Rhombencephalo-synapsis with turricephaly.

Dear Sir,

Rhombencephalosynapsis is a rare malformation characterized by fused cerebellar hemispheres, fused dentate nuclei, and vermian agenesis. It has varied clinical presentations and is usually diagnosed in childhood or infancy. However, uncommonly, it may be detected in adult patients. Classic features are evident on magnetic resonance imaging (MRI); however, computed tomography (CT) may be able to suggest the diagnosis.

A nine-month-old female child presented with global developmental delay. There was no history suggestive of birth asphyxia. She had a normal full-term vaginal delivery. On examination, she had a developmental age of 4-5 months and a development quotient of 66%. She presented with a single episode of a partial seizure for which CT of the head was done.

On contrast enhanced computed tomography (CECT) of the brain, there was absence of vermis, with fused cerebellar hemispheres and a diamond-shaped fourth ventricle suggestive of rhombencephalosynapsis [Figures 1 and 2]. There was also evidence of turricephaly or tower skull, best depicted on volume-rendered images [Figure 3]. No other structural defects were seen in the brain. The MRI of the patient was not done due to financial constraints, but the CT features in this case were characteristic of rhombencephalosynapsis.

Figure 1

Axial computed tomography of the brain showing absence of vermis with fused cerebellar hemispheres

Figure 2

Axial computed tomography image showing diamond-shaped fourth ventricle (arrow)

Figure 3

Volume-rendered image showing evidence of turricephaly

Rhombencephalosynapsis is an uncommon malformation of the posterior fossa which is characterized by vermian agenesis or severe hypogenesis, fusion of the cerebellar hemispheres, and fusion of the dentate nuclei. It is thought to be due to maldevelopment of the rhombic lips in the early fetal period and to occur following an insult between the 28th and 44th day of gestation.[1] The first description of rhombencephalosynapsis was published by Obersteiner in 1914.[2] The clinical presentation of these patients is variable and depends on the presence of posterior fossa and other structural abnormalities. No specific clinical syndrome has been associated, and most cases are detected in infancy or childhood.[3]

Most symptomatic patients have supratentorial anomalies and a rudimentary cerebellum. The usual clinical manifestations include hypotonia, motor and cerebellar dysfunction, strabismus, and developmental delays.[4] The largest series showed a wide range of findings which varied from mild truncal ataxia and normal intelligence to cerebral palsy.[5] Many patients die in infancy; however, occasional reports of findings detected in adult age are present. There is poor correlation between neuroimaging findings and clinical manifestations.[3] CT has been less commonly reported to suggest the diagnosis. The MR features of rhombencephalosynapsis are characteristic. A diamond-shaped fourth ventricle, instead of the normal crescent shape, is seen on axial sections; a flat and uninterrupted continuity of the base of the cerebellar hemispheres, transversely oriented folia in the inferior cerebellum, and large corpus medullare are seen, all of which represent fused cerebellar hemispheres. There can be associated deficiency or absence of the septum pellucidum, dysgenesis of the corpus callosum and the anterior commissure, fused fornices, and fused thalami.[1]