*A 13 year-old child presented with seizures.
What is the most likely diagnosis?
1. Dandy Walker Variant
2. Mega Cisterna Magna
3. Subtotal Cerebellar Agenesis (Chiari IV malformation)
4. Arachnoid Cyst
Answer
Answer: Subtotal Cerebellar Agenesis
Case Discussion:
T1W sagittal and FLAIR coronal images show a small vermian remnant and a hypoplastic pons, with flattened anterior prominence.
Subtotal agenesis of cerebellum, also called Chiari IV malformation, is a very rare condition that is characterized by severely hypoplastic, rudimentary cerebellar hemispheres along with a normal-sized, fluid-filled posterior fossa and pontine hypoplasia. Clinical features vary from mild to severe (1).
The Chiari IV malformation is distinct from the Dandy–Walker malformation, the posterior fossa being of normal size in the former, but it is indistinguishable from primary cerebellar agenesis or pontocerebellar hypoplasia (2). MR features of pontocerebellar hypoplasia are a thin flat pons, with loss of the anterior curve; a small cerebellum, with predominant flattening of hemispheres and shortened cerebellar fissures; and a normal-sized posterior fossa (3).
References:
1. Choh, N. A., & Choh, S. A. (n.d.). MRI demonstration of subtotal agenesis of the cerebellum with closed-lip schizencephaly. Annals of Saudi Medicine, 31(2), 207–8. doi:10.4103/0256-4947.78212
2. Robertson R, Caruso PA, Truwit CL, Barkowich AJ. MRI of the brain and spine. In: Scott W, Atlas, editors. Disorders of brain development. 3rd ed. Philadelphia: Lippincott Williams and Wilkins; 2002. pp. 293–4.
3. Goasdoué P, Rodriguez D, Moutard ML, Robain O, Lalande G, Adamsbaum C. Pontotocerebellar hypoplasia: Definition of MR features. Pediatr Radiol. 2001;31:613–8.