Pressure in the Back of the Head: Causes, Symptoms and Treatment of Chiari Malformation

The Arnold-Chiari malformation, commonly referred to simply as Chiari malformation, is a congenital defect of the central nervous system. In this condition, parts of the cerebellum and sometimes the brainstem are pushed through the large opening at the base of the skull, the foramen magnum, into the spinal canal. This malformation usually occurs because the posterior part of the skull, called the posterior fossa, is too small, causing the normal brain structures to be pushed downward.

Chiari malformations vary widely in severity, ranging from almost unnoticed incidental findings to severe defects that become apparent before or shortly after birth.

Chiari Malformation Type I (CM I) 

Type I is the most common form, occurring in about 0.5 - 3.5% of the population. Women are slightly more affected than men (ratio 1.3:1). In this type, one or both cerebellar tonsils descend more than 5 millimeters through the foramen magnum into the spinal canal. A syringomyelia, a fluid-filled cavity within the spinal cord, often occurs as well.

Many individuals have no symptoms and the malformation is often discovered incidentally on an MRI. Only about 0.01- 0.04% of people with radiological findings develop symptoms. Typical complaints include headaches in the back of the head or neck (around 80% of cases), often worsening with increased intracranial pressure, such as when coughing or straining (Valsalva maneuver). Other common symptoms include visual disturbances, balance problems, dizziness, hearing issues and general fatigue. Rarely, patients report pain or weakness in individual limbs, such as one-sided shoulder pain with muscle weakness. Typical neurological signs affect the spinal cord: patients often show a “dissociated sensory loss,” meaning reduced pain and temperature sensation while deep sensation remains intact, often accompanied by motor weakness. Additionally, coordination problems (ataxia), inaccurate movements (dysmetria), or involuntary eye movements (nystagmus) may occur. Mild cranial nerve deficits (IX–XII) can also be present, caused by pressure on the cerebellum or brainstem or by fluid-filled cavities in the spinal cord (syringomyelia).

Sleep apnea may occur because the throat muscles are weakened by compression of the brainstem, upper spinal cord, or lower cranial nerves. It is also possible for a Chiari malformation to be visible on MRI without causing any symptoms. This is referred to as a “silent” Chiari. Therefore, nonspecific complaints such as fatigue or migraines are not necessarily caused by the malformation.

In symptomatic CM I, surgery is clearly indicated. The goal of surgery is to decompress the posterior fossa so that cerebrospinal fluid can flow normally again.

Surgery usually involves:

• Suboccipital craniectomy: removal of a portion of the skull at the foramen magnum

• Laminectomy: removal of the posterior arch of the first cervical vertebra (C1), sometimes including C2 or C3

• If necessary: expansion of the dura or partial removal of the cerebellar tonsils

Treatment is generally successful, especially if the surgery is performed early. In long-standing cases with muscle weakness or gait disturbances, complete recovery may not always be possible.

Chiari Malformation Type II (CM II) 

Type II is a more severe form and is less common, occurring in approximately 0.44 per 1000 births, with no gender difference. Folate supplementation during pregnancy can reduce the incidence of type II. In CM II, not only the cerebellar tonsils but also the brainstem are displaced downward, and the cerebellum is often underdeveloped. CM II almost always occurs together with an open spine (myelomeningocele).

Symptoms usually appear in childhood and include swallowing difficulties, high-pitched breathing noises, aspiration of fluids or saliva, and paralysis of the arms or legs (sometimes tetraplegia). Treatment also involves decompression of the posterior fossa. If hydrocephalus is present, a VP shunt is often placed first to drain excess cerebrospinal fluid from the brain to the abdominal cavity. As with all surgeries, there are risks, including insufficient pressure relief, cerebrospinal fluid leakage, infections, or wound-healing problems. Smaller procedures are less invasive but may be insufficient, while larger procedures reduce the chance of repeat surgeries but carry a higher risk of complications.

Chiari Malformation Type III (CM III)

Type III is very rare, making up only 1- 4.5% of all Chiari malformations. In this type, almost the entire hindbrain, sometimes including the brainstem, herniates into a meningoencephalocele, an outpouching in the neck region. This form is usually recognized before or shortly after birth.

Chiari Malformation Type IV (CM IV)

Type IV is not a herniation but a severe underdevelopment of the cerebellum. The cerebellum is greatly reduced or barely formed, leading to severe neurological impairments.

Chiari malformations represent a spectrum of defects with widely varying severity. Type I is the most common and can often be discovered incidentally, while types II, III and IV usually appear in childhood and often cause serious symptoms. When symptoms are present, surgery is the main treatment to relieve pressure and restore normal cerebrospinal fluid flow.

Sources: 

Abu-Isa, J., & Lutz, K. (2026). Chiari-Malformation. Source

Hidalgo, J. A., Tork, C. A., & Varacallo, M. A. (2025). Arnold-Chiari Malformation(Archived). In StatPearls. StatPearls Publishing. Source

Khamouye, A. E., Jehri, A., Echnin, J., Chellaoui, A., Ibahiouin, K., Hilmani, S., Naja, A., & Lakhdar, A. (2024). Chiari Malformation: 15 Cases and Review of the Literature. European Journal of Medical and Health Sciences, 6(4), 103–107. Source

Rodríguez-Blanque, R., Almazán-Soto, C., Piqueras-Sola, B., Sánchez-García, J. C., Reinoso-Cobo, A., Menor-Rodríguez, M. J., & Cortés-Martín, J. (2023). Chiari Syndrome: Advances in Epidemiology and Pathogenesis: A Systematic Review. Journal of Clinical Medicine, 12(20), 6694. Source

Zhao, J.-L., Li, M.-H., Wang, C.-L., & Meng, W. (2016). A Systematic Review of Chiari I Malformation: Techniques and Outcomes. World Neurosurgery, 88, 7–14. Source