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Rhombencephalosynapsis is a congenital abnormality of the cerebellum characterized by the absence of the vermis and continuity of the cerebellar hemispheres, dentate nuclei, and superior cerebellar peduncles. It either occurs as an isolated anomaly (rare) or as part of a wider cerebral malformation and it has variable degrees of neurological impairment.
The condition is very rare and thought to be sporadic. No familial cases have been identified 9.
Clinical presentation includes truncal and/or limb ataxia, abnormal eye movements, head stereotypies, delayed motor development, and other features determined by supratentorial abnormalities (see below) 10. Overall patients tend to die in childhood or early adult life 9.
Rhombencephalosynapsis has been seen to be associated with:
Gomez-Lopez-Hernandez syndrome: comprises rhombencephalosynapsis, developmental delay, scalp alopecia, and trigeminal anesthesia 5
vertebral fusion anomalies
Embryologically rhombencephalosynapsis is now considered to result from a failure of vermian differentiation. The fused development of the cerebellar hemispheres is thought to result from an insult between the 28th and 44th day of gestation 6,8. The classic appearances is of a transversely oriented single lobed cerebellum.
Rhombencephalosynapsis was traditionally thought to be a complete fusion of cerebellar hemispheres. However, off late cases of partial fusion have also been reported 6,8.
Rhombencephalosynapsis is best seen on MRI brain, and is characterized by 1-4,7,8:
absent anterior (rostral) vermis
deficient posterior (caudal) vermis
nodulus tends to be formed
fusion of the cerebellar hemispheres, with transversely oriented inferior cerebellar folia
fusion of dentate nuclei
fusion of the superior cerebellar peduncles
Additional frequently associated abnormalities include:
fusion of the thalami
fusion of inferior colliculi
absent septum pellucidum
other supratentorial abnormalities 8
Treatment and prognosis
Variable clinical progression ranging from early death to varying degrees of cerebellar dysfunction and neurodevelopmental delay. Some patients may reach adulthood 3.
History and etymology
It was first reported by Heinrich Obersteiner (1847-1922), an Austrian neurologist, in 1914 3.
Imaging differential considerations include:
- 1. A. James Barkovich. Pediatric Neuroimaging. (2005) ISBN: 9780781757669 - Google Books
- 2. Sandalcioglu I, Gasser T, van de Nes J, Menken U, Stolke D, Wiedemayer H. Fusion of the Cerebellar Hemispheres Ventral to the Brainstem: A Rare Hindbrain-Related Malformation. Childs Nerv Syst. 2006;22(1):73-7. doi:10.1007/s00381-004-1065-5 - Pubmed
- 3. Truwit C, Barkovich A, Shanahan R, Maroldo T. MR Imaging of Rhombencephalosynapsis: Report of Three Cases and Review of the Literature. AJNR Am J Neuroradiol. 1991;12(5):957-65. PMC8333516 - Pubmed
- 4. Patel S & Barkovich A. Analysis and Classification of Cerebellar Malformations. AJNR Am J Neuroradiol. 2002;23(7):1074-87. PMC8185716 - Pubmed
- 5. Whetsell W, Saigal G, Godinho S. Gomez-Lopez-Hernandez Syndrome. Pediatr Radiol. 2006;36(6):552-4. doi:10.1007/s00247-006-0150-1 - Pubmed
- 6. Demaerel P, Morel C, Lagae L, Wilms G. Partial Rhombencephalosynapsis. AJNR Am J Neuroradiol. 2004;25(1):29-31. PMC7974185 - Pubmed
- 7. Utsunomiya H, Takano K, Ogasawara T, Hashimoto T, Fukushima T, Okazaki M. Rhombencephalosynapsis: Cerebellar Embryogenesis. AJNR Am J Neuroradiol. 1998;19(3):547-9. PMC8338264 - Pubmed
- 8. Demaerel P, Morel C, Lagae L, Wilms G. Partial Rhombencephalosynapsis. AJNR Am J Neuroradiol. 2004;25(1):29-31. PMC7974185 - Pubmed
- 9. Malcolm I. Levene, Frank A. Chervenak. Fetal and Neonatal Neurology and Neurosurgery. (2009) ISBN: 9780443104077 - Google Books
- 10. Bosemani T, Orman G, Boltshauser E, Tekes A, Huisman T, Poretti A. Congenital Abnormalities of the Posterior Fossa. Radiographics. 2015;35(1):200-20. doi:10.1148/rg.351140038 - Pubmed