Intraneural ganglion: a case report with electron microscopic observations.

We report a case of common peroneal mononeuropathy caused by an intraneural ganglion in a 9-year-old boy. The mass and the contiguous nerve fascicles were excised under the operating microscope. Histologically, the cyst wall was composed of layers of elongated cells merging with fascicles that exhibited changes suggestive of a pressure-ischemia effect. Electron microscopy showed that the cells forming cyst wall were myofibroblasts, similar to the cells found in ganglia arising from joints elsewhere in the body. A review of the English literature on intraneural ganglia discloses 44 additional cases, of which 86% involved the common peroneal nerve. The most common clinical feature was motor dysfunction (followed by pain, sensory loss, and the presence of a palpable mass), and a significant male predominance is noted. The pathogenesis of this nerve lesion is discussed in light of our findings.