Arnold Chiari Malformation

The Arnold Chiari Type II Malformation (ACMII) is present in 99% of patients with a myelomeningocoele. The malformation consists of an abnormal hindbrain with the medulla, and sometimes the , inferior aspect of the and the fourth ventricle herniating through an enlarged into the cervical canal. The ACM is often associated with other abnormalities of the developing brain with approximately one third of patients having partial or total agenesis of the corpus callosum, and two thirds of these having below average intelligence (Venes et al 1986).

Although the exact process of the development of the ACM is still unknown, it is believed that the ACM develops in association with failure of the neural tube to close and is due to the inability to maintain pressure within the ventricular system due to leakage of the CSF through the open neural tube. The size of the posterior fossa is determined by the ventricular system and is determined prior to the development of the cerebellum. Consequently, the small posterior fossa does not allow normal development of the cerebellum and causes it to be displaced both cranially and caudally (Stevenson 2004, McLone and Dias 2003).

Hydrocephalus is thought to be caused by the ACM and not the cause of the ACM. This is supported by the fact that is often not present on early antenatal ultrasound; however the ACM can be seen from as early as 11-12 wks gestation (Bernard et al 1997). Hydrocephalus is however thought to further deform and impede normal development during fetal and postnatal life. Hydrocephalus will also exacerbate and accelerate any clinical manifestations of hindbrain compression and ACM (McLone and Dias 2003). SPINA BIFIDA Signs and Symptoms

In an ACMII the cranial nerves are often displaced and under traction, resulting in a variety of symptoms including: swallowing difficulties (bulbar functions), , vocal cord and upper limb weakness (Shaer 1997).

Infants and children under the age of 2 years will most often present with cranial nerve (CN) and signs (Stevenson 2004). Compression of CN 10 will result in neurogenic (aspiration, choking, nasal regurgitation, increased feed time and weight loss). Infants may also present with upper limb weakness or quadraparesis, , weak cry, hypotonia, opisthotonos and developmental delay. A symptomatic ACM is a neurosurgical emergency in this age group with respiratory difficulties, in particular inspiratory and apnoeas being potentially fatal (McLone and Dias 2003, Stevenson 2004). It has also been noted that the presence of signs of ACM in infants is associated with a poor prognosis and requires prompt attention. Most studies suggest that the greatest cause of mortality in infants with spina bifida is due to ACM dysfunction (Wagner et al 2002).

In comparison, ACM in an older child, although serious, is rarely an emergency. Older children may present with cervical myelopathy, upper limb weakness and , changes in dexterity, handwriting and self-care, occipital headaches or craniocervical pain and upper limb or trunk associated with cerebellar compression (Stevenson 2004, McLone and Dias 2003).

Table: Symptoms in children with brainstem compression Infants Older Children may also present with Stridor Sleep disturbances Snoring Nystagmus Impaired vocal-cord and palatal movement Headache Characteristic high pitched cry pain or stiffness Chewing and swallowing difficulties Increasing weakness Recurrent aspirations Spasticity Apnoea and Reduced balance Unusual sweating and skin discolouration Loss of sensation Nystagmus Upper limb dysfunction Tonal changes changes in urodynamics Upper limb/trunk ataxia SPINA BIFIDA Surgical management

The literature suggests that the first line of management for symptomatic ACM should be close monitor- ing of the VP . Resolution of hydrocephalus will often result in reversal of brainstem symptoms and more extensive surgery may be avoided (McLone and Dias 2003, Sgouros 2008, Talamonti et al 2007). If shunt revision does not improve symptoms, a posterior fossa decompression may be performed involv- ing cervical laminectomies at the affected area and a suboccipital craniotomy may be performed. (Ste- venson 2004, Shaer 1997).

The physiotherapist may notice upper limb weakness during routine reviews and should be alert to the signs of potential ACM dysfunction, particularly in the young child in which it requires prompt evaluation.

Reference List

Bernard JP, Suarez B, Rambaud C, Muller F and Ville Y (1997) Prenatal diagnosis of before 12 weeks’ gestation: direct and indirect ultrasonographic semeiology. Ultrasound Obstetrics and Gynecology 10:406-409 McLone DG and Dias MS (2003) The Chiari II malformation: cause and impact. Childs Nervous System 19:540-550 Sgouros S (2008) Chiari II malformation and In Qzek MM, Cinalli G and Maixner WJ (eds) Spina Bifida Management and Outcomes. Italy: Springer 237-248. Shaer CM (1997) The infant and young child with spina bifida: major medical concerns. Infants & Young Children, 9(3):13-25. Stevenson KL (2004) Chiari Type II malformation: past, present, and future. Neurosurgical Focus 16(2) Article 5 Talamonti G, D’Sliberti G and Collice M (2007) Myelomeningocele: long-term neurosurgical treatment and follow-up in 202 patients Journal of (5Suppl Pediatrics) 107:368-386. Venes JL, Black KL and Latack JT (1986) Preoperative evaluation and surgical management of the Arnold-Chiari II malformation. Journal of Neurosurgery 64(3):363-70. Wagner W, Schwarz M & Perneczky A (2002) Primary myelomeningocele closure and consequences. Current Opinion in Urology, 12(6):465-468.