Airway management of type-III arnold chiari malformation: An anaesthetic challenge

Arnold Chiari malformation (ACM) is defined as protrusion of meninges and brain components into a congenital defect in the cranium or in the vertebral column. It was originally described by the Austrian pathologist Hans Chiari through autopsy of 40 children with hindbrain dysplasia in 1891. Initially, he classified ACM into three types (I, II, III), and four years later he added the type IV into the classification. In 2018, a newer classification was suggested by Fatima et al. [1] to include some additional variants of ACM like type-0, type-1.5, and type 3.5 into the original classification. Type-III ACM is the rarest variety which may be associated with cervical cerebellar hydroencephalocele with high fatality rate. The incidence of occipitomeningoencephalocele is 1 in 5000 live births. As of 2018, roughly 60 cases of type III ACM have been reported [1]. We report a case of type-III ACM associated with large occipitomeningoencephalocele with herniation of the dysmorphic cerebellum, vermis and kinking/herniation of medulla with cerebrospinal fluid (CSF), and tethering of spinal cord with posterior arch defect of the C1–C3 vertebrae. The airway management of such a case with herniation of brain components is an anaesthetic challenge because it involves all the vital structures of the brain and spinal cord.

A two-month-old full-term female infant born by normal vaginal delivery with a birth weight of 2.3 kg and now with 3.2 kg body weight was scheduled for repair of occipitomeningoencephalocele (Figure 1A). There was a history of ICU admission at birth for a period of 10 days. She was admitted for poor sucking reflex and some associated infection. There was no history of any seizure episodes. On examination, the child had normal head circumference (38 cm) with normal knee and plantar reflexes, normal muscle tone of upper and lower limbs, normal breathing pattern during sleep and awake state, and normally reacting pupils to light, but the child was irritable, crying, and sometimes vomiting fully after feeding. Magnetic resonance imaging (MRI) scan shows a large midline defect of 19 mm in occipital bone, an occipitomeningoencephalocele of size 4.2 x 2.0 x 4.9 cm (CC*AP*TR) with skin cover containing dysmorphic cerebellum, vermis and kinking/herniation of medulla with CSF, and tethering of spinal cord (Figure 1B). Cardiorespiratory function and High resonance computed tomography (HRCT) of chest was normal. Complete blood count, a renal function test, and liver function tests were within normal limits. Preoperatively, 6-hour nil per orally was advised with injection of dextrose-containing fluid 12 mL/ hour as a supplementation. The child was shifted to the operating theatre with operation room prewarmed with a body warmer, and she was connected to a pulse oximeter, with Non-invasive blood pressure (NIBP), electrocardiogram, and temperature probe. Preoperative vitals were as follows: oxygen saturation (SPO2) 98%, NIBP 70/50 mm of Hg, and heart rate 150/min. The head was supported with a soft padded gel ring, and rolled cotton bandages were kept below the shoulders for alignment and to prevent neck extension during intubation (Figure 2A). Premedication was done with intravenous injection of glycopyrrolate 30 mcg and fentanyl 6 mcg. The patient was induced with 10 mg propofol and incremental increases of inhalational anaesthetics sevoflurane. Oropharyngeal intubation was done with 3.5 mm uncuffed Endotracheal (ET) tube without any neck extension. After confirmation of ventilation with bilateral air entry in the chest and capnography, intravenous injection of cisatracurium 0.6 mg was given. Anaesthesia was maintained with oxygen and air ratio of 1:1 and sevoflurane 1 minimum alveolar concentration (MAC). Intravenous injection of paracetamol 50 mg was given before the surgical incision. Surgery was done in prone position. During decompression of meningoencephalocele, oxygen saturation once decreased to 89 % and recovered after manual ventilation with 100 % oxygen. During the entire period of surgery, the intracranial pressure was controlled by monitoring the Mean Arterial Pressure (MAP), End tidal carbon dioxide (ETCO2), and oxygen saturation (SPO2). Surgery was completed with aspiration of 200 mL of cerebrospinal fluid (CSF) and the excision of the dysmorphic part of the cerebellum with tight primary Duraplasty (Figure 2B). Anaesthetic dose reversal was done with intravenous injection of neostigmine 150 mcg and glycopyrrolate 30 mcg, and patient was extubated after achieving adequate tidal volume and muscle tone. The child was then kept in High-Definition Unit for 4–5 hours for observation before being shifted to the paediatric intensive care unit.

Figure 1

Figure 2

The aetiology of type III ACM is not exactly known. It is assumed to be due to incorrect neuralisation during the process of embryonic ventricular extension causing a prolapse of the Cerebellum and brainstem [2,3]. The anaesthetic challenge for intubating such patients lies in the prevention of spinal cord compression and encephalocele rupture during the process of intubation and intraoperative anaesthetic management and measures during the process of extubation to prevent aspiration of the contents into the respiratory tract because of derangement of pontomedullary centre and afferent-efferent tracts of cranial nerves causing poor sucking and gag reflex [2].

Intubation in type III ACM is a challenge because of the prolapse of the cerebellum and other brainstem structures along with the associated occipitomeningoencephalocele which may get compressed by the process of extending the neck during intubation. This can be overcome by either placing the patient in a lateral position or in a supine position while supporting the head in different ways [4]. Mowafi et al. used sterile surgical towels to make stacks to support the swelling, while traditionally the head can also be placed in doughnut-shaped support [5]. In our case, the head was supported with a soft padded gel ring and rolled cotton bandages which were kept below the shoulder for alignment and to prevent neck extension during intubation thus preventing the compression of the cerebellar and other brainstem structures.

Postoperatively these patients may develop hydrocephalus, leading to raised intracranial pressure which will result in scar dehiscence and CSF leak. A study conducted by Mahapatra et al. suggested that in neonates and infants, no attempt should be made to cover the bone defect by a bone graft [6]. In our indexed case, the posterior arch defect was not closed to prevent the rise in intracranial pressure. In 60–70% of case, patients with posterior encephaloceles develop hydrocephalous post-operatively, requiring a ventriculoperitoneal shunt [7]. It may be noted that hydrocephalous, which was not present preoperatively, may become apparent after the repair of an encephalocele.

The surgical outcome is highly dependent on the preoperative location and severity of the encephalocele. The long-term survival of occipital encephaloceles is only about 50% [8]. ACM III is known to be accompanied by meningoencephalocele of the top of cervical vertebra and occipital region, cerebellar prolapse, and hydrocephalus [9]. New-borns with ACM III often suffer from respiratory failure, swallowing dysfunction, hypertonia or amyotonia. Type III ACM in association with respiratory failure shows poor prognosis [10]. Using sevoflurane with propofol as an adjuvant (3 mg·kg⁻¹) and premedicating with Fentanyl (2 mg·kg⁻¹) causes shorter sevoflurane exposure time and safe anaesthetic induction [11]. Intracranial complications such as cerebellar herniation, pneumocephalus, or subdural haemorrhage may occur as surgical complications of ACM repair and sometimes may present with Acute foramen magnum syndrome (acute cerebellar herniation) which may cause non-awakening of patient from anaesthesia [12].

1. The anaesthetic challenge for intubating type-III ACM patients lies in the prevention of spinal cord compression and rupture of encephalocele during the process of intubation, intraoperative anaesthetic managements and measures during the process of extubation to prevent aspiration of the contents into the respiratory tract because of derangement of pontomedullary centre and afferent-efferent tracts of cranial nerves causing poor sucking and gag reflex.

2. Using sevoflurane with propofol as an adjuvant and premedicating with Fentanyl causes shorter sevoflurane exposure time and safe anaesthetic induction.