Brain overgrowth associated with megalencephaly-capillary malformation syndrome causing progressive Chiari and syringomyelia

BACKGROUND: Megalencephaly-capillary malformation (M-CM) syndrome is a rare overgrowth syndrome characterized by macrocephaly, port-wine stains, asymmetric brain growth, hydrocephalus, and developmental delay. Cerebellar tonsil herniation is often seen, but rarely with syringomyelia. CASE DESCRIPTION: A newborn with M-CM syndrome developed a progressive Chiari malformation type I (CM-I) with syringomyelia. At 4 months, he was treated for subdural hematomas, while at 10 months, he required a shunt for hydrocephalus. At 16 years of age, he newly presented a left hemiparesis and ataxia. Notably, successive volumetric measurements of the posterior fossa/cerebellum showed disproportionate cerebellar growth over time that correlated with the appearance of a CM-I. Following a suboccipital craniectomy with C1-laminectomy and duraplasty, he neurologically improved. CONCLUSION: M-CM with CM-I and syringomyelia rarely present together. Here, we treated an infant with M-CM who developed a progressive CM-I malformation and syringomyelia reflecting disproportionate growth of the cerebellum/posterior fossa over a 16-year period.