A man with paraesthesia, headache, and vertigo

A 35 year old man presented to hospital with three months’ progressive paraesthesia of his right arm, leg, and torso. He also complained of intermittent headaches, particularly after coughing, and episodes of vertigo. Examination revealed hyperreflexia and numbness, with preserved joint position sense, in the right limbs. Magnetic resonance imaging (MRI) was performed (fig 1). What is the diagnosis? Fig 1 Sagittal T2 weighted MRI scan of the neck and cervical spine Chiari malformation type 1. The MRI scan shows tonsillar descent characteristic of Chiari malformation type 1, and a resulting syringomyelia (fig 2).