Chiari malformations are a group of complex brain abnormalities.
Chiari malformations (CM) are a group of congenital abnormalities that affect the hindbrain. In the CMs, the part of the cerebellum is located below the foramen magnum in the brain, and may develop when the bony space is smaller than the normal, causing the brainstem to be pushed downward to the foramen magnum. The pressure that ensues due to this structural deformity on the cerebellum and brainstem affects the functions, blocking the flow of cerebrospinal fluid (CSF).
The causes of Chiari malformations are categorized into primary and secondary. Primary CM can occur with the structural defects in the brain or the spinal cord during the fetal development either due to lack of the proper nutrient in the maternal diet (during development) or genetic mutations. Hence, this is called primary or congenital CM. Primary CM is more common than the secondary CM. When the CM occurs later in life, it is called secondary or acquired CM. This can happen if there is an excessive drainage of the spinal fluid from the lumbar or thoracic areas of the spine which can occur either because of injury or infection.
Depending on the severity of the CM and the parts of the brain affected, Chiari malformation can be divided into type I, type II, type III and type IV.
Primary type I CM is also attributed to the linkages to chromosomes 9 and 15. It is suggested that the disorder occurs in the para-axial mesoderm, resulting in the formation of the smaller posterior fossa. There are other theories regarding the cause of Arnold Chiari Malformation, one of the interesting one is called “CSF loss theory”. According to this hypothesis, there is an escape of the fluid in the myelomeningocele which results in inadequate stimuli of the mesenchymal condensation at the base of the skull.
Earlier it was believed that CM occurred one in every 1,000 births. With the development of the diagnostic imaging in the past few decades, the occurrence is found to be more common. Today CM may reach up to 5 cases per 1000 births with female predominance over male subjects . Since, there are cases where the child born with ACM does not show symptoms until they reach adolescence, the exact epidemiological profile of the disease is still not known. The disorder is more common among women than men. Type II malformations are more prevalent among the different types of CM.
The pathophysiological complications that lead to the consequences of this malformation can be due to the following:
Type I CM is generally asymptomatic. In complicated cases, surgery can help to reduce the symptoms associated with the malformation.
There are cases documented where CM becomes progressive, leading to serious complications. The complications associated with the disorder are as follows:
Patients with type I CM do not show any symptoms. Adolescents and adults may develop symptoms of CM later in their life. Patients with CM often complain of neck pain or numbness. There are abnormal feelings in the extremities, muscle weakness and balance troubles. There are altered vision profiles, buzzing in the ears, vomiting, nausea, trouble in swallowing food, and hearing loss. Worsening of the conditions of this malformation leads to insomnia, sleep apnea, persistent headache and depression . Patients may have difficulty in hand coordination and the fine motor skills are also affected.
Children and infants may show symptoms such as difficulty in swallowing and excessive drooling, weakness in arms, breathing problems and developmental delays. Parents are therefore advised to document the symptoms, and convey them to the pediatrician for early diagnosis.
Adult patients with type 1 CM, may initially present with benign paroxysmal vertigo and could be confused as a trivial benign positional vertigo . Patients in the mid age may present with shortness of breath as an inaugural sign due to alveolar hypoventilation .
Though there are no specific symptoms associated with this malformation, it is often discovered only when complications arise.
If this disease does not show any symptoms and interfere with the daily activities, treatment is not necessary. Symptomatic treatment is quite common in the absence of the correct diagnosis, for example, if pain persists; analgesics are advised to manage the symptoms. However, if there are multiple symptoms that affect the patient on the day-to-day basis, surgery is the only treatment modality that can cease the progression of the disease. The goal of surgery in Chiari malformation is two-fold:
Some of the common surgical procedures performed in patients with CM are as follows:
Surgery of the malformation has shown to reduce the symptoms significantly, prolonging the periods of remission.
There are no preventive measures to combat Arnold Chiari malformation; genetic counseling can prove beneficial to the parents of the child to determine the risk in future children.
Patients with Arnold Chiari malformation (ACM) generally do not show any symptoms, therefor the condition is often diagnosed during the course of diagnosis for another disorder. However, there may be symptoms such as headache, dizziness, vomiting and nausea. Medical and surgical options are available for the treatment of this disorder.