Chapter 39. Spinal Sonography and Applications of Ultrasound for Central Neuraxial Blocks
What is the best choice for ultrasound (US) transducer and frequency setting in ultrasound imaging of the spine for central neuraxial blocks (CNBs) in the adult population?
A. High-frequency linear-array transducer
B. Low-frequency linear-array transducer
C. High-frequency curved-array (convex) transducer
D. Low-frequency curved-array (convex) transducer
D is correct. US imaging of the spine typically requires the use of low-frequency US (2–5 MHz) and curved-array (convex) transducers. Low-frequency US is required for adequate tissue penetration at the depth (5–7 cm) at which the neuraxial structures are located in adults. In addition to offering lower frequencies and better penetration, curved-array transducers are also preferred over linear-array transducers as they offer a wider field of view, which aids recognition of sonoanatomical landmarks. It may be possible to use a linear-array transducer in children, or in very thin adults where the depth to the vertebral canal is less than 5 cm.
Which two scan planes (axis) complement each other to obtain anatomical information during an ultrasound (US) examination of the spine with the patient in the sitting, lateral decubitus, or prone position?
A. Median plane and transverse plane
B. Coronal plane and sagittal plane
C. Transverse plane and sagittal plane
D. Coronal plane and transverse plane
C is correct. The anatomical information obtained from the transverse scan and the sagittal scan (longitudinal axis) complement each other during an US examination of the spine. The paramedian sagittal scan (see Figure 39–1) allows identification of vertebral levels, location of paramedian interlaminar spaces, and estimation of depth to the epidural and intrathecal space.
The transverse scan can be performed over the spinous process (see Figure 39–2A) or through the interspinous/interlaminar space (see Figure 39–2B). The former produces the transverse spinous process view, which clearly indicates the position of the neuraxial midline, whereas the latter produces the transverse interspinous view, which precisely identifies the interlaminar window through which the needle may be advanced, the depth to the epidural space, and canal.
Axis of scan: paramedian sagittal scan (A) at the level of the lamina; (B) at the level of the articular process; and (C) at the level of the transverse process.
Axis of scan: transverse scan (A) at the level of ...