CT-observations of the intra- and extracanalicular disc herniation.

A retrospective analysis of 45 patients with intra- and extracanalicular lumbar disc herniations (ICDH, ECDH), collected over a 3 year period, is presented. When an intra- or extracanalicular DH was suspected, 1.5 mm axial cuts were made with a GE9800 from the cranial pedicle through the intervertebral canal to the pedicle of the lower vertebral body. Constructions were then made in coronal and paraxial planes to identify the pathology and its relation to the nerve root. 47% of all ICDH and ECDH were found at the level L4/5, 24% each at the levels L3/4 and L5/S1 respectively and 4% at the level L2/3. In 78% of our patients, the disc fragment was extruded and found well above the level of the disc space, in 22% at the level of the disc space. The coronal reformated views were in general better for demonstrating the course of the compressed nerve root at the levels L2/3-L4/5, while at L5/S1 the paraxial reformated view may yield better images. The distance from the midline of the spinal canal to the medial and lateral edge of the ECDH averages 16.4 +/- 3.4 and 33.3 +/- 3.6 mm and in some cases the lateral edge was found 39-44 mm from the midline. Pitfalls in the diagnosis of ECDH may be caused by scar tissue, sometimes by an upwardly displaced nerve root or ganglion and, very rarely, by a neurinoma. Pitfalls in therapy, i.g. false negative intraspinal exploration in cases of intra- or extracanalicular disc herniations or exploration of the wrong intervertebral canal, may result due to insufficient neuroradiological analysis or from insufficient consideration of the anatomical situation by the neurosurgeon.