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THIS Images in Anesthesia feature demonstrates the image quality obtainable from scanning the lower extremity of a cadaver in order to facilitate ultrasound-guided peripheral nerve blocks (PNB). Training methods to improve the performance of ultrasound-guided PNB are required, but have yet to be sandardized.1 A novel approach is to use cadaveric model simulations, which provide the learner with anatomic examination and the ability to practice nerve blocks in a stress-free environment without time constraints and the potential for patient discomfort. Cadaveric ultrasound imaging can also help the learner of these techniques to acquire an in-depth knowledge of the relevant regional anatomy in order to facilitate successful identification of nerve structures under ultrasound guidance, and to acquire expertise and confidence in performing these blocks.2 Dissections can be performed to confirm nerve or blood vessel identity whenever uncertainty exists (e.g., small nerves of the periphery). The cadaver model can also be used to acquire the critical skills necessary to accurately align the needle and probe to ensure visibility of the entire needle,3,4 while tracking or following the needle to the target nerve.5 In order to successfully practice these needle insertion techniques, it is beneficial to have a knowledge of the ultrasonographic anatomy of both cadavers and living patients. This imaging article serves as a guide for this important initial process. A recently-published companion Images in Anesthesia feature demonstrated the similarities of ultrasound images obtained from cadaveric and live subjects, and identified the relevant regional anatomy and clinical issues for upper extremity blocks.6 Here, we consider these issues for the most common nerve blocks of the lower extremity, namely those of the femoral and sciatic nerves. Ultrasound images (MicroMaxx, SonoSite Inc, Bothel, WA, USA; HFL38 13-6MHz linear probe for femoral and popliteal and C60 5-2 MHz curved probe for sciatic) were obtained from the lower extremity of a male adult cadaver (embalmed six months previously in the usual manner6 at the authors’ institution) and were compared with the images from a living adult male. The cadaver was in legal custody of the Division of Anatomy of the authors’ institution at the time of the imaging. The embalming and imaging procedures were performed with permission from the Division of Anatomy and in compliance with the institutional ethical standards for the use of human material in medical education. Ethics approval was obtained from the local Institutional Research Ethics Board for ultrasound scanning on the volunteer (one of the authors). Gaining an appreciation of the correlation between ultrasound appearance and histological findings of muscles and tendons is important for interpreting ultrasound images. Silvestri et al. reported that nerve fascicles generally appear hypoechoic, where the hyperechoic background usually represents the connective tissue within and surrounding the nerves (including the bright adipose tissue).7 The connective septa surrounding the muscles is also hyperechogenic, as is the fascia of the compartmental membranes.8 This difference in echogenicity is likely due to the higher acoustic impedance of the denser connective tissue. In the periphery, the nerves tend to appear more hyperechoic which may be due to relatively more connective tissue than nerve tissue (i.e., fewer fascicles in periphery than centrally). However, the distinction between fascia and connective septa or perimysium will be challenging in most cases. There are several common elements related to the accompanying images. With many portable ultrasound 475

Cadaveric ultrasound imaging for training in ultrasound-guided peripheral nerve blocks: Lower extremity