The Fetal Posterior Fossa

Mahew Whitehead, MD Associate Professor, Neuroradiology Director, Pediatric Neuroradiology Educaon Vice Chief, Radiology Academic Affairs Children’s Naonal Medical Center Washington, DC

3 NORMAL

27 Weeks

Height

Inferior vermian distance Xi Y, et al. MR imaging of the fetal cerebellar vermis: Biometric predictors of adverse neurologic outcome. J Magn Reson Imaging. 2016;44(5):1284-1292 Learning Objectives

1. To review normal embryologic development of the cerebellum, brainstem, meninges, and meningeal spaces to help improve understanding of posterior fossa pathology

2. To introduce a pattern approach for diagnosis of posterior fossa fluid collections

5 Introduction

• Posterior fossa disease challenging! • Parenchymal malformations and insults • Fluid collections: normal variation vs. pathologic cystic, ventricular, and meningeal fluid spaces • Imaging patterns often characteristic • Differential diagnosis considered within framework of developmental posterior fossa anatomy

Fetal MRI: Utility in posterior fossa anomalies (PFA)

• PFA: 1/5000 births • 2nd most common reason for fetal MRI (1st: ventriculomegaly) • Prognosis: Type? Associated/additional abnormalities? • PFA and additional abnormalities better seen with MRI

PFA diagnostic accuracy (Griffiths, et al): -US: 65% -MRI: 88% (p<0.001) -3-fold reduction in “High confidence, incorrect Dx” -44% changed prognosis • PF anomalies found on US (isolated or otherwise) warrant MRI

Griffiths PD, et al. Anatomical subgroup analysis of the MERIDIAN cohort: Posterior fossa abnormalities. Ultrasound Obstet Gynecol. 2017 [Epub ahead of print]

Anatomy

8 Normal Anatomy – Sagittal T1WI

Lingula Central lobule Anterior Culmen

Declive Folium Tuber Posterior Pyramis Uvula

Nodulus Axial T2WI Coronal T2WI Embryology

11 Posterior Fossa: Coming of age Brainstem segments Cerebellum born Cerebellum extraventricular Meninx transforms Torcular posioned

1st 2nd 3rd Trimester Trimester Trimester

Neuronal Migraon

Magendie 5 – 10 weeks

Tortori-Dona P, Rossi A, Biancheri R. Brain Malformaons. In: Tortori-Dona P, Rossi A, eds. Pediatric neuroradiology: brain, head, neck and spine 1st ed. Berlin, Germany: Springer; 2009

Posterior Fossa: Coming of age Brainstem segments Cerebellum born Cerebellum Meninx transforms extraventricular

Luschka?

1st 2nd 3rd Trimester Trimester Trimester

Neuronal Migraon Cerebellum formed

Magendie By 18 Weeks

1. Fastigial point 2. Primary fissure 3. Covered 4th ventricle roof

18 Wk 21 Wk 24 Wk 32 Wk Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis (e. Epidermoid) e. Dandy-Walker (f. Enteric) f. Joubert 2. Insults g. Pontocerebellar a. Parenchymal bleed/infarct 4. Tumor c. Infection b. Dural sinus thrombosis

Cysts

u Definitive classification requires histologic evaluation of wall -Arachnoid: arachnoid -Blake pouch: arachnoid, ependyma, glia, choroid plexus -DW: arachnoid, ependyma, glia, neurons

u Cyst type can generally be gathered based on location and MR appearance

18 Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Arachnoid Cyst 24 weeks Enlarging Arachnoid cyst, Hydrocephalus 14 months post natal Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

27 Weeks

Blake Pouch Cyst Blake Pouch Cyst

Neonatal MR Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

29 weeks Enlarged “Mega” Cisterna Magna Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Fibrous Arachnoid Cyst Hemorrhage, adhesions, and hydrocephalus 30 Weeks Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Cerebellar asymmetry Low transverse cerebellar diameter 19 Weeks Unilateral Cerebellar Hypoplasia, presumed insult

23 days Disruptive (hemorrhagic) cerebellar hypoplasia DWM Mimic

Sanapo L, Whitehead, MT, et al. Fetal intracranial hemorrhages: role of fetal MRI. Prenat Diagn. 2017;37(8): 827-836. Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

ZIKA

25 Wk Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Dural Sinus Thrombosis

21 Wk 12 d Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Chiari II Malformation 32 Wk

22 Wk Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Walker-Warburg

11 Wk

Chong BW, et al. A magnetic resonance template for normal cerebellar development in the human fetus. Neurosurgery. 1997;41(4):924-8 Walker-Warburg

Whitehead MT, Fricke ST, Gropman AL. Structural Brain Defects. Clin Perinatol. 2015 Jun;42(2):337-61 Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Diencephalic-Mesencephalic junction Malformation Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Rhombencephalosynapsis

Whitehead MT, Choudhri AF, Grimm J, Nelson MD. Rhombencephalosynapsis as a cause of aqueductal stenosis: an under-recognized association in hydrocephalic children. Pediatric Radiology 44(7):849-56

Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Dandy-Walker Spectrum u Dandy-Walker Malformation = 1. Vermis aplasia or hypoplasia with counter-clockwise rotation 2. Markedly enlarged, cystic 4th ventricle 3. Posterior fossa enlargement u Overarching theory: -Rhombencephalon arrested development -Failed regression of AMA -Expansion of 4th ventricle thru AMA between CP and vermis

Dandy-Walker Continuum 22 weeks Dandy-Walker Continuum

52 days

Chapman T, et al. Establishment of normave values for the fetal posterior fossa by magnec resonance imaging. Prenat Diag 2018 Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Joubert Syndrome Joubert Syndrome (Oro-facial-digital syndrome VI)

19 weeks

Saleem SN, et al. Role of MR imaging in prenatal diagnosis of pregnancies at risk for Joubert syndrome and related disorders. AJNR Am J Neuroradiol 2010;31(3):424-9 DWM & related disorders

Cerebellum vermis dysplasc normal hemispheres apposed

Hypoplasc/malrotated vermis hemispheres splayed

choroid no éaperture torcular +/-hydro MTM no inversion

MCM BPC DWC DWM Joubert Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Pontine Tegmental Cap Dysplasia Decreased TCD, Occipital Cephalocele

20 weeks Pontocerebellar hypoplasia, Cephalocele

5 days 20 weeks Arhinencephaly Trisomy 21 Trisomy 18

• 2nd most common trisomy

• Brain microdysgenesis

• Neural tube defects (6%)

• HPE or arhinencephaly Differential Diagnosis

1. Cysts: 3. Hindbrain Malformations a. Arachnoid duplication a. Chiari b. Blake Pouch cyst b. Walker-Warburg c. Enlarged “Mega” cisterna magna c. Diencephalic-mesencephalic d. Fibrous arachnoid d. Rhombencephalosynapsis e. Dandy-Walker 2. Insults f. Joubert a. Parenchymal bleed/infarct g. Pontocerebellar c. Infection 4. Tumor b. Dural sinus thrombosis

Brainstem Tumor Conclusion u Posterior fossa anomalies are common indications for fetal MRI u Most able to be classified by appearance u Prognosis depends on type and presence/ absence of additional abnormalities DWM & related disorders

Cerebellum vermis dysplasc normal hemispheres apposed

Hypoplasc/malrotated vermis hemispheres splayed

choroid no éaperture torcular +/-hydro MTM no inversion

MCM BPC DWC DWM Joubert References 1 Wong AM, et al. Prenatal MR imaging of Dandy-Walker complex: midline sagittal area analysis. Eur J Radiol 2012; 81(1):e26-30 Saleem SN, et al. Role of MR imaging in prenatal diagnosis of pregnancies at risk for Joubert syndrome and related disorders. AJNR Am J Neuroradiol 2010;31(3):424-9 Vatansever D, et al. Multidimensional analysis of fetal posterior fossa in health and disease. Cerebellum 2013;12(5):632-44 Chen SC, et al. Fetal posterior fossa volume: assessment with MR imaging. Radiology 2006;238(3):997-1003 Glenn OA. MR imaging of the fetal brain. Pediatr Radiol 2010;40(1):68-81 Griffiths PD, et al. Anatomical subgroup analysis of the MERIDIAN cohort: Posterior fossa abnormalities. Ultrasound Obstet Gynecol. 2017 [Epub ahead of print] Raybaud C, et al. MR imaging of fetal brain malformations. Childs Nerv Sys 2013; 19(7-8):455-470 Bekker MN, et al. The role of magnetic resonance imaging in prenatal diagnosis of fetal anomalies. Eur J Gynecol Reprod Biol 2001;96(2): 173-8 Wuest A, et al. Enlarged posterior fossa on prenatal imaging: differential diagnosis, associated anomalies and postnatal outcome. Acta Obstet Gynecol Scand. 2017;96(7):837-843 Snoek R, et al. Accuracy of diagnosis and counseling of fetal brain anomalies prior to 24 weeks of gestational age. J Matern Fetal Neonatal Med. 2017 [Epub ahead of print] Nelson MD, et al. A different approach to cysts in the posterior fossa. Pediatric Radiology 2004; 34:720-32 Tortori-Donati P, et al. Brain Malformations. In: Tortori-Donati P, Rossi A, eds. Pediatric neuroradiology: brain, head, neck and spine 1st ed. Berlin, Germany: Springer; 2009 Samo M, et al. Progressive lesions of Central Nervous System in microcephalic fetuses with suspected congenital Zika virus syndrome. Ultrasound Obstet Gynecol. 2016 [Epub ahead of print] Robinson AJ, et al. Diagnostic imaging of posterior fossa anomalies in the fetus. Semin Fetal Neonatal Med. 2016 Oct;21(5):312-20. Poretti A, et al. Cerebellar hypoplasia: differential diagnosis and diagnostic approach. Am J Med Genet 2014;166C(2):211-26 Nagaki M, et al. Comparison of brain imaging and neuropathology in cases of trisomy 18 and 13. Neuroradiology 1987;29(5):474-9 Tortori-Donati . Cystic malformations of the posterior cranial fossa originating from a defect of the posterior membranous area. Mega cisterna magna and persisting Blake's pouch: two separate entities. Childs Nerv Syst. 1996;12(6):303-8. Ber R, et al. Normal fetal posterior fossa in MR imaging: new biometric data and possible clinical significance. AJNR Am J Neuroradiol. 2015;36(4):795-802. Massoud M, et al. Prenatal unilateral cerebellar hypoplasia in a series of 26 cases: significance and implications for prenatal diagnosis. Ultrasound Obstet Gynecol. 2014;44(4):447-54 Cassart M, et al. Fetal intracranial tumors: a review of 27 cases. Eur Radiol. 2008;18(10):2060-6. Goasdoue P, et al. Pontoneocerebellar hypoplasia: definition of MR features. Pediatr Radiol. 2001;31(9):613-8. Andescavage NN, et al. Complex Trajectories of Brain Development in the Healthy Human Fetus. Cereb Cortex. 2016. [Epub ahead of print] Štrafela P, et al. Zika Virus-Associated Micrencephaly: A Thorough Description of Neuropathologic Findings in the Fetal Central Nervous System. Arch Pathol Lab Med. 2017;141(1):73-81. Bosemani T, et al. Cerebellar disruptions and neurodevelopmental disabilities. Semin Fetal Neonatal Med. 2016;21(5):339-48. Xi Y, et al. MR imaging of the fetal cerebellar vermis: Biometric predictors of adverse neurologic outcome. J Magn Reson Imaging. 2016;44(5):1284-1292. Poretti A, et al. Fetal Diagnosis of Rhombencephalosynapsis.Neuropediatrics. 2015;46(6):357-8. Martino F, et al. Prenatal MR imaging features of isolated cerebellar haemorrhagic lesions. Eur Radiol. 2016;26(8):2685-96. Rehder R, et al. Variation of the slope of the tentorium during childhood. Childs Nerv Syst. 2016;32(3):441-50.

References 2

Poretti A, et al. Pre- and Postnatal Neuroimaging of Congenital Cerebellar Abnormalities. Cerebellum. 2016;15(1):5-9. Amir T, et al. Differential diagnosis of ventriculomegaly and brainstem kinking on fetal MRI. Brain Dev. 2016;38(1):103-8. Chapman T, et al. Diagnostic imaging of posterior fossa anomalies in the fetus and neonate: part 2, Posterior fossa disorders. Clin Imaging. 2015;39(2): 167-75. Tarui T, et al. Long-term developmental outcome of children with a fetal diagnosis of isolated inferior vermian hypoplasia. Arch Dis Child Fetal Neonatal Ed. 2014;99(1):F54-8. Patek KJ, et al. Posterior fossa anomalies diagnosed with fetal MRI: associated anomalies and neurodevelopmental outcomes. Prenat Diagn. 2012;32(1): 75-82. Correa GG, et al. Neuroimaging of Dandy-Walker malformation: new concepts. Top Magn Reson Imaging. 2011;22(6):303-12. Righini A, et al. Fetal MRI features related to the Chiari malformations. Neurol Sci. 2011;32 Suppl 3:S279-81. Garel C, et al. The fetal cerebellum: development and common malformations. J Child Neurol. 2011c;26(12):1483-92. Liu F, et al. Development of the human fetal cerebellum in the second trimester: a post mortem magnetic resonance imaging evaluation. J Anat. 2011;219(5):582-8. Bolduc ME, et al. Spectrum of neurodevelopmental disabilities in children with cerebellar malformations. Dev Med Child Neurol. 2011;53(5):409-16. Poretti A, et al. Outcome of severe unilateral cerebellar hypoplasia. Dev Med Child Neurol. 2010;52(8):718-24. Limperopoulos C, et al. Diagnosis of inferior vermian hypoplasia by fetal magnetic resonance imaging: potential pitfalls and neurodevelopmental outcome. Am J Obstet Gynecol. 2006;194(4):1070-6. Sanapo L, Whitehead, MT, et al. Fetal intracranial hemorrhages: role of fetal MRI. Prenat Diagn. 2017;37(8):827-836. Whitehead MT, et al. Rhombencephalosynapsis as a cause of aqueductal stenosis: an under-recognized association in hydrocephalic children. Pediatr Radiol. 2014;44(7):849-56. Namavar Y, et al. Clinical, neuroradiological and genetic findings in pontocerebellar hypoplasia. Brain. 2011;134(Pt 1):143-56. Poretti A, et al. Cerebellar and Brainstem Malformations. Neuroimaging Clin N Am. 2016;26(3):341-57. Siebert JR. A pathological approach to anomalies of the posterior fossa. Birth Defects Res A Clin Mol Teratol. 2006;76(9):674-84. Robinson AJ. Inferior vermian hypoplasia--preconception, misconception. Ultrasound Obstet Gynecol. 2014;43(2):123-36. Adamsbaum C, et al. MRI of the fetal posterior fossa. Pediatr Radiol 2005; 35: 124–40. Aust N Z J. Utility of fetal MRI for workup of fetal central nervous system anomalies in an Australian maternal-fetal medicine cohort. Obstet Gynaecol. 2016 ;56(3):267-73. Chong BW, et al. A magnetic resonance template for normal cerebellar development in the human fetus. Neurosurgery. 1997;41(4):924-8

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