Skeletal Radiol (2006) 35: 165–171 DOI 10.1007/s00256-005-0031-y CASE REPORT S. Fiona Bonar Wayne Viglione Julie Schatz Richard A. Scolyer Stanley W. McCarthy Received: 15 May 2005 Revised: 26 June 2005 Accepted: 26 June 2005 Published online: 20 December 2005 # ISS 2005 An unusual variant of intraneural ganglion of the common peroneal nerve Abstract A highly unusual variant of an intraneural ganglion of the common peroneal nerve in a 30-year- old male is presented. There was extrusion of the contents of the cyst into the substance of the nerve, dissecting between the fibres and expanding the nerve in such a way that it mimicked an intraneural tumour clinically, radiologically and histolog- ically. A comprehensive review of the entity is undertaken. Keywords Common peroneal nerve . Ganglion . Cyst . Myxoid tumour Introduction Intraneural ganglia, although uncommon, are well recog- nised and most commonly affect the common peroneal (lateral popliteal) nerve. They may also affect a variety of other nerves including the ulnar, radial, median, sciatic, tibial and posterior interosseous nerves, all of which tend to occur adjacent to a joint or bursa [1, 2]. Radiologically, in the vast majority of cases, distinction between an intraneu- ral ganglion cyst and an intraneural tumour is possible using Magnetic Resonance Imaging (MRI). We present a unique case of an intraneural ganglion of the common peroneal nerve in which there was apparent extrusion of its contents which tracked into and expanded the nerve along 20 cm of its length, mimicking a neural tumour clinically, radiolog- ically, and histologically. This case underscores the im- portance of consideration of an intraneural ganglion in the differential diagnosis in any instance of a diffusely enlarged nerve with multiloculated cystic spaces. Case report A 30-year-old male, a butcher by trade, who liked to play soccer, presented in April 2001 with a 1-year history of pain in the lateral aspect of his left leg. It was associated with a 4- month history of weakness and foot drop, with some di- minished sensation on the dorsum of the foot. He was unable to run. On examination, he had diminished sensation in the first web space on the left foot, with total weakness of the extensors hallucis longus and brevis and digitorum brevis. On examination, he had an area of tenderness over the region of the fibular head, and had a positive Tinel’ s sign in the popliteal fossa. Nerve conduction studies Presented at the Closed Program Meeting of the 30th International Skeletal Society Meeting San Francisco, 2003 S. F. Bonar (*) Douglass Hanly Moir Pathology, 95 Epping Road, Macquarie Park, NSW, 2113, Australia e-mail: fbonar@dhm.com.au W. Viglione St George Hospital, Belgrave St, Kogarah, NSW, Australia J. Schatz . R. A. Scolyer . S. W. McCarthy Royal Prince Alfred Hospital, Missenden Rd, Camperdown, NSW, Australia