Han-Sung Kwon M.D. Department of Obstetrics and Gynecology Konkuk University School of Medicine Seoul, Korea

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1 Han-Sung Kwon M.D. Department of Obstetrics and Gynecology Konkuk University School of Medicine Seoul, Korea

3 Embryologic features of the developing hindbrain

4 Embryologic features of the developing hindbrain

5 CM cerebellum

6 Definitions of cerebellar pathologies

7 DDx of cerebellar pathologies DWM Vermian hypoplasia Megacister na magna Blake s pouch cyst PF arachnoid cyst

8 US findings : PF arachnoid cyst

9 US findings : PF arachnoid cyst

10 Dandy Walker Malformation Classic triad 1. complete or partial agenesis of the vermis; 2. cystic dilation of the 4th ventricle 3. enlarged posterior fossa, with upward displacement of the transverse sinuses, tentorium, and torcula Dandy WE: Am J Dis Child 8: , 1914

11 US findings : DWM US triad Enlarged cisterna magna (>10mm) Large vermian defect Variable degree of ventriculomegaly

12 US findings : Vermian hypoplasia 1) hypoplastic vermis with normal torcular 2) normal or slightly increased size of the cisterna magna 3) no tentorial or torcular elevation

13 US findings : DWM

14 US findings : Blake s pouch cyst Mid-sagittal section of fetal brain Walls of the Blake s pouch cyst are visible and the fourth ventricle is contiguous with space delineated by these septa This space is less echogenic than the subarachnoid space of the surrounding cisterna magna

US findings : Blake s pouch cyst Mid-sagittal section of fetal brain 1) normal anatomy and size of the vermis 2) mild to moderate anti-clockwise rotation of

15 US findings : Blake s pouch cyst Mid-sagittal section of fetal brain 1) normal anatomy and size of the vermis 2) mild to moderate anti-clockwise rotation of the vermis 3) normal or slightly increased size of the cisterna magna 4) evidence of the BPC roof within the cisterna magna 5) No tentorial or torcular elevation

16 Difficulties encountered in the sonographic categorization Assessment of the position of torcular and evaluation of the integrity of the cerebellar vermis The torcular Herophili cannot be imaged clearly with sonography due to acoustic shadowing from the skull bones and inferred its position by observing the angulation of the tentorium The main advantage of MRI over ultrasound was better visualization of the torcular, while assessment of the integrity of the vermis remained difficult, particularly in mid gestation

17 Difficulties encountered in the sonographic categorization

Integrity of the cerebellar vermis Vermian morphology is roughly appreciated by evaluating the primary fissure and the anterior/posterior lobe

18 Integrity of the cerebellar vermis Vermian morphology is roughly appreciated by evaluating the primary fissure and the anterior/posterior lobe ratio should be equal to ½ Primary fissure is constantly seen from 28 to 30 weeks & the other fissures are inconstantly observed after weeks

19 Integrity of the cerebellar vermis

22 Six questions for DDx 1. Are the PF fluid spaces normal, enlarged or reduced? 2. Is the tentorium normally inserted and oriented? 3. Is cerebellar biometry normal? 4. Is cerebellar and brainstem morphology normal? 5. Is the 4th ventricle normally shaped? 6. Is cerebellar echogenicity or signal normal? Garel C. Pediatr Radiol (2010) 40:

echogenicity are normal (Brainstem morphology is normal) The fourth

23 Six questions for DDx Increased PF fluid spaces The tentorium is normally inserted and oriented Cerebellar biometry, morphology and echogenicity are normal (Brainstem morphology is normal) The fourth ventricle shape is normal The cisterna magna is enlarged Mega cisterna magna

24 Six questions for DDx Increased PF fluid spaces The tentorium is normally inserted and oriented Cerebellar biometry and echogenicity are normal The fourth ventricle shape is normal There is mass effect on the vermis, one hemisphere, the brainstem and/or the cranial vault (may be unilaterally) The cerebellar echogenicity (signal) is normal Arachnoid cyst

normal The fourth ventricle shape is enlarged Vermian biometry and

25 Six questions for DDx Normal or slightly Increased PF fluid spaces The tentorium is normally inserted and oriented Cerebellar biometry are normal The fourth ventricle shape is enlarged Vermian biometry and morphology is normal The cerebellar echogenicity (signal) is normal Blake s pouch cyst

ventricle is enlarged Cerevellar & vermian biometry and morphology is

26 Six questions for DDx Increased PF fluid spaces Position of the tentorium is too high and the torcular is elevated The fourth ventricle is enlarged Cerevellar & vermian biometry and morphology is abnormal The cerebellar echogenicity (signal) is normal Dandy-Walker malformation

27 Six questions for DDx Increased PF fluid spaces The tentorium is normally inserted and oriented Cerebellar biometry are normal The fourth ventricle is enlarged Vermian biometry and morphology is abnormal The cerebellar echogenicity (signal) is normal Inferior vermian hypoplasia or agenesis

28 Six questions for DDx Normal or slightly increased PF fluid spaces The tentorium is normally inserted and oriented Two cerebellar hemispheres are reduced in size The fourth ventricle shape is normal The cerebellar echogenicity (signal) is normal Cerevellar hypoplasia

29 Six questions for DDx Decreased PF fluid spaces Chiari II malformation Abnormal cerebellar echogenicity (signal) Ischaemic and/or haemorrhagic lesions

30 Pitfalls in diagnosis Confusion between different entities Premature diagnosis of abnormal vermian formation Difficulties in the ultrasonographic differentiation between the cerebellar hemispheres and the vermis Late development of cerebellar hypoplasia/atrophy Differential diagnosis of unilateral cerebellar findings Malinger G 2009 Prenat Diagn

31 Confusion between different entities D-W varient Limperopoulos et al Inferior vermian hypoplasia(vh): communication between the 4 th ventricle & the cisterna magna, delayed closure of the vermis should be diagnosed & a good prognosis VH: prognosis is not yet clear since it can be a dominant benign trait or part of a genetic syndrome (fragile X ) Vermian agenesis including DWM: the vermis is actually hypoplastic, the prognosis may be better Klein et al., 2003

Premature diagnosis of abnormal vermian formation Diagnosis of the different forms of vermian hypoplasia should not be performed before 18-24 weeks of gestation Delayed development Artifact:

32 Premature diagnosis of abnormal vermian formation Diagnosis of the different forms of vermian hypoplasia should not be performed before weeks of gestation Delayed development Artifact: increasing the angle from the transthalamic axial plane Apparently normal but superiorly rotated 1) normal variations in the development of the cerebellum 2) increased pressure produced by the developing vermis may cause invagination & dehiscence of a Blake s pouch cyst 3) late closure of the fourth ventricle caused by a late fenestration of Blake s pouch Robinson & Goldstein, 2007

33 Difficulties in the ultrasonographic differentiation between the cerebellar hemispheres & the vermis Rhombencephalosynapsis

34 US findings : DWM? BPC? VH?

35 Prognosis of PF anomalies Additional intracranial anomalies or extracranial anomalies was associated with a worse outcome regardless of the type of PFA 20% of cases of DWM, VH, and non-isolated MCM had a chromosome abnormality detected chromosome analysis and high density microarray (ex. 6p subtelomeric deletion) Isolated MCM, Blake s PC normal neurodevelopmental postnatal outcome Neurodevelopmental delay has been reported in 40% to 60% of children with DWM, with the identification of additional anomalies leading to a worse prognosis Klein O, Childs Nerv Syst 2003 Boddaert N, Neuroradiology 2003

36 Isolated VH:? prognosis Prognosis of VH

38 Take Home Messages 2D/3D Ultrasound and fetal MRI are helpful in the characterization of fetal posterior fossa abnormalities Six questions for DDx Isolated megacisterna magna and Blake s pouch cysts have a good chance of intrauterine resolution, being associated with normal developmental outcome in over 90% of cases Dandy Walker malformation and vermian hypoplasia have a guarded prognosis, with a very high likelihood of associated anomalies and/or neurologic impairment

39 Thank you for your attention!

Measurements of the Posterior Fossa in Normal Fetus MRI

Measurements of the Posterior Fossa in Normal Fetus MRI Ber Roee, 3 rd year medical student, Sackler School of Medicine, Tel Aviv University Supervised by: Dr. Katorza Eldad, Antenatal Diagnostic Unit,The