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Neuroradiology Case of the Month

April 2001

Clinical Presentation: A 26-year-old male roofer with mild mental retardation and emotional instability but no other neurological symptoms presented for MRI of the brain MR because of newly diagnosed testicular cancer.

Radiographic findings: Axial T2-weighted image (Fig. 1) showed fusion of the cerebellar hemispheres. The cerebellar vermis was hypoplastic and the cerebellar folia continued across the midline. There is no supratentorial abnormality except old contusions in the frontal lobes.

Diagnosis: Rhombencephalosynapsis

Figure 1. Rombencepholsynapsis with fusion of the left and right cerebellar hemispheres.	Figure 2. Normal case for comparison.

Discussion: Rhombencephalosynapsis is a rare cerebellar malformation [1-3] with about thirty case reports including only two adults. The cases often have vermian hypogenesis. The nodulus is often formed but the remainder of the vermis is absent. The common associated brain anomalies include fusion of hemisphere, dentate nuclei, superior cerebellar peduncles, thalami, absence of septum pellucidum, olivary hypoplasia, anomalies of limbic system and hydrocephalus.

Rhomencapholosynapsis is thought to be caused by failure of the vermian differentiation during the third gestational month [1] It has been suggested that undivided cerebellar hemispheres may be a more appropriate term than fusion.

References:

1. Utsunomiya H, et al. Rhombencephalosynapsis; Cerebellar embryogenesis. AJNR Am J Neuroradiol 1998;19:547-549
2. Montull C, et al. Neuroradiological and clinical findings in rhombencephalosynapsis. Neuroradiology 2000;42:272-274
3. Takanashi J, et al. Partial midline fusion of the cerebellar hemispheres with vertical folia: A new cerebellar malformation? AJNR Am J Neuroradiol 1998;20:1151-1153