Normal Findings

The skull varies considerably in shape and consists of a superior portion, the vault, and an inferior portion, the base. Along the base lie the orbits, sella turcica, and the temporal bones. The skull bones are composed of outer and inner tables of compact bone separated by the diploic space containing bone marrow. The inner table contains grooves for vascular structures such as the middle meningeal artery branches, and care should be taken not to confuse these for linear fractures. Pacchionian depressions house arachnoid granulations that are related to venous lacunae communicating with the superior sagittal sinus.

From the midline they commonly extend 2.5 to 3.0 cm, and any inner table depression beyond that distance should be considered something else, possibly an inner table erosion secondary to a neoplasm. [1 Beyond age 3 the cranial sutures appear similar to the adults, and portions undergo actual closure at variable ages. Normal intracranial calcifications consist of dural, pineal, habenular, choroid plexus, arachnoid granulation, and basal ganglia calcifications. The latter can be seen in hypothyroidism and pseudohypothyroidism, but are most often physiological.

For the spine, the lateral view is the single most useful projection because it can demonstrate most post-traumatic lesions of the cervical spine. The lateral projection clearly demonstrates the vertebral bodies, apophyseal joints, anterior arch of the atlas, atlanto-odontoid distance, odontoid process, spinous processes, and disc spaces. A mandatory requirement is the demonstration of the C7 vertebral body. The four smooth contour lines of the normal cervical spine are apparent on the lateral view and should be evaluated to exclude interruption or angulation. The lines include the anterior and posterior vertebral lines, the spinolaminar line (defines the posterior margin of the spinal canal), and the posterior spinous line. Evaluation of the prevertebral soft tissues can also be performed because the retropharyngeal and retrotracheal spaces are adequately demonstrated.

The anterior projection demonstrates the C3 to C7 vertebral bodies, intervertebral disc spaces, lateral masses, uncinate processes, uncovertebral (Luschka) joints, and the spinous processes that, superimposed upon the bodies, resemble teardrops. To provide adequate visualization of C1 and C2, a variant of the anteroposterior projection is often obtained, termed the open-mouth or odontoid view. The atlanto-occipital and atlantoaxial joints, odontoid process, and lateral masses of C1 and C2 are effectively demonstrated.

The oblique view of the cervical spine demonstrates neural canal stenosis secondary to degenerative spur formation arising from the uncinate processes anteriorly or from the respective facet joint posteriorly. The oblique view of the lumbar spine is the single most useful view in evaluating for suspected spondylolytic defects through the pars interarticularis.

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