Symptoms of Chiari develop as a result of compression of the medulla and upper spinal cord and disturbance of cerebrospinal fluid (CSF) flow through foramen magnum. The typical Chiari headache is an intense occipital pain or a more generalised, ‘explosive’ headache, usually triggered by Valsalva-like manoeuvres such as coughing or physical activity. A study of 19 Chiari I patients analysed the triggers of their headaches: ten suffered from headaches lasting an average of 11 min, brought on by coughing, sneezing, laughing, sexual activity or other physical efforts. Eight patients had classical occipital headaches but six described frontal pain (Martins et al. 2010).

The pathophysiology of these symptoms probably centres on the pressure differences between the spine and intracranial compartments that come about during and immediately after Valsalva manoeuvres. The possible mechanisms by which disordered flow of CSF through the foramen magnum results in formation of syringomyelia cavities are discussed in Chap. 6. The pathophysiology of Chiari II is likely to be more complex than with Chiari I, but similar mechanisms are likely to operate in the generation of symptoms, although the additional effect of hydrocephalus , in further exacerbating the downward displacement of brainstem structures, has to be borne in mind.

When a person carries out moderately forceful exhalation against a closed airway (Valsalva manoeuvre), the resultant rise in intrathoracic pressure affects venous return, cardiac output, arterial pressure and heart rate. These effects can occur when the thoracic and abdominal muscles are strongly contracted, such as when a person strains while having a bowel movement or when lifting a heavy weight. Both actions are usually accompanied by involuntary breath holding. The normal physiological response in Valsalva occurs in clear phases. An initial rise in intrathoracic pressure forces blood out of the pulmonary circulation and into the left atrium. At the same time return of systemic blood to the right atrium is impeded. As a consequence the cardiac output is reduced and stroke volume falls. When forced exhalation ceases the pressure on the chest is released, allowing the major intrathoracic vessels to re-expand. Venous blood can also once more enter the heart and exit into these vessels and so cardiac output increases. The pressure changes have a direct effect, positive and negative, on the pressures and blood flow in the unvalved spinal and cerebral venous structures.

During labour, pushing down involves a series of particularly prolonged Valsalva manoeuvres. An inevitable concern, therefore, is whether or not labour might aggravate or complicate the anatomy or pathophysiology of a Chiari and/or an associated syrinx cavity. Theoretically, at worst, there is a potential risk of brainstem compression from forced impaction of the tonsils. At the very least, pressure rises might be expected to aggravate any preexisting symptoms, and they might even cause deterioration in the patient’s neurological state. Spinal or epidural anaesthetics could also introduce new variables into the events of labour for Chiari or syringomyelia patients (Nel et al. 1998). The concerns relate to possible dural puncture and then CSF egress and also physical and pressure alterations in the epidural compartment. Abnormal CSF pressures might influence the effectiveness of the anaesthetic. Inadvertent or intended puncture, in the case of a spinal anaesthetic, of the lumbar theca might, in turn, affect intracranial or intraspinal pressures.

In addition to the effects of Valsalva, both the uterine contractions and the pain that they generate are also likely to increase CSF pressure, both inside the cranium and the spinal canal. Measuring the CSF pressure in normal patients during labour has revealed considerable elevations when pain is intense. Pressures may be as high as 70 cm H₂O, which is more than three times the upper limit of normal (Mueller and Oro 2005).

Yet, despite the recognition that syringomyelia and Chiari symptoms, in particular headaches, get worse with straining and exertion, we know relatively little about the consequences of pregnancy, labour and delivery, in terms of precipitation, worsening or even improvement of maternal symptoms and signs. Nor do we know whether or not a sudden or repeated episodes of a ‘high venous pressure’ event can cause the formation of a syrinx in the first place, but there are clear episodes in some patient’s clinical histories where this may be considered to have been possible, and such episodes may certainly be considered to have possibly aggravated a preexisting syrinx state if La Place’s law is operative. There is, however, no report of such events occurring during pregnancy, labour or delivery.

There is, unfortunately, very little literature and virtually no research to guide either the patients or their obstetricians and anaesthetists on the appropriate management of the Chiari or syringomyelia during pregnancy and labour. Reliable scientific data on the consequences, or potential interactions, of the physiological or interventional events occurring during pregnancy and labour are not available. There is no clear guidance at all in the literature, whether from large studies or case reports which specifically highlight or clearly identify common or uniform problems or pathological sequelae with a normal, or assisted, vaginal delivery and the use of epidural or intrathecal anaesthesia in patients with Chiari or syringomyelia. Nor, indeed, has there been any evidence to demonstrate increased safety or benefit conferred on pregnant mother with these conditions, by employing a Caesarean section .

Neurosurgeons are, nevertheless, frequently asked to advise on what is the best or safest mode of delivery for Chiari and syringomyelia patients. Is a vaginal delivery safe or is a Caesarean section necessary? Is a ‘supported’ delivery, with an epidural, or possibly even a spinal anaesthetic, permissible?

Women who are diagnosed with Chiari sometimes report that previous pregnancies or births first triggered the onset of their symptoms, or made them worse. One large series of 364 Chiari patients reported 16 female patients who identified pregnancy as an event precipitating their symptoms (Milhorat et al. 1999). Some women, already diagnosed with Chiari, reported that their symptoms became slightly worse during the pregnancy but then resolved spontaneously and fairly quickly after delivery. A further paradox is that in some cases patients’ symptoms actually got better during the pregnancy, for periods at least (Mueller and Oro 2005). Equally, many women, when first diagnosed with Chiari, have already completed pregnancies successfully without having experienced any aggravation of their symptoms.