[Far lateral lumbar disc herniation: clinical and radiographical features of three cases].

The authors report three operated cases of far lateral lumbar disc herniation (FLLDH) during the past two years and discuss their diagnostic pitfalls. Until recently FLLDH was hardly ever diagnosed because the myelography was negative in almost all cases. Since the advent of CT and/or MRI, FLLDH has been found to be not such a rare entity. FLLDH has also been found to reveal characteristic clinical features and radiographical findings. Usual lumbar disc herniations occur at L4/5 or L5/S1 levels, producing low back pain with the pain or sensory disturbance from the posterolateral thigh down to the foot. In contrast, FLLDH affects upper lumbar levels and produces severe anterolateral thigh pain, dysesthesia resulting from nerve root or dorsal root ganglion (DRG) compression in the foraminal or extraforaminal region. The level predilection of these two groups can be attributed to the difference of the facet joint planes between the upper and lower lumbar levels. The facets with a coronal plane are resistant to lateral bending and rotational forces, but those with a sagittal plane are unstable resulting in more shearing stress to the intervertebral discs. A patient with definite neurological signs but a negative myelography should be examined for FLLDH by using a high-resolution CT or MRI. MRI clearly shows the detailed anatomical relationships between herniated disc and nerve root or DRG in the foraminal and extraforaminal regions. As well as thin-sliced axial images, sagittal MR images that include the foraminal zone are useful for detecting a direct nerve root compression from FLLDH. The authors conclude that gait disturbance due to severe leg pain, antero-lateral thigh pain or dysesthesia are characteristic of FLLDH, and that either a foraminal or extraforaminal herniated disc or both on a CT and/or MRI are diagnostic radiographical findings of FLLDH.