"Unveiling Chiari Malformation: Understanding Cases and Surgical Interventions"

Arnold Chiari Malformation

Dr S. Rajkumar,  Brain & Spine Surgeon, Dr. T.C.R. Ramakrishnan, Chief Neurologist,  Dr. R. Senthilkumar, Anaesthesiologist

Introduction:
Arnold-Chiari or Chiari malformations describe a group of deformities of the posterior fossa and hindbrain, which includes the cerebellum, pons, and medulla oblongata. These deformities lead to problems ranging from cerebellar tonsillar herniation through the foramen magnum to the absence of the cerebellum, with or without other associated intracranial or extracranial defects such as hydrocephalus, encephalocele, syrinx, or spinal dysraphism.

Chiari I is the least severe and often found incidentally. It is characterized by one or both pointed (not rounded) cerebellar tonsils that project 5 mm below the foramen magnum, measured by a line drawn from the basion to the opisthion (McRae Line).

Case Report:
We report 2 cases in this article that we operated last month in our institution.

CASE 1:
32 yrs female presented to our neurology opd with complaints of hoarseness of voice, difficulty in swallowing, occipital headache and neck pain, clinical examination showed right 6th nerve palsy, reduced gag reflex, right 12th nerve palsy, MRI showed chiari malformation with syringobulbia. We did Foramen magnum decompression+ Excision of arachnoid bands + Tonsillar cauterisation + Lax duraplasty with fascia lata.Immediately after surgery patients swallowing difficulty resolved and hoarseness of voice improved.

CASE 2:
23years old male presented to neurology opd with complaints of neck pain, paresthesia over right shoulder, breathing difficulty while sleeping. On examination he had dissociated sensory loss over right neck, shoulder{cape distribution}, also he had wasting of right deltoid. MRI showed cerebellar tonsil descent with extensive syringomyelia ( C2 - D2 ).
We did foramen magnum decompression+ tonsilar cauterisation +lax duraplasty. After surgery patients preoperative symptoms started to resolve and he is on regular follow up.

Discussion
There are multiple proposed theories, including molecular, hydrodynamic, and mechanical, with the likelihood that different mechanisms can have the same resulting Chiari malformation.
Reduced volume of the posterior fossa leads to displacement of the cerebellar tonsils through the foramen magnum in Chiari I malformation. Causes include primary congenital hypoplasia or secondarily from acquired morphologic changes, such as premature closure of sutures, calvarial dysplasia, or genetic/syndromic. Mutations on chromosomes 1 and 22 have been identified as possible causes for hereditary posterior fossa hypoplasia.

Epidemiology
Chiari I malformation is the most common type and occurs in approximately 0.5 to 3.5% of the general population with a slight female predominance .

Pathophysiology
Neurologic signs and symptoms can arise from 2 mechanisms:
Direct compression of neurological structures against the surrounding foramen magnum and spinal canal
Syringomyelia or syringobulbia development
The obstruction of cerebrospinal fluid (CSF) outflow eventually results in syrinx development. 

Fluid-filled cavities (syrinx) develop within the spinal cord or brainstem, resulting in neurologic symptoms as the cavity expands.

Clinical presentation
In Chiari I malformation, the most common presentation is suboccipital headaches and/or neck pain (80%). Symptoms are exacerbated when asked to perform the Valsalva maneuver. Other common presentations include ocular disturbances, otoneurologic symptoms (dizziness, hearing loss, vertigo), gait ataxia, and generalized fatigue. Myelopathy classically presents with “dissociated sensory loss” (loss of pain and temperature sensation, preserved fine touch and proprioception) and motor weakness.

Cerebellar signs, including ataxia, dysmetria, and nystagmus, and lower cranial nerve deficits (IX, X, XI, XII CN) result either from direct compression of the cerebellum or medulla at the foramen magnum or from syringomyelia or syringobulbia.
Sleep apnea can occur in a patient with Chiari malformation due to a weakness of pharyngeal muscles elicited by the brainstem, upper spinal cord, or lower cranial nerve compression.

Evaluation
MRI of the head and cervical spine is the test of choice in evaluating Chiari I. This will demonstrate cerebellar tonsillar descent greater than 5 mm below the foramen magnum (McRae line). In addition, a decreased size of the posterior fossa and a syrinx may be seen

Surgical Management
The main treatment for Chiari malformation is surgical with the goal of re-establishing the CSF flow across the craniovertebral junction and relieving pressure on the cerebellum and hindbrain by decompressing the posterior fossa.
Better surgical results are seen when surgery is performed within 2 years of symptoms onset.

Surgical Techniques
The standard surgical technique for Chiari I is a posterior fossa decompression. This is obtained by a suboccipital craniectomy enlarging the foramen magnum, often in conjunction with C1, and possible C2, laminectomy. The dura will be opened, with subsequent dissection of arachnoid adhesions if present. Depending on the available dural expansion and size of the posterior fossa, a duraplasty may need to be performed. The dural graft can be an autograft such as occipital fascia or tensor fascia lata (TFL)  or artificial dura. Tonsillar cauterization may also be performed.Follow up MRI is recommended at 3,6 months and 1year.

Prognosis
Chiari I has a good prognosis, but it also depends on the presence of pre-existing neurological deficits. Most patients who have no neurological deficits have an excellent outcome.

Take Home 
Chiari  malformation should be considered in sub occipital headache worsened  by valsalva espicially if.

Look for brainstem signs, dissociative sensony loss in sub occipital headache patients.
Early surgery (< yrs of symptom onset) carries a good prognosis)