Neurology Cat 1 Flashcards
Dysgenesis of the corpus callosum - definition
primary agenesis: the corpus callosum never forms
secondary dysgenesis: the corpus callosum forms normally and is subsequently destroyed
Dysgenesis of the corpus callosum: epidemiology
1/20 000
M:F = 2:1
Risk factor: maternal alcohol consumption
Dysgenesis of the corpus callosum: Clinical presentation
Dictated by associated abnormalities
may have dysmorphic faces - hypertelorism
Dysgenesis of the corpus callosum: radiographic features - Antenatal Ultrasound
third ventricle
-dilated
- can be elevated or dorsally displaced
- may communicate with the interhemispheric cistern
- may project superiorly as a dorsal cyst
- choroid may be seen as an echogenic structure in the roof of the cyst
lateral ventricles
- widely spaced parallel bodies (racing car sign)
- small frontal horns
- colpocephaly: which can give a “teardrop” configuration on axial scans
septum pellucidum: absent
interhemispheric fissures: widened
gyri: may be seen in a “sunray appearance” on the sagittal plane
colour Doppler study may show an abnormal course of pericallosal arteries
Dysgenesis of the corpus callosum: Prognosis
Variable depending on the presence of other abnormalities
Dysgenesis of the corpus callosum: Differential diagnosis
Ddx of an interhemispheric cyst
Cavum septum pellucidum
Cavum vergae
cavum velum interpositum
interhemispheric arachnoid cyst
Dysgenesis of the corpus callosum: radiographic features - MRI
ventricles
- run parallel rather than the normal “bow-tie” configuration giving a racing car appearance on axial imaging
- colpocephaly (dilatation of the trigones and occipital horns) gives a characteristic “Texas longhorn”/moose head/viking helmet appearance on coronal imaging
- dilated high-riding 3rd ventricle appears to communicate with the interhemispheric cistern or project superiorly as a dorsal cyst
cortex
- bundles of Probst
- radial gyri (absent cingulate gyrus)
- everted cingulate gyrus
limbic system
- hypoplastic fornices
- hypoplastic hippocampi
Chiari 1 Malformation: Definition
Most common variant. Caudal descent of the cerebellar tonsils through the foramen magnum
Chiari 1 Malformation: Epidemiology
0.5-3.5% of the general population
F >M = 3:1
Chiari 1 Malformation: Clinical Presentation
- Occipital headache
- Exacerbated by cough, Valsalva, neck extension, or physical exertion
- Less common: Cerebellar, brainstem, bulbar, cord motor/sensory symptoms
- Cerebellar symptoms: Ataxia, dysarthria, oscillopsia, nystagmus
- Brainstem & Bulbar symptoms: Vertigo, diplopia, dysphagia, aspiration, apnea, syncope, bradycardia, sudden death (rare)
- Spinal cord dysfunction: Motor & sensory losses, hyporeflexia, hyperreflexia, clonus, gait disturbance, neuropathic joint, urinary incontinence, positive Babinski sign, scoliosis
- 15-30% of adults with CM1 are asymptomatic, up to 35% of children with 5-10 mm of tonsillar herniation are asymptomatic
- Not much difference in clinical symptoms between complex Chiari & typical Chiari 1
Chiari 1 Malformation: Associations
- cervical cord syrinx in ~35% (range 20-56%): more common in symptomatic patients
-
hydrocephalus in up to 30% 2,3 of cases
- thought to result from abnormal CSF flow dynamics through the central canal of the cord and around the medulla
- skeletal anomalies in ~35% (range 23-45%) 2,3:
Chiari 1 Malformation: Diagnostic clue
Pointed cerebellar tonsils (unilateral or bilateral) extending ≥ 5 mm below foramen magnum (basion-opisthion line, a.k.a. McRae line)
- Mild variations in measurement reported in literature; measurement on its own may not be definitive of diagnosis
- No consensus statement on exact definition
Chiari 1: CT
- Crowding of foramen magnum on axial CT images
- Sagittal reconstructed images are very helpful
- Partially imaged superior aspect of spinal cord syrinx may be identified
- Associated osseous anomalies may include small posterior fossa, short horizontal clivus, retroverted dens, basilar invagination, platybasia, hypoplastic occipital condyles, segmentation anomalies (such as atlantooccipital assimilation), scoliosis
Chiari 1 Malformation: MRI
- T1WI, T2WI, FLAIR
- Pointed (not rounded) cerebellar tonsils extending ≥ 5 mm below foramen magnum
- Crowded foramen magnum with small/effaced cisterns ± brainstem compression (kinking)
- ± small posterior fossa, elongated 4th ventricle
- ± syringohydromyelia/syrinx, scoliosis
- Syrinx reported in 30-70% of cases
- Patients with syrinx more likely to have scoliotic curve > 20⁰ (~ 70%) than those without syrinx (~ 45%)
- Other descriptions usually considered subtypes
- Chiari 1.5: Brainstem herniation
- Obex located below foramen magnum
- Complex Chiari: Medullary kink, retroflexed dens, abnormal clival-cervical angle, atlantooccipital assimilation, basilar invagination, platybasia
- Chiari 1.5: Brainstem herniation
- MR cine
- Restricted CSF flow through foramen magnum ± increased brainstem/cerebellar tonsil motion (pistoning)
- Clinical utility of this sequence debatable
- Restricted CSF flow through foramen magnum ± increased brainstem/cerebellar tonsil motion (pistoning)
Chiari 1 Malformation: Treatment
- Posterior fossa decompression: Suboccipital craniectomy with C1 laminectomy ± duraplasty, arachnoid opening/dissection, cerebellar tonsil cautery/resection
- Decrease of syrinx size in majority of patients after decompression
- Complex Chiari 1 may also require odontoid resection or CCJ fusion
- Scoliosis may improve from decompression alone but often requires bracing or additional surgery
- Postoperative complications in ~ 20% of adults & 37% of children
- Most common: CSF leak, pseudomeningocele, infection
- Increased risk with duraplasty
- 1-11% postoperative mortality
- Most common: CSF leak, pseudomeningocele, infection
- Conservative management for asymptomatic or minimally symptomatic children without syrinx
Chiari II: Definition
Chiari 2 malformation: Constellation of intracranial anomalies, mainly hindbrain herniation, in setting of open spinal dysraphism [either myelomeningocele (MMC) or myelocele/myeloschisis
Chiari II: Epidemiology
M = F
0.44/1000
Decreased risk with folate therapy
Chiari II: Clinical presentation
- ### Most common signs/symptoms
- 80-90% develop hydrocephalus requiring shunting, though less incidence of shunting in those who undergo prenatal repair of the open spinal dysraphism
- Varying degrees of lower extremity paresis/spasticity, clubfoot, bowel/bladder dysfunction
- ± epilepsy, symptoms from brainstem compression (swallowing difficulties, stridor, apnea)
- Laboratory
- Fetal screening: ↑ alpha-fetoprotein
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- Fetal screening: ↑ alpha-fetoprotein
Chiari II: radiological features - diagnostic clue
- ### Best diagnostic clue
- Small posterior fossa with inferior cerebellar and brainstem herniation in presence of open spinal dysraphism
- ### Location
- Intracranial (supratentorial + infratentorial) and intraspinal neuroectoderm + surrounding mesoderm (skull, spine)
- ### Morphology
- Grading system for Chari II malformation on fetal MR based on posterior fossa morphology
- Grade 1: 4th ventricle and cisterna magna are patent
- Grade 2: 4th ventricle is effaced, cisterna magna is patent
- Grade 3: 4th ventricle and cisterna magna are effaced
- Grading system for Chari II malformation on fetal MR based on posterior fossa morphology
Chiari II: radiological features - CT
- ### Bone CT
- Small posterior fossa with bony deformities from pressure of cerebellum and brainstem
- Large foramen magnum with notched opisthion
- Posterior concavity/scalloping of clivus and petrous temporal bones
- Low-lying tentorium/torcular Herophili inserts near foramen magnum
- Small posterior fossa with bony deformities from pressure of cerebellum and brainstem
Chiari II: radiological features - MRI
- Hindbrain herniation (postnatal repair)
- Caudal descent of pointed tonsils/vermis into foramen magnum
- Towering appearance of cerebellum with upward herniation through widened incisura
- Cerebellar hemispheres wrap around brainstem
- Elongated, effaced, inferiorly displaced 4th ventricle with flattened fastigium
- Cerebellar atrophy over time; most severe form: Vanishing cerebellum
- Significant hindbrain herniation is not usually present in setting of prenatal repair
- Small posterior fossa with downward-sloping tentorium, low torcular Herophili
- Tectal beaking, brainstem caudal displacement ± cervicomedullary kink
- ± ventriculomegaly
- Midline anomalies: Large massa intermedia, callosal hypogenesis/dysgenesis, absent septum pellucidum
- ± neuronal migrational anomalies: Heterotopia, polymicrogyria, rhombencephalosynapsis
- Falx insufficiency with interdigitation of hemispheric gyri
- Stenogyria (elongated, compact gyri) after shunting (differs from polymicrogyria)
- Significant hindbrain herniation not always present on fetal MR in setting of open spinal dysraphism (~ 8%)
Chiari II: radiological features -USS
- ### Grayscale ultrasound
- Prenatal US key for early diagnosis
- Nearly all cases can be identified in 2nd trimester
- Lemon sign: Bifrontal concavity of calvarium
- Banana sign: Cerebellum wraps around brainstem
- Postnatal head US
- Findings follow MR, though posterior fossa more difficult to visualize due to distance from transducer
- Mastoid fontanelle view may be helpful for posterior fossa visualization
- Useful for following change in ventricular size to know if CSF diversion (shunting) required
- Findings follow MR, though posterior fossa more difficult to visualize due to distance from transducer
- Prenatal US key for early diagnosis
Chiari II: treatment
- Folate supplement for pregnant mothers (preconception → 6 weeks postconception) significantly decreases MMC risk
- Surgical management
- MMC classically repaired in first 48 hours after delivery
- Early intervention required to reduce risk of infection
- Many different techniques described: Primary skin closure, myocutaneous flap, fasciocutaneous flap
- CSF diversion/shunting ultimately required in 80-90%
- Required in majority of patients (~ 60% in neonatal period); 10-20% do not develop hydrocephalus
- Posterior fossa decompression in those who do not improve with shunting
- There has been shift away from this practice in recent years
- MMC classically repaired in first 48 hours after delivery
- Fetal MMC repair in select patients
- Must have hindbrain herniation and upper level of spinal defect T1-S1
- Reduces need for shunting; may improve neurologic outcomes in some patients
Arachnoid cyst: Terminology
Intraarachnoid CSF-containing sac that does not communicate with ventricular system
Arachnoid cyst: epidemiology
- 75% in children
- M:F = 3-5:1
- Most common intracranial cystic abnormality
- 1% of all intracranial masses
- 2% incidental finding on imaging for seizure
Arachnoid cyst: treatment
- Usually none
- Majority of ACs are found incidentally
- Resection (may be endoscopic)
- Fenestration/marsupialization
- Shunt (cystoperitoneal is common option)
Arachnoid cyst: differentials
- ## Epidermoid Cyst
- Scalloped margins
- Insinuating growth pattern
- Creeps along into CSF cisterns
- Surrounds, engulfs vessels/nerves
- ACs displace but usually do not engulf vessels, cranial nerves
- Does not suppress on FLAIR
- Restricted diffusion (bright) on DWI
- ## Chronic Subdural Hematoma
- Signal not identical to CSF
- Often bilateral, lentiform-shaped
- ± enhancing membrane
- Look for foci of blooming on T2*
- < 5% of ACs hemorrhage
- ## Subdural Hygroma
- Often bilateral
- Crescentic or flat configuration
- ## Other Nonneoplastic Cysts
- Porencephalic cyst
- Surrounded by gliotic brain, not compressed cortex
- History of trauma, stroke common
- Neurenteric cyst
- Rare; spine, posterior fossa = most common locations
- Often proteinaceous fluid
- Neuroglial (glioependymal) cyst
- Rare
- Usually intraaxial
- Porencephalic cyst
Arachnoid cyst: Radiology features - diagnostic clues
- ### Best diagnostic clue
- Sharply demarcated, round/ovoid extraaxial cyst that follows CSF attenuation/signal
- ### Location
- Middle cranial fossa (MCF) (50-60%)
- Cerebellopontine angle (CPA) (10%)
- Suprasellar arachnoid cyst (SSAC), variable types (10%)
- Noncommunicating = cyst of membrane of Liliequist
- Communicating = cystic dilation of interpeduncular cistern
- Miscellaneous (10%)
- Cerebral convexity
- Quadrigeminal plate
- Retrocerebellar
- ### Size
- Varies from few mm to 5 cm or more
- ### Morphology
- Sharply delineated, translucent cyst
- Displays features of extraaxial mass
- Displaces cortex
- “Buckles” gray-white interface
Arachnoid cyst: Radiology features - CT
- ### NECT
- Usually CSF density
- Hyperdense if intracyst hemorrhage present (rare)
- May expand, thin/remodel bone
- Usually CSF density
- ### CECT
- Does not enhance
- ### CTA
- Posterior displacement of middle cerebral artery (MCA) in MCF ACs
- Cisternography may demonstrate communication with subarachnoid space
Arachnoid cyst: Radiology features - MRI
- ### T1WI
- Sharply marginated extraaxial fluid collection isointense with CSF
- ### T2WI
- Isointense with CSF
- ### PD/intermediate
- Isointense with CSF
- ### FLAIR
- Suppresses completely
- ### T2* GRE
- No blooming unless hemorrhage present (rare)
- SWI can demonstrate veins displaced around AC
- ### DWI
- No restriction; nearly identical to ventricles
- ### T1WI C+
- Does not enhance
- ### MRA
- Cortical vessels displaced away from calvarium
- ### MRV
- Can demonstrate anomalies of venous drainage
- ### MRS
- Can predict pathology in > 90% of similar-appearing intracranial cystic lesions
Colloid cyst: definition
Colloid cysts of the third ventricle are benign epithelial lined cysts with characteristic imaging features. Although usually asymptomatic, they can rarely present with acute and profound hydrocephalus.
Colloid cyst: epidemiology
Age: 3rd-4th decades, rare in children
M = F
Colloid cyst: Clinical presentation
- ### Most common signs/symptoms
- Headache (50-60%)
- Less common = nausea, vomiting, memory loss, altered personality, gait disturbance, visual changes
- Acute foramen of Monro obstruction may lead to rapid onset hydrocephalus, herniation, death
- 40-50% asymptomatic, discovered incidentally
- 5-15% 5-year risk of future progression necessitating operative intervention
- ### Clinical profile
- Adult with headache
Colloid cyst: Treatment
- Most common = complete surgical resection
- Neuronavigation-guided endoscopic removal + capsule coagulation
- 50% experience short-term memory disturbance (usually resolves)
- Recurrence rare if resection complete
- Options
- Stereotactic aspiration (difficult with extremely viscous/solid cysts)
- Imaging features that may predict difficulty with percutaneous therapy
- Hyperdensity on CT/hypointensity on T2WI suggest high viscosity
- Ventricular shunting
- Observation (rare; not recommended, as sudden obstruction can occur with even small CCs)
*
Colloid cyst: Radiology - general features
- ### Best diagnostic clue
- Hyperdense foramen of Monro mass on NECT
- ### Location
- > 99% are wedged into foramen of Monro
- Attached to anterosuperior 3rd ventricular roof
- Pillars of fornix straddle, drape around cyst
- Posterior part of frontal horns splayed laterally around cyst
- < 1% found at other sites
- Lateral, 4th ventricles
- Extraventricular CCs (very rare)
- Parenchyma (cerebellum)
- Extraaxial (prepontine, meninges, olfactory groove)
- > 99% are wedged into foramen of Monro
- ### Size
- Variable (few mm to 3 cm)
- Mean: 15 mm
- ### Morphology
- Well-demarcated round > ovoid/lobulated mass
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- Well-demarcated round > ovoid/lobulated mass
Colloid cyst: Radiology - CT
- ### NECT
- Density correlates inversely with hydration state
- 2/3 hyperdense
- 1/3 iso-/hypodense
- ± hydrocephalus
- Rare
- Hypodense
- Change in density/size
- Density correlates inversely with hydration state
- ### CECT
- Usually does not enhance
- Rim enhancement (rare)
Colloid cyst: Radiology - MRI
- ### T1WI
- Signal correlates with cholesterol concentration
- 2/3 hyperintense on T1WI
- 1/3 isointense
- Small CCs may be difficult to see
- May have associated ventriculomegaly
- Signal correlates with cholesterol concentration
- ### T2WI
- Signal more variable
- Generally reflects water content
- Majority isointense to brain on T2WI
- Small CCs may be difficult to see
- Less common findings
- 25% mixed hypo/hyper (“black hole” effect)
- Rare
- Fluid-fluid or blood-fluid level (cyst “apoplexy”), Ca⁺⁺ rare
- Signal more variable
- ### FLAIR
- Does not suppress
- ### DWI
- Does not restrict
- ### T1WI C+
- Usually no enhancement
- Rare: May show peripheral (rim) enhancement
- ### MRS
- Normal brain metabolites absent
Colloid cyst: Differential diagnosis
- ## Neurocysticercosis
- Multiple lesions within parenchyma and cisterns
- Associated ependymitis or basilar meningitis common
- Ca⁺⁺ common
- Look for scolex
- ## Cerebrospinal Fluid Flow Artifact (MR “Pseudocyst”)
- Multiplanar technique confirms artifact
- Look for phase artifact
- ## Vertebrobasilar Dolichoectasia/Aneurysm
- Extreme vertebrobasilar dolichoectasia (VBD) can cause hyperdense foramen of Monro mass
- Look for flow void, phase artifact on MR
- ## Neoplasm
-
Subependymoma
- Frontal horn of lateral ventricle
- Attached to septum pellucidum
- Patchy/solid enhancement
-
Craniopharyngioma
- 3rd ventricle rare location
- Usually not wedged into foramen of Monro, fornix
- Ca⁺⁺, rim/nodular enhancement common
-
Pituitary adenoma
- Rare in 3rd ventricle
- Enhances (usually strongly, uniformly)
-
Subependymoma
- ## Choroid Plexus Mass
-
Choroid plexus papilloma
- Rare in 3rd ventricle
- Tumor of early childhood
-
Xanthogranuloma
- Rare in 3rd ventricle
- Ovoid > round
- Can be hyper- or hypodense ± Ca⁺⁺
- Can obstruct foramen of Monro
- Can be indistinguishable on imaging studies
-
Choroid plexus cyst
- Usually found in infants
- Anechoic at ultrasound
-
Choroid plexus papilloma
Colloid cyst: complications
- Varies with presence/rate of growth, development of cerebrospinal fluid (CSF) obstruction
- Colloid Cyst Risk Score (CCRS)
- 5-point measure to predict symptomatic clinical status, stratify risk for hydrocephalus
- Age < 65 years; headache, cyst ≥ 7 mm, FLAIR hyperintense, anatomic risk zone (I-III from front to back of 3rd ventricle)
- CCRSs 2 to 5 = 13% → 100% symptomatic, 8% → 83% develop hydrocephalus
- 5-point measure to predict symptomatic clinical status, stratify risk for hydrocephalus
- Colloid Cyst Risk Score (CCRS)
- Prognosis excellent when CCs diagnosed early and excised
- 90% stable or stop enlarging
- Older age
- Small cyst
- No hydrocephalus
- Hyperdense on NECT, hypointense on T2-weighted MR
- 10% enlarge
- Younger patients
- Larger cyst, hydrocephalus
- Iso-/hypodense on NECT, often hyperintense on T2WI
- May enlarge rapidly, cause coma/death
- Rare: Hemorrhage with cyst “apoplexy”
- Rare: Regression
