Foramen magnum decompression surgery for Chiari malformation

Written by: Mr Sanj Bassi
Published: | Updated: 31/05/2023
Edited by: Lisa Heffernan

At the base of your skull, there’s an oval-shaped opening where the spinal cord is linked to the brain. This opening is known as the foramen magnum. A foramen magnum decompression is a procedure used to treat a condition called Chiari malformation, where the lower part of the brain at the skull base (cerebellum) extends into the spinal cord. Mr Sanj Bassi talks more about this procedure.

A surgeon performing an operation

What causes Chiari malformation?

Chiari 1 malformation occurs when the cerebellum (lower part of the brain) is pushed into the spinal canal. While often asymptomatic, this can cause symptoms like headaches, balance problems and vision problems.


Furthermore, this condition can stop the flow of cerebrospinal fluid (CSF) to the brain and central spinal canal. The purpose of CSF is to act as a shock absorber and to create a cushion between the brain and the skull. This lack of CSF flow causes fluid to build up, which in turn causes an obstruction that we call a syringomyelia. This can lead to discomfort, stiffness and other symptoms.


A Chiari malformation can be caused as a baby while developing in the womb. It can also be associated with the skull of the baby being too small for the brain.


Symptoms of Chiari malformation

Many people with Chiari malformation don’t experience any symptoms and don’t require treatment, but the condition can cause the following:

  • Blurred vision
  • Headaches, normally at the back of the head
  • Neck pain
  • Muscle weakness
  • Difficulty walking
  • Problems with balance and coordination


How can Chiari malformation be diagnosed?

Chiari malformation can be diagnosed using MRI scans.


What is foramen magnum decompression

There is more than one type of Chiari malformation, but foramen magnum decompression is used to treat Chiari 1 malformation. Foramen magnum decompression involves removing a small part of the base of the skull and sometimes parts of the top of the spine to take the pressure off the cerebellum.


  1. Before the surgery, your surgeon will take a look at your medical history and walk you through the surgery and the associated risks.
  2. During the surgery, the patient will be given a general anaesthetic to be fully asleep for the procedure. A small part of the base of the skull and the top of the spine (in some cases) are then removed through the incision. The surgery usually lasts about three hours in total.
  3. After the surgery, pain is especially common around the wound, but with time patients may experience a reduction in symptoms such as headaches. Every surgery has its risks and your consultant should discuss these with you fully beforehand.


Would you like more information about foramen magnum decompression? If so, please contact Mr Sanj Bassi of the London Neurosurgery Partnership.

By Mr Sanj Bassi

Mr Sanj Bassi is a London-based neurosurgeon who has an interest in both adult and paediatric neurosurgery. He practises at various clinics in the capital including the Bupa Cromwell hospital and the London Neurosurgery Partnership.

Mr Sanj Bassi treats a wide range of conditions including brain tumours, brain haemorrhages, hydrocephalus, chiari malformations and facial pain, as well as spinal problems including sciatica, back pain, spinal claudication and spinal stenosis. Outside of his clinic he is dedicated to research and has been widely published in leading peer-reviewed journals and forms an integral part of various professional bodies such as the Royal College of Surgeons.

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