Periop Mgmt - Spina Bifida

Question 1

What is Spina Bifida?

Answer 1

Spina bifida (SB) is a congenital neural tube defect (NTD) that results from incomplete spinal column closure during embryonic development.

Neural tube defects are among the commonest birth defects.

NTDs include cranial defects such as anencephaly. SB includes open and closed NTDs affecting the spinal cord. The most important distinction for anaesthetists is between closed and open SB.

The incidence of SB is six in every 10,000 births (0.06%) in the UK

Question 2

What surgery might patients with SB require?

Answer 2

1. Neonatal closure
2. Cerebrospinal fluid (CSF) diversion procedures
3. Urological intervention
4. Major orthopaedic surgery

Question 3

Classify Spina Bifida

Answer 3

1. Spina bifida occulta
2. Meningocele
3. Myelomeningocele
4. Myelocele.

Question 4

How does closed NTD occur?

Answer 4

Closed NTD results from failure of fusion of the posterior vertebral bodies.

The defect is enclosed by skin and the neural tissues are not exposed.

Pigmented patch of hair or sacral dimple at the site of the dysraphism.

May have tethered cord

Question 5

What are the clinical manifestations of a closed neural tube defect?

Answer 5

Clinical manifestations vary greatly:

o patients may have no sequelae or may have symptoms
o back pain
o neurogenic bladder dysfunction
o musculoskeletal involvement.

Question 6

What is Spina Bifida Aperta?

Answer 6

Spina bifida aperta or open spina bifida is characterised by exposed neural tissue and includes meningocele and myelomeningocele.

Question 7

What is Myelomeningocele?

Answer 7

Myelomeningocele, the most significant form of SB, is a fluid-filled sac containing spinal cord tissue that protrudes through the vertebral column.

This incomplete closure at the distal cord leads to dysfunction of bladder, bowel and lower limb sensory and motor deficits.

Question 8

What is Meningocele?

Answer 8

Meningocele is a variant where the cord is not contained within the herniated sac.

o Spina bifida aperta presents with a visible lesion at birth or can be diagnosed antenatally on ultrasound.
o Exposed neural tissue renders patients susceptible to further damage and infection. They therefore require rapid evaluation and treatment.

Question 9

What is the pathophysiology of Spina Bifida?

Answer 9

Spina bifida occurs as a result of failure of fusion of the neural folds.

The neural tube is formed between the 3rd and 6th week of gestation.

Absence of distension causes a Chiari II malformation, small posterior fossa and cerebral disorganisation.

SB results from genetic and environmental factors.
↑ prevalence with:
o Trisomy 13 and 18
o Maternal diabetes, obesity, exposure to toxins,
o Medications (antiepileptic drugs)
o Hyperthermia

Folate supplementation has significantly reduced the incidence of NTDs

Question 10

How is Spina Bifida diagnosed?

Answer 10

Antentally with US or postnatally on clinical examination.

Third ventricle dilatation &small head circumference (may need VP shunt)
- ‘lemon sign’ (inward concavity of the frontal bones)
- ‘banana sign’ (an anteriorly effaced cerebellum).

Abnormalities of the bony spine, disruption of skin contours, or a cystic sac may be present.

Question 11

What are the orthopaedic complications of Spina Bifida?

Answer 11

Scoliosis
Kyphosis
Hip dislocation
Talipes equinovarus (clubfoot)
Congenital vertical talus (rocker bottom foot)

Question 12

What are the cardio-respiratory complications of Spina Bifida?

Answer 12

Brainstem dysfunction:
Apnoea, VC palsies, poor cough, atypical responses to hypoxia and hypercarbia.

Scoliosis may precipitate restrictive lung disease

Right ventricular dysfunction

Question 13

How might neonates present with Chiari Malformation due to Spina Bifida?

Answer 13

Neonates may present with vocal cord dysfunction leading to stridor, swallowing difficulties or apnoea.

Question 14

How might hydrocephalus present clinically?

Answer 14

Rapid increase in head circumference
Vomiting
Irritability
Somnolence
Sun setting eyes

indicate acutely raised intracranial pressure (ICP).

In older patients:
Headaches
Cognitive disturbances
Behavioural changes
Cerebellar signs

Question 15

What is the treatment of Hydrocephalus

Answer 15

This is a neurosurgical emergency and warrants rapid investigation to prevent worsening neurological injury – VP shunt

Endoscopic third ventriculostomy (ETV) is an alternative treatment – may be preferred when obstruction to flow is below the level of the third ventricle.

Question 16

What are other complications of Spina Bifida?

Answer 16

Increased risk of seizure disorder.

Urinary tract complications:
Incontinence, retention, Vesicoureteral reflux

Bowel dysfunction:
Lesion Above conus medullaris – increased sphincter tone, constipation
Lesion below conus medullaris – sphincter flaccidity and incontinence.

Pressure ulcers

Question 17

What neurological dysfunction might a person with Spina Bifida present with?

Answer 17

The neurological dysfunction is related to the level of the lesion.

Patients with a low sacral lesion may be asymptomatic whereas lumbar or thoracic lesions can cause significant impairment.

• Hydrocephalus
• Tethered cord.
• Chiari II malformation
• Seizures

The degree of motor function is influenced by complications such as hydrocephalus, musculoskeletal issues and pressure sores.

Question 18

How does Chiari II malformation occur?

Answer 18

The Chiari II malformation is present in nearly all patients with a myelomeningocele.

o Characterised by downward displacement of the cerebellar tonsils and medulla.
- Lack of distension of the embryonic ventricular system leads to a normal sized cerebellum developing in a small posterior fossa.
- It causes obstructed flow of CSF resulting in hydrocephalus.

Question 19

What procedures might a child with spina bifida present for?

Answer 19

o antenatal or postnatal closure
o VP shunt insertion and revision
o Chiari II release
o Tethered cord release
o MRI
o Urological
o Lower limb orthopaedic and scoliosis surgery

Question 20

What neurological considerations would you assess in your preoperative assessment?

Answer 20

o sensory or motor deficits, presence of hydrocephalus
o CSF diversion procedure is preferable before major elective surgery.
o Chiari II malformation predisposes patients to risk of brainstem herniation.
o Compliance with medication and seizure frequency should be determined for those with epilepsy.
o Neurosurgical review of functional shunt status.

Question 21

What special considerations would you have with your airway assessment?

Answer 21

Airway assessment :
o Consider positioning with macrocephaly, kyphoscoliosis, contractures or pressure areas.
o Caution with excess neck extension in those with Chiari II.

Respiratory assessment:
o assessment of bulbar function and any restrictive lung defects.
o baseline oxygen saturation, arterial blood gas and pulmonary function testing

Question 22

What cardiovascular and renal considerations would you assess as part of your preoperative assessment?

Answer 22

Cardiovascular assessment
o baseline functional status, METS
o Wheelchair bound? Consider echo
o Significant respiratory compromise – right heart investigations

Renal assessment
o Bladder dysfunction, baseline renal function, consider creatinine in context of low muscle mass

Question 23

What is your intraoperative management plan for a patient with Spina Bifida?

Answer 23

1. Latex-free environment (prevalence of allergy as high as 64%)
2. Standard monitoring +/- A line, core temperature, IONM
3. Anticipate difficult IV access – US
4. Optimise positioning for airway management - pillows, shoulder roll, videolaryngoscopy prevents excessive neck movement.
5. Bulbar palsy, vocal cord paralysis and raised ICP may increase the risk of aspiration.
6. Low-normal tidal volumes (around 6-7 ml/kg) to prevent excessive airway pressures
7. Permissive hypercapnia is acceptable.
8. Additional supports for limbs with contractures
9. Cautious Fluid management
10. Reno-protective drugs
11. Reverse NMBD
12. NA is controversial ? increased risk SC damage - Attributable to abnormalities of the cord such as tethering, low lying conus, diastematomyelia or associated intra-spinal abnormalities such as cysts or tumours.

Question 24

What are the post operative considerations for a patient with Spina Bifida?

Answer 24

1. Multimodal analgesia
2. NSAIDs may be contraindicated in renal dysfunction.
3. Careful titration of opioids with respiratory dysfunction.
4. Patients may require prolonged care in PACU and supplemental oxygen or CPAP.
5. Those with hydrocephalus or Chiari malformation should be monitored for an extended period for neurological deterioration.

Question 25

How is pain and sensation altered in patients with Spina Bifida?

Answer 25

Sensation and pain perception can vary greatly.
Afferent pathways may be disrupted, leading to absence of pain perception, but spinal reflexes, such as withdrawal from pain and deep tendon reflexes, can still be preserved.

Question 26

When is Myelo-meningocele surgery performed?

Answer 26

Meningomyelocele closure is usually performed within 72 h of birth

Discussion with neurosurgeons to determine the presence/severity of hydrocephalus and whether a CSF diversion procedure will be performed simultaneously.

Primary closure can affect ventilation with significant increases in airway pressures observed.

Question 27

What are the perioperative considerations for posterior fossa decompressive craniectomy for Chiari II release?

Answer 27

The surgical strategy is to increase the diameter of the foramen magnum and decompress the posterior fossa.

Prone positioning and intraoperative neck flexion necessitate careful placement and fixation of the tracheal tube to minimise the risk of endobronchial migration.

Blood loss can be rapid and haemostasis difficult to achieve.
Intravenous access appropriate for massive transfusion and a fluid warmer

Decompression of CSF may cause brainstem traction, which can lead to bradycardia and possible asystole.

An infusion of adrenaline should be available and CVC

Question 28

What is tethered cord syndrome?

Answer 28

Tethered cord syndrome is attachment of the filum terminale to inelastic structures.

This limits movement of the cord within the canal which can result in stretching of and damage to the cord. It is associated with SB and can cause progressive motor and sensory dysfunction.

Diagnosis is confirmed with MRI.

Question 29

What are the anaesthetic considerations for tethered cord release?

Answer 29

It is corrected with division and release of the filum.

Neuromuscular blocking agents and volatile anaesthetic agents. should be omitted.

The dura is opened during tethered cord release so postoperative CSF leakage is possible.

Question 30

What are the advances in Spina Bifida management?

Answer 30

Fetoscopic surgery has led to significant improvement in neurological sequelae and quality of life.

Prenatal repair reduces the need for CSF shunting (68% vs 98%), hindbrain herniation and improved motor score and mental development.

Question 31

What are risks associated with spinal surgery?

Answer 31

Posterior spinal fusion carries a higher risk of complications than in patients without SB.

Rates of infection
Instrumentation failure
Non-union are higher with up to 50% of patients experiencing a major complication.

An anterior approach may necessitate one-lung ventilation.

Question 32

What are the risks of Kyphectomy?

Answer 32

Patients are predisposed to pressure ulcers at the site of kyphotic vertebrae.

Kyphectomy is performed to improve functional sitting position and reduce risk of pressure ulcer.
Kyphectomy presents numerous risks (likely restrictive lung defects)

1. Assess lung and right heart function to determine fitness for surgery
2. Risk of significant blood loss and haemodynamic instability
3. Significant risk of decrease SC signals