A 23-year-old man presents with weakness and tingling in the left upper limb for 18 months. On examination, there is atrophy of the thenar muscles of the left hand.
23岁，男性，左上肢无力、刺痛18个月，检查发现左手鱼际肌萎缩。
A, Sagittal T2-weighted image of the cervical spine in neutral position shows focal cord atrophy and high signal (red arrow) from C4 to C6 vertebral level. There is no cord compression in neutral position.
B, Sagittal T2-weighted image of cervical spine in flexion shows high signal from C4 to C6 vertebral level.Forward shifting of the posterior dural wall. The posterior epidural space appears prominent (crescent-shaped) with hyperintensity .
C, Sagittal T2-weighted image of cervical spine in extension shows high signal from C4 to C6 vertebral level.
D, Axial T2-weighted image at the level of the C4 vertebral body showing flattening of the cord with hyperintense signal (red arrow).
A、颈椎中立位矢状 T2 加权图像显示从 C4 到 C6 椎体水平的局部脊髓萎缩和高信号（红色箭头）。中立位时无脊髓压迫。
B、颈椎屈曲位矢状 T2 加权图像显示从 C4 到 C6 椎体水平的局部脊髓萎缩和高信号（红色箭头）。后硬膜壁向前移位。后硬膜外腔突出（星号）
C、颈椎伸展位矢状 T2 加权图像显示从 C4 到 C6 椎体水平的高信号。
D、C4 椎体水平的轴向 T2 加权图像显示脊髓扁平，信号强度较高（红色箭头）。
HIRAYAMA DISEASE
平山病
Background:
Hirayama, et al reported 12 cases of predominantly young males with progressive monoparesis and acral wasting of the upper limb in 1959. Thus, Hirayama disease, also known as juvenile unilateral muscular atrophy of the upper extremity, occurs due to dynamic changes during neck flexion in adolescence with forward displacement of the thecal sac due to prominent posterior epidural space.
背景：1959 年，Hirayama 等人报道了 12 例以年轻男性为主的上肢进行性单侧轻瘫和肢端萎缩症患者。Hirayama 病又称青少年单侧上肢肌肉萎缩，是由于青少年颈部屈曲时发生动态变化，后硬膜外腔突出导致硬膜囊向前移位而发生的。
Clinical Presentation:
Gradually progressive upper limb muscle weakness and atrophy. There is oblique amyotrophy, ie, wasting of forearm muscles with sparing of brachioradialis.
临床表现：上肢肌肉逐渐无力、萎缩，有斜肌萎缩，即前臂肌肉萎缩，肱桡肌无力。
Key Diagnostic Features of MRI:
Neutral position
Abnormal T2 signal in the cervical cord at the site of the maximum forward shift without an apparent cause.
Flexion
Forward shifting of the posterior dural wall. The posterior epidural space appears prominent (crescent-shaped) with hyperintensity on T1- and T2-weighted images and flow voids.
Widened laminodural space
MRI 的主要诊断特征：
中立位 颈髓在最大前移位部位出现异常 T2 信号，但无明显原因。
屈曲 后硬膜壁向前移位。后硬膜外腔突出（新月形）在 T1 和 T2 加权图像上呈现高信号且有流空。
椎板硬膜腔增宽
Differential Diagnosis:
Amyotrophic lateral sclerosis: spine MRI would show spinal cord atrophy and, on brain MRI, hyperintensity of corticospinal tracts. There would be no forward dural displacement on flexion MRI of the spine. ALS occurs between 40–60 years of age and progresses relentlessly with death after 3 to 5 years of symptom onset. Hirayama disease progresses over 3 to 5 years and then stabilizes.
Longitudinally extensive transverse myelitis is characterized by extensive cord signal, while in Hirayama disease, there is a localized cord signal with focal atrophy.
鉴别诊断：
肌萎缩侧索硬化症：脊柱 MRI 可显示脊髓萎缩，脑部 MRI 可显示皮质脊髓束高信号。脊柱屈曲 MRI 不会显示前向硬脊膜移位。ALS 发病年龄在 40-60 岁之间，病情持续恶化，症状出现后 3 至 5 年内死亡。平山病在 3 至 5 年内进展，然后稳定。
纵向广泛性横贯性脊髓炎的特点是广泛的脊髓信号，而平山病的特点是局部脊髓信号和局灶性萎缩。
Treatment:
Generally self-limiting. However, early recognition and using a cervical collar to avoid neck flexion are recommended to prevent disease progression.
治疗：一般可自行痊愈。但建议及早发现并使用颈托以避免颈部屈曲，以防止病情恶化。
Teaching Point:
In any young male patient with unilateral muscular weakness of the upper extremity, an additional flexion view of the cervical spine in the sagittal section should be acquired.
教学要点：对于任何患有单侧上肢肌肉无力的年轻男性患者，应获取颈椎矢状面的额外屈曲图像。
Shrishail Adke (@ShreeAdke); Anjali Bhoir; Khushboo Tekriwal
Department of Radiology, Seth GS Medical College and KEM Hospital, Mumbai, India