MRI of difficult discs.

Diagnosis of disc herniation is a daily task for radiologists. Although diagnosis is usually straightforward, it may become more difficult due to disc location. Disc herniations in the neural foramen or lateral to it can be overlooked if sagittal images are not obtained far enough laterally, and are often best seen on coronal images. Intradural disc herniations should be recognised preoperatively by their distinctive shape; recognition prepares the surgeon for the need to perform a durotomy and dural repair. Sequestered discs are often lentiform and inconspicuous on sagittal images. They can be missed if axial images are obtained only through the level of the intervertebral disc. Mimics of disc herniation must also be kept in mind when reviewing magnetic resonance imaging (MRI) studies: these include disc osteophyte complex, epidural haematoma, facet joint cyst, and tumours such as meningioma, nerve sheath tumours, and metastases.