Anatomy of the spinal cord, nerve root and vertebral body. Cross sectional (axial) view of the spine showing a sketch (left) and MRI T2-weighted image (right) revealing: (1) spinal cord (posterior columns); (2) dorsal root and dorsal root ganglion; (3) spinal nerve; (4) posterior primary ramus (continues to innervate paraspinal muscles); (5) ventral root; (6) anterior primary ramus (continues to form plexus); (7) vertebral spinous process; (8) vertebral body and intervertebral cartilaginous disc
The spinal vertebrae and its supporting ligamentous and muscular scaffolding affords protection to the spinal cord and exiting nerve roots while at the same time offering considerable mobility and flexibility. The vertebral body is located anterior to the spinal cord and in the thoracolumbar segments represents the familiar ‘box-like’ structure that is seen on radiographic images of the spine. Each vertebral body is separated by an intervertebral disc comprised of a viscous nucleus pulposus with an annulus fibrosus surrounding it in a circumferential manner. It is herniation of the nucleus pulposus that gives rise to most compressive radiculopathies in adults. The posterior spinous process and two posterolateral transverse processes represent three elongated bony projections to which stabilizing ligaments attach. The lateral pedicles connect each vertebral body to the posterior spinal and transverse processes. It is through the gap between each pedicle that spinal nerves exit in a space known as the intervertebral foramen.
Nerve roots are susceptible to the same injuries as peripheral nerves including compression, transection, infection, and infiltration. Congenital disorders of vertebral body development and alignment including hemivertebrae , spondylosis and scoliosis  can be associated with radiculopathy in the pediatric age group.
The key clinical features of a radiculopathy include: (1) severe back pain and paraspinal muscle spasm; (2) pain and paresthesia radiating in a dermatomal distribution; and (3) muscle weakness.
The dermatomal pattern of sensory symptoms must be differentiated from that of individual peripheral sensory nerves (Fig. 17.2). Dermatomes are areas of skin supplied by sensory neurons arising from a single spinal root. This pattern of sensory innervation is of early embryonic origin as paired blocks of mesodermal tissue (known as somites) give rise to sensory innervation to segments or regions of skin in a rostrocaudal or head-to-tail axis. Dermatomal areas have been mapped [5, 6] and differ from cutaneous nerve supply by individual peripheral sensory nerves.
Dermatomal (a) and peripheral sensory nerve (b) distributions of the ventral (left) and dorsal (right) body. Figure credit: J.A. Kiernan, University of Western Ontario . Permission was obtained to use this figure
Muscle weakness due to radiculopathy also occurs in a predictable pattern. Efferent motor fibers originating from a single spinal root level are collectively referred to as a myotome. Most muscles have contributions from two or more myotomes although typically, one level will predominate (Figs. 17.3 and 17.4). Muscle weakness that corresponds to a myotomal pattern, rather than that of a single peripheral nerve lesion, provides an opportunity to clinically and electrophysiological differentiate root lesions from peripheral nerve lesions. When clinically evaluating a patient with a suspected radiculopathy, physicians should become accustomed to evaluating a pattern of weakness, pattern of sensory deficit and integrity of deep tendon reflexes with a goal of differentiating a patient with a radiculopathy versus a peripheral nerve lesion. Muscle testing that is normal in one situation and abnormal in the other is ideal for helping to differentiate root versus nerve lesions (Fig. 17.5). Muscles that are normal or abnormal in both situations are not helpful for distinguishing between the two types of lesions.
Upper extremity: differentiating spinal root versus brachial plexus versus peripheral nerve lesions. Bold = predominant innervation
Lower extremity: differentiating spinal root versus brachial plexus versus peripheral nerve lesions. Bold = predominant innervation
Clinical and electrophysiological testing used to differentiate an L5 root from a common peroneal nerve lesion. This example illustrates how muscles predicated to be normal in one situation and abnormal in the other are the most valuable for this assessment. Muscles that are normal or abnormal in both situations are not helpful
Lesions at the spinal nerve root can result in sensory and motor symptoms since both fibers travel together through the intervertebral foramen. However, in cases of radiculopathy due to disc herniation or spondylosis (causing ventral and/or dorsal nerve root compression), electrodiagnostic testing can help differentiate radiculopathies from more distal lesions. Lesions that are proximal to the dorsal root ganglion will result in clinical symptoms without any abnormality on sensory nerve conduction studies since the sensory nerve fibers remain in continuity with their dorsal root ganglia and thus do not degenerate. By comparison, given the intramedullary location of motor neurons in the ventral spinal cord, any compressive lesion will disrupt communications between the motor neuron and the motor nerve. The key electrodiagnostic finding in classic radiculopathy that permits it to be differentiated from plexopathies and peripheral neuropathies is the finding of intact sensory nerve action potential (SNAP) amplitudes confirming the proximal site of injury. In radiculopathies, compound motor action potential (CMAP) amplitudes may be reduced, F waves at appropriate myotomes may be abnormal, and needle electromyography (EMG) findings will typically indicate a myotomal pattern of denervation. Caution must be taken in the case of diseases that infiltrate or extend into the intervertebral foramen (e.g., malignancy, infection) since dorsal root ganglia may be damaged in such cases, resulting in wallerian degeneration of sensory and motor fibers affecting both SNAP and CMAP amplitudes.
A 15 year old young man suffered an injury after attempting to perform a backward somersault during which he landed awkwardly. Although he did not suffer any initial pain or symptoms, he developed severe, escalating back pain over the next 2 days that radiated bilaterally down the backs of both legs. He reported paraesthesias over the backs of his lower legs and the dorsal and plantar surfaces of both feet (L5 and S1 distributions). He had no bowel or bladder symptoms at any time and no saddle paresthesias. Due to increasing pain, he presented to the emergency room for evaluation. MRI of the spine (Fig. 17.6) confirmed a large central disc extrusion at L3/4 causing canal stenosis and impinging upon bilateral L5 and S1 nerve roots. He underwent L3 and L4 partial laminectomy with discectomy and excision of the apophyseal ring fragment. Post-operatively, his pain resolved but he was left with a persistent right foot drop. Neurology consultation 6 months after the injury confirmed the right foot drop. Muscle strength in his right leg (Medical Research Council scale): gluteus medius 5, gluteus maximus 5, iliopsoas 5, quadriceps 5, hamstrings 5-, tibialis anterior 2, peroneus longus 3, tibialis posterior 4-, gastrocnemius 4-, extensor hallicus longus 0. Strength testing of his left leg revealed: gluteus medius 5, gluteus maximus 5, iliopsoas 5, quadriceps 5, hamstrings 5-, tibialis anterior 4+, peroneus longus 4+, tibialis posterior 4+, gastrocnemius 4+, extensor hallicus longus 4. Reflexes were intact at the patellae but absent at both ankles. Sensory testing noted decreased pinprick sensation at the dorsal surfaces of both feet. Nerve conduction studies (Fig. 17.6) were consistent with severe bilateral (right > left) L5 and S1 radiculopathy. SNAP amplitudes were robust despite low CMAP amplitudes, indicating a proximal location of nerve root impingement. Late responses (bilateral tibial and peroneal F-responses and bilateral tibial H-reflexes) were absent. Needle EMG confirmed reinnervation in proximal L5/S1 muscles (e.g., gluteus medius) with ongoing denervation in distal muscles. Given that axonal continuity was demonstrated to all muscles studied, clinical improvement was predicted which was indeed observed in the following 12 months. This case illustrates some of the key electrophysiological findings that are seen in radiculopathies.
MRI (T2-weighted imaging) and nerve conduction study findings in a 16-year-old male with central disc protrusion (arrow) causing bilateral L5 and S1 radiculopathies
Etiology of Radiculopathies in Children
Pediatric radiculopathies are uncommon with no good epidemiological studies available to estimate the incidence of this problem. Adult population studies have estimated an annual incidence of cervical radiculopathy to be 107.3 per 100,000 for men and 63.5 per 100,000 for women . The incidence of lumbar radiculopathies has been estimated to be 1–2% in the general population . Pediatric case reports and case series have provided some insight into the varied etiology of this problem in childhood. These have included trauma with or without an underlying congenital spine abnormality (hemivertebrae, spondolithesis, congenital scoliosis or narrowing of the intervertebral foramen) [3, 4], infections or mechanical compression, tumor, or infiltrative lesion.
The likelihood of impingement of a specific spinal nerve root is largely dependent on the underlying etiology. Cervical radiculopathies are most commonly caused by disc calcification . Over 300 pediatric cases of cervical disc calcification have been published, most commonly involving C5-C6 or C6-C7, with few cases involving the thoracic or lumbar nerve roots . The etiology of disc calcification has yet to be determined, but trauma , infection, and inflammation  have been raised as possibilities. Although calcification may cause spinal stenosis and evidence of corticospinal tract involvement, less than 30% of children with cervical disc calcification will demonstrate clinical symptoms of radiculopathy . Griesl syndrome is an uncommon non-traumatic complication of any inflammatory condition of the upper neck or otolaryngological procedure, which causes subluxation of the atlantoaxial joint. There may be an infectious, influenza-like prodrome, followed by significant neck and/or throat pain, torticollis and often atlantoaxial subluxation . Approximately 15% of patients will experience neurological symptoms including a cervical radiculopathy . Traumatic cervical radiculopathies are most commonly caused by high-speed motor vehicle accidents with seat belt injuries, in which high velocity traction injuries are also likely to damage the brachial plexus causing avulsions of the cervical roots which will be discussed below.
Pediatric thoracic root disease is the least common site of a radiculopathy and when present, is most commonly caused by spinal arachnoid cysts. One large case series of patients with spinal arachnoid cysts including 31 pediatric patients noted 36% (11/31) to involve thoracic nerve root(s), 19% (6/31) thoracolumbar, 13% (4/31) lumbrosacral, 13% (4/31) thoracocervical, 10% (3/31) sacral, 7% (2/31) lumbar, and 3% (1/31) cervical . Another one case series found 5 of 15 patients with spinal arachnoid cysts to be children . All five children had thoracic spinal arachnoid cysts; 2/3 of the 15 patients had associated radiculopathies with their arachnoid cyst; however, this was not reported for specific age groups. In pediatric patients, unlike the general population, spinal arachnoid cysts are more often intradural.
The most common cause of pediatric lumbosacral radiculopathies is disc disease, usually due to an intra-canal or intra-foraminal herniated nucleus pulposus . Under the age of 15 years, the frequency of radiculopathy ranges from 0.05% in a population-based study based upon 6500 patients seen at the Mayo Clinic , to as high as 42% when comparing children referred to for disc disease at a tertiary-care pediatric hospital . The reported incidence in Japanese children who underwent operation for back pain was 15.4% in patients under 20 years of age and 4.6% under 15 years . Newer studies have reported an incidence ranging from 1 to 5% in patients under the age of 20 years [22–24]. In one series, 91.4% of adolescent patients with lumbar disc disease complained of back and leg pain , congruent with another study in which 85.1% of adolescent patients had both complaints . There is no clear gender predominance of disc herniation. Risk factors for developing lumbar disc disease include: family history, lumbar load (similar to our case presented above), strenuous exercise, and obesity . Since disc herniation is relatively rare in children, other etiologies should be considered. These include: non-spondylotic etiologies such as juxta-facet cysts, and spondylolytic causes, commonly seen in athletes, with symptomatology from spondylolisthesis, ragged-edge osteophytes, periosteal edema, and hematomas . The rare possibility of an intraspinal or vertebral tumor must also be considered. These most commonly occur in the lumbrosacral regions and can include Ewing’s sarcoma , osteoblastoma , childhood chordoma , neurofibromatosis , schwannoma , and Langerhans histiocytosis-X .
Discal cysts can be located anywhere along the lengths of the spinal cord and produce radiculopathies. Characteristics of discal cysts may include: symptoms of unilateral single nerve root compression; lesions occurring at a slightly younger age and at a higher intervertebral disc level than the typical disc herniation; minimal degeneration of the involved disc on imaging studies; communication between the cyst and the corresponding intervertebral disc; intralesional, bloody-to-clear serous fluid content of the cyst; and, an absence of either disc material inside the cyst . About 75% of patients (all-ages) with discal cysts will have symptoms of sciatica .
Radiculopathy symptoms including back pain and paresthesias with nerve root thickening can be seen in systemic inflammatory disorders. Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is associated with MRI evidence of root thickening and gadolinium enhancement (Fig. 17.7) in approximately 40% of affected children  and 60% of adults  although the majority of such patients will not complain of any clinical symptoms of nerve root involvement. Adults with CIDP have occasionally been reported to demonstrate symptoms of a painful polyradiculopathy that has been attributed to spinal nerve root impingement secondary to root inflammation and thickening that on rare occasions may be so severe as to cause lumbar stenosis  and even produce symptoms of spinal cord compression . Nerve root thickening is by no means unique to CIDP. Homogeneous nerve root enlargement is also reported in patients with Charcot-Marie-Tooth disease [40, 41], Guillain-Barré syndrome , and infectious causes including HIV and CMV . Polyradiculopathy without nerve root thickening is also reported with: neurobrucellosis , herpes simplex virus , cytomegalovirus , herpes zoster virus  and Lyme disease . Nodular nerve root thickening can be seen in neurofibromatosis-related nerve sheath tumors , neoplasias (e.g., neurolymphomatosis)  and granulomatous disease . Infiltrative etiologies can also occur at any spinal level. These can include hematological malignancies as acute lymphoblastic leukemia or lymphoma but can also be seen with solid tumors such as osteosarcoma [52, 53].
MRI coronal STIR T2-weighted image of the brachial plexus in a 16-year-old patient with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) showing nerve root thickening (arrow)
The brachial and lumbosacral plexi arise from mixed spinal nerves after they emerge from the intervertebral foramina and give rise to three main nerve trunks. The word plexus arises from the Latin word plectere meaning braid or twine. Neurologists and neurophysiologists must have a thorough working knowledge of plexus anatomy in order to correctly localize lesions within these structures. Schematic diagrams of the brachial plexus (Fig. 17.8) and lumbosacral plexus (Fig. 17.9) are particularly useful as physicians can draw or visualize these structures when attempting to differentiate root from plexus from nerve lesions [54, 55].
Brachial Plexus Anatomy
The brachial plexus is located between the base of the neck and the axilla. It is divided into roots, trunks, divisions, cords, and nerves, although roots and nerves are not considered part of the actual plexus. The brachial plexus arises mainly from 4 cervical and 1 thoracic anterior primary rami or roots (C5 to T1). The C4 spinal root does provide nerve fibers to the dorsal scapular nerve which (like the long thoracic nerve) arises directly from roots, although the C4 root is not traditionally considered to be a contributor to the brachial plexus (Fig. 17.8). Two upper cervical roots (C5, C6) fuse to form the upper trunk; the middle root (C7) forms the middle trunk; and two lower cervical roots (C8, T1) form the lower trunk. Two nerves, the suprascapular and subclavian, arise from the upper trunk. Each trunk then divides into divisions: anterior and lateral. Divisions then unite to form three cords: medial, posterior and lateral before finally dividing into multiple terminal nerves. Careful clinical and electrodiagnostic testing can help to localize a lesion within the brachial plexus.
Brachial plexopathies can have varied presentations depending on the site of the lesion and underlying etiology. Since the brachial plexus eventually gives rise to all sensory and motor nerves of the arm and hand, lesions within the plexus cause areas of numbness and paresthesia, along with specific patterns of muscle weakness. Pain can be a predominant clinical feature for some etiologies, including trauma and compressive or infiltrative lesions. Other diseases such as genetic disorders, including hereditary neuropathy with liability to pressure palsy (HNPP), may give rise to painless weakness and sensory loss. Etiologies will be discussed in greater detail below. Like all peripheral neural elements, an intact plexus is essential for normal limb growth. The long-term sequela of plexus injuries early in life can include limb length discrepancy and orthopedic complications such as joint contractures and restricted range of motion, as well as malpositioned joints that heighten the risk of uneven wear and arthritis. Upper trunk lesions at birth (Erb palsy) in particular can give rise to malposition of the glenohumeral joint that requires long-term orthopedic monitoring and can respond to successful relocation of the humeral head . Lower trunk lesions (Klumpke paralysis) due to traumatic root avulsion or tumor infiltration can give rise to an ipsilateral Horner syndrome, which manifests clinically as a triad of ptosis, miosis, and anhidrosis. This is generally attributed to injury of sympathetic preganglionic neurons at T1 that innervate the superior cervical ganglion; there are reports of children with C7, C8 and/or T1 root avulsions presenting with this syndrome . Early injury to sympathetic fibers (typically as neonatal brachial plexus injury) can manifest as iris heterochromia as the sympathetic fibers play an important role in normal changes in eye color change in the first few months of life.
When evaluating a patient with a potential plexopathy, neurophysiologists must perform sensory and motor nerve conduction studies as well as needle electromyography. Absent or reduced sensory nerve responses can provide important clues to the location of plexus lesions (Fig. 17.10) as well as to differentiate plexus lesions (where SNAP amplitudes are reduced or absent) from radiculopathies (where SNAP amplitudes remain intact). Nerve conduction studies and even more importantly needle EMG can accurately localize lesions within the plexus and aid in differentiating patterns of denervation from that seen in lesions affecting roots or peripheral nerves (Fig. 17.3).
Etiology of Brachial Plexopathy in Children
The potential causes of brachial plexopathies even after their localization are numerous. Trauma particularly that associated with birth injuries (described below) is a common cause. Physicians must remain alert to non-accidental injuries, particularly in infants and toddlers, who may not be developmentally capable of recounting the circumstances of their injury . Immune causes of brachial plexus neuropathy, also known as Parsonage-Turner syndrome can give rise to severe, abrupt-onset shoulder girdle pain followed by muscle weakness and amyotrophy. Although this is more common in adults, it has been described in children as young as 3 months old . Other inflammatory causes of brachial plexus lesions can include Lewis-Sumner syndrome or multifocal acquired demyelinating sensory and motor neuropathy (MADSAM), an asymmetrical form of chronic inflammatory demyelinating polyneuropathy (CIDP) that is occasionally reported in childhood. This disorder may respond to intravenous immunoglobulin (IVIg) therapy [60, 61].
Hereditary brachial plexus neuralgia or hereditary neuralgic amyotrophy (HNA) is an autosomal dominant disorder resulting from SEPT9 gene mutations. HNA can mimic Parsonage-Turner syndrome. Although the initial presentation of hereditary neuralgic amyotrophy can occur as early as the toddler years , it is more common in late adolescence . Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder resulting from a deletion or, less commonly, a point mutation of PMP22. About 20% of patients with HNPP may present with a brachial plexopathy. Onset is typically seen around adolescence and is typically characterised by episodes of painless muscle weakness and paresthesias that result from focal demyelination. Pain and muscle atrophy—dominant features of hereditary neuralgic amyotrophy and immune brachial plexitis are not seen or are less severe in children with HNPP . Electrodiagnostic testing is key since nerve conduction studies can demonstrate focal conduction block even in asymptomatic nerves . Pediatric brachial plexopathy can also occur from extrinsic compression or infiltration from various primary or metastatic tumors including neurofibroma, sarcoma, neuroblastoma, lymphoma or infantile myofibromatosis [66, 67]. Although symptom onset can be insidious, it can also be present at birth mimicking neonatal brachial plexus palsy.
Neonatal Brachial Plexus Palsy
Neonatal brachial plexus palsy (NBPP), previously referred to as obstetrical brachial plexus palsy, results from injury to the brachial plexus at or around the time of birth. Given the location and structure of the brachial plexus it is susceptible to traction or compression injury. Although NBPP is often attributed to traumatic and/or difficult delivery (e.g., shoulder dystocia, breech delivery, difficult vaginal extraction of a large infant)  the most significant risk factor for NBPP appears to be large infant size, specifically birth weight ≥4 kg [69, 70]. However, non-traumatic causes may in some cases be associated, including: uterine anomalies and fetal malposition (i.e., compression against maternal sacral promontory) [71, 72]. NBPP has been well described in deliveries with no evidence of trauma or fetal distress, including routine and/or early Caesarean section .
The incidence of NBPP is about 1.5–4 per 1000 live births [74, 75]. The majority of infants (66–85%) with NBPP exhibit mild, transient symptoms resulting from neurapraxia or ‘bruising’ of the nerve fibers within the plexus; such infants will demonstrate a complete clinical recovery by around 1 month and require no intervention beyond routine physical therapy [76–79]. However, a smaller subset of infants with NBPP (15–33%) will suffer a more severe injury attributable to axonotmesis (partial tearing of the nerve), neurotmesis (complete tearing of the nerve) or the most severe, nerve root avulsion where the nerve root is torn out of the spinal cord (Fig. 17.11). Patients with NBPP can therefore be thought to exist along a continuum with more severe nerve damage not surprisingly associated with a lower likelihood of spontaneous recovery and a higher risk of long-term deficits.
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