ANATOMY FOR DIAGNOSTIC IMAGING arteries, which are variable in number and level of origin. No single injection will opacify the entire anterior spinal artery. The main feeding vessel in spinal angiomas may arise distant from the lesion and may be missed if a thorough examination is not performed. The arteria radicularis magna (artery of Adamkiewicz) usually arises on the left side between T8 and T12. When opacified it is seen to turn cranially from its origin towards the midline of the spinal cord and to bifurcate into a small ascending and a large descending contribution to the anterior spinal artery. This angiographic feature is called the 'hairpin appearance'. Angiographically directed embolization of angiomatous vessels is sometimes possible. Bronchial angiography In the catheterization of intercostal arteries and their branches, such as for bronchial angiography and in particular for bronchial embolization, there is a risk of damage to the blood supply of the cord by embolization to the radiculomedullary branches. Magnetic resonance imaging (see Fig. 3. 12) MRI is useful for imaging the spinal cord - it is noninvasive and the entire cord can be seen in a few sagittal images. The spinal cord is well seen against the CSF in either T1- or T2-weighted images. The enlargements of the cord in the cervical and lower thoracic areas are visualized, and the cauda can be seen close to the posterior aspect of the subarachnoid space beyond the lower limit of the cord. Differentiation between grey and white matter within the cord is not always possible. A thin line of low-T1, high-T2 signal intensity seen down the centre of the normal cord on sagittal sections is not the central canal but represents a truncation artefact. Nerve roots are visible, especially where they are outlined by fat in the intervertebral foramen. Epidural fat is invariably present posteriorly and, to a lesser extent anteriorly. The amount of epidural fat in the nerve roots increases from their cranial to their caudal ends. In contrastenhanced MRI, bright epidural veins contrast with negligible signal from nerve roots. The spinal nerves of the cauda equina can be seen outlined by the CSF, usually lying posteriorly in the thecal space, except for those passing anteriorly from the exit foramina. RELEVANT MRI ANATOMY - CERVICAL SPINE (Fig- 3. 20) Spinal angiography This is a lengthy procedure involving injection of contrast into the vertebral arteries, the deep cervical arteries, several intercostal and lumbar arteries and the sacral branch of the internal iliac artery to identify the radiculomedullary
Vertebral body In order to maintain the axial load imposed by weight bearing, the vertebral body is composed of both a thick outer cortical shell of compact bone and an inner supporting
