CHAPTER 33 Intercostal block
Sonoanatomy
The chest wall is best imaged in a coronal (vertical) plane. Using a 6–13 MHz linear transducer, the relevant intercostal space is visualized. The ribs appear as dense dark oval structures with a bright surface (periosteum; Fig. 33.4). A dark shadow is cast deep to the rib on ultrasound, illustrating the phenomenon of echo shadowing. Echo shadowing is an echo-free zone immediately behind a structure of high absorbance or reflectivity, such as bone, calculi or metal prosthesis. The pleura and lungs are visualized deep to the intercostal space between the echo shadows (Fig. 33.4).

Figure 33.4 Ultrasound appearance of the intercostal space. R: rib; M: intercostal muscle; P: pleura.
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