Intraspinal Anomalies in Early Onset Scoliosis: Current Concepts.

Early onset scoliosis (EOS) is deformity of the spine below the age of 5 years. Children with EOS are at risk of impaired thoracic cage development and pulmonary maturation. Initial evaluation consists of determining the etiological cause for EOS, i.e., congenital, neurogenic, idiopathic, or syndromic. The advent of magnetic resonance imaging in recent times has lead to increased awareness of neurogenic causes leading to EOS. Evaluation of spinal cord anomalies in EOS is very important as early diagnosis and treatment can help in deformity stabilization and regression. Also, any surgical or nonsurgical intervention to correct the deformity without prior treatment of spinal cord anomalies can lead to disastrous neurological complications.

INTRODUCTION

The scoliotic deformity as described by scoliosis research society has been divided into three types depending on the age of the patients: infantile(0–3 years), juvenile(4–9 years), and adolescent (above 10 years).[1] This definition focuses more on the spinal deformity rather than considering development of thoracic cavity as whole. This classifications indicated the three phases of development of the child.[2] However, the growth of a child is maximum during the infancy and adolescent during which maximum deformities are seen and deformities during juvenile period is rare. The term early onset scoliosis (EOS) was coined by Dickson,[3] which he defined as scoliotic deformity before the age of 5 years. EOS can be idiopathic, syndromic, neurogenic, and congenital.[4] The term EOS focuses more on complete physiological development of thoracic cavity rather than on the magnitude of scoliotic curve.[1]

DEVELOPMENT OF SPINE, LUNG, AND THORACIC CAGE

The development of thoracic cavity including lung parenchyma, rib cage, and spine is closely related to each other. During the first 5 years of life, the growth of spine from T1 to S1 is rapid at an average rate of 2 cm/year (10 cm in first 5 years of life). In the next 5 years, from 5 to 10 years of age, the growth slows down to an average of 1 cm/year. After the age of 10 years to adulthood, the growth rate again increases to an average of 2 cm/year.[5] Children with scoliotic deformity are at greatest risk of curve progression during the two growth spurt, i.e., during first 5 years of life and during adolescent.[4]

In EOS, the risk of curve progression is maximum during the first 5 years of life, which is the crucial period for development of lung. At birth, only the conductive airways are developed along with presence of small number of respiratory bronchiole and alveoli. The complete development of respiratory system as in adults takes by 8 years of age when there is complete branching of the airways. Spinal deformity affects lung volumes, alveolar growth, and lung compliance.[4] Scoliotic deformity leads to increased work of breathing respiratory rate due reduction in tidal volume. Depending on the age of onset, the severity of restrictive lung disease increases. The deformity developed before birth has the worst outcome as the pulmonary development is limited. Restrictive lung disease leads to pulmonary hypertension and in severe cases to cor pulmonale.[678]

During the embryonic growth, the development of spine occurs during 5th to 8th week of gestation. The development of vertebral column and spinal cord is closely related to each other. Any insult to fetal development during this period can lead to congenital spinal deformities along with intraspinal anomalies.[91011] Intraspinal anomalies are seen in approximately 20%–50% of patients presenting with congenital scoliosis.[12] Before the advent of magnetic resonance imaging (MRI), myelography was the tool for diagnosis with an incidence rate of 5%–18%.[13] Timely diagnosis of this associated condition is important to prevent neurological deterioration and deformity progression.

During the development of vertebral column, the deformities can occur due to failure of formation, failure of segmentation, or combination of both. The incidence of intraspinal anomalies is more common in patients who have congenital failure of segmentation as compared to failure of formation and combined etiology.[1415]

CLINICAL PRESENTATION AND EVALUATION

The evaluation of patient presenting with congenital deformity begins with thorough history taking and detailed clinical examination. The clinical examination begins from inspection of shoulder, pelvis, deformity of the spine, and cutaneous manifestations. Both upper and lower extremities should be evaluated for limb-length discrepancy and orthopedic deformities such as clubfoot, genu varum, and genu valgum. The neurological examination should be conducted in detail to look for bladder–bowel incontinence, motor deficits, sensory deficits, reflexes, tone, and spasticity. The gait evaluation should be conducted in detail; abnormalities associated with gait can indicate associated intraspinal pathologies.[13161718]

The examination of respiratory system is also important. The examination of respiratory system begins with inspection to look for respiratory rate, movement of air within each hemithorax, associated wheezing, any areas of restricted air movement, and use of accessory muscle of respiration to diagnose increased work of breathing.[18] Auscultation should be performed to evaluate presence of murmur and movement of air within the lung cavity.

INVESTIGATIONS

Radiographic investigation

The radiographic investigation consists of whole-spine X-ray from C7 to pelvis in anteroposterior (AP) and lateral planes. The AP X-ray is used to assess the magnitude of deformity by Cobbs angle. Bending films can also be used to assess the flexibility of the spine. Standing films are always preferred over supine films to assess the effect of gravity on the deformity.[19] The lung capacity can be indirectly assessed by evaluating the thoracic deformity AP X-ray. On AP X-ray, space available for lung (SAL) can be calculated by taking the ratio height of concave hemithorax with respect to height of convex hemithorax. The SAL is used to measure the restriction of lung growth due to thoracic wall deformity.[82021] Risser grade should be seen on AP X-ray to evaluate the amount of growth remaining in particular child.[22] The AP X-ray is also used to calculate the rib vertebral angle difference as described by Mehta.[7] Apart from scoliosis, other vertebral defects can be noted on X-ray such as anomalies of vertebral bodies (hemivertebra, unsegmented bar, block vertebra, wedge vertebra, etc.), dysplastic pedicles, and lamina.[23]

An MRI should always be carried out in all patients presenting with EOS as the incidence of intraspinal anomalies in various studies was 18.3%–47%.[141524252627282930313233] Any intervention to correct the spinal deformity in presence of spinal cord anomalies can lead to disastrous neurological deterioration.

Investigations other than X-ray and MRI are directed toward evaluating the pulmonary function in view of thoracic deformity. These investigations include pulmonary function test, pulse oximetry, arterial blood gas analysis, hemoglobin level, and hematocrit level to assess the degree of blood oxygenation.[34] Restrictive lung disease can lead to thoracic insufficiency syndrome (TIS), and sleep studies can be very effective in diagnosing TIS.[3536]

TETHERED CORD SYNDROME

Tethered cord syndrome (TCS) is a group of anomalies in which the spinal cord is adhered by inelastic structure below the level of second lumbar vertebrae, restricting the normal movement of the spinal cord within the spinal canal.[37383940] The growth of the vertebral column with respect to restricted movement of the spinal cord leads to stretching of the spinal nerve roots and the conus medullaris. TCS can also be seen in meningomyelocele, diastematomyelia and in normal lying conus medullaris with fatty infiltration (fatty filum terminale).[13] The restricted movement of the spinal cord leads to ischemic injury to the conus affecting its metabolism and hence leading to neurological deficits. In fatty infiltration of the filum terminale, there is alteration of the membranes leading to abnormal electrical activities across the membrane, leading to neurological deficit.[3940]

The presenting symptoms also can vary from cutaneous manifestations, urological problems, neurological abnormalities, and orthopedic deformities. The patients with congenital TC most commonly present during the childhood, however the presentation can be delayed till adult hood and presents as adult tethered cord.[234142]

The cause of scoliosis in children with TC is ischemic injury to the spinal cord, leading to abnormal paravertebral muscle tone and dysfunctioning of sensory system [Figure 1]. Scoliosis can be presenting symptom in 25% of patients with TCS.[43]

Figure 1

A 4-year-old boy presented with tuft of hair over the skin at lumbosacral area—A. On investigation, he was found to have congenital scoliosis with D1-2 hemivertebra on X-ray—B. MRI of the spine showed tethering of the spinal cord at lumbosacral area—C

The aim of tethered cord release (TCR) in patients with congenital spinal deformity is to prevent deformity progression as well as to stabilize the neurological deficit and prevent further deterioration. The risk of deformity progression after dethering depends on the age of presentation of patient (Risser grade) and the angle of deformity (Cobbs angle). Patients with Cobbs angle >40° and Risser grade 0–2 have maximum chances of curve progression. McGirt et al.[44] in their study on effect of TCR on scoliosis showed that patients with Cobbs angle <40° have 5.9 times less chances of curve progression as compared to patients with cob angle >40°. Also the risk of curve progression is 3.4 times less in patients with Risser grade 3–4 as compared to patients with Risser grade 0–2. They also concluded that the risk of curve progression in patients with both the risk factor, i.e., Cobbs angle >40° and Risser grade 0–2 is 100% and risk factor for curve progression in patients with Cobbs angle <40° and Risser grade 3–4 is none.[44] McLone et al.[45] in their study on effect of curve progression in scoliosis after TCR secondary to meningomyelocele showed that the curve improved in 21% patients and was stabilized in 42% patients with Cobbs angle <40° after a follow-up duration of 2–4 years.

DIASTEMATOMYELIA

Diastematomyelia or split spinal cord malformations (SSCM) are group of congenital spinal anomalies in which the spinal cord is split into two parts. Pang has classified diastematomyelia into two types: type I SSCM, also known as diastematomyelia, in which the spinal cord is split into two by bony or cartilaginous septum, and each cord has its individual dural sleeve. In type II SSCM, the spinal cord is split by fibrous septum with a common dural sleeve for both the cord. Type II SSCM is also known as diplomyelia.[4647]

SSCM is more commonly seen in females as compared to males and type I is more common than type II. Patients with diastematomyelia also show cutaneous abnormalities such as hairy patch over lumbosacral area, cavernous hemangioma, dermal sinus, and dimple.[48] Scoliotic deformity is seen in 30%–79% of the patients with diastematomyelia.[49] Other orthopedic deformities include gait abnormalities and foot deformities. Neurological insult can lead to weakness in lower limbs, spasticity, abnormal reflexes, sensory deficits, and bladder and bowel incontinence.[50]

Neurological deterioration in SSCM is due to low anatomical position of the spinal cord, which is fixed by abnormal spur that restricts the normal ascend of the cord during growth leading to stretch induced injury to the cord [Figure 2].[51]

Figure 2

A 5-year-old girl child presented with numbness in her toes with slowly progressing clawing of her toes in both lower limb—A. On investigating, she was found to have thoracolumbar scoliosis on X-ray—B. MRI scan revealed diastematomyelia in thoracic spine—C

ARNOLD–CHIARI MALFORMATION

ACM is a disorder of hindbrain in which there is a herniation of posterior fossa contents through foramen magnum. ACM can be divided into four types. In type I there is a downward herniation of cerebellar tonsil from foramen magnum typically more than 4–5 mm. In Chairi II malformation, there is caudal descent of cerebellar vermis along with the descent of rhombencephalon. In Chiari III malformation, posterior fossa contents are herniated through bifid cervical canal. Type IV ACM is characterized by agenesis of cerebellum.[352]

Herniation of posterior fossa contents through the foramen magnum leads to mechanical obstruction of cerebrospinal fluid (CSF) flow leading to formation of syrinx with the spinal canal. Syrinx is a condition in which there is fluid-filled cavity in the parenchyma of spinal cord in rostrocaudal axis.[5354] Mechanical blockage to the CSF circulation within the subarachnoid space at foramen magnum or within the spinal cord is the main cause.[5556] Syrinx is seen in 50–75% of patients with ACM type 1. The syrinx in these patients is seen at the lower cervical and upper thoracic level with a normal spinal cord between the herniated fourth ventricle and syrinx.[57]

Patients with Chiari malformation in addition to aforementioned symptoms present with pain, most common site being neck or occipital region followed by shoulder, back, and extremities. The pain is increased in activities such as laughing, running, coughing, or any injury while playing. In acute condition, the pain is felt like an electric shock whereas in chronic cases it is deep and burning in nature. Patients with syringomyelia presents with dissociative anesthesia, occipitocervical pain, and weakness of upper limb and lower limb.[1358]

Scoliosis is seen in 50%–90% of patients with ACM and scoliosis is seen in 15%–65% of type I ACM.[56] The cause of scoliosis in ACM is due to alteration of trunk muscle innervations, imbalance of paravertebral muscle tone, and abnormal proprioception. Deformity correction in patients with ACM and syringomyelia has high risk of neurological injury due to further descent of the tonsils leading to intramedullary hypertension, traction on spinal cord, reduction in blood supply due to pressure changes, and intramedullary pressure changes within the spinal cord.[5259]

Suboccipital decompression relieves the anatomical and physiological block of the CSF flow across the foramen magnum resulting in pulsatile flow of CSF and decrease in syrinx size.[56] The surgical procedure aims at increasing the posterior fossa volume. Suboccipital decompression consists of removal of occipital bone and posterior arch of C1. In more aggressive approach the dural sac is opened to release the adhesion and duraplasty is performed.[13]

Various studies in literature had shown decompression of cerebellar tonsils in ACM helps in stabilization and regression of the curve. Brockmeyer et al.[60] in their study showed improvement of curve after suboccipital decompression in 62% of patients. Sengupta et al.[61] showed curve improvement after suboccipital decompression in 71.4% of patients. James et al.[62] showed 42% patients did not required spinal fusion after decompression of cerebellar tonsils. However, in some studies the improvement in the curve progression was only temporary.[62] Phillips et al.[63] in retrospective study of four patients showed that neurosurgical drainage had delayed the curve progression but did not completely halt the curve progression. Ghanem et al.[64] studied 12 patients with ACM with syringomyelia. In their study seven patients had associated scoliosis. Neurosurgical decompression helped in stabilization and regression of curve in two patients and progression of curve was seen in five patients. Farley et al.[65] in study of nine patients with ACM and associated scoliosis showed that after neurosurgical decompression, there was temporary stabilization of the curve; however, eight patients showed curve progression at final follow-up, which required spinal fusion.

The risk of deformity progression after suboccipital decompression depends on age of the patients, Cobb’s angle, and rotation of the vertebra. The risk of curve progression is less in younger children below 8–10 years of age, Cobb’s angle less than 50°, and nonstructural curves. The risk of curve progression is high in patients older than 10 years, Cobb’s angle more than 50°, structural curves, double major curves, presence of vertebral rotation (perdriolle 2+), and associated kyphosis. No correlation was found between curve progression or regression with respect to gender, neurological deficit at presentation, and frontal balance.[66]

MANAGEMENT OF INTRASPINAL ANOMALIES WITH ASSOCIATED EOS

The aim of treatment in patients with EOS with intraspinal anomalies was to prevent neurological deficits and deformity progression with an attempt to maximize the growth of spine and thoracic cage. The definitive fusion should be delayed up to the age of 10 years in patients with EOS. Early fusion before the age of 10 years may lead to increased chances of pulmonary symptoms.[4] Patients with thoracic spine length less than 18 cm at maturity have increased chances of pulmonary compromise. Normal thoracic height is 11 cm at birth, 18 cm by 5 years of age, and 25 cm by 10 years.[67] Various treatment options are available for deformity correction or preventing progression in patients with EOS, which includes cast jackets, growth friendly implants that include distraction-based implants (growth rods, vertical expandable prosthetic titanium rib, magnetically controlled growth rods), guided growth implants (Shilla technique), and compression-based implants.[46869]

In patients with EOS associated with intraspinal anomalies, the surgical intervention for spinal anomalies have shown to improve the curve magnitude in various studies.[7071] Curve regression or curve stabilization after surgical intervention for intraspinal anomalies depends on age of the patients, magnitude and morphology of the curve, Risser grading, and vertebral rotation at the time of presentation. Patients at high risk for curve progression after neurosurgical intervention for intraspinal anomalies include patients with delayed age of presentation after 10 years, Cobb’s angle more than 40°, Risser grade 0–2, vertebral rotation (perdriolle 2+), structural scoliosis, and double major curves.[4466] These high-risk patients can be considered for simultaneous neurosurgical intervention and deformity correction with growth friendly implants. In recent literature, various studies have been published where simultaneous surgical intervention was performed for intraspinal anomalies and spinal deformity with good correction rate and minimum complication rates. Jon et al.[72] in their study showed that TCR and deformity correction can be safely performed in patients with EOS. Neurosurgical monitoring has helped in performing these complex surgeries along with reducing the complication rates.[72] Simultaneous surgeries help to avoid the risk of repeated anesthesia and cost of repeated hospitalization; to reduce the complications of revision surgeries such as dural leaks, increased blood loss, and neurological deficits; and also decrease the rehabilitation and recuperation time.[7374] Patients with low risk for deformity progression after neurosurgical intervention can be kept under routine observation, and instrumented fixation can be considered only if deformity progresses.

CONCLUSION

With the advent of MRI, there has been increasing awareness among surgeons of neurological causes leading to spinal deformity. EOS with spinal cord anomalies is formidable challenge to surgeons as this associated condition can lead to long-term morbidity. Recent advances in the surgical and nonsurgical techniques for deformity corrections in EOS and importance of development of thoracic cage has helped in reduction of long-term morbidity. Early diagnosis and treatment of this associated pathology helps to avoid neurological deterioration and improve scoliosis outcome.

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Conflicts of interest

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Summary of literature on incidence of intraspinal anomalies in early onset scoliosis and the most common anomalies

Summary of various presenting symptoms in patients with intraspinal anomalies