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Shrivastava: Anaesthetic challenges in complicated labour: unruptured intracranial aneurysm

Literature review

Intracranial aneurysms are uncommon during pregnancy. Haemodynamic stress is a key factor contributing to the breakdown of the arterial internal elastic lamina and risk of aneurysm formation, progression and rupture.1 Hypertension, smoking, alcohol consumption and familial disorders contribute to its progression, necessitating multidisciplinary care for successful management. Other occurrences are idiopathic or caused by rare disorders such as cerebral or vertebral arteriovenous malformation, arterial dissection, vasculitis and tumour.2

The incidence of intracranial aneurysm is approximately 2% in the general population, with 80–90% arising from the internal carotid artery (anterior circulation aneurysm), which includes the anterior or posterior communicating arteries or the middle cerebral artery.3 The remaining 10–20% arise from the vertebrobasilar arterial system (posterior circulation aneurysm).2 The incidence of intracranial aneurysm in pregnancy is similar to that of the general population. Rupture is more common during pregnancy (20 cases in 100,000 pregnancies) owing to pregnancy-related physiological changes.4 The most common site of unruptured aneurysm in pregnant patients (in contrast to non-pregnant patients) is the internal carotid artery (64% vs. 38%); other sites include the superior cerebellar artery (14% vs. 0%), anterior inferior cerebellar artery (7% vs. 0%), anterior cerebral–anterior communicating artery (7% vs. 12%) and internal carotid–posterior communicating artery (7% vs. 8.5%).5 Aneurysms measuring > 6 mm are at greater risk of rupture than those < 6 mm in size (91% vs. 50%). Aneurysms most prone to rupture are located in the posterior communicating arteries.6,7

Allen et al.1 report that the prevalence of intracranial aneurysm is 5% in the general population, with subarachnoid haemorrhage (SAH) occurring in 16 patients per 100 000 cases, which accounts for 0.4–0.6% of all deaths. A total of 10% of patients die before reaching the hospital and < 33% experience a good outcome from treatment. The incidence of SAH in pregnancy is 0.01–0.05%, with a maternal mortality rate of 11% in treated cases and a fetal mortality rate of 5% in treated cases.

Definitive treatment involves either open neurosurgical clipping or endovascular therapy. Endovascular therapy is an established, relatively atraumatic, treatment involving percutaneous passage of a platinum coil into the sac of the aneurysm and electrolytic detachment of the coil from its steel delivery wire. The presence of one or multiple coils within the aneurysm causes thrombosis of the sac. Complications of endovascular aneurysm coiling include intraoperative rupture, intra- or post-operative arterial occlusion, distal thromboembolism, coil migration and a mass effect from the thrombosed aneurysm.8 Although endovascular treatment was once reserved for patients considered unsuitable for surgery,9 the results of the 2002 International Subarachnoid Aneurysm Trial10 demonstrated superior functional outcomes at 1 year for patients treated endovascularly in comparison with patients treated surgically.

Anaesthetic management of caesarean section in a parturient with unruptured intracranial aneurysm under general anaesthesia or subarachnoid or epidural block should:

  • include neuroanaesthesia and obstetric anaesthesia;

  • ensure that the transmural pressure of the aneurysm remains stable to prevent rupture.3

Transmural aneurysmal pressure (TP) is calculated as follows:

TP = MAP ( mean arterial pressure ) ICP ( intracranial pressure ) .

An increase in MAP and/or a reduction in ICP elevates transmural pressure, which can lead to aneurysmal rupture. However, very few cases have been reported in the literature,4 and guidelines for the management of intracranial aneurysm during pregnancy and evidence-based recommendations for obstetric anaesthesia in patients with unruptured intracranial aneurysm during labour do not exist.3,5

General anaesthesia has a higher mortality risk (16.75%) than regional block, and the majority of maternal deaths are primarily due to difficulties in airway management.11 Every elective intubation demands careful evaluation of airways, aspiration prophylaxis and a rapid sequence approach. If anatomical difficulties for airway management are identified and regional block is not an option, awake tracheal intubation should be considered. Rapid sequence intubation of oedematous airways or awake intubation can increase the risk of aneurysmal rupture.11 Laryngoscopy and tracheal intubation resulting in haemodynamic change may cause dangerous increases in TP, increasing the risk of rupture2 and of acute fetal distress owing to a reduction in maternal MAP and fetal heart rate.2,3 The incidence of intraoperative aneurysmal rupture is 1–2% and is higher in patients with difficult airways.2,3 Esmolol, lidocaine and a deep anaesthetic plane (caused by high doses of anaesthetics and monitored with bispectral index monitoring) at the time of intubation reduce hypertensive response to laryngoscopy.2,3 Remifentanil, both as a bolus dose and in continuous infusion, is now the drug of choice for reducing potent stimulation prior to laryngoscopy.2 Neuroaxis block is the technique of choice in most cases since it is safer for both mother and fetus.3 Puncture of the dura mater can reduce intracranial pressure and trigger the rupture of an aneurysm.

With the high prevalence of diagnosed unruptured aneurysms (approximately 2% of the general population) and the large number of neuroaxis blocks performed every year, a high incidence of post-spinal block SAH might be expected. However, our review of the literature revealed only 11 reports of post-spinal block SAH.3 Spinal block should be relatively safe, particularly when small-gauge needles are available, although there is a small risk of acute cerebral spinal flow hypotension and a lack of MAP elevation. The neurosurgical team reported in Carvalho et al.3 prefers epidural block. Epidural block is an extremely safe technique in the absence of accidental puncture of the dura mater, which could be catastrophic. The decision is made on a case-by-case basis, weighing the risks and benefits of each procedure and the experience of the anaesthetist.

Allen et al.1 report the case of a patient aged 29 years at 31 weeks’ gestation who presented with pain around the right eye, headache, blurred vision and sluggish right pupillary light reflex with third cranial nerve palsy and right ptosis gradually becoming complete. Computerized tomography angiography revealed a posterior communicating artery aneurysm and endovascular coiling was performed. Treatment included 2 mg/kg propofol as it provides superior attenuation of the pressor response to laryngoscopy in comparison with thiopental. Remifentanil infusion of 0.2 μg/kg/min was instituted immediately prior to induction, approximately 90 seconds prior to intubation. Remifentanil controls pressor response to rapid sequence induction12 and is safe for both mother and fetus, even when administered by infusion during caesarean section.13,14 For rapid sequence intubation, 0.6–1.0 mg/kg rocuronium bromide, unlike suxamethonium, does not increase intracranial pressure. Anaesthesia was maintained with 0.05–0.20 μg/kg/min remifentanil infusion and 0.8–2.0% sevoflurane in oxygen and air. Heparin was administered to double the baseline activated clotting time. Antiplatelet drugs were avoided as stenting was unnecessary. The aneurysm was successfully treated. Intravenous infusion of unfractionated heparin was continued for 24 hours following an initial bolus of 3000–5000 units. Recovery was uneventful. Ptosis resolved and the patient delivered a healthy baby vaginally at full term.

Invasive arterial pressure monitoring is used less frequently during endovascular therapy than during open surgery, but in aneurysms more prone to rupture invasive monitoring is mandatory because of the risk of poor utero-placental perfusion with hypotension and the risks posed by hypertension on the integrity of the aneurysm.1 Ventilatory management that favours hypoventilation increases intracranial pressure and hyperventilation, possibly reducing uterine perfusion.1 Continuous cardiotocograph monitoring is essential to detect signs of fetal distress or the onset of labour and fetal heart rate variability.1 Consideration must be given to maternal hydration if large volumes of intravenous iodinated contrast have been used, although this may be less pressing with current radiological technology, in which digital ‘road mapping’ is used to provide prolonged views of vascular architecture.1

This raises the question: what is the procedure for patients in labour?

Barbarite et al.,5 at the University of Miami, conducted a systematic review. The authors searched PubMed for articles containing the phrases ‘pregnancy’ and ‘intracranial aneurysm’ and published during the period January 1991–June 2015 and assessed 109 full-text articles (from 392 potentially eligible articles identified) for eligibility. The meta-analysis included 17 case reports, five case series and one retrospective study with an evidence-based medicine (EBM) grade of A1, involving a total of 44 patients (50 intracranial aneurysms) during pregnancy. All 23 papers showed coil embolization to be superior to surgical clipping. A total of 1.8% of women of childbearing age (16–44 years) had intracranial aneurysms. Adverse outcomes were reported in five (11.9%) fetuses.5 The rate of caesarean section was higher in those with an unruptured cerebral aneurysm than in the general population (71% vs. 29%).

Rupture was confirmed by imaging in 36 of the 50 aneurysms (72%).5 Of these, 78% (28 aneurysms) ruptured during the third trimester (including two in labour), 11% ruptured in the second trimester and 8% during the first trimester.

Grindheim et al.15 reported a significant drop in blood pressure during mid-pregnancy followed by a progressive increase until term, correlating with the increased rate of aneurysm rupture during the third trimester. Macdonald-Wallis et al.16 reported that blood pressure began to increase from week 18 in women with gestational hypertension and pre-eclampsia and week 30 in women with essential hypertension, representing an increasing risk of rupture. This means that caution is required in patients early in the course of pregnancy with small or asymptomatic aneurysms. The literature reports aneurysms reaching 18 mm in size in the third trimester, with worsening headaches and blurred vision, and 40% of aneurysms that were clipped during the first trimester enlarged, ruptured and required coil embolization.5 Surgical management of unruptured aneurysms reduces the complication rate by 31.9% compared with untreated aneurysms.

Coil embolization is associated with lower complication rates than clipping in patients with ruptured aneurysms (9.5% vs. 23.1%).5

Of the 44 patients included in the study,5 38 (87%) underwent caesarean section and six (13%) gave birth vaginally. Of the 38 who underwent caesarean section, 12 patients who gave birth before receiving treatment for a ruptured aneurysm as part of a combined neurosurgical–obstetric approach. In two additional patients with ruptured aneurysms, surgical clipping preceded caesarean delivery. Five patients went into labour with a previously untreated and unruptured aneurysm, one of whom experienced aneurysm rupture during vaginal delivery and was immediately delivered by caesarean section. A second patient also experienced aneurysm rupture during vaginal delivery. Barbarite et al.5 reported a maternal complication rate of 18.20% in all patients and of 14.35% in patients with an unruptured aneurysm. One patient died 12 days after surgical clipping from cerebral oedema and herniation owing to internal carotid artery aneurysm rebleeding. Aneurysms are known to rupture in the third trimester and post partum. Third nerve palsy with reduced visual acuity has also been observed.5,17

D’Haese et al.18 have reported similar findings: clipping an aneurysm following caesarean section has produced good fetal and maternal outcomes. Dogan et al.17 reported spontaneous carotid cavernous aneurysm rupture in a term pregnancy after caesarean section that was managed with coils.

Coil embolization is performed more often than clipping (47.7% vs. 36.4%) and results in shorter operating times and shorter hospital stays,19,20 which decreases fetal exposure to anaesthesia and permanent deficit to the newborn.18 It is prudent to be aggressive with smaller aneurysms to prevent rupture and associated risks: the literature reveals that 62% of aneurysms between 3 and 6 mm rupture, as do 91% of aneurysms measuring ≥ 6 mm. Neurosurgical treatment is recommended for unruptured aneurysms that are symptomatic, show signs of instability or measure ≥ 6 mm.5 Smaller aneurysms between 3 and 6 mm should be monitored and considered for treatment if they become larger, unstable or symptomatic.

Digital subtraction angiography (DSA) is used more often than computed tomography in the diagnosis of intracranial aneurysms; during the embolization procedure, DSA delivers higher doses of radiation, but the amount of radiation is negligible. Fetal shielding, excluding fluoroscopy near the uterus, and safer technologies have been employed successfully to combat radiation damage.5

Eric et al.5 have shown that, in parturients with intracranial aneurysm at term, a combined management strategy of childbirth followed by aneurysm treatment creates optimal conditions for neurosurgeons and improved outcomes for the fetus: the fetus is protected from anaesthesia-related changes in maternal blood pressure, intraoperative aneurysm rebleeding and postoperative maternal complications such as cerebral vasospasm.5,18 The fetus is spared from risk of hypoxia, dehydration and acidosis, which result from poor uterine perfusion and increased vascular resistance as a consequence of hyperventilation and osmotic diuretics often used during surgery.18 This strategy also spares the mother from undergoing multiple anaesthetic procedures.

Eric et al.5 show a clear preference for caesarean section delivery (84.2%) in pregnant women with intracranial aneurysms, in comparison with the general population (32.8%). Lumbar puncture associated with spinal and epidural anaesthesia during vaginal delivery has been reported to increase the risk of aneurysm rupture owing to the loss of cerebrospinal fluid (CSF) and increased vessel transmural pressure.5 Whether or not straining during vaginal delivery causes aneurysm rupture is debated in the literature, but data suggest that this depends on whether or not the aneurysm has been treated prior to delivery. It has been reported that, of three patients who went into labour with previously untreated and unruptured aneurysms, two experienced aneurysm rupture during vaginal delivery; however, no complications were reported in patients who underwent vaginal delivery with previously treated aneurysms.5

Bateman et al.21 state that the ‘[e]stimated incidence of SAH is approximately 15-fold higher for parturient and postpartum women than for pregnant women in the USA’. African-American women are three times more likely to develop SAH than Caucasian women and > 50% of SAH occurs in the postpartum period. When pregnant and non-pregnant patients were compared for SAH, pregnant patients showed a lower percentage of clipping and coiling (12.7% vs. 44.5% respectively).

In contrast, Kim et al.22 state that ‘pregnancy and delivery do not increase the risk of aneurysm rupture’.

This raises the question: does vaginal delivery increase the risk of intracranial aneurysm rupture? The outcome is poor once rupture occurs.

Yamada et al.23 report the case of a Japanese woman aged 40 years who had two aneurysms, originating in either side of the internal carotid artery, as revealed by magnetic resonance angiography. Data suggest that the risk of aneurysm rupture in Japanese women is higher in the perinatal period than during the first 32 weeks.23 With a family history of SAH, advanced age and a history of smoking, the patient elected to undergo caesarean section.

Liu et al.24 report the case of a woman aged 31 years in the 26th gestational week of pregnancy who presented with a sudden onset of left eyelid ptosis, weakness of right limbs, drowsiness and complete palsy of the left oculomotor nerve. Cerebral angiograms revealed a giant basilar tip aneurysm located between the left posterior cerebral and superior cerebellar arteries. Stent-assisted coiling was performed under general anaesthesia. She was given a dose of 75 mg/day clopidogrel and 100 mg/day aspirin orally for 3 days. She died 10 days later. It is accepted practice in obstetrics to treat a ruptured cerebral aneurysm in a pregnant woman as though she is not pregnant. In cases of unruptured aneurysm during pregnancy, the correct choice of treatment to prevent SAH is controversial.24

Confronted with this paradox, most experts suggest that an unruptured aneurysm during pregnancy should be treated as if it were symptomatic or enlarging. The giant aneurysm was located in the posterior circulation and was unclippable. The patient was symptomatic, and the literature shows excellent results for coiling in such cases. Thus, and because at the 24th week of gestation the fetus would not be mature enough to survive, it was decided that coiling would be performed. In such circumstances, with a high-risk lesion and potentially imminent labour, it is best not to treat the aneurysm aggressively. Had the pregnancy been carefully observed until the 28th week of gestation, the baby could first have been delivered, followed by treatment of the aneurysm.

Ortiz et al.25 report the case of a young pregnant woman diagnosed with a cavernous carotid aneurysm that enlarged during pregnancy and yet, after delivery, decreased in size. During endovascular surgery, the patient received heparin to avoid thromboembolic complications. According to the recommendations of the US Food and Drug Administration (FDA), heparin is safe for the fetus but should be discontinued before caesarean section.26 There are no current reports on stent-assisted coiling in pregnancies. Using a stent will require the patient to take aspirin and clopidogrel orally. Low doses of aspirin, such as 80 mg/day, appear to have no adverse effect.24 Clopidogrel has been shown to be non-teratogenic in two animal species; human evaluation was reported in one case report only.24

Anderson27 has stated that ‘[n]o one knows what the risk of rupture of a cerebral aneurysm is with vaginal delivery’ and argues that the method of delivery for women with an unruptured aneurysm should be informed by obstetric considerations. Anderson has shown that women known to have an unruptured aneurysm have a very high rate of caesarean delivery, yet this is not supported by evidence and ‘may not be necessary’.27

Kim et al.22 have stated that ‘[c]aesarean delivery would be indicated in several circumstances, such as when the clinical state of the mother is severe’, for example in cases of coma, brainstem damage or when aneurysm is diagnosed during labour.

Young et al.28 induced delivery in a woman at 34 weeks’ gestation prior to surgery for a cerebral aneurysm ruptured by amniotomy prior to corrective neurosurgery. Neither labour nor vaginal delivery caused neurological injury to the mother. Subsequent neurosurgery was successful and both mother and infant continued to do well several months later. Patients in labour with an unruptured cerebral aneurysm may also present with ischaemic events.29


  • The establishment of formal guidelines for an algorithmic approach to managing intracranial aneurysm during pregnancy and labour is encouraged.

  • A review of the literature on treatments for intracranial aneurysm during pregnancy and labour shows varying results, differing on a case-by-case basis.

  • Risk reduction in cases of intracranial aneurysm must focus on both mother and child.

  • Neurosurgical treatment during pregnancy is safe and effective. Coil embolization following aneurysm rupture results in fewer maternal complications than neurosurgical clipping.

  • Endovascular methods are associated with reductions in operating times and hospital stays and are beneficial to both mother and child.

  • Whether patients in labour should deliver vaginally or by caesarean section must be determined on a case-by-case basis and by the stage of gestation: < 28 weeks or > 28 weeks of gestation.

  • In cases of enlarged unruptured aneurysm with a symptomatic parturient, a combined procedure may be followed, delivery of the baby followed by coiling or clipping.

  • If an aneurysm ruptures during labour, the patient should be treated surgically as any other patient.

  • Allen et al.1 have reported that a patient in labour has successfully delivered vaginally after prior treatment for an unruptured aneurysm.

  • There is currently no evidence to support prophylactic caesarean section for the avoidance of acute SAH.

  • Lumbar puncture associated with spinal and epidural anaesthesia during vaginal delivery has been reported to increase the risk of aneurysm rupture owing to loss of CSF and increased TP, but this risk may be mitigated by newly available smaller gauge needles.

  • Ultrasonography may be beneficial.



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