- Radiographic measurement techniques, skull base craniometry, skull base lines
Pathology-Based Imaging Issues
- This chapter provides a broad summary of the varied measurement techniques used for evaluating the spine. The main focus for the reader should be the tables and the multiple schematics that define the variously named lines and angles. These summarize the classic measurement techniques for the skull base, rheumatoid disease, and some of the most commonly used measurements for assessing trauma. The rest of the measurements defined below are a mixture of miscellaneous measurements and those that do not translate well into a table (i.e., equations).
- Torg-Pavlov Ratio
- The practical utility of this measurement is controversial. Less than 0.80, as seen on the lateral view, is considered to be cervical stenosis, and such a small canal potentially increases risk for cord injury.
- Maximum Canal Compromise (%)
- AP canal diameter at the normal levels (immediately above and below the level of injury) and at the level of maximum compromise are defined. The measurement of normal levels is taken at the midvertebral body level. Di is the AP canal diameter at the level of maximum injury, Da is the AP canal diameter at the nearest normal level above the level of injury, and Db is the AP canal diameter at the nearest normal level below the level of injury.
- In spinal cord injury patients, midline T1 and T2 MR provide an objective, quantifiable, and reliable assessment of cord compression that cannot be defined by CT alone.
- Maximum Cord Compression (%)
- AP cord diameter at the normal levels immediately above and below the level of injury and at the level of maximum cord compression is defined. di is the AP cord diameter at the level of maximum injury, da is the AP cord diameter at the nearest normal level above the level of injury, and db is the AP cord diameter at the nearest normal level below the level of injury. If cord edema is present, then measurements are made at the midvertebral body level just above or below the extent of the edema where the cord appears normal.
- Cobb Measurement of Kyphosis
- Lines are drawn to mark the superior endplate of the superior next unaffected vertebral body and the inferior endplate of the inferior next unaffected vertebral body, which are then extended anterior to the bony canal. Perpendicular lines are then extended, and the angle between the 2 perpendicular lines is measured.
- Tangent Method for Kyphosis
- Lines are drawn along the posterior vertebral body margin on the lateral view of the affected body and the next most superior body that is unaffected. The angle between these 2 vertically oriented lines is measured.
- Also called the geometric center of the vertebral body, this measurement is defined by drawing diagonal lines between opposite corners of the body, with the centroid at the intersection.
- Apical Vertebral Translation
- Lateral displacement of the apex of the coronal curve is relative to the center sacral vertical line (CSVL) on AP plain film. The apical vertebral translation (AVT) is the horizontal distance between the centroid of the apical body and the CSVL.
- Sagittal Balance
- Sagittal alignment is defined on the lateral view using a C7 plumb line. The distal reference point is the posterior superior aspect of the sacrum. There is a positive number if C7 plumb line falls anterior to the reference point, and a negative number if it falls posterior to the reference.
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