title: Compression of the ulnar nerve in Guyon's canal caused by a large hypothenar cyst.
abstract: OBJECTIVE
  We report the case of a 77-year-old man who presented with a long-standing, large swelling of the left hypothenar eminence. This was associated with recent-onset paresthesia and numbness of the ring and little fingers. Magnetic resonance imaging demonstrated a cystic lesion that occupied almost the entire bulk of the hypothenar eminence.
  
  
  METHODS
  Surgical exploration revealed a 7-cm, encapsulated, yellow-brown cyst, around which were stretched the superficial sensory branches of the ulnar nerve. The hypothenar musculature lay flattened against the deep border of the mass.
  
  
  RESULTS
  The cyst was removed and Guyon's canal was released. Histologic examination confirmed a large cyst containing proteinaceous debris and blood breakdown products. It might have resulted from hemorrhage into a long-standing ganglion. Removal of the cyst led to full resolution of the patient's symptoms.
  
  
  CONCLUSIONS
  This represents an unusual cause of ulnar tunnel syndrome. It is rare to encounter such a large cyst in the hand and interesting in the sense that the resulting symptoms were relatively mild and took many years to develop.
authors.affiliation: St Andrew's Centre for Plastic Surgery and Burns, Broomfield Hospital, Chelmsford, United Kingdom. adamsiera@yahoo.co.uk
authors.forename: Adam
authors.initials: A
authors.lastname: Sierakowski
authors.forename: Claire Jane
authors.initials: CJ
authors.lastname: Zweifel
authors.forename: Simon
authors.initials: S
authors.lastname: Payne