Figure 12a. Guyon tunnel syndrome in a 54-year-old man with a pisotriquetrum ganglion. Transverse 5-12-MHz US scan (a) and axial CT arthrogram (b) show a rounded, hypoechoic ganglion (*), which displaces the ulnar artery (curved arrow) and compresses the ulnar nerve (straight arrow) against the pisiform (P). T = triquetrum.