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Case 2

DDx

Rhombencephalosynapsis

Congenital Vermian Hypoplasia

Vermian Agenesis or hypogenesis

Cerebellar hemispheres are not fused.

Chronic shunting

Distortion, especially in Chiari II malformation with rotation or unilateral herniation

Diagnosis

Rhombencephalosynapsis

Congenital Vermian Hypoplasia

Chronic Shunting

Rhombencephalosynapsis

Congenital fusion of

Cerebellar hemispheres

Dentate nuclei

Superior cerebellar peduncles

Vermian Agenesis

Rhombencephalosynapsis

CT

Fusion of cerebellar hemispheres.

Narrow diamond or a keyhole-shaped 4th ventricle.

Lambdoidal craniosynostosis

Rhombencephalosynapsis

MRI

Fusion of cerebellar hemispheres.

Narrow transverse dimension of cerebellum.

Keyhole-shaped 4th ventricle.

Absent or severely hypoplastic vermis.

Absent primary fissure of cerebellum.

Rhombencephalosynapsis

MRI: Isolated Rhombencephalosynapsis is less common than with associations. May also see…

Holoprosencephaly

Septo-optic dysplasia

Rounded fastigial recess of 4th ventricle

Aqueductal stenosis…hydrocephalus

Dysgenesis of the corpus callosum

Fusion or apposition of the dentate nuclei

“Horseshoe-shaped’

Cortical dysplasias

Rhombencephalosynapsis

Etiology

Failure of induction or differentiation of normal midline structures.

Disturbed cerebellar development at 33-34 days of gestation

Genetic

Acquired

Maternal Hyperpyrexia

Maternal Diabetes

Maternal alcohol or phencyclidine (PCP)

Rhombencephalosynapsis

Prognosis

Short lifespan usual

Worst prognosis with associated midline supratentorial anomalies and hydrocephalus

Occasional survival to early adulthood.

Developmental delay

Psychiatric disorders

Self-injurious (common)

Bipolar

Hyperactive