1. PET imaging in rhomboencephalosynapsis
Dasha Pechersky, S.Ali Nabavizadeh, Drew Torigian, Abass Alavi, Pablo Tebas,
Alexander Mamourian
Hospital of the University of Pennsylvania,
Philadelphia, PA

2. Disclosures
The authors have no disclosures to report

3. Purpose
Rhomboencephalosynapsis is a midline brain malformation characterized by the absence of the cerebellar vermis and fusion of the cerebellar hemispheres.
We report the unusual finding of diffusely decreased cerebellar metabolism on fluorodeoxyglucose (FDG)-PET/CT in a patient with rhomboencephalosynapsis, which to our knowledge has not been reported previously in the literature.

4. Case report
33 year old man incidentally found to have partial absence of the septum pellucidum and fusion of his cerebellar hemispheres, after head imaging post assault.

5. Imaging C A B D
A and B: Coronal and axial T1-weighted MPRAGE MR images demonstrate fusion of the cerebellar hemispheres with transversely oriented cerebellar folia and hypogenesis of the vermis
C and D: Sagittal MIP PET and axial fused PET/CT images demonstrate diffusely decreased FDG activity in the cerebellum and brainstem relative to the cerebrum FDG uptake is preserved in the expected location of the dentate nuclei, and extends towards the midline, posterior to the 4th ventricle 

6. Summary
Rhombencephalosynapsis is a rare dysplasia of the cerebellum characterized by: the absence/incomplete development of the vermis, fusion of the cerebellar hemispheres, dentate nuclei, thalamic fusion, absent olfactory bulbs, dysgenesis of the corpus callosum, holoprosencephaly, absence of the septum pellucidum
May be seen in isolation or with other syndromes, including Cerebello- Trigeminal Dermal Dysplasia and VACTERL syndrome
Decreased FDG-PET/CT metabolism in the cerebellar hemispheres; presumably secondary to pathophysiological effects related to the underlying congenital disorder.
Other diagnostic considerations for diffusely decreased FDG uptake in the cerebellum include chronic alcohol abuse, long term use of antiepileptic medication, neurodegenerative disorders such as multiple system atrophy, and diffuse idiopathic cerebellar calcification.

7. References
1. Sandeep Patel and A. James Barkovich. Analysis and Classification of Cerebellar Malformations. AJNR :
2. Justyna Paprocka, Ewa Jamroz, Ewa Ścieszka, and Ewa Kluczewska. Isolated rhomboencephalosynapsis – a rare cerebellar anomaly. Pol J Radiol Jan-Mar; 77(1): 47– 49
3. Ishak GE, Dempsey JC, Shaw DW, Tully H, Adam MP, Sanchez-Lara PA, Glass I, Rue TC, Millen KJ, Dobyns WB, Doherty D. Rhombencephalosynapsis: a hindbrain malformation associated with incomplete separation of midbrain and forebrain, hydrocephalus and a broad spectrum of severity. Brain 2012 May;135: