Table 1.

Achondroplasia foramen magnum score (AFMS).

AFM risk score	MRI determined classification
AFMS 0	Normal cranio-cervical junction (CCJ)
AFMS 1	Narrowed cranio-cervical junction with cerebrospinal fluid (CSF) surrounding the cord
AFMS 2	Loss of CSF signal surrounding the cord at the CCJ without cord remodeling
AFMS 2a	Loss of CSF signal posterior to the cord
AFMS 2b	Loss of CSF signal posteriorly and anteriorly
AFMS 2c	Loss of CSF signal posteriorly, anteriorly and at the sides
AFMS 3	Remodeling of the cord at the CCJ
AFMS 3a	CSF signal remains visible at the CCJ
AFMS 3b	No CSF signal is visible at the CCJ
AFMS 4	High T2 signal in the cord at the CCJ
AFMS 4a	CSF signal remains visible at the CCJ
AFMS 4b	No CSF signal is visible at the CCJ