Generalized hypotonia due to lower cervical spinal cord lesions usually have increased dynamic tone of the lower extremities and decreased dynamic tone of the upper extremities (Figure 125.1). Neonates with acute lower cervical spinal cord injury present with hypotonia and decreased dynamic tone in all extremities. Increased dynamic tone of the lower extremities develops after several weeks. The most common cause of lower cervical spinal cord lesions is trauma. Spinal cord injury is readily detectable by MRI of the spine and somatosensory evoked potentials.

Figure 125.1.—Salient features of lower cervical spinal cord hypotonia. Arrow indicates the anatomical location of the injury (lower cervical spinal cord). C: cervical; MRI: magnetic resonance imaging.

The most common cause of lower cervical spinal cord lesions is trauma. Spinal cord trauma may be associated with extradural arachnoid cyst (Figure 125.2).

A	B

Figure 125.2.— [A] Median sagittal spinal cord image demonstrates an area of decreased ecogenicity in the lower cervical spine and an extradural arachnoid cyst. [B] Transverse midthoracic image demonstrates cord compression by an extradural arachnoid cyst.