Variations of the ulnar nerve in Guyon's canal: in vivo demonstration using ultrasound and 3 T MRI.
BACKGROUND
The clinical importance of Guyon's canal is emphasized due to the various branching patterns of the ulnar nerve. So far, the arborization pattern of the ulnar nerve in Guyon's canal has been investigated mostly by cadaveric studies.


OBJECTIVE
To demonstrate anatomic variations of the ulnar nerve in Guyon's canal in vivo by using high definition ultrasound (US) and 3 T magnetic resonance imaging (MRI).


METHODS
US imaging and 3 T MRI with an 8-channel coil was applied to 30 hands of 15 volunteers. The main trunk and the branched superficial and deep ulnar nerves, including neural bifurcation or trifurcation, were recognized on US and confirmed by 3 T MR images. The ulnar artery and vein and its branches were traced on color Doppler US and also visualized by MRI. The branching pattern of the ulnar nerve was determined from the inlet to the outlet of Guyon's canal.


RESULTS
Of 30 hands, 21 (70%) revealed bifurcation and 9 (30%) had trifurcation branching pattern of the ulnar nerve. In 16 hands (54%), imaging demonstrated that a single nerve entered the canal and divided into two trunks, one superficial and one deep, then exited the canal. The bifurcation occurred predominantly just after entering the canal inlet. The typical trifurcation pattern indicated that a single trunk entered the canal and divided into two, then one of the two bifurcated, producing a trifurcated pattern with two superficial and one deep bundle. Of 15 participants, symmetrical branching of bilateral hands was identified in 4 cases (27%), whereas 11 (73%) had asymmetrical branching.


CONCLUSIONS
US and 3 T MRI readily delineated the branching pattern of the ulnar nerve in Guyon's canal in vivo. Morphological understanding about this neural branching can be informative in presurgical planning and also in diagnosis.
Niitsu
Mamoru
M
Department of Radiology, Faculty of Health Sciences, Tokyo Metropolitan University, Arakawa, Tokyo, Japan. niitsu@hs.tmu.ac.jp
Kokubo
Naomi
N
Nojima
Shoko
S
D005260:Female; D006225:Hand / Q000000981:diagnostic imaging / Q000294:innervation*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D014459:Ulnar Nerve / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D014463:Ultrasonography; D055815:Young Adult