Unilateral Cerebellar Hypoplasia: A Rare Cause of Childhood Seizures.

Cerebellar malformations are a rare group of disorders with clinical heterogeneity. The usual posterior fossa malformations comprise of the cystic lesions like Dandy-walker complex, enlarged cisterna magna or arachnoid cysts. The vermis is a commonly associated structure in both cystic and non-cystic posterior fossa malformations. The congenital malformations affecting the cerebellar parenchyma are however very rare. Magnetic resonance imaging (MRI) is an excellent modality to detect and accurately classify these malformations. We describe a case of 14 years old boy with unilateral cerebellar hypoplasia and recurrent seizures with emphasis on the MRI features of this rare entity. Copyright:

Case Report

A 14-year-old boy, with normal birth and development, presented with multiple episodes of generalized tonic–clonic seizures for the previous three years. No preceding aura or any localizing features of the seizures was observed. No focal neurologic deficit was noted. No significant past medical history of head trauma, febrile seizures, or meningoencephalitis was reported. However, the patient had poor scholastic performance. No similar history of seizures was observed in his family. Electroencephalography showed generalized spike and wave discharges. Multiplanar and multisequence noncontrast magnetic resonance imaging (MRI) of the brain was performed using 3.0T MRI scanner (Discovery 750; GE Healthcare, Milwaukee, Wisconsin). A markedly reduced volume of the right cerebellar hemisphere was observed [Figures 1 and 2]. The residual right cerebellar hemisphere showed normal pattern of folia and gray white matter differentiation, suggestive of right cerebellar hypoplasia. The vermis was normal in bulk and in morphology. The right middle cerebellar peduncle showed reduced volume and normal signal intensity. The space created by hypoplastic right cerebellum was filled with cerebrospinal fluid (CSF). The fourth ventricle, midbrain, pons, and medulla were normal. The left cerebellar hemisphere was normal in bulk and signal intensity. The patient was started on sodium valproate and clobazam on which he was seizure free.

Figure 1

Axial T2WI of right cerebellar hypoplasia in craniocaudal sequence. A: There is marked hypoplasia of the right cerebellar hemisphere and replacement by CSF. The left cerebellar hemisphere is normal in bulk and signal intensity. B: At the level of internal auditory canals, the residual right cerebellum can be seen anteriorly. The normal bulk of vermis can also be seen. C: At the level of medulla, only a thin strip of residual right cerebellum is seen anteriorly. In all the images, the residual right cerebellum shows normal grey white differentiation and foliation. The left cerebellar hemisphere shows normal volume and morphology.

Figure 2

Coronal T1WI of right cerebellar hypoplasia in anteroposterior sequence. A: There is marked hypoplasia of the right cerebellar hemisphere and normal volume of left cerebellum. B: At a slightly more posterior plane, the thin strip of residual right cerebellum is seen superiorly. In both these T1 weighted images, the grey white matter differentiation and preserved folia in the residual right cerebellum can be better appreciated than T2 weighted images.

Discussion

A rational classification of cerebellar malformation was proposed by Patel and Barkovich,[1] in 2002, with clear definitions and practical usability. Cerebellar malformations are classified into those with hypoplasia and those with dysplasia based on imaging criteria. Hypoplasia refers to reduced cerebellar volume with normal shape and texture of cerebellum, that is, normal pattern and size of the folia and fissures. Dysplasia refers to abnormal shape or texture of cerebellum, that is, abnormal pattern of foliation and/or gray matter heterotopia.

Unilateral cerebellar hypoplasia (UCH) affects one cerebellar hemisphere with or without the involvement of vermis and is believed to arise from an antenatal vascular (hemorrhagic or ischemic) insult.[2] The clinical presentation of UCH varies from an asymptomatic incidentally detected pathology to a one with severe neurologic deficits. The commonly reported clinical features include developmental and speech acquisition delay, hypotonia, ataxia, and disorders of eye movement.[3] However, atypical features such as seizures as noted in our case have also been reported.[34] The involvement of vermis is often associated with cognitive decline and truncal ataxia.[5] The key imaging feature of cerebellar hypoplasia is asymmetry of the cerebellar hemispheres, which may range in severity from mild asymmetry to near total aplasia. Approximately half of the cases show vermian involvement. The posterior fossa volume is usually normal. Hypoplasia of the ipsilateral superior, middle cerebellar peduncles, and pons is usually seen.[6]

Thus, UCH has a wide spectrum of typical (predictive of cerebellar pathology such as ataxia, hypotonia, and psychomotor retardation) and atypical clinical features (such as seizures and abnormal ocular movements) and a characteristic imaging appearance.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.