herniation of nucleus pulposus (HNP)
focal protrusion of disc material secondary to rupture of annulus
fibrosus confined within the posterior longitudinal ligament
location:
- L4/5 (35%); L5/S1 (27%); L3/4 (19%); L2/3 (14%); L1/2 (5%);
thoracic spine affected in 3:1000 disc operations
- posterolateral (49%): weakest point (posterior longitudinal
ligament tightly adherent to posterior margin of disc)
- posterocentral (8%)
- lateral/foraminal (<10%)
- intraosseous/vertical (14%): "Schmorl node"
- extraforaminal/anterior (29%): commonly overlooked
- bilateral: on both sided of the posterior ligament
findings:
- disc (low T1) displaces posterior ligament/epidural fat (high T1)
- enlarged (edematous) nerve root: "trumpet sign"
- see:
- degenerative disc disease
- extradural mass
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© 2002, C.E. Kahn, Jr.
2002-04-18