooth featureless brain. Classical lissencephaly presents with diffuse hypotonia, early
developmental delay, spastic quadriplegia, opisthotonus, and severemental retardation.Development
of medically refractory epilepsy at a very early age
with increasingly complex seizure patterns is very
common. There are two main types:
1. Type 1 “classical” lissencephaly (lissencephaly with band heterotopia): only four cortical layers.
2. Type 2 lissencephaly (cobblestone cortex):
no cortical layers.
Two separate mutations, a hemizygous mutation
in the DCX/XLIS gene on chromosome
Xq22.3q23 and a heterozygous (dominantly
inherited) mutation in the LIS1 gene on chromosome 17p13.3 can lead to classical lissencephaly.
The DCX mutation also results in subcortical
band heterotopia consists of a discrete extensive
plate or band of gray matter situated between
the cortex and the lateral ventricle. On imaging,
classical lissencephaly shows a smooth brain with
vertical orientation of the sylvian fissures giving
the cerebrum a “figure 8” appearance on axial
images, while band heterotopia shows a very
characteristic layered pattern from cortex to midline: normal thickness cortex with shallow sulci, a
variable thickness white matter band, an interposing gray matter band (the heterotopic band),
and a deeper white matter layer extending to
the ventricular margin or midline.
Which one of the following is most likely
based on the imaging shown?
a. Cobblestone cortex
b. Focal cortical dysplasia
c. Lissencephaly with band heterotopia
d. Periventricular nodular heterotopia
e. Polymicrogyria
a. Cobblestone cortex
In cobblestone cortex (Type 2 lissencephaly) the
brain surface is irregular because of the presence
of heterotopic tissue which results from overmigration of glioneural elements. In general,
this malformation shows a cobblestone cortex,
dilated ventricles, abnormal white matter, a small
brainstem, a hypoplastic vermis, and cerebellar
polymicrogyria. It is associated with eye malformations as well as congenital muscular dystrophy, e.g., Walker-Warburg syndrome, Muscleeye-brain disease, Fukuyama congenital muscular dystrophy.
Which one of the following is most likely based on the imaging shown below?
a. Lissencephaly with band heterotopia
b. Porencephalic cyst
c. Pachygyria
d. Schizencephaly
e. Semilobar holoprosencephaly
d. Schizencephaly
Schizencephaly (clefted brain) is a brain malformation characterized by a full-thickness cerebral
cleft. This cleft extends from the pial surface of
the cortex to the ependymal lining of the lateral
ventricle, and is almost always lined by abnormal
gray matter (polymicrogyria). Schizencephaly
may result from disruption of any of the three
phases of cortical development (proliferation,
migration, and organization), but polymicrogyric
cortex surrounding the cleft suggests that it is a disorder of cortical organization, probably secondary
to hypoperfusion or ischemic cortical injury. As
such, itmay represent a spectrumwheremild damage results in polymicrogyria while severe damage
may involve the deep radial-glial fibers and result
in schizencephaly. It may be unilateral (60%) or
bilateral, and either:
1. Closed-lip schizencephaly (left hemisphere
in MRI shown), the margins of the cerebrospinal fluid (CSF)-filled, gray matter lined
cleft are closely opposed to one another
along the entire length of the cleft. A small
dimple is often seen in the ventricular wall
where the cleft enters.
2. Open lip schizencephaly (right hemisphere
in MRI shown) the cleft margins are widely
separated, lined with polymicrogyria,
absent septum pellucidum, dilated ventricles, scalloping and thinning of the inner
vault of the calvarium (direct transmission
of CSF pulsations), and the contralateral
cerebral cortex may be dysplastic. On
T2WI, a large vessel may be seen traversing
the CSF cleft.
Unilateral closed-lip schizencephaly commonly
presents with epilepsy, while open lip schizencephaly generally presents with microcephaly,
contralateral hemiparesis, and mental retardation. Bilateral schizencephaly manifests as severe
mental retardation with early onset epilepsy.
Blindness because of optic nerve hypoplasia
may be seen in 30% of cases. Porencephalic cysts
are intraparenchymal and lined by white matter
Which one of the following is most likely based on the imaging shown below?
a. Agyria
b. Lissencephaly with band heterotopia
c. Pachygyria
d. Polymicrogyria
e. Walker-Warburg syndrome
d. Polymicrogyria
Polymicrogyria (multiple malformed convulsions)
is caused by disturbances in the late stages of neuronal migration or in the early stages of cortical
organization (typically between 17 and 25-26weeks
of gestation). These disturbances result in the
abnormal development of the deep layer of cerebral cortex which manifests as multiple small gyri separated by small sulci generating an irregular
bumpy cortical surface. Causes include intrauterine ischemia, intrauterine infection (CMV or
toxoplasmosis), metabolic disorders (e.g., peroxisomal storage disorders, pyruvate dehydrogenase deficiency), or genetic syndromes (e.g., Aicardi syndrome, DiGeorge syndrome, and Warburg Micro syndrome). The most common sites for PMG are the sylvian cortex (80%) and frontal lobes (70%) followed by the parietal, temporal and occipital lobes. Involvement may be either bilateral
(60%) or unilateral (40%), focal or diffuse, symmetric or asymmetric. MRI shows a bumpy irregular
appearance of the outer surface of the cortex
because of multiple small gyri, diffuse cortical
thickening, and an irregular corrugated appearance
of the inner cortical surface (gray-white matter
junction). Most common presentation is seizures
(80%), but diffuse polymicrogyria can present with
microcephaly, hypotonia, and infantile seizures
with marked developmental delay (also possibly
contralateral hemiplegia).
Which one of the following is most likely based on the imaging shown?
a. Alobar holoprosencephaly
b. Anencephaly
c. Dandy-Walker malformation
d. Porencephalic cyst
e. Schizencephaly
a. Alobar holoprosencephaly
Holoprosencephaly (HPE) is the most common
developmental defect of the forebrain, with a live
birth prevalence of approximately 1 in 10,000.
The formation of two hemispheres from a single
telencephalic vesicle begins around the 37th
embryonic day. This division takes place as a
result of induction by bone morphogenetic protein from the midline roof plate. The etiology
of HPE is heterogeneous and might be due to
either genetic causes (Sonic hedgehog pathway
most common) or environmental factors, including maternal diabetes and exposure to teratogens
such as alcohol. SHH is a protein that encodes a
morphogen which mediates notochordal-ventral
neural tube and development of craniofacial
structures (facial deformities are also seen in association with the HPE spectrum). In HPE, the
forebrain fails to divide into two separate hemispheres; rather, it develops into a single, unpaired forebrain called the holoprosencephalon. The degree of failure of hemisphere cleavage is classified as alobar, semilobar, and lobar HPE. Alobar HPE is the most common and most severe form, resulting in either stillbirth or a very short lifespan. In alobar HPE, the holosphere remains
undivided as a single flattened mass of brain surrounding a midline holoventricle that is large and shaped like an inverted “U” or crescent. It is usually associated with severe facial deformities like
premaxillary agenesis, cleft lip/palate, ocular
hypotelorism, ethmocephaly (proboscis between
the eyes), and in severe cases, cyclopia. On imaging, the holosphere is noted to be displaced in the
most cephalad part of the intracranial cavity.
There is complete absence of the interhemispheric fissure, falx cerebri, and corpus callosum.
The gyri recti are also absent. This is associated
with aplasia of the olfactory bulbs and optic
nerves. The basal ganglia and thalami are fused
and located in the floor of the holoventricle.
The sylvian fissures and third ventricle are not
present. A dorsal cyst is frequently seen communicating with the monoventricle.
Which one of the following is most likely based on the imaging shown below?
a. Atretic cephalocele
b. Encephalocele (meningoencephalocele)
c. Gliocele
d. Meningocele
e. Meningoencephalocystocele
b. Encephalocele (meningoencephalocele)
Cephaloceles are complex neural axis malformations which manifest as herniation of the meninges and often cerebral tissue through a defect in
the calvarium. Incidence is 1 in 10,000—1 in
1000 depending on series. They are usually midline, but vary in location with occipital (75%) site
commonest in Europe and North America. They
are thought to be attributable to nonseparation of
neural and surface ectoderm leading to defective
formation of the occipital bone. They can be classified by contents:
1. Meningocele: contains CSF and lined by
meninges.
2. Gliocele: contains CSF and lined by glial
tissue.
3. Encephalocele (meningoencephalocele):
contains CSF and brain.
4. Meningoencephalocystocele: contains
CSF, brain and ventricles.
5. Atretic cephalocele: small nodule of fibrous
fatty tissue.
Occipital cephaloceles are often large but usually
covered with normal skin and hair, with herniation
of the infra and/or supratentorial structures
through a narrow pedicle. Herniated brain tissue
may be normal, dysplastic, or may show new/old
ischemic or hemorrhagic changes because of
strangulation of the blood vessels at the neck of
the sac. The tentorium is frequently reduced into crescentic folds and is inserted inferior to the
petrous ridge, leading to a narrow, funnel-shaped
lower posterior fossa. The falx is usually thin,
hypoplastic, and may either attach to the superior
margin of the defect or herniate into the encephalocele. Because of traction, the cerebral parenchyma is pulled posteriorly, and nonherniated
brain may assume abnormal positions in the skull.
The anterior commissure, septum pellucidum,
and fornices are absent in 80% of cases. Hydrocephalus may affect the entire ventricular system or it may be limited to the extracranial portion of the ventricles. Other associated anomalies like cerebellar cortical dysplasia, heterotopias, Chiari or Dandy-Walker malformation, and partial/complete absence of corpus callosum may be seen. By definition, Type III Chiari malformation includes an occipital or cervicooccipital encephalocelewith herniation of themedulla, 4th ventricle and cerebellum, and sometimes the occipital
lobes (rare).
A newborn infant has an apneic event with cyanosis and he was brought to the hospital. His evaluation was remarkable for developmental delay, bilateral lower-extremity frog-leg flaccid paralysis, with a large open defect in his lower back. At birth, the defect was covered by a transparent membrane, which subsequently ruptured and drained clear fluid for several weeks. Based on the imaging below, what is the cause of the infant’s apneic events?
a. Dermal sinus tract
b. Dorsal enteric fistula
c. Lipomyelomeningocele
d. Myelocele
e. Type II Chiari malformation
e. Type II Chiari malformation
MRI depicting cerebellar vermian displacement,
downward displacement of cerebellar tonsils and
brainstem, cervical hydrosyrinx, ventriculomegaly,
and pachygyria. (Right) T2-weighted MRI of the
lumbosacral spine depicting hydrosyrinx, tethered
cord, and unrepaired lumbosacral myelomeningocele. In a Chiari II malformation, there is displacement of the cerebellum, part of the brainstem, and
the fourth ventricle into the cervical canal (below
the basion-opisthion line). A lumbar myelomeningocele is seen in almost all the cases. Several prominent theories exist regarding etiology:
1. Traction theory: primary defect is tethering
of the spinal cord which leads to abnormal
traction and pulling of the posterior fossa
contents into the cervical canal.
2. Crowding theory: primary defect is in the
mesodermal development involving the
cranial base rather than neuroectodermal
tissue, resulting in a smaller posterior fossa,
underdevelopment of the occipital bone,
and basal chondrocranium, which is unable
to accommodate rapidly developing neural
tissue which herniates through the foramen
magnum.
3. Unified Theory/Hydrodynamic Oligo-CSF
states that neurulation is the primary defect.
There is lack of expression of the specific
surface molecules required for neural tube
closure, leading to incomplete occlusion of
the neural tube and leakage of CSF through
the neural tube. Subsequent hypotension develops within the ventricular system. This
disruption in the CSF dynamics has an effect
all along the neural tube (from rostral to the
caudal). At the level of lateral ventricle, the
germinal matrix is disrupted, leading to malformation of the cortical development. At
the level of the third ventricle, there is
enlargement of massa intermedia because
of extended contact between the thalami.
In the posterior fossa, the rhombencephalic
vesicle fails to expand, therefore stopping
the induction of the perineural mesenchyma
of the posterior fossa. All of this leads to a
smaller posterior fossa, which is unable to
accommodate the developing rhombencephalon. The result is displacement of cerebellum and brainstem into the cervical
canal.
4. Primary defect in the genetic programming
of hindbrain segment and growth associated structures of chondrocranium
The MRI shown below demonstrates features of which one of the following conditions?
a. Chiari I malformation
b. Chiari II malformation
c. Chiari III malformation
d. Chiari IV malformation
e. Basilar invagination
a. Chiari I malformation
Chiari I malformation is defined as inferior
displacement of the cerebellar tonsils below the
basion-opisthion line. Tonsillar herniation can
be due to multiple causes:
1. Intracranial pressure: both intracranial
hypertension and intracranial hypotension.
2. Congenital or acquired osseous anomaly or
pathology of the posterior fossa and craniovertebral junction caused by softening of the
skull base, leading to a decrease in the size
of the posterior fossa (e.g., osteogenesis
imperfecta, Paget’s disease, platybasia, or basilar invagination).
3. Congenital causes: mesodermal abnormalities leading to a short clivus, reduced height
of the supraocciput, and increased slope of
tentorium severely reduce posterior fossa
volume with subsequent overcrowding of
the contents and inferior displacement of
the tonsils and/or vermis.
Stridor and hindbrain dysfunction are the most
common clinical presentations during the first
3 months in a child with a type I Chiari malformation. The stridor usually disappears by 3 months of
age. Another common clinical presentation in
children is a headache, which may be generalized,
or can be localized to occipital region. In children,
this headache becomes exacerbated by physical
exercise, straining, or coughing. Other symptoms
related to cerebellar or brainstem dysfunction, such as cranial nerve palsy or otoneurologic disturbances, such as tinnitus, vertigo, and dizziness,
dysmetria (tremors and down-beating nystagmus). Disorders of motor, sensation, and reflexes
are seen when there is an associated syrinx in the
cervical/thoracic cord. MRI is done to assess
whether clinically significant hindbrain herniation is present and likely cause; normal tonsillar
descent below the basion-opisthion line is up to
6 mm in 5- to 15-year-olds and up to 5 mm in anyone over 15 years. Secondary features include a
pointed appearance of the cerebellar tonsils, compression of cerebellar cistern (demonstrated by
effacement of vallecula and cisterna magna), retroflexion of the odontoid process, compression of
the fourth ventricle, and syringohydromyelia.
You plan to perform a foramen magnum decompression on the patient shown below. Which one of the following investigations
may be helpful?
a. CSF flow study
b. CT cisternography
c. CT cervical angiogram
d. Flexion/extension X-rays
e. Nerve conduction studies
a. CSF flow study
Syringohydromyelia may be seen in the cervical
cord in 30-50% of Chiari I malformations. In
healthy patients, an increase in the cerebral blood
volume during the cardiac systole causes displacement of the corresponding amount of CSF from the basal cistern into the cervical subarachnoid space. In diastole with cerebral venous outflow, there is a caudo-cranial diastolic CSF wave. In hindbrain herniation, syrinx formation may occur due to partial obstruction of the CSF flow channel around the craniocervical junction and Venturi effect with enhanced intramedullary pulse
pressure causing extracellular fluid accumulation
in the distended cord. The syrinx may form anywhere along the cord, hence whole spine MRI
is advised in patients with tonsillar herniation
symptoms, such as sensori-motor weakness of
the extremities, and/or loss of bladder/bowel control. MRI CSF flow studies can also be performed
to study the CSF motion in and around the foramen magnum to predict likely benefits of decompressive surgery. In addition, before surgical
intervention, a low tentorium should be evaluated
with MR venography to document a low-lying
torcula and transverse sinus to avoid damage during decompressive surgery.
Which one of the following is most likely based on the clinical image shown below?
a. Achondroplasia
b. Closed spinal dysraphism
c. Klippel-Feil syndrome
d. Sturge-Weber syndrome
e. Wyburn-Mason syndrome
b. Closed spinal dysraphism
This infant displays segmental infantile hemangiomas, a dimple, a pseudotail, and a deviated gluteal cleft suggesting the presence of a closed (occult) spinal dysraphism. Other midline lesions
to look for include a. The clinical presentation
varies to some degree by age. Younger children
tend to present with cutaneous markers that lead
to an evaluation for CSD, but on formal testing,
most have mild signs of lower motor neuron dysfunction and abnormalities on urodynamic testing. Older children and adolescents tend to
present with either cutaneous stigmata or with
progressive neurologic deficits. Some affected
individuals remain asymptomatic into adulthood,
at which time they may develop back pain with or
without radiculopathy and perineal dysesthesias.
Features associated with closed spinal dysraphism
are summarized below:
If present, clinical evaluation for TCS should
be performed as far as possible given the age of
the patient. If there is a high clinical suspicion
(or age >3-5 months or bulky lesion precluding
USS) spinal MRI should be performed and
depending on significance of findings, referral
to neurosurgeon or neurologist made. Spinal
US can be performed in those under 3-5 months
and low clinical suspicion of TCS, but inappropriate visualization will necessitate MRI.
Which one of the following is most likely
based on the findings in the image below?
a. Lipomyelomeningocele
b. Meningocele
c. Myelocele
d. Myelocystocele
e. Myelomeningocele
e. Myelomeningocele
Open spinal dysraphism (OSD) is a clinical diagnosis and a neurosurgical emergency. Myelomeningocele accounts for 99% of OSD, myelocele is
rare, and hemimyelocele and hemimyelomeningocele extremely rare. In all cases there is defective closure of the primary neural tube (primary neurulation) resulting in the neural placode being exposed through a midline skin defect on the back. In myelomeningocele, neural placode protrudes above skin surface, whereas in myelocele, the placode is flush with skin surface. The abnormality is most commonly found at lumbosacral region and a Chiari II malformation is invitable due to CSF leak. Surgical repair and closure of the defect is required as soon as possible. While
imaging is not necessarily required before
closure, MR imaging should be performed to
assess for associated pathology at other levels
(e.g., split cord malformation, lipoma, dermoid/
epidermoid, Chiari II malformation) and is crucial in patients presenting with progressive neurological deficits postoperatively (e.g., exclude
cord ischemia, arachnoid cyst, scar tethering).
