THE NORMAL CONUS
To determine if the cord is low lying or potentially tethered its important to know what is the lowest level you can see a conus and still call it normal.
The radiology literature varies with a conus at the L2/3 disc or L3 level considered within the normal range.
- At birth the normal conus will most commonly be at the L1/2 level but can also be at the L2/3 level. The thecal sac is at the S2 level
- This because the cord grows at a slower rate than the vertebral column.
- By 2/12 the conus usually lies around the L1/2 level.
This is the statement from the International Society of Pediatric Neurosurgeons.
" Any conus medullaris lying caudal to the mid-body of L2 is considered abnormally low (95% confidence limits) and therefore potentially tethered." (Link to reference in next tab).
NORMAL: Conus at or above mid L2 is normal at any age (Orange).
ABNORMAL: Conus below mid-L2 abnormal (Green)
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