Abstract: Introduction: Cerebellar hypoplasia (CH) is a rare developmental abnormality of the posterior fossa, characterized by underdevelopment of the cerebellum. Its prenatal detection is critical for prognostic and genetic counseling, as it may be isolated or associated with a wide spectrum of syndromes and chromosomal anomalies.
Methods: We report the case of a fetus evaluated during the second trimester for suspected posterior fossa abnormalities. Standard obstetric ultrasound and targeted neurosonography were performed, followed by fetal MRI for further clarification.
Results: Ultrasound revealed a small posterior fossa with reduced cerebellar volume, particularly involving the vermis. The transverse cerebellar diameter was below the 5th percentile for gestational age. The cisterna magna was preserved. Fetal MRI confirmed cerebellar hypoplasia with intact brainstem structures and no supratentorial anomalies. No extracranial malformations were noted. Amniocentesis was performed, and chromosomal microarray was normal. TORCH screening was negative. The diagnosis of isolated cerebellar hypoplasia was retained.
Discussion: Cerebellar hypoplasia can result from genetic mutations, congenital infections (such as CMV), vascular insults, or metabolic disorders. When isolated, prognosis is variable and depends on the degree of hypoplasia and postnatal development. Detailed imaging and exclusion of infectious and genetic causes are crucial for prenatal counseling.
Conclusion: This case illustrates the importance of a systematic approach in evaluating posterior fossa abnormalities. Accurate diagnosis and etiological exploration of cerebellar hypoplasia enable appropriate counseling and guide perinatal management decisions.
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