Chiari I malformation: Case report of a postnatal diagnosis and literature review

Abstract

Mode of delivery and intrapartum analgesia for women with Chiari I malformation pose a challenge to the obstetrician and anaesthetist. Clinicians often advocate caesarean section delivery under general anaesthetic to prevent an uncontrolled rise in intracranial pressure or a fall in cerebrospinal fluid pressure during labour that may result in neurological complications, or rarely, brainstem herniation. This case report discusses a woman with hitherto undiagnosed Chiari I malformation who delivered by CS due to obstetric concerns, but remained asymptomatic throughout the preceding labour and in spite of multiple epidural insertion attempts. We discuss considerations for future pregnancies, and review the literature to challenge the view that women with Chiari I need planned caesarean or must avoid epidural/spinal analgesia; instead presenting evidence to support the safety and suitability of vaginal delivery and neuroaxial block in labouring parturients with this condition.

Introduction

Chiari malformations form a spectrum of structural defects of the skull and cerebellum: four different subtypes (I–IV) are recognised; each with increasing extents of cerebellar with or without brainstem herniation. Chiari I (projection of the cerebellar tonsils more than 5 mm below the foramen magnum) remains the most common, with an estimated incidence of 0.5–3.5% ¹ and a slight female preponderance 3:1. ² Frequently, Chiari I is identified incidentally on neuroimaging; in the majority of cases, the condition is either idiopathic or genetic in origin.

Of those with Chiari I malformation, it is estimated that 70% are asymptomatic. ² For those with symptoms, 80% will report a suboccipital headache or neck pain; other features include ocular or otoneurological disturbances, gait ataxia, or cerebellar signs. MRI is the diagnostic tool of choice. Surgical treatment is favoured for women with severe or worsening neurological symptoms, or those with large syringomyelia cavities; for women who are asymptomatic or minimally symptomatic, the recommendation is observation or strategies aimed towards symptom relief (e.g. NSAIDs or temporary cervical collars). ³ Posterior fossa decompression (with or without dural opening or shunting of syrinx) forms the mainstay of neurosurgical therapy.^1,4

Management of Chiari malformation during pregnancy and the intrapartum period is a subject of particular controversy, due to a theoretical increased risk of brainstem herniation during labour or as a consequence of neuroaxial analgesia.

This article will describe the presentation of a woman diagnosed with Chiari I malformation postnatally.

Case history

A 35-year-old woman in her first pregnancy presented seven days postnatally with severe bilateral neck pain and upper limb weakness. Observations were stable, and she was afebrile and normotensive. The woman was entirely unable to move her neck and shoulders without encountering severe pain; neurological examination was otherwise normal with a negative Kernig’s sign. She denied photophobia, headache, loss of consciousness or any postural effect.

There was no history of headaches or spinal problems.

Her antenatal course had been straightforward until induction of labour for reduced fetal movements at 38 weeks of gestation, with delivery by caesarean section due to failure to progress. Delivery was uncomplicated, with minimal blood loss and discharge home the following day. During labour, she opted for an epidural, later resited due to problems with adequate pain control and a further CSE was necessary prior to caesarean section.

In obstetric triage, the woman was given simple analgesia, which provided minimal relief. Blood tests were unremarkable. She was reviewed by the medical and anaesthetic teams who agreed that the presentation did not correlate with classical meningitis, subarachnoid haemorrhage or a dural tap; but that the severity of pain was disproportionate for a musculoskeletal mechanism. An MRI was recommended which revealed a small spinal cord syrinx spanning C5 to T1, and low lying cerebellar tonsils (8 mm below the foramen magnum); the ‘overall features suggesting a Chiari I malformation with associated syrinx’ (Figure 1).

Figure 1.

MRI of patient's cervical spine: topmost arrow indicates cerebellar herniation, bottom arrow indicates syrinx in spinal cord.

Imaging findings were discussed with radiology and neurosurgery teams with advice to admit for analgesia. The neurosurgical team reviewed the woman throughout her admission and she was discharged after two days.

At neurosurgical follow-up several months later, the woman was evaluated as fit for conservative management and suitable for vaginal delivery and neuroaxial block in future pregnancies.

Discussion

Neurological symptoms and signs of Chiari I can arise either from the direct compression of neurological structures in the foramen magnum or spinal canal, or through the formation of a syrinx (a fluid-filled cavity in the spinal cord) which can subsequently cause obstruction to CSF flow or cause compression as it expands.

Symptoms of a Chiari malformation can typically be provoked in one of two ways: a rise in intracranial pressure, or a fall in CSF pressure. Evidently, labour can pose a risk in both respects: uterine contractions and maternal effort can exacerbate the former, whereas neuroaxial block and specifically the risk of dural puncture (1–2% incidence) can trigger the latter. ² Pregnancy itself is associated with a physiological increase in CSF pressure.

As a result, there are concerns that this patient cohort is at risk of neurological deterioration during vaginal delivery and neuroaxial block; management has therefore traditionally favoured elective caesarean section with general anaesthesia.

Whilst the perceived risk of brainstem herniation and devastating maternal implications is ‘frequently feared’ by obstetricians and anaesthetists, ⁵ evidence suggests that this is not only unlikely, but unsubstantiated. A recent systematic review of literature from 1991 to 2018 did not show a single instance of brain herniation, furthermore it concluded that ‘very few adverse outcomes have ever been reported in pregnant patients with a Chiari I Malformation’, with caesarean sections and vaginal deliveries shown to be safe and suitable modes of delivery with either general or spinal anaesthesia. Similarly, a 14-year retrospective case series at Birmingham Women’s hospital also showed that vaginal delivery was associated with an overall healthy outcome for mother and offspring with no neurological complications in the perinatal period. ⁶

Neuroaxial block is both a safe and viable anaesthetic option for women with Chiari I malformation during labour; with no worsening neurological symptoms,^7–9 nor a higher incidence of anaesthetic complications such as postdural puncture headache following delivery. ⁷

An analysis of mode of delivery by Waters et al. provides a useful mechanism for risk stratifying women. The retrospective case series identified that for those who are asymptomatic or manifest headache only as sequelae of their Chiari malformation, decision regarding mode of delivery should be based on obstetric considerations alone; whereas those manifesting papilloedema or hydrocephalus should be considered high risk for both vaginal delivery and neuroaxial block. ⁹

In practice, antepartum diagnosis of a Chiari malformation has been shown to influence both mode of delivery and woman’s options of intrapartum analgesia, even when serious maternal morbidity rates with vaginal delivery or neuroaxial block remained comparable to normal controls and women who received the diagnosis postpartum. ¹⁰

The woman discussed here is a typical example of a parturient who was unaware of having a Chiari malformation and whose antenatal and intrapartum course were not adversely affected. Instead, her presentation several days after delivery suggests that the Chiari I malformation was unlikely to have been aggravated by the use of epidural, or at worst, resulted in minimal and transient symptoms, without any associated temporary or lasting neurological sequelae. The subsequent neurosurgical evaluation confirms that the options of vaginal delivery or neuroaxial block should not be withheld now that she has a diagnosis of Chiari I.

Conclusion

Chiari I malformations remain common among women, with little evidence of an increased risk of complications. The existing assumption that these women require a planned caesarean section or that epidural/spinal anaesthetic should be avoided needs to be challenged.

Multidisciplinary decision-making remains vital, with coordination between maternal medicine clinics, obstetric anaesthesia services and input from neurosurgical colleagues.