Clinical History
The patient presented with growth retardation. She was small for her age, with her weight and height both being under the 3rd percentile. She had strabismus and there were no other focal neurological signs. She was born by normal vaginal delivery at 28 weeks' gestation and weighed 900 grams. Pregnancy and neonatal period were normal.
Imaging Findings
A 27-month-old girl was referred to our hospital because of growth retardation. She was small for her age. Her weight and height were under 3rd percentile. She was vocalising well and her motor development was normal. She had strabismus and there was no other focal neurological signs. She was born through normal vaginal delivery at 28th gestational week and weighed 900 grams. Pregnancy and neonatal period were normal. There was no family history of congenital central nervous system (CNS) disorders. Magnetic resonance imaging (MRI) revealed left aplasic cerebellar hemisphere (totally absent), mild contralateral and vermian (especially inferior part) hypoplasia. Brain stem was small but symmetric (Fig. 1a, b, c). In addition, there were left temporooccipital laminar heterotopia (Fig. 2a, b, c) and a left frontal bony defect (Fig. 3). Lateral ventricles were asymmetric, because of the left temporooccipital heterotopic tissue (Fig. 2, 3). There were no neuroradiological findings of inborn errors of metabolism, leukodystrophy, exposure to hypoxia or inflammatory CNS disease.
Discussion
Cerebellar anomalies are rare pathological conditions with a spectrum ranging from aplasia causing neonatal death to mild asymptomatic hypoplasia. The most common malformation involving the cerebellum is the absence of all or part of the inferior vermis, which may be familial or associated with Joubert syndrome. Unilateral cerebellar aplasia (UCA) is one of the least frequent malformations of the cerebellum. The patients with UCA may or may not have symptoms.
The pathogenesis of UCA is poorly understood and may not be uniform. In perinatal asphyxia at term, the cerebellum is almost always spared. In their ongoing study of perinatal asphyxia in term neonates, Boltshauser et al. occasionally saw minor lesions but never resulting in a substantial cerebellar defect. Therefore a prenatal event might be considered. Cerebellar hemorrhages were well-known to occur in prematures and had been repeatedly reported in very low-birth weight preterm babies of 26-28 weeks gestastional age, however, these lesions usually affected only part of a cerebellar hemisphere. As etiologic factors, they considered a localised hypoxic-ischemic lesion, an infarct, more likely than a hemorrhagic event. In our case, pregnancy period and delivery was normal except for premature birth and low birth-weight. The neonatal period and the previous personal history were uneventful. Although her mental and motor development were normal, she was shorter and thinner than her peers. Besides left UCA, MRI showed right cerebellar, vermian and brain stem hypoplasia, left temporooccipital heterotopia and left frontal bony defect. Because of other concomitant anomalies, we thought that chromosomal, inductional and/or migrational anomalies are responsible for cerebellar aplasia. So, using the term "agenesis" is more accurate than "aplasia" in this case.
The cerebellum develops from centers in the rhombic lip of the metencephalon. These grow into the cerebellar hemispheres and fuse centrally to form the vermis, fusion starting anterosuperiorly; the posteroinferior part of the vermis fuses last. Cerebellar dysgenesis may, therefore, be diffuse or severe with a large cisterna magna, hypoplastic brain stem and neuronal migrational abnormalities. Using MRI, we demonstrated left temporooccipital laminar heterotopia in addition to other anomalies. We cannot certainly say whether the left frontal bony defect is the result of dysgenesia or a normal developmental variation.
In cerebellar anomalies, sign and symptoms range from mild to severe. The most striking and consistent clinical features were nonprogressive ataxia, strabismus with or without nystagmus, as in our case, mental retardation of varying degrees and speech delay with dysarthria. Our case was premature and growth was delayed. She had strabismus as in some cases in the literature. The cause of strabismus probably was due to brain stem hypoplasia affecting the occulomotor nuclei. There was no other neurological sign or symptom.
Cerebellar anomalies can be documented by autopsy, pneumoencelagraphy or computed tomography (CT). Modern imaging modalities especially MRI have allowed us to recognize UCA in vivo. MRI with the properties of multiplanary imaging and high resolution in soft tissues provides accurate diagnosis and clearly documents the cerebellar and any associated abnormalities as found in our case. MRI also provides to see any signal abnormalities which is not seen on CT images in most cases. Our case showed no signal abnormality.
Differential Diagnosis List
Unilateral cerebellar aplasia
Final Diagnosis
Unilateral cerebellar aplasia
