Arnold–Chiari malformation

Arnold–Chiari malformation, or often simply Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness in the head and face, difficulty swallowing, dizziness, nausea, impaired coordination, and, in severe cases, paralysis.


Symptoms

• Headaches aggravated by Valsalva maneuvers, such as yawning, laughing, crying, coughing, sneezing or straining

• Tinnitus (ringing in the ears)

• Dizziness and vertigo

• Nausea

• Nystagmus (irregular eye movements)

• Facial pain

• Muscle weakness

• Impaired gag reflex

• Restless Leg Syndrome

• Sleep Apnea

• Dysphagia (difficulty swallowing)

• Impaired coordination

• Dysautonomia: tachycardia (rapid heart), syncope (fainting), polydipsia (extreme thirst), chronic fatigue

The blockage of Cerebro-Spinal Fluid (CSF) flow may also cause a syrinx to form, eventually leading to syringomyelia. Central cord symptoms such as hand weakness, dissociated sensory loss, and, in severe cases, paralysis may occur.

Diagnosis
Diagnosis is made through a combination of patient history, neurological examination, and Magnetic Resonance Imaging (MRI). The radiographic criteria for diagnosing a congenital Chiari I Malformation is a downward herniation of the cerebellar tonsils greater than 5 mm below the foramen magnum. Other imaging techniques involve the use of 3-D CT imaging of the brain and cine imaging (a movie of the brain) can be used to determine if the brainstem is being compressed by the pulsating arteries that surround it.

In the Syndrome of Occipitoatlantoaxial Hypermobility, cerebellar tonsillar herniation is typically only evident on an up-right MRI, due to the fact that the Chiari Malformation is gravitationally acquired by means of connective tissue weakness. 3-D CT imaging may aid in the diagnosis of related disorders such as retroflexed odontoid. Invasive cranial traction (lifting of the head off the spine) is often used as a confirmation of the diagnosis.

The diagnosis of a Chiari II Malformation can be made prenatally through Ultrasound.

Treatment
Once symptomatic onset occurs, a common treatment is decompression surgery, in which a neurosurgeon usually removes the lamina of the first and sometimes the second or even third cervical vertebrae and part of the occipital bone of the skull to relieve pressure. The flow of spinal fluid may be accompanied by a shunt. Since this surgery usually involves the opening of the dura mater and the expansion of the space beneath, a dural graft is usually applied to cover the expanded posterior fossa.

A small number of neurological surgeons believe that detethering the spinal cord as an alternate approach relieves the compression of the brain against the skull opening (foramen magnum), obviating the need for decompression surgery and associated trauma. However, this approach is significantly less documented in the medical literature, with reports on only a handful of patients. It should be noted that the alternative spinal surgery is also not without risk.