Differential Diagnosis in Neurology

4.2. Congenital Defects of the Spinal Cord

Dysraphic Disorders (Neural Tube Defects)

General considerations:

• Primary neurulation occurs throughout the brain and spinal cord, to upper sacral levels. It occurs by a process of neural folding.
• Secondary neurulation occurs in the sacral and coccygeal regions by a process that canalizes a solid cord of cells.
• Axial malformations:
  • Failure of neural tube closure that is associated with skeletal modeling defects that occur around a malformed neural tube are anencephaly, meningomyelocele and craniorachischisis
  • Bony defects secondary to axial mesodermal development without a persistent open neural tube. These are encephaloceles and meningoceles in which there is herniation of the neural tube through a bony defect. In spina bifida occulta and diastematomyelia the defects are entirely skin covered.

Neural Tube Closure Defects

Craniorachischisis

• General Considerations:
  • Most severe dysraphism
  • Brain and spinal cord are exposed to CSF
• Clinical Features:
  • Necrosis degeneration and angioma-like formation of the cord
  • May have preserved optic nerve development

Myelomeningocele

• General considerations:
  • Meninges and spinal cord are herniated through a large vertebral defect
    • Distended meningeal sac filled with CSF and covered by a thin membrane or by skin
    • The spinal cord may be closed or there may be dilatation of the central canal with herniation of the posterior cord
  • Myelocoele
    • A flat open spinal cord exposed to CSF
    • The spinal cord at the site of the defect is a flat, discoidal highly vascular mass known as the area medullovasculosa
    • The posterior spinal cord is open at birth
    • The nerve roots end within the vascular mass
  • Clinical features:
    • Associated spinal anomalies are:
      • Syringomyelia; hydromyelia; diastematomyelia, diplomyelia and double central canal
    • Hydrocephalus is common in association with Chiari Type II malformations
    • Lesions above T12 have a high incidence of other spinal cord malformations; more common in females than males
    • Low lesions have equal sex incidences; but are less severe clinically

Meningocele

• General considerations:
  • A variant of spina bifida cystica
  • Vertebral defect combined with a cystic lesion of the back
  • Usually at the lumbosacral level
  • The dura and arachnoid are herniated through the vertebral defect; the spinal cord remains in the canal
  • Narrow canal connects the cyst with the vertebral canal
• Clinical features:
  • Associated diastematomyelia, tethered cord and hydromyelia
  • Insensibility of lower extremities; bladder; bowel and sexual dysfunction; weakness and wasting of all muscles below the knees; areflexia at the knee and ankle.

Spina Bifida Occulta

• General considerations:
  • Least severe of the neural tube defects
  • Closed defect of the embryonic neural bud that undergoes secondary canalization
• Clinical features:
  • Associated sacral agenesis; anomalies of the anorectal and urogenital systems
  • Associated spinal cord anomalies are: hydromyelia, diplomyelia (longitudinal splitting or duplication of the cord); tethering
  • Defects are low lumbar and sacral
  • Associated sacrococcygeal teratoma and lipoma
  • Pes cavus and neurogenic bladder occur; other abnormalities of micturition; wasting and sensory loss of the affected roots

Syringomyelia

• General considerations:
  • Lower cervical cord is the most common location; lumbar may cause the most pronounced deficits
  • Found in association with Type I Arnold-Chiari malformations in 40% of patients; can be asymmetrical
  • Incomplete fusion of the posterior columns or the persistence of the large canal of the embryonic state; may be focal and asymptomatic
  • Normal ependymal lining becomes gliotic:
    • The syrinx may originate at the base of the posterior horn and extend into the central grey and anterior commissure
• Clinical features:
  • Loss of pain and temperature at the segmental level. A suspended sensory loss: normal sensation above and below the lesion
  • Light touch, vibration, position sensibility is relatively spared
  • Amyotrophy of muscles innervated by specifically involved anterior horn cells (cervical cord-intrinsic hand muscles; frequently the 4th and 5th finger extensors; benediction sign)
  • Claw hand in late stages (both thenar and hypothenar eminences are involved-"main en Graeffe")
  • Weakness and atrophy is often asymmetric
  • Horner's sign (C8–T1 involvement); destruction of the sympathetic ciliary center of Budge
  • Bowel and bladder involvement is late
  • Loss of segmental reflexes at the involved level; hyperactive reflexes below this level
  • Babinski sign is present with corticospinal tract involvement
  • Pain may be severe early in the course of the illness; deep ache or burning quality
  • Associated syringobulbia may occur; usually at the junction of the alar and basal palate (level of the vestibular nuclei laterally in the medulla)
  • Severe thoracic scoliosis is common
  • Rarely there is extension into the centrum semiovale (syringoencephalia)
  • Charcot joints occur (shoulder, thoracic spine or hip; rarely at the elbow and wrist) due to lack of proprioception, pain and from repeated trauma
  • Autonomic dysfunction of the hands; diffuse swelling and subcutaneous edema (neurogenic edema)
  • Associated with Chiari I, small posterior fossa

Lumbar Syrinx

• Clinical features:
  • Atrophy of proximal and distal leg muscles
  • Dissociated sensory loss in lumbar and sacral dermatomes
  • Loss of deep tendon reflexes
  • Bowel and bladder dysfunction; severe if Onuf's nucleus S2–S4 is involved
  • Extensor toe signs

Diplomyelia (Duplication of the Cord)

• General consideration:
  • Two complete spinal cords wrapped in their own dura
  • May coexist with diastematomyelia
• Clinical features:
  • Spasticity with a neurogenic bladder

Diastematomyelia

• General features:
  • A fibrous band that splits the spinal cord; attached from the superior dura to the spinal canal
  • More common: thoracic > cervical > lumbar
• Clinical features:
  • Spasticity of the legs
  • Bowel and bladder dysfunction
  • Loss of lower extremity deep tendon reflexes

Tethered Cord

• General considerations:
  • Fibrous filum terminale attaches to the sacrum; cord is pulled down; conus medullaris is then below L1
• Clinical features:
  • Often first manifest in middle age
  • Women may have lower leg weakness if maintained in the dorsal lithotomy position (childbirth or prolonged vaginal procedures)
  • Pes cavus (asymmetric)
  • Bladder dysfunction
  • Hyperactive reflexes
  • Often associated with lipoma of the sacral cord (bright on T1 weighted MRI)

Chiari Malformations

• General considerations:
  • Chiari I
    • Cerebellar tonsillar herniation
    • Tonsils are often atrophic, sclerotic and connected by fibrous adhesions to the back of the medulla
    • Cervical roots angled slightly upwards (by myelography)
    • May be asymptomatic
    • Often associated with late onset hydrocephalus and cerebellar ataxia
    • 50% of patients have syringomyelia; 90% of idiopathic syringomyelia patients have a Chiari I malformation
    • Rare familial occurrence of Chiari I and syringomyelia occurs. It is also associated with craniocervical anomalies (platybasia, basilar impression, Klippel–Feil suboccipital dysplasia, and craniosynostosis)
• Clinical features:
  • Signs of a cervical syrinx
  • Severe C2 headache with any Valsalva maneuver, but particularly with cough
  • Ataxia of upper and lower extremities. Often symptomatic in mid-life; ataxia of gait is the most prominent feature in this instance
  • Small slanted posterior fossa, short neck, low set hairline
  • Occasional down beat nystagmus exacerbated on lateral gaze

Neurogenic Cyst

• General considerations:
  • Occur in the ventral thoracic cord
  • Early developmental defeat
• Clinical features:
  • Compression of the cord with weakness, spasticity and bladder dysfunction

Off Midline Skin Malformations with Underlying Developmental Defects

• Dimples (dysraphism)
• Hair patch (AVM, dysraphism)
• Large hairy mole (malignant melanosis of the dura)

Congenital Bony Defects that Compromise the Spinal Cord or Root Exit Foramina

Developmental Spinal Stenosis

• General considerations:
  • Measurements:
    • Cervical cord C2–C7, 24–26 mm
    • Thoracic cord > than 14 mm
    • Lumbar cord L1–L2 > 24–26 mm
• Block vertebrae (all achondroplasia patients)
• Short pedicle syndrome (lumbar)
• Trefoil configuration of the canal (lumbosacral levels)
• Lateral recess stenosis (primarily at L5–S1 levels)

Achondroplasia

• General considerations:
  • Block vertebrae at all levels of the spinal cord
  • Stenosis at the foramen magnum and lower thoracic levels
• Clinical features:
  • Stenosis of T10–T12, L1–L2
    • Severe pain in an upper lumbar distribution
    • Bowel and bladder dysfunction
  • Stenosis of the foramen magnum causes:
    • Automatic breathing deficit (Ondine's curse); most frequently seen after foramen magnum decompression
    • Spastic quadriparesis

Congenital Abnormalities of the Cervical Vertebrae and Foramen Magnum

• General considerations:
  • Anatomy of the atlas and axis:
    • The atlas has a ring like structure, but no vertebral body
    • It has synovial articulations with the occipital condyles of the skull and caudally with the odontoid process
    • The odontoid process has 3 major ligaments that anchor it to the skull:
      • Posterior cruciate (most important)
      • Two lateral alar ligaments
      • In an adult during flexion the atlas should not move more than 3 mm from the axis. In children the separation is 5 mm
    • The tip of the odontoid process should not extend rostrally more than 3 mm above a line from the hard palate to the inner table of the skull at the foramen magnum (Chamberlain's line). Bull's and the digastric line are other measurements of this parameter that are rarely used

Occipitalization of the Atlas

• General consideration:
  • A congenital fusion of the atlas and foramen magnum
  • Neurological symptoms occur when the anterior–posterior diameter of the spinal canal posterior to the dens is less than 19 mm
• Clinical features:
  • Spastic quadriparesis
  • Ataxia of legs greater than arms

Basilar Invagination

• General considerations:
  • The odontoid process is > 3 mm above Chamberlain's line
  • The cervical spinal cord is compressed
• Clinical features:
  • Paresthesias of the hands
  • Lhermitte's sign with neck flexion
  • Sudden medullary compression with cardiac arrhythmia, respiratory arrest and sudden death
  • Symptoms develop in childhood or early adult life
  • The head may be elongated with a decreased vertical diameter
  • Short neck; decreased range of motion to all planes
  • Ataxia; legs > arms
  • Spastic quadriparesis
  • Rarely, papilledema (CSF obstruction); subarachnoid block in many patients
  • Increased CSF protein in 50%

Platybasia

• General considerations:
  • A flattening of the base of the skull. The normal angle between the planum sphenoidale and the clivus is 135° If this angle is increased to >135° there is platybasia
  • Possible AD inheritance males > females
  • Associated with other skull base defects:
    • Maldevelopment or hypoplasia of the basiocciput
    • Partial or complete atlanto-occipital fusion
    • Atlantoaxial dislocation
    • Stenosis of the foramen magnum
  • Distortion of the pons, medulla, cerebellum; traction on lower cranial nerves
  • Vertebral artery obstruction with head turning
• Clinical features:
  • Vertigo and drop attacks with head turning (obstruction of the vertebral artery)
  • Intermittent hoarseness and swallowing abnormalities due to traction of the lower cranial nerves
  • Spastic quadriparesis; ataxia legs > arms
  • Can be acquired with:
    • Paget's disease
    • Osteogenesis imperfecta
    • Rickets'
    • Rheumatoid arthritis

Malformations of the Axis and Atlas

• General considerations:
  • There are five ossification centers in the axis and atlas that may develop abnormally:
    • The body and tip of the axis
    • The lateral mass of C1 and the central part of the axis
    • A fracture through the most rostral ossification center of the odontoid separates the tip from the body and is frequently asymptomatic
    • These malformations may occur concomitantly with basilar impression or independently

Dens Atresia

• General considerations:
  • Part of the odontoid process is fused to the body of C2
  • Anterior dislocation of the axis with cord compression
• Clinical features:
  • Spastic quadriplegia
  • IX, X, XI (spinal accessory component XII involved by traction)
  • Head movement causes pain
  • Mild sensory loss or paresthesias in cervical dermatomes
  • Respiratory involvement

Odontoid Process ossification defects

• Tip of the odontoid process fracture; usually asymptomatic and occurs with violent head flexion
• Base of the odontoid fails to ossify; concomitant basilar invagination

Gorlin's Syndrome

• Short atlas
• Odontoid malformations

Congenital Fusion of Cervical Vertebrae

• General considerations:
  • Congenital fusion of cervical vertebrae is most common at C4–C5
  • Fusion of the upper thoracic and entire cervical spine occurs
  • AD and AR inheritance
• Clinical features:
  • Short neck and low hair line
  • Limitation of neck movement to the lateral planes
  • Spinal stenosis occurs above and below the congenital fusion
  • Associated clinical signs:
    • Syringomyelia
    • Cardiovascular defects 4%
    • Genitourinary anomalies 2%
    • Congenital deafness (faulty development of the osseous inner ear)
    • Sprengel's deformity (branchiomeric deformity at C4–C5; elevation and maldevelopment of the shoulder and scapula)

Spina Bifida

• General considerations:
  • Mild dysraphic defect
  • Asymptomatic unless associated with other congenital deficits:
    • Myelomeningocele
    • Neurenteric or other cysts
    • Lipoma
    • Tethered cord

Differential Diagnosis of Congenital Spine Defects

The general physical examination is most helpful with this differential diagnosis. A patient with a short neck with limited lateral movement suggests basilar impression or platybasia. If the usual acquired causes are present such as Paget's disease, osteogenesis imperfecta (blue sclera) and rheumatoid arthritis (ulnar hand deviation) and rarely rickets, the diagnosis should be suspected. Intermittent lower cranial nerve involvement, particularly hoarseness is common as intermittent brainstem vascular insufficiency with movement of the head to the lateral planes causes vertebral artery occlusion. In a patient with increased reflexes induced by neck flexion, there may excess mobility of the spine at C1–C2. This is often accompanied by paresthesias of the hands. A short neck with low hairline and a shallow posterior fossa should also be sought which is common with osseous cervical congenital malformations.

Chiari I malformation are often associated with a cervical syrinx. Hoarseness and ataxia point to this diagnosis as does a severe C2 headache with cough.

An acquired thoracic spine scoliosis or kyphoscoliosis point to a reduplication or diastematomyelia of the cord. If the scoliosis is C shaped, there is disruption of paraspinal musculature unilaterally. If there is an S shaped defect, it is a congenital defect with compensation. An astrocytoma may also grow asymmetrically and motor neuron disease and primary muscle disease may affect paraspinal musculature asymmetrically causing a "C" scolioisis. Severe scoliosis and kyphosis are also seen with Emery–Dreifuss muscular dystrophy, fiber type disproportion and limb girdle muscular dystrophy type II B (LGMDIIB). Syrinxes are frequently asymmetric and may extend from the cervical to the sacral cord, producing a C shaped scoliosis. Burns on the hands and arms, as well as suspended sensory loss and segmental atrophy, identify this diagnosis.

A tethered cord often is announced in young adults during delivery. A prolonged dorsal lithotomy position during a difficult birth may cause paralysis of the legs.

Tufts of hair and strawberry hemangiomas of the skin often have underlying spinal and vertebral body defects. These include spinal bifida, A-V malformations and myelomeningoceles. A tuft of hair off the midline may be the marker of a neurogenic cyst that connects with the intradural space.

A patient with a short neck and abnormally raised and malformed shoulder and scapula has Klippel Feil syndrome with Sprengel's deformity.