Spina bifida is a congenital neural tube defect with a spectrum of severity. Neural tube defects in survivable form are estimated to occur in 1-3 in 1000 live births; with modern management 25-year survival is over 80%. Many of these survivors will have a significant neurological deficit, in spite of which they will strive to achieve as normal a lifestyle as possible; for women this includes pregnancy and childbirth. Traditionally, spina bifida is categorised as occulta and cystica:
• Spina bifida occulta. Its reported prevalence is between 5% and 36% of the population and it is not usually associated with a neurological deficit. It may only be discovered incidentally on radiography or when a woman presents for regional analgesia. It is a vertebral defect and occurs when the two halves of the vertebral arch fail to fuse.
• Spina bifida cystica. This is a collective term for the more severe forms of spina bifida, which include spina bifida with meningocoele, myelomeningocoele or myeloschisis.
Common to all these malformations is a sac-like protrusion through the defect in the vertebral arch. The neurological deficit depends on the severity and level of the defect and, to an extent, on the effect of subsequent surgery. Some women may have associated cardiac, musculoskeletal or genitourinary anomalies.
Problems and special considerations
Pregnancy in women with spina bifida can prove to be a serious challenge to both obstetric and anaesthetic staff, depending on both the severity of the neurological deficit and any associated skeletal abnormality. Kyphoscoliosis and distortion of the pelvis may make vaginal delivery or positioning for regional anaesthesia difficult. There may be an intraventricular shunt to maintain normal cerebrospinal fluid pressure.
There is an increased risk of accidental dural puncture, particularly when the needle is inserted at the level of the defect. The spinal cord may be tethered and may terminate at an abnormally low level. There is a risk of abnormal spread of local anaesthetic, resulting in either excessive cranial spread or inadequate sacral spread. This may be exacerbated if the woman has had previous corrective surgery. There is also often anxiety regarding the conduct of regional anaesthesia, particularly in patients with an established neural deficit.
Caesarean section, if required, may be difficult because of previous urological surgery, such as ileal conduit.
Latex allergy is more common in patients with spina bifida cystica.
Management options
Ideally, women should be seen by the anaesthetist in the antenatal period, when the nature and level of the lesion and any neurological deficit can be identified and the risks of regional anaesthesia can be assessed and explained. Women who have spina bifida occulta usually have lesions in the low lumbar or sacral areas, with minimal impact on regional techniques, and may be offered regional analgesia or anaesthesia when appropriate. The patient should be warned that there may be an increased risk of an inadequate or failed block, and also of dural puncture as the supporting ligaments (interspinous and ligamentum flavum) may be abnormal at the level of the lesion. It should be remembered that spinal cord tethering may be present in these patients, especially if they give a history of neurological abnormalities and cutaneous manifestations. Occasionally, spina bifida occulta may only be discovered incidentally during siting the epidural or spinal, but this is not a reason to deny appropriate analgesia or anaesthesia.
In spina bifida cystica, there may be significant neurological deficit including skeletal abnormalities and impairment of bladder and bowel function. Some women may be wheelchair-bound. The aim is to achieve as normal a pregnancy and labour as possible for the individual; for this, effective antenatal consultation and team planning are essential in order that all the options for delivery are discussed and documented. Before regional analgesia is contemplated, baseline clinical findings should be documented in the records, including neurological assessment and, where possible, pre-existing spinal and pelvic x-ray films (pelvic radiography in pregnancy may not be advisable). Magnetic resonance imaging enables the identification of the underlying anatomic abnormality and is recommended in the presence of neurological symptoms that may suggest tethering of the spinal cord, or in women with a history of previous back surgery. Its benefit in asymptomatic patients is controversial, and not all authorities would insist on scanning. The neurological examination is helpful in assessing whether the pain pathways of labour are intact and how regional analgesia can be used to help in labour and delivery. Women may have been told that they will not feel the pain of labour because of their pre-existing sensory deficit. However, this ignores the fact that most are neurologically intact above the lower lumbar segments and therefore will experience the normal pain of the first stage of labour, although it is true that the pain of the second stage may be modified. The increased risk of failed regional analgesia/anaesthesia and dural tap must be explained.
For analgesia in labour, epidural analgesia is generally not contraindicated. However, siting the epidural may be difficult and it is advisable to insert it above the defect and/or the scar from previous surgery. For caesarean section, regional anaesthesia is acceptable. Spinal anaesthesia may be more predictable than epidural anaesthesia, particularly for spread of the block to the sacral roots. Normal volumes of subarachnoid injectate may be used. However, depending on the complexity of the previous surgery and the wishes of the woman, some may opt for general anaesthesia. This usually poses no particular problems, although tracheal intubation and mechanical ventilation may be difficult in some patients with kyphoscoliosis. These patients have a normal response to suxamethonium.
Key points
• Antenatal assessment of women with spina bifida is important.
• Magnetic resonance imaging should be considered in the presence of neurological features or history of previous back surgery.
• Regional analgesia or anaesthesia may be difficult but should not be denied, and women should be warned of the risks of accidental dural tap and inadequate block.
• Spinal anaesthesia may be preferable to epidural anaesthesia for caesarean section.
Further reading
Griffiths S, Durbridge J. Anaesthetic implications of neurological disease in pregnancy. Contin Educ Anaesth Crit Care Pain 2011; 11: 157-61.
May AE, Fombon FN, Francis S. UK registry of high-risk obstetric anaesthesia: report on neurological disease. Int J Obstet Anesth 2008; 17: 31-6.
Murphy CJ, Stanley E, Kavanagh E, Lenane PE, McCaul CL. Spinal dysraphisms in the parturient: implications for perioperative anaesthetic care and labour analgesia. Int J Obstet Anesth 2015; 24: 252-63.