There are a number of systems for lumbar nerve root anomaly classification with the Neidre and MacNab classification the most commonly cited; other systems include the Postacchini classification, and the Kadish and Simmons classification 2.
Classification
Neidre and MacNab classification modified with the addition of a fourth type proposed by Burke et al. 1,2:
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type 1: "conjoined"
type 1a: two nerve roots arise from a common dural sheath
type 1b: two nerve roots arise close in the thecal sac but do not have a common dural sheath
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type 2: "redundant" - two separate nerve roots exit through one foramen
type 2a: no extra nerve root, there is one neural exit foramen without a nerve root
type 2b: extra nerve root with all neural exit foramina containing a nerve root or roots
type 3: "anastomotic" - normal adjacent nerve roots are connected by a vertical connecting/bridging segment
type 4: "confluent" - two contributions from two adjacent nerve roots arising from the thecal sac coalescing to form a single nerve root that exits the neural exit foramen (very rare)
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