The Arnold-Chiari malformation or just Chiari malformation (named after the Austrian pathologist Hans von Chiari and the German pathologist Julius Arnold) comprises a series of developmental disorders and malformations in the posterior fossa. Affected patients typically become symptomatic in adolescence or young adulthood exhibiting a wide variety of symptoms. The most common are Chiari malformations type I and II, which we discuss in more detail below. Find out here about common symptoms and learn more about the therapy options at Inselspital.
Approximately 1% of healthy adults who undergo magnetic resonance imaging (MRI) of the head show caudal displacement of the cerebellar tonsils, that is, a downward displacement of parts of the cerebellum. If this displacement is more than 5 mm, this is sufficient for the diagnosis of Chiari malformation type I. However, only 0.01 to 0.04% of those affected show symptoms. Chiari malformation type I is most commonly diagnosed around the age of 40 with a discrete female predominance.
Chiari malformation type II occurs in 1 of 1000 births. When a child is born with spina bifida (myelomeningocele), the vast majority (about 95%) also suffer from a Chiari malformation type II.
Chiari malformation type I comprises a heterogeneous group of posterior fossa abnormalities with the common feature of impaired cerebrospinal fluid (CSF) circulation in the craniocervical area. It is caused by caudal displacement of the cerebellar tonsils into the foramen magnum, the exit canal of the spinal cord from the base of the skull. This may result in compression of the brainstem, hydrocephalus (accumulation of CSF in the cerebrospinal fluid chambers), or syringomyelia (cavity formation in the spinal cord).
The most common symptoms are:
- Pain in the head or neck
- Possible radiation of symptoms to arms or legs
- Weakness in one or more extremities
- Sensory disorders in one or more extremities
- Unsteadiness of gait
- Sometimes also visual disturbances (double images), tinnitus or speech disorders
In this form of malformation, the cerebellar tonsils, as well as the cerebellum and brainstem, are displaced downward and put the lower cranial nerves under tension. Most often, this also causes hydrocephalus. This malformation is often associated with an open spine (myelomeningocele), a serious developmental disorder at the embryonic stage in which the neural tube, from which the spinal cord originates, is not completely closed.
In this form of malformation, the cerebellar tonsils, as well as the cerebellum and brainstem, are displaced downward and put the lower cranial nerves under tension. Most often, this also causes n hydrocephalus. This malformation is often associated with an open spine (myelomeningocele), a serious developmental disorder at the embryonic stage in which the neural tube, from which the spinal cord originates, is not completely closed.
Typical symptoms occur in childhood and include:
- Breathing difficulties
- Pauses in breathing
- High-pitched, wheezing breath sounds (stridor)
- Aspiration (inhalation of fluids and saliva)
- Paresis of the arms
- Paresis of arms and legs (tetraparesis)
Magnetic resonance imaging (MRI) of the skull and cervical spine is the diagnostic procedure of choice. Real-time MRI (also called MR fluoroscopy) allows continuous observation in real time and displays motion as a series of images. This can be helpful in assessing CSF flow through the foramen magnum.
Often, Chiari malformation type I is discovered incidentally and patients are asymptomatic. Surgery is not indicated in these cases. In asymptomatic Chiari associated with cervical syringomyelia however, it must be discussed individually with the patient whether surgery is not advisable. In symptomatic Chiari, there is a clear indication for surgery and the symptoms usually respond well to surgery. In the case of prolonged weakness or gait disturbances, complete recovery does not always occur. For this reason, surgery should be performed early if symptoms are present.
The goal of surgery is the decompression of the posterior fossa to restore normal cerebrospinal fluid drainage from the skull into the spinal intradural space. The surgery involves a suboccipital craniectomy. This means that a portion of the skull bone behind the foramen magnum is removed. This is followed by a laminectomy of the 1st cervical vertebra (C1). In this surgical procedure on the spine, the vertebral arch with the spinous process is removed in order to relieve the excessive pressure.
Depending on the extent of the caudal displacement of the cerebellar tonsils, a laminectomy of cervical vertebrae C2 and/or C3 may also be performed in addition in individual cases. In most cases, it is necessary to open the dura and perform an extensionoplasty for additional decompression of the posterior fossa, especially if the patient also has syringomyelia. Free unobstructed pulsation of CSF toward the spinal canal must be seen during surgery or confirmed by ultrasound if it is decided not to open the dura.
Again, treatment involves decompression of the posterior fossa via suboccipital craniectomy and laminectomy of C1. However, a ventriculoperitoneal shunt or VP shunt for short must often be implanted in advance to treat the hydrocephalus. This is a surgically created connection between the ventricular system of the brain and the abdominal cavity through which excess CSF can be drained into the abdomen, where it is reabsorbed.
Possible complications following decompression of the posterior fossa and suturing in a duraplasty include the occurrence of a pseudomeningocele. The risk for this is approximately 6%. A pseudomeningocele is an abnormal accumulation of cerebrospinal fluid under the skin due to a CSF leak in the duraplasty.
Our specialized neurosurgical team has many years of experience in the surgical treatment of Chiari malformations. To ensure maximum safety for our patients during surgery, each operation is performed using the latest technological procedures such as continuous intraoperative monitoring.
For children with Chiari malformation, we work closely with our colleagues in pediatrics and neuropediatrics at the Children's Hospital.
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