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
