[Extreme lateral lumbar disk herniation. Apropos of a series of 25 cases].

Twenty-five cases of extreme lateral disc herniation (ELDH) were identified amongst 680 operated lumbar discs (3.7%). Their anatomical, radiological and clinical features are presented. They were found at all levels between L3 and S1. At the L5-S1 level 12 ELDH occurred amongst 253 disc herniations (5%), at the L4-L5 level, 8 ELDH amongst 400 herniations (2%), and at the L3-L4 level, 5 ELDH amongst 21 herniations (24%). No clinical features were encountered which could allow to differentiate between an ELDH and a classical disc herniation of the above level. Twenty-three patients underwent lumbar myelogram. This was normal in 6. In 12 it showed a slight shortening and widening of the above situated nerve root sleeve. The same abnormality can be found with downward migration of a classical herniation of the above situated disc or with a lateral recess stenosis. Twenty-five patients underwent computed tomography (CT.). In 24, the ELDH could be unequivocally identified. Disc material occupied the intervertebral foramen or the extravertebral space just beyond it, replacing the normal fat. In order to identify an ELDH, CT has to be done whenever myelogram is normal or equivocal. If the patient is to be investigated by CT only, slices through the intervertebral foramen and the disc below the clinically suspicious level have to be included. Operation in all cases consisted in total or partial unilateral laminectomy with facetectomy.