Hypotonia due to rostral cervical spinal cord lesions may have increased or decreased dynamic tone. Neonates with acute cervical spinal cord injury present with hypotonia and decreased dynamic tone. Increased dynamic tone develops after several weeks. Generalized hypotonia due to rostral cervical spinal cord involvement is usually associated with apnea and bowel and bladder incontinence (Figure 124.1).

Figure 124.1.— Salient features of rostral spinal cord hypotonia. Arrow indicates the anatomical location of the injury (upper cervical spinal cord). C: cervical; MRI: magnetic resonance imaging; SSER: somatosensory evoked response.

Cranial nerve functions are normal unless the spinal component of cranial nerve XI or cranial nerve XII or its motor nucleus are damaged. The spinal component of cranial nerve XI can be damaged in the spinal canal as its fibers (that arise from the lateral aspect of the cervical spine) travel up to enter the cranial vault through the foramen magnum. The cranial nerve XII nucleus and nerve are located very low in the medulla and can be damaged during rostral cervical spinal cord injury. The most common cause of rostral cervical spinal cord injury is trauma. Trauma may occur during delivery. Neonates with achondroplasia are more prone to rostral cervical spinal cord injury due C1 -C2 subluxation (hypoplastic odontoid process) or occipital bone encroachment upon the foramen magnum (Figure 124.2).
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Figure 124.2.—Median sagittal cervical spinal cord images. [A] T2-weighted image demonstrates an rostral cervical spine injury (compare the signal of the cord at the foramen magnum and at lower cervical cord segments). [B] T2-weighted image after surgery (widening of the foramen magnum by removing the encroaching occipital bone).

Unexplained vascular accidents may also occur. Spinal cord injury is readily detectable by MRI of the spine (Figure 124.3) and somatosensory evoked potentials.

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Figure 124.3.— Median sagittal cervical spinal cord images. [A] T1-weighted image demonstrates an infarct in the cervical spine as an area of increased signal. [B] T2-weighted image demonstrates an infarct in the cervical spine as an area of increased signal.