Summary: We report the MR findings in two cases of
Hirayama disease, a kind of cervical myelopathy related to
flexion movements of the neck. In flexion MR studies, we
can see the striking and pathognomonic picture of anterior
shifting of posterior dura at the lower cervical spinal canal.
In nonflexion studies, we find that asymmetric cord atro-
phy, especially at the lower cervical cord, though subtle, is
highly suggestive of Hirayama disease. When it is seen, a
flexion MR study is warranted to prove this diagnosis.
Hirayama disease, also termed
nonprogressive juvenile spinal
muscular atrophy of the distal upper limbs,
is a kind of cervical
myelopathy related to flexion movements of the neck (1– 6).
The pathogenetic mechanism of this disease is attributed to
forward displacement of the posterior wall of the lower cervical
dural canal when the neck is in flexion, which causes marked,
often asymmetric, flattening of the lower cervical cord (1, 6 –9).
We report two cases of Hirayama disease and describe the
pathognomonic findings at flexion magnetic resonance (MR)
imaging. We also discuss the mechanism behind this character-
istic appearance and describe findings suggestive of Hirayama
disease on routine nonflexion MR studies