Figure 14. Common peroneal nerve entrapment by a ganglion in a 54-year-old man. Longitudinal 5-12-MHz US scan of the posterolateral knee shows a ganglion (*) that expands along the common peroneal nerve (arrowheads), thus leading to a compressive syndrome. The ganglion can be differentiated from the nerve substance on the basis of its cystic structure. F = fibula.