Ultrasound Anatomy

Most of the structures seen on MRI are visible on ultrasound using a high-frequency (10 MHz or more) linear probe. The tunica albuginea and Buck's fascia are not readily distinguished, but appear as a smooth, echogenic structure surrounding the less echogenic corpora16 (Figs. 4.6 and 4.7). In the tumescent state, the corpus caverno-sum is slightly less echogenic than the spongiosum, but the two are not markedly different and the radiologist must be careful to identify each correctly. The tunica around the corpus spongiosum is thinner than around the corpora cavernosa, and

Fig. 4.6 Two axial images of the shaft of the tumescent penis: the first (a) taken at an angle of 45° to avoid diffraction artifact, and the second (b), in the standard transverse plane with the probe ventral. The urethra (white arrow) is sometimes seen well within the corpus spongiosum. Tunica albuginea and Buck's fascia (black arrows) appear as one echogenic layer, thickest around the corpora cavernosa. White arrowheads show superficial vessels, and black arrowheads the cavernosal vessels

importantly, subepithelial connective tissue and the thin tunica albuginea are impossible to distinguish from each other in the glans, which has implications for the staging of small tumors located in this area.9 The urethra is visible within the corpus spongiosum and can be traced through the glans to the external urethral meatus (Fig. 4.7). Cavernosal vessels are easily seen in the erect state, but with the correct Doppler settings should also be seen without erection.1 7 The dartos fascia layer is difficult to reliably distinguish but ultrasound does show well the difference between skin and corpus cavernosum, spongiosum, or glans.

The penis should be scanned both from the dorsal and the ventral aspect. For very superficial tumors it can be difficult to move the focal zone superficially enough

Fig. 4.7 Longitudinal image of the glans. White arrowheads mark the end of the tumescent corpus cavernosum, and black arrows show the urethra. The glans (marked with an asterisk) is not shown optimally on this image; for a better view of its outlines see Fig. 4.9, which also shows a tumor

Fig. 4.7 Longitudinal image of the glans. White arrowheads mark the end of the tumescent corpus cavernosum, and black arrows show the urethra. The glans (marked with an asterisk) is not shown optimally on this image; for a better view of its outlines see Fig. 4.9, which also shows a tumor

for sharp images and a spacer may be useful; an alternative is to scan from the opposite aspect. Lymph nodes are well seen in the groin, but much less reliably identified in the pelvis. In normal nodes a fatty hilum is often visible, with smooth nodal parenchyma of uniform thickness and a radiating vascular pattern; normal and pathological appearances will be described in detail later in this chapter.

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