Plantar flexors, hip extensors

Plantar aspect of foot

Ankle jerk

Thoracic disc herniations, although less common, are not rare and frequently involve the lower thoracic discs. They are frequently missed or diagnosed late because their pain referral pattern may confuse the inexperienced clinician. Patients usually present with axial and/or radicular pain that may be felt in the abdominal wall region or trunk, simulating intra-abdominal pathology. Not infrequently, small thoracic disc herniations are incidentally discovered on MRI films in the absence of any clinical symptoms.

Imaging Studies

Annular tears initially appear on MRI as high-intensity zones (HIZs) onT2-weighted images. These can be easily seen on sagittal and axial MRI cuts as small areas of increased signal and are usually found in the posterior or posterolateral aspects of the annulus (Figure 3-9). That region may enhance following contrast administration.

Herniated discs cannot be seen in plain films. When they herniate through the vertebral endplate, however, a situation that is frequently seen and believed to be secondary to endplate injury, they become visible. These herniations are called Schmorl's nodes. They are commonly seen in spinal X-rays as small circumscribed endplate defects that are continuous with the discs (Figure 3-10). Axial CT through such a node will show a soft tissue defect that is isodense and continuous with the disc and may be surrounded by sclerotic bony margins. MRI images will show basically the same picture. Bone marrow edema adjacent to a Schmorl's node will appear in the acute stage. It will appear hypoin-tense on T1- and hyperintense on T2-weighted images (Figure 3-11).

Anterior herniations are commonly seen on imaging studies. They may lift the anterior longitudinal ligament and at times assume a rather larger size. On CT examination a soft tissue with density identical to that of the intervertebral disc will be seen extending anteriorly.

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