ULTRASOUND EVALUATION OF FOREARM ULNAR NERVE SCHWANNOMA

Schwannoma is an a well defined  encapsulated tumor of nerve sheath that grow eccentrically along the nerve axis, within the epineurium .  Schwannoma derive from cells representing the supporting tissue of a nerve, &  they typically appear as ovoid mass arising from the surface of a nerve separated from the unimpaired nerve fascicles . The nerve usually  stretched  & eccentrically courses over the capsule of the mass.  Sonography is usually unreliable in distinguishing between schwannomas and neurofibromas, as  both appears  as discrete homogeneous ovoid hypoechoic masses, with a healthy nerve at the proximal and distal ends of the mass .  A reliable sonographic diagnosis of a nerve tumor can only be made when the lesion found to be in continuity with nerve . The presence of cystic degeneration favours schwannoma rather than neurofibroma . Neurofibroma are surgically inseparable from the host nerve and can undergo malignant transformation ,where as schwannoa being discrete & eccentric ,  thus ,  often allowing the tumor to be surgically excised without loss of neurologic function.

CASE – A 35 y male presented with a small nodular swelling in distal part of  left forearm along ulnar aspest near wrist . The nodule was slightly painful and causes pain in ulnar half of hand on compressing it . No overlying skin changes or pulsations seen . No any pain noted on digital or wrist movements.

AT USG – A well defined encapsulated  oval hypoechoic solid nodular mass of about  16 x 10 x 12 mm size noted in inter mascular plane along ulnar vessels proximal to left wrist [ fig 1 ]. The lesion was  seen along ulnar nerve with neural fascicular continuity present &  established proximal & distal to the mass [ fig 2]. No significant internal vascularity or cystic or calcific foci noted . Adjacent ulnar vessels were  also seen normal . No muscle or bony or wrist  joint pathology seen . In view of encapsulated  focal nodular mass along ulnar nerve, a possible diagnosis of nerve tumor , likely schwannoma was made .  The lesion was proved ulnar nerve schwannoma  at surgery & biopsy [ fig 3 & 4 ].  

                                   Fig 1- LS & TS US scans of left distal forearm proximal to wrist,  showing a well defined hypoechoic  solid nodular mass adjacent to ulnar vessels [ along neurovascular bundle ] 

                                  Fig 2 - LS scan with conjoint image of the mass  , here the mass shows ulnar nerve fascicular continuity at its both proximal & distal ends , suggests the diagnosis of nerve tumor[ schwannoma ]

                                 Fig 3 - Per operative view of the nerve tumor . The tumor was removed without any neural damage .

                                     Fig 4 - Post operative gross specimen of dissected ulnar nerve sheath tumor [ schwannoma ]

PS – The case study in intended for medical professionals & imaging specialists for academic purpose.

  - My special thanks to Dr. Vishal Gupta , orthopaedic surgeon , Bhilwara [ raj., India ] , for operative feed back.


Read More: 1[  http://www.ajronline.org/doi/full/10.2214/ajr.182.1.1820123

                   2]  Peer et al J Ultrasound Med 21:315–322, 2002