Chiari malformation type 1
On this page, Dr Christian Brogna explains what Chiari malformation type 1, its symptoms and the best treatment.
Definition
Chiari malformations are defined by a set of alterations of the hindbrain involving the cerebellum, the brainstem, the spinal cord and the skull base. The hindbrain is an embryonic sketch from which the pons, cerebellum and bulb originate.
Chiari type I malformation is the most common variant of Chiari malformations. It is characterized by a “descent” of the cerebellar tonsils through the foramen magnum with consequent alterations of the flow of the cerebrospinal fluid.
Classification
At the end of the nineteenth century. two pathologists, Julius Arnold and Hans Chiari, described in children a clinical and pathological condition characterized by a deformity of the cerebellum and brain stem.
Nowadays Chiari malformations constitute a spectrum of pathologies that can involve both adults and children and adolescents.
According to the radiological and clinical picture, different types of Chiari malformations are distinguished:
- Chiari type 1: it is the most common variant, characterized by the descent of the cerebellar tonsils through the foramen magnum of the base of the skull – One consideration: there is no universally accepted definition, since there is not always a direct connection between symptoms and the magnetic resonance. This can arouse the patient, who apparently receives non-unique diagnoses from various specialists.
- Chiari types 2, 3, 4: they are congenital, characterized by evident malformations of the cerebellum, skull base, brainstem and spinal cord.
- Chiari type 0 and 0.5: on the magnetic resonance there is no clear evidence of cerebellar tonsils descent into the foramen magnum, but the symptoms are those typical of Chiari type I malformation.
- Chiari type 1.5: with intermediate characteristics between Chiari type 1 and type 2.
What are the causes of Chiari Malformation type 1?
Chiari malformation type 1 can have a genetic basis, or be secondary to diseases of the base of the skull (craniosynostosis, platybasia, metabolic bone disorders).
It can also be caused by increased pressure in the brain due to hydrocephalus or a brain tumor. It can also occur in patients with lumbo-peritoneal shunts.
There is also a condition called “Tethered cord” in which the final part of the spinal cord is anchored at the lower back, causing traction on the spinal cord and of the trunk of the brain connected to it with consequent descent of the cerebellar tonsils.
How many are affected?
Chiari malformation type 1 is the most frequent with an incidence of about 1 newborn in 1000. This is a low estimate, since in many cases the clinical manifestation occurs in adolescence or adulthood. MRI studies suggest that about 1% of the pediatric population may be affected.
Pathophysiology of Chiari malformation type 1
The classic description foresees a descent of the cerebellar tonsils inside the foramen magnum of at least 5 mm. However, there are children and adults whose symptoms are manifested by a descent of the cerebellar tonsils of only 3 mm. In Chiari type 1 there is no association with spina bifida (Chiari type 2).
In Chiari malformation type 1 the pathophysiology is to be found in the direct compression of the nervous structures and in the obstruction to the outflow of liquor at the level of the foramen magnum occupied by the cerebellar tonsils.
Obstruction to the flow of CSF can lead to the formation of cavities and cysts filled with cerebrospinal fluid within the spinal cord.
Chiari malformation type 1 can be associated with syringomyelia in 20-85% of cases depending on the case series, and involves the cervical and thoracic spinal cord. The development of syringomyelia is directly dependent on the impaired cerebrospinal fluid flow.
In 10% of patients with Chiari malformation hydrocephalus can occur, which is the accumulation of excess cerebrospinal fluid within the ventricular cavities.
In some cases there are associated alterations of the skeletal system and of the skull base (platybasia, basilar invagination, Sprengel deformity, atlanto-occipital assimilation, Klippel-Feil, Gorham-Stout, Crouzon, Pfeiffer).
What are the symptoms of Chiari malformation type 1?
Chiari malformation patients may be asymptomatic or have the following symptoms.
The most common, in both children and adults, is headache in the occipital and cervical region (“neck pain”). Headache is often exacerbated by physical exertion or by the neurosurgeon’s Valsalva maneuver. The headache is due to intracranial hypertension..
Other associated symptoms may be due to direct compression of the brain stem: syncopal episodes.
How is Chiari malformation type 1 diagnosed?
Chiari type 1 malformation is diagnosed with magnetic resonance imaging of the brain, which must always be associated with that of the entire spine in which to perform a syringomyelia.
Patients with a dubious picture may benefit from cine-MRI for diagnostic framing; cine-MRI is a specific MRI sequence that can provide information on the pathological flow of cerebrospinal fluid at the foramen magnum.
The findings of magnetic resonance, and possibly of dynamic X-ray and CT are correlated by the neurosurgeon with patient’s symptoms in order to have a correct clinical diagnosis and treatment.
What is the treatment of Chiari Malformation type 1?
Treatment is surgical in symptomatic patients with an MRI picture showing the descent of the cerebellar tonsils or a cine-MRI showing a reduction / obstruction of CSF flow at the level of the foramen magnum and / or associated syringomyelia.
The goal of surgical treatment is to restore normal cerebrospinal fluid flow at the foramen magnum of the base of the skull. This also enlarges the foramen magnum with a meningeal dural plastic. A small skin incision is performed at the base of the neck and the surgery is perfomed under the microscope.
The prognosis is good with more than 85% of patient’s improvement. The patient returns to work normally 4-6 weeks after surgery. It is important to increase the daily activity and avoid weight lifting in the first phase after surgery.
Bibliography:
Frič R, Eide PK. Chiari type 1-a malformation or a syndrome? A critical review. Acta Neurochir (Wien). 2020 Jul;162(7):1513-1525. doi: 10.1007/s00701-019-04100-2. Epub 2019 Oct 28. PMID: 31656982.