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|Year : 2016 | Volume
| Issue : 6 | Page : 1381-1383
Rhombencephalosynapsis: A rare cerebellar malformation associated with aqueductal stenosis and obstructive hydrocephalus
Umesh Kalane1, Ashish Atre2
1 Department of Pediatric Neurology, Deenanath Mangeshkar Hospital and Research Center, Pune, Maharashtra, India
2 Department of Radiology, Star Imaging and Research Center, Pune, Maharashtra, India
|Date of Web Publication||11-Nov-2016|
Dr. Umesh Kalane
Flat no. 202, G Building, Wonder City Society, Katraz Serve No. 75, Pune, Maharashtra
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kalane U, Atre A. Rhombencephalosynapsis: A rare cerebellar malformation associated with aqueductal stenosis and obstructive hydrocephalus. Neurol India 2016;64:1381-3
A 2-year-old boy was presented for evaluation of developmental delay. He had both motor and cognition delay. He developed neck holding by 9 months of age and started sitting at 1 year of age. He was able to stand with support by the age of 2 years; however, he could not walk independently at presentation. There was significant speech delay and he could not express words with meaning; he was, however, able to follow simple commands. He was first in birth order, born of non- consanguineous marriage, and without significant family history of neurological disorders. His birth history was also unremarkable.
On examination, he had a head size of 50 cm, which was on the 90th percentile for his age standard. The anterior fontanel was closed. No obvious dysmorphic features were noted. On neurological examination, there were no deficits; however, mild limb hypotonia was noted with brisk deep tendon reflexes, suggesting pyramidal tract involvement. His electroencephalography and brainstem auditory evoked response (BERA) tests were normal. His magnetic resonance imaging (MRI) of the brain showed complete absence of cerebellar vermis, and across the midline continuity of the cerebellar hemispheres and deep cerebellar nuclei with posteriorly pointing fourth ventricle, consistent with rhomboencephalosynapsis [Figure 1]. In addition, there was gross ventriculomegaly affecting both lateral and third ventricles. The septum pellucidum was absent with severe narrowing of the aqueduct [Figure 2]. Based on the MRI brain findings, he was diagnosed as a case of rhomboencephalosynapsis with aqueductal stenosis causing obstructive hydrocephalus, which is a rare cerebellar malformation disorder.
|Figure 1: Axial T2 image showing cerebellar hemispheric fusion across the midline with continuity of white matter tracts, absence of vermis, and posteriorly pointing 4th ventricles|
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|Figure 2: Axial T2 image showing aqueductal stenosis with hydrocephalus and rhombencephalosynapsiscerebellar|
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Rhombencephalosynapsis is a cerebellar anomaly characterized by lack of separation of the cerebellar hemispheres with vermian hypogenesis or agenesis and fusion of the cerebellar hemispheres, the middle cerebellar peduncles, and the dentate nuclei. Obersteiner, in 1914, described rhombencephalosynapsis for the first time. The vermian maldevelopment is characterized by an absence of the anterior vermis and a deficiency of the posterior vermis; the nodulus tends to be formed.,,,, It is not associated with disconnected cerebellar hemispheres, such as seen in Dandy–Walker malformation, Joubert syndrome, or tectocerebellar dysgraphia.,,, Until now, there have been approximately 50 case reports worldwide. Their number is increasing with the use of MRI. All published cases are mostly sporadic, as in our case, with a single familial occurence. MR features of rhombencephalosynapsis are characteristic. A diamond-shaped fourth ventricle, instead of the normal crescentic shape, is seen on axial sections, and this abnormal configuration of the fourth ventricle indicates vermian hypogenesis or agenesis., Fusion or apposition of the dentate nuclei and middle cerebellar peduncles can be observed behind a pointed fourth ventricle, as seen in our case [Figure 1].
Rhombencephalosynapsis has been described in conjunction with Gomez–Lopez–Hernandez syndrome and VACTERAL association., Deficiency or absence of the septum pellucidum is described in literature, as was seen in our case. Rhombencephalosynapsis is also associated with multiple forebrain abnormalities including absent olfactory bulbs, dysgenesis of the corpus callosum, absent septum pellucidum, and, in rare patients, atypical forms of holoprosencephaly.,,,
Aqueductal stenosis, which may cause congenital hydrocephalus, is commonly associated with this anomaly, as was also seen in our case. Therefore, rhombencephalosynapsis should be suspected in infants in whom both congenital hydrocephalus and a flat-based cerebellum without formation of the cerebellar vallecula is observed.
A spectrum of severity, ranging from mild (the partial absence of nodulus, anterior, and posterior vermis), to moderate (the absence of posterior vermis with some anterior vermis and nodulus present), to severe (the absence of posterior and anterior vermis with some nodulus present), to complete (the absence of the entire vermis including nodulus) has been proposed.
The clinical presentation of rhombencephalosynapsis is variable and ranges from severe congenital hydrocephalus, severe cerebral palsy and mental retardation, to mild truncal ataxia and normal cognition. In our case, the presentation was delayed development with a large head due to the presence of hydrocephalus.
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[Figure 1], [Figure 2]