Classical Arnold Chiari malformation: Type II

A 3-month-old male baby presented with progressive swelling over the lower back since birth.

The patient underwent MRI brain and whole spine imaging in our department. MRI brain showed typical findings of caudal displacement of cerebellar tissue and vermis for a distance of ~ 2.8 cm below Mc Rae’s line. However, no evidence of cervico-medullary kinking was seen. There was mild stretching of aqueduct and fourth ventricle. There was crowding of posterior fossa structures with low lying torcula and tenting of tentorium cerebelli. There was presence of tectal beaking and dysgenesis of posterior part of corpus callosum. MRI of spine showed syringomyelia and diastematomyelia type II involving upper and lower dorsal cord respectively. Spinal dysraphism with associated myelomeningocele was seen involving lumbosacral spine. Bilateral moderated hydronephrosis was seen likely due to neurogenic bladder. There was segmentation anomaly in form of butterfly vertebra involving dorsal vertebral body.

Background

Arnold-Chiari malformation with an incidence of 0.4: 1000 live-birth is one of the CNS abnormalities that has formed 3% of all abortion and 1-2% recurrent risk [1] and is classified to three types. Type I Chiari, type II Chiari and type III Chiari. Arnold-Chiari malformation type II is the most common and seen in neonates and infants which characterized by displacement of cerebellar tonsils, parts of the cerebella, fourth ventricle, pons and medulla oblongata through the foramen magnum into the spinal canal. This is usually associated with hydrocephalus and myelomeningocele [2]. The posterior fossa in Chiari type II malformation is even smaller than in Chiari I malformation. The cerebrospinal fluid (CSF) cisterns are poorly developed due to lack of fourth ventricular expansion as a consequence of in-utero derivation of CSF circulation to the neural tube defect, all of which results in hindbrain structures downward herniating with subsequent compression of these structures against the foramen magnum.

Clinical Perspective

CM-II's can present in various ways. This is mainly due to the wide range of severity of the malformation and the numerous associated abnormalities that are not uncommonly seen. However, because myelomeningocele is typically present, CM-II can usually be detected at birth [3]. The patient's presentation varies by age, In Neonatal, patients typically present with myelomeningocele. Other manifestations include arm weakness, stridor, dysphagia, aspiration, and apneic spells. In Child, patients will usually have progressive hydrocephalus. In Young adult, can have scoliosis or syrinx.

MR is often required to detect other intracranial and spinal abnormalities. These associations will help the clinician to form the prognosis and guide the treatment options.

Outcome

If Chiari malformations cause no symptoms and do not interfere with activities of daily living, no treatment is usually necessary. In other cases, medications can be used to relieve symptoms such as pain.

In adults and children with Chiari malformations, several types of surgery can be performed. These include: Posterior fossa decompression surgery, Electrocautery Spinal laminectomy.

Surgery is the only treatment that can correct functional defects or stop progression of damage to the central nervous system. Surgery usually results in a significant reduction of symptoms and a prolonged period of remission.

Take-Home Message/Teaching Points

Arnold Chiari malformation is a rare entity. Clinical history and imaging are essential to know the various intracranial and spinal associations. MRI helps in correlation the other findings to make the ultimate diagnosis.