13.8 Neurological aspects of spinal disorders in children

Spinal neurological conditions in the paediatric population can be part of a systemic disorder or a focal abnormality within the spine and neural axis (Table 13.8.1). When a child presents with signs and symptoms of possible underlying neurosurgical pathology, both developmental and acquired aetiologies must be considered.

Normal spinal cord development can be divided broadly into three processes. Aberrations at each of these stages may be responsible for clinical disorders that are included under the broad term spinal dysraphism

The first stage in development of the neuraxis is gastrulation. It is during this stage that the germ cell layers of the embryo are established: these comprise ectoderm, mesoderm, and endoderm. Anomalies that have their origins early in development will commonly affect each of these layers. This is exemplified with neurenteric cysts where there is a persistent connection between the gut epithelium and the nervous system or split cord malformations where there is duplication of the spinal cord and vertebral body defects.

By the end of gastrulation the ectodermal plate has been formed and soon after the process of neurulation begins.

In primary neurulation a midsagittal groove is seen in the neuroectodermal plate. As this deepens, the edges of the groove fold towards each other and eventually join to form the neural tube. This process forms the brain and the spinal cord as far as the conus medullaris.

Secondary neurulation describes the process by which the terminal components of the CNS are formed: the tip of the conus medullaris, the cauda equina, and the filum terminale. This involves tissues located within the tail bud, caudal to the neural tube, known as the caudal cell mass. Vacuoles form within the caudal cell mass. These cavities become confluent with the central canal of the neural tube. This terminal dilatation forms the distal neural tube. Much of the dilatation regresses in a process termed caudal regression or retrogressive differentiation. The associated differential growth of vertebral column and neural tube results in a more cranial placement of the conus. The filum terminale remains as a connection between the conus and its original caudal attachment.

Spinal dysraphism is a term encompassing a broad spectrum of spinal anomalies arising from any disturbance during any of the stages of neural development and categorized broadly into open and closed neural tube defects.

Failure of the neural tube to fuse leads to open defects such as myelocoeles and meningomyelocoeles. Neural tissue is exposed or covered by a thin meningeal layer. Neurulation is a process that is in part dependent on folate metabolism and folate deficiency is a major aetiological factor in open neural tube defects. Supplementation of the diet with folate prior to conception significantly reduces the risk of an open neural tube defect. Antenatal diagnosis can be made on ultrasound examination, by a raised maternal serum alpha feta-protein (AFP), or by amniocentesis measuring AFP and acetylcholinesterase.

Developments in the management of prenatally identified meningomyelocoeles include in utero repair of the defect. The benefits of this intervention compared to early postnatal closure are still undergoing evaluation through a randomized controlled trial. Some of the perceived advantages of in utero surgery are reduced hindbrain herniation (Arnold–Chiari II malformation) and a reduced need for a ventriculoperitoneal (VP) shunt.

A multidisciplinary approach is required to manage open neural tube defects and this should be undertaken in a unit with appropriate expertise.

Following delivery, it important to maintain a sterile environment for the exposed tissues and a sterile, moist, non-adhesive dressing which prevents pressure on the neural sac should be applied to the open defect. The child is nursed prone. There is a high incidence of latex allergy and latex exposure should be avoided.

Surgical closure of the defect is usually required within the first few days of life after appropriate imaging for brain ventricular size and following a thorough evaluation to assess the neurological level of the lesion and exclude associated cardiac and renal anomalies. In the perioperative period, the clinician should look for cerebrospinal fluid (CSF) leaks, superficial or deep wound infection, deterioration of neurological level, or the development of acute hydrocephalus. Shunt placement to control hydrocephalus is required in between 50–70% of cases.

Open neural defects are associated with significant long-term implications in respect of urological function, mobility, spinal deformity, and cognitive development. Minimizing the risk of urinary tract infections during infancy and the early introduction of clean intermittent catheterization helps reduce the incidence of renal scarring. Long-term mobility is strongly correlated with the neurological level of the lesion: lower lesions resulting in better prospects for independent ambulation. Lower limb treatment may involve surgical correction of deformity and the use of orthotic supports (see Chapter 13.9). Comorbidities such as respiratory compromise and weight gain contribute to the loss of mobility seen in adulthood.

Closed neural tube defects include a group of anomalies of caudal spinal cord development in which the neural tissues, in contrast to myelomeningocoele, are covered by overlying skin. The term occult spinal dysraphism or spina bifida occulta is used to describe this group. The term occult is a misnomer as in many instances there is some feature of the overlying skin that signifies an underlying anomaly: such features are known as the cutaneous stigmata of spinal dysraphism. The following conditions are included under the term spina bifida occulta.

The split cord malformation can occur with or without the presence of a dividing bony, cartilage, or fibrous septum. The two cords may lie within the same dural sac or separately. The two hemicords are often asymmetric with the smaller cord usually on the side of a smaller limb or foot. A focal hairy patch is the cutaneous stigmata commonly associated with this condition (Figure 13.8.1).

Most commonly a subcutaneous lipoma passes through a defect in the lumbosacral fascia, the posterior bony elements and the dura to be attached to the terminal spinal cord (Figure 13.8.2). Various anatomical forms are recognized depending on the point of attachment of the lipoma in relation to the conus. For practical purposes, the terms lipomyelomeningocoele, lipomyelocoele, and spinal lipoma are synonymous. These are complex developmental malformations which may or may not be associated with neurological or urological symptoms at the time of presentation. Symptoms may occur as a result of primary neuronal dysgenesis or as a result of mechanical stretching (tethering) as the child grows.

This is perhaps the mildest of the dysraphic states. It is thought to result from a developmental defect of secondary neurulation and regression of the caudal cell mass. The filum terminale is shortened resulting in a low conus and thickened (>2mm diameter) by abnormal fatty or fibrous infiltration that affects its viscoelastic nature (Figure 13.8.3). This may result in undue traction on the conus during flexion and extension of the spine.

These are remnants of the embryological connection between the skin (cutaneous ectoderm) and nervous tissue (neuroectoderm). An epithelial lined, midline tract extends from the skin surface through the subcutaneous tissue and spinal coverings to the intradural compartment where the tract terminates usually on the dorsum of the spinal cord. These tracts are significant as they can act as a portal for infection (spinal abscess or meningitis) or as a nidus for intraspinal dermoid formation.

These intraspinal cysts of endodermal origin are thought to represent a persistent communication between the ectoderm and the underlying endoderm. They have a lining of mucus secreting or gut epithelium. There is commonly a ventral defect through the vertebral body connecting to a cyst in the retroperitoneum or posterior mediastinum.

Any of the anomalies described earlier can be associated with the tethered cord syndrome. This is not a pathological entity in itself but rather a clinical syndrome that results from traction on the spinal cord or nerves as the child grows.

Experimental studies on the pathophysiology of tethered cord syndrome suggest that excessive traction on the spinal cord can produce impaired oxidative metabolism in the spinal cord, diminished blood flow, and local ischaemic changes. The severity and reversibility of these changes probably relate to duration and magnitude of the traction highlighting the importance of identifying this condition early.

The clinical syndrome of tethering is sometimes referred to as the neuro-orthopaedic syndrome and comprises a variety of symptoms that might be orthopaedic, urological, or neurological. It should be considered in any dysraphic patient presenting with new, changing or progressive symptoms.

A subcutaneous lipoma, midline cutaneous punctum (particularly if associated with a history of discharge) lumbosacral appendage, or focal hairy patch is highly suggestive of occult spinal dysraphism (Figure 13.8.4). Lower-risk lesions include very low, sacrococcygeal dimples and gluteal crease deviation. Diffuse hypertrichosis, haemangioma, and naevi, if found in isolation, are of less concern.

The development of foot deformity (pes cavus, claw toes) or a rapidly progressive scoliosis may indicate a tethered cord or a recurrence following initial release. Asymmetry in foot size or a leg length discrepancy may also indicate tethering.

A spectrum of abnormalities can occur including a neurogenic bladder, faecal and urinary incontinence, and frequent urinary tract infections. A formal assessment with urodynamic studies is essential.

There may be upper or lower motor neuron signs or a combination of both. Asymmetrical weakness may present as decreased leg movements in the infant whilst the older child may present with delayed ambulation and gait abnormalities. Trophic ulceration of the feet may occur as a result of sensory deficits.

Classically the pain worsens on spinal flexion or with vigorous exercise. The pain is often poorly localized and usually does not have the typical features of sciatica.

A clinical suspicion of tethered cord syndrome should be confirmed by further investigations.

This has limited application as the acoustic window into the lumbar spine closes after 2–3 months of age: in the infant it is a useful technique to assess the level of the conus.

These are of little diagnostic help and their role is primarily in the monitoring of spinal deformity.

This is the imaging modality of choice in dysraphic disorders. It has a very high specificity and sensitivity and permits evaluation of the position of the spinal cord, the anatomical features of the dysraphic anomaly and any associated abnormalities such as syringomyelia.

Surgical treatment can halt the progression of established neurological deficits in the majority of patients. Symptoms vary in their response to untethering, pain will commonly resolve after successful untethering whereas foot weakness or deformity is less likely to improve.

Numerous clinical studies have demonstrated that patients with urological dysfunction fare better with prompt detethering. An objective assessment of urological function can be made using urodynamic measurements. Postoperative measurements can be useful during long-term surveillance demonstrating early recurrence of cord tethering and the need for further intervention.

Although the role of surgery in symptomatic patients appears clear, in asymptomatic patients, it remains controversial. Many clinicians will advocate prophylactic surgery in order to prevent the development of neurological deficits that may not recover with therapeutic surgery. The exception to this is dermal sinus tract where the perceived natural history and risk of infective complications make prophylactic surgical intervention essential in the majority of cases.

Other considerations with tethered cord syndrome are the associated spinal and foot deformities. Studies suggest that detethering procedures in patients with a myelomeningocoele, tethered cord and scoliosis measuring less than 40 degrees will produce a plateau in curve progression. Larger curves will continue to progress necessitating operative correction and ultimately fusion.

Although central nervous tumours are the second most common type of childhood neoplasia, tumours of the spinal cord are relatively rare. The majority of central nervous tumours are intracranial and only 10% are located in the spine. Spinal tumours are classified into three broad groups.

Intramedullary lesions (Figure 13.8.5) make up 40% of spinal cord tumours, the most common types being astrocytomas and ependymomas. Although 10–15% of astrocytomas are high-grade malignant tumours, the majority of these intramedullary lesions are low grade and present in an insidious manner.

Characteristically, the pain is a diffuse axial pain that worsens at night secondary to venous congestion and the associated dural distension. Pain usually precedes the onset of neurological symptoms.

This is of gradual onset. As intramedullary tumours are usually centrally located, dorsal column abnormalities are uncommon, motor signs appear early whereas sphincter dysfunction tends to develop late.

May occur in the context of intramedullary spinal neoplasms and is thought to be related to the high protein concentration in the CSF.

Pain and an abnormal posture or deformity should raise the suspicion of a spinal tumour.

Surgical excision is the mainstay of treatment for intramedullary spinal tumours. The degree of surgical clearance possible will be governed by the tumour type. Infiltrative astrocytomas are less amenable to radical excision and high-grade tumours have a poor prognosis with median survival of 6–12 months. Removal of ependymomas is often curative. Patients should be monitored for development of postlaminectomy spinal deformity. The laminoplasty approach, which preserves the posterior tension band of the vertebral column, reduces this risk.

This group (Figure 13.8.6) comprising 20% of spinal cord tumours includes meningiomas and peripheral nerve sheath tumours. Again the most common feature is pain followed by neurological dysfunction. Both tumour types are associated with neurofibromatosis.

Magnetic resonance imaging (MRI) of the whole neural axis will help distinguish between solitary lesions and those arising from metastatic spread from an intracranial primary. Peripheral nerve sheath tumours produce characteristic erosion and enlargement of the neural foramina seen on plain radiographs.

The treatment of choice is surgical excision. Incomplete excisions run a high risk of recurrence. Malignant transformation of peripheral nerve sheath tumours is also a concern, especially in patients with NF-1 and those treated with adjuvant radiation.

Primary or metastatic extradural tumours make up 40% of spinal cord neoplasms. Metastatic lesions from a systemic malignancy can produce spinal cord compression in up to 5% of cases. Primary extradural lesions originate from various structures.

This is the sarcoma that most frequently affects the paediatric spine. The lytic lesions within the vertebral body are often associated with soft tissue masses, the commonest site being the sacrum. The recent improved chemotherapeutic agents have produced better 5–10-year survival rates.

These are histologically similar lesions, differentiated on size. Osteoblastomas are larger than 1.5cm in diameter. The lumbar spine is a common site with the posterior elements more frequently affected than the vertebral bodies. Patients may present with a painful scoliosis, the lesion being located on the apex of the curve convexity. The pain is classically worse at night and relieved by non-steroidal anti-inflammatory drugs. The typical appearance of the central nidus can be identified on computed tomography (CT) scanning. Radionucleotide bone scans and MRI are also helpful. Although osteoid osteomas usually run a self-limiting course, osteoblastomas often require surgical intervention.

Otherwise known as Langerhans cell histiocytosis, can produce either solitary or multiple lytic lesions in the spine. Pathological fractures of the vertebral body may result in a vertebra plana deformity. There may also be an intraspinal extension of the soft tissue tumour. The usually self-limiting nature of this condition makes it amenable to symptomatic management with a period of spinal bracing. More aggressive lesions may require surgery, chemotherapy and low dose radiation.

Approximately one-third of aneurymal bone cysts (ABCs) are found in the spine, most frequently the posterior elements. They are expansile thin-walled lesions with a multiloculated appearance and fluid-fluid levels on MRI or CT imaging. Pain, a palpable mass, spinal deformity, and neurological deficits are common presenting features. Embolization has been used both as a treatment modality and preoperatively to reduce bleeding during surgical excision. Recurrence rates are almost 30% and tend to occur within the first year.

Osteochondromas are benign cartilage capped bony protuberances. Five per cent of cases are located in the spine, commonly affecting either the transverse or the spinous process. Multiple lesions can be found in hereditary multiple exostosis. In those patients with multiple lesions, the risk of malignant transformation to a chondrosarcoma is higher. In solitary lesions the risk is less than 1%. Surgical excision is the treatment of choice.

Neuroblastoma is an embryonal tumour originating from neural crest cell precursors. It is the fourth most common paediatric malignancy. Half of these cases will occur before the age of 2 years. The majority will be located in the abdomen either in the adrenals or in the paraspinal sympathetic chain. Most will have raised serum and urinary VMA (vanillylmandelic acid) and HVA (homovanillic acid) levels. Treatment options include chemotherapy, radiation, steroids, and surgery depending on whether the tumour is localized or disseminated.

Lymphomas and leukaemia usually occur in the spine as a result of metastatic spread but rarely the spine may be the primary tumour site. In general these tumours are very sensitive to chemotherapy and radiotherapy. Surgical decompression should only be considered if these treatments fail or if the neurological state is deteriorating rapidly.

The combination of a varied clinical presentation and the diverse nature of the conditions producing neurological abnormalities in the paediatric patient can pose a clinical challenge. A multidisciplinary approach that allows for a thorough assessment and investigation of the paediatric patient with axial pain and neurological signs is essential.