Home > Procedures > Brain Surgery > Foramen Magnum Decompression

Foramen magnum decompression is a brain surgery procedure to treat Chiari malformation. Learn more about this condition and procedure below.

Chiari malformation is a congenital condition where the brain tissue extends into the spinal canal. It may occur if part of a person’s skull is either abnormally small or misshapen. This can cause it to press onto the brain and force it downwards. 

In some people, Chiari malformation is a progressive disorder, leading to serious complications. Other patients may not experience any associated symptoms. In which case, no intervention is required. 

Some of the complications associated with Chiari malformation are:


Hydrocephalus is the accumulation of excess fluid within the brain.

Spina Bifida

Spina bifida occurs if the spinal cord or its covering is not completely developed. If the spinal cord is uncovered, it can lead to serious conditions for the patient, such as paralysis.


Some people with Chiari malformation can develop syringomyelia. This is where a cavity or cyst (syrinx) forms within the spinal column.

Tethered cord syndrome

In this condition, the spinal cord attaches to the spine and causes the spinal cord to stretch. It can lead to serious nerve and muscle damage in the lower body.

What is the goal of foramen magnum decompression surgery?

Foramen magnum decompression surgery helps control the symptomatic progression of the Chiari condition. It helps to relieve compression, and restore the normal flow of cerebrospinal fluid (CSF). 

The main aim of this surgery is to stop on-going deterioration. Around 80% of patients experienced significant improvements in their neck pain or headaches post-surgery.

The surgery is performed to remove the bone situated at the back of the skull. Doing so widens the foramen magnum which creates more space for the brain. 

What are the suitable patient types for Foramen magnum decompression surgery?

The choice of treatment for Chiari malformation varies. It is dependent on the form of malformation, its severity, and associated symptoms. Patients with asymptomatic Chiari malformations do not need any treatment. Patients whose Chiari malformations lead to headaches are prescribed analgesics for pain control. 

However, surgery is recommended for patients whose headaches do not subside despite using analgesics. Surgery is also considered for patients with any significant symptoms or who, upon examination show the development of abnormal neurological findings. 

Overall, a patient may be a suitable candidate for surgery if they have an abnormal collection of cerebrospinal fluid (CSF) in their spinal cord. Or if the Chiari malformation is obstructing the flow of CSF causing severe or worsening symptoms.

Preparation for Foramen magnum decompression surgery

The neurosurgeon will explain the surgical procedure in detail to the patient. They will also discuss its risks and benefits, as well as answer any patient queries. 

The doctors will discuss your medical history. This includes things such as any allergies, vitamins, medicines, bleeding history, reactions to anaesthesia, prior surgeries. 

Several days before the surgery, the team of doctors will conduct pre-surgical tests. This includes blood tests and electrocardiograms.

Doctors will advise the patient to stop taking any specific medication. This can include anti-inflammatory medicines and blood thinners.

What are the side effects of this surgery?

As with any type of surgery, this surgery also has its risks. Specific complications associated with Foramen Magnum Decompression include:

  • Variable risk of head and neck pain
  • Risk of CSF leakage around the brain. It may require surgical repair. The use of biologic glue and new closure techniques reduce the risk of CSF leakage.
  • Risk of pseudomeningocele. This is an abnormal collection of CSF under neck tissues.
  • Nerve or brain damage causing permanent disability.

What happens during the Foramen magnum decompression surgery?

The surgery takes about 2 to 3 hours. The recovery time in hospitals is usually 2 to 4 days, depending on the patient.

Step 1: Preparing the patient

The patient lies down on the operating table, where he or she is given anaesthesia. Once the effect of the anaesthesia has started, the patient’s head is placed in a skull fixation device attached to the table. This helps hold the head in position during the surgical procedure. The doctor shaves the scalp (around an inch-wide strip of hair) at the planned incision site and preps the skin with antiseptic.

Step 2: Making a skin incision

Surgeons make the incision strategically. This is so they can see the skull as well as the top of the spine after lifting the skin and muscles and folding them back. The incision is usually about 3 inches long.

Step 3: Removing the bone

The surgeon removes a small section of the skull at the back of the head. This is known as a suboccipital craniectomy. In some cases, doctors may remove the bony arch of the C1 vertebra, known as a laminectomy. This step now exposes the protective covering of our brain and spinal cord called the dura. Bone removal helps to relieve compression of the tonsils.

Step 4: Opening the dura

Surgeons open the dura to see the tonsils and cisterna magna. Some surgeons may perform a Doppler ultrasound study during the surgery to determine if it is even required to open the dura. As in some cases, the removal of the bone alone may help restore the normal CSF flow.

Step 5 (optional step) Reducing the tonsils

The stretched and damaged cerebellar tonsils can be shrunk using electrocautery. This step is dependent on the size of the herniation. Shrinkage of the tonsils ensures the flow of CSF out of the 4th ventricle is not blocked.

Step 6: Attaching the dura patch

Synthetic material or a patient’s deep scalp tissue from just outside the skull, also known as pericranium, is sutured into place. This helps enlarge the dura and space around the tonsils. A dural sealant is used to cover the suture line to prevent any CSF leak. 

Step 7: Closing the incision

The strong neck muscles are sutured together with the skin and a dressing is placed over the site of the incision.

What happens after the surgery?

Monitoring and discharge from hospital

Doctors will closely monitor the patient’s vitals post-surgery. They  will normally be discharged from the hospital in 1 or 2 days after surgery, once they have stabilised. The patient will need support at home for the next 24 to 48 hours.

It’s important to follow the doctor’s home care instructions for about 2 weeks post-surgery or until the next follow-up appointment. 


There will be some initial restrictions in physical activities. All strenuous activities including housework and sex would be restricted too. 

The patient should expect restrictions in smoking as it may delay healing.

Similarly the patient should expect restrictions in drinking alcohol. This may increase the risk of bleeding and can interact negatively with the pain medicine.

Until the surgeon gives a go-ahead, the patient is expected to not drive, return to work, or fly in air travel.

Incision Care

The doctor provide advice on how to care for the incision area. He or she will also recommend a suitable shampoo and soap as well as the frequency of washing.

Do not scrub your incision. Pat it dry gently.

Call your doctor if you observe any swelling around the incision or if you notice any drainage.

Avoid any hair colour for 6 weeks post-surgery. 


The doctor may prescribe pain relief medication for headaches which are common post-surgery.

The patient should take all pain medicines as advised by the surgeon. They can reduce the amount and frequency of administration as and when pain subsides. 

The doctors will also prescribe any medicines to manage the side effects of medications prescribed post-surgery. This can include such as laxatives and stool softeners.

Doctors may also prescribe anti-seizure medicines to manage any such side effects post-surgery.

It’s important to call your doctor if you experience any side effects such as drowsiness or balance problems. Do not take any medicines without your doctor’s approval.


Doctors recommend walking 5-10 minutes every 3-4 hours. Then gradually increase the walking time as you are able. 


There will be a follow-up with the doctor, ideally 10 to 14 days after surgery. At this appointment they will remove the sutures and assess recovery. It may take up to 4 to 6 weeks for actual recovery from the surgery.

Patients can discuss with their doctor when they can resume work. Usually, they may be able to return to work in 4 to 6 weeks post-surgery. 

What is the success rate of Foramen magnum decompression surgery?

Results of Foramen Magnum Decompression surgery depend on the severity of Chiari malformation. The extent of any previous brain or nerve injury before this treatment may also influence the results. Around 85 to 95% of patients experience major relief in their symptoms. Some patients may continue to experience residual symptoms caused by syringomyelia. Also, if any injury in the spinal cord has become permanent before the surgery is performed, the surgery won’t be able to reverse the damage.