Congenital Cerebellar Malformation



Congenital Cerebellar Malformation


Bernadette L. Koch, MD



DIFFERENTIAL DIAGNOSIS


Common



  • Chiari 1 Malformation


  • Chiari 2 Malformation


Less Common



  • Cerebellar Hypoplasia


  • Cerebellar Dysplasias (Unclassified)


  • Dandy-Walker Spectrum


Rare but Important



  • Rhombencephalosynapsis


  • Molar Tooth Malformations (Joubert)


  • Chiari 3 Malformation


ESSENTIAL INFORMATION


Helpful Clues for Common Diagnoses



  • Chiari 1 Malformation



    • Key facts: Caudal protrusion of pointed cerebellar (CB) tonsils, below foramen magnum (FM)



      • Normal CB tonsils rounded


      • CB position below “opisthion-basion line”: 1st decade (6 mm), 2nd-3rd decade (5 mm), 4th-8th decade (4 mm), and 9th decade (3 mm)


      • Underdeveloped bony posterior fossa → downward hindbrain herniation


    • Imaging



      • CB tonsils low and pointed; CSF at foramen magnum effaced; small bony posterior fossa


      • Cine MR: Motion of CB tonsils


      • ± syrinx, presyrinx edema, or ventriculomegaly


      • ± short clivus, dorsal tilt of dens, craniovertebral anomalies


      • Rarely develop over time; rarely resolve without treatment


  • Chiari 2 Malformation



    • Key facts



      • ˜ 100% associated with open neural tube defect, usually myelomeningocele


      • ↓ incidence with ↑ in folate replacement


    • Imaging



      • Small posterior fossa, large FM


      • Large funnel-shaped foramen magnum


      • “Cascade” or “waterfall” herniation of tissue downward, behind medulla


      • “Peg” = uvula/nodulus/pyramid of vermis


      • Cervicomedullary “kink”


      • “Towering” cerebellum through incisura → compressed “beaked” tectum


      • 4th ventricle elongated, without fastigium (posterior point)


      • Low insertion of tentorium/torcular


      • ± syringohydromyelia (20-90%)


      • ± corpus callosum dysgenesis (90%)


      • ± posterior arch C1 anomalies, diastematomyelia, Klippel-Feil syndrome


      • ± aqueduct stenosis, GM heterotopia, absent septum pellucidum/fused forniceal columns, stenogyria


Helpful Clues for Less Common Diagnoses



  • Cerebellar Hypoplasia



    • Key facts: Inherited or acquired, isolated or syndromic


    • Imaging



      • Isolated small CB hemisphere(s) with normal fissures and interfoliate sulci


      • + brainstem hypoplasia = pontocerebellar hypoplasia


      • ± vermian hypoplasia, abnormal CB fissures, cortical dysplasia


      • ± Dandy-Walker spectrum, molar tooth syndromes, rhombencephalosynapsis


      • Presence of gliosis suggests atrophy rather than congenital hypoplasia


  • Cerebellar Dysplasias (Unclassified)



    • Key facts: Developmental abnormality


    • Imaging



      • CB hemispheres &/or vermis; abnormal orientation of fissures and lobules


      • Affected structure usually small


      • Focal or diffuse, single or multiple, unilateral or bilateral


      • Diffuse usually associated with supratentorial anomalies: Congenital muscular dystrophies, lissencephalies, polymicrogyria


  • Dandy-Walker Spectrum



    • Key facts: Continuum = “classic” Dandy-Walker malformation (DWM) → CB vermian hypoplasia → Blake pouch cyst (BPC) → mega cisterna magna (MCM)



      • Intelligence normal in up to 50% of “classic” DWM cases


    • Imaging



      • “Classic” DWM: Cystic dilatation of 4th ventricle → large posterior fossa, torcular-lambdoid inversion, superiorly rotated hypoplastic vermis



      • CB vermian hypoplasia: Vermis hypoplasia ± upward rotation; normal-sized posterior fossa and brainstem


      • BPC: Herniation of inferior 4th ventricle through foramen of Magendie into vallecula and retrovermian cistern; enhancing choroid plexus in cyst wall


      • MCM: Enlarged pericerebellar cisterns communicate with basal subarachnoid spaces; normal vermis/4th ventricle; cistern crossed by falx cerebelli


      • Imaging cannot precisely distinguish between mild DWM, BPC, and MCM


      • ± associated callosal anomalies, cortical dysplasia, heterotopia


Helpful Clues for Rare Diagnoses



  • Rhombencephalosynapsis



    • Key facts



      • Fusion of CB hemispheres, dentate nuclei, and superior CB peduncles


    • Imaging: Complete or partial fusion CB hemispheres



      • Absent primary fissure on sagittal; transverse folia on axial and coronal; keyhole-shaped 4th ventricle on axial


      • Fused horseshoe-shaped dentate nuclei


      • Absent posterior CB notch and vallecula


      • Absent or severely hypoplastic vermis


      • ± absent septum pellucidum, olivary hypoplasia, anomalies of limbic system, multiple cranial suture synostoses


      • ± corpus callosum dysgenesis, aqueductal stenosis, cortical dysplasia


  • Molar Tooth Malformations (Joubert)



    • Key facts: Joubert anomaly is prototype



      • Joubert patients present with episodic hyperpnea, abnormal eye movements, ataxia, and mental retardation


      • Identical imaging findings in some patients without classic Joubert syndrome symptoms; some with renal or ocular anomalies, hepatic fibrosis/cysts, hypothalamic anomalies


    • Imaging: “Molar tooth” = large superior CB peduncles (do not decussate in dorsal midbrain) on axial images



      • Sagittal: Small, high CB vermis


      • Coronal: “Split vermis”


      • Axial: Small dysplastic vermis → triangular-shaped mid 4th ventricle and bat wing-shaped superior 4th ventricle


  • Chiari 3 Malformation

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Aug 10, 2016 | Posted by in PEDIATRICS | Comments Off on Congenital Cerebellar Malformation

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