Anomalies of the brachial plexus and its terminal branches
are not uncommon. Variations in the course and branches
of the musculocutaneous nerve have been noted (Clemente,
1985; Bergman et al. 1988) and its absence was reported by
Le Minor (1990). Several anomalies were present in the left
plexus of a 59-y-old Japanese man (Fig.). There were no
anterior and posterior divisions of the middle trunk,
although there were communications between the posterior,
medial and lateral cords. The musculocutaneous nerve was
absent (Le Minor, 1990) and the medial and lateral roots of
the median nerve did not unite in the axillary fossa but in the
upper arm about 5 cm distal to the lower border of
latissimus dorsi (Adachi, 1928; Buch-Hansen, 1955). The
hitherto unreported findings were branches arising directly
from the lateral cord to supply coracobrachialis, both heads
of biceps brachii and brachialis. The lateral cutaneous nerve
of the forearm was derived from the lateral cord with a small
contribution from the medial root of the median nerve.
Since there were communications between the posterior
cord (a continuation of the middle trunk) and the medial
and lateral cords, it is theoretically possibly, but not proven,
that the root values of branches innervating the flexor
muscles of the arm and forearm and the skin of lateral
border of the forearm were normal.