Baker’s Cyst on MRI: What a Knee Examination Can Show

A Baker’s cyst is a fluid-filled sac that forms behind the knee. It is also known as a popliteal cyst. It may cause no symptoms and be discovered incidentally during an examination. However, a large cyst can sometimes cause pain, pressure, swelling, and restricted movement of the knee.

Magnetic resonance imaging makes it possible to determine the location and size of a Baker’s cyst and assess its contents and the surrounding tissues. At the same time, a knee MRI can help identify a possible cause of fluid accumulation, such as a meniscus injury, cartilage damage, osteoarthritis, inflammation of the synovial lining, or a ligament injury.

In brief: on MRI, a Baker’s cyst appears as a fluid-filled structure at the back of the knee. MRI shows not only the cyst itself but also abnormalities within the joint that may have contributed to its development.

What Is a Baker’s Cyst?

The knee joint contains synovial fluid, which reduces friction between the joint surfaces and allows the knee to move smoothly. The amount of this fluid may increase because of injury, inflammation, or degenerative changes.

As pressure inside the joint rises, some of the fluid may move into a bursa located between the semimembranosus tendon and the medial head of the gastrocnemius muscle. The bursa expands, forming a Baker’s cyst at the back of the knee.

A Baker’s cyst is not a malignant tumour. However, any new or unexplained lump behind the knee should be examined by a doctor because similar symptoms can occur with other conditions.

What Causes a Baker’s Cyst?

In adults, a Baker’s cyst is most commonly associated with another disorder or injury of the knee joint that causes excessive production of synovial fluid.

Possible causes include:

• osteoarthritis of the knee;
• rheumatoid arthritis or another inflammatory type of arthritis;
• medial or lateral meniscus injury;
• damage to the articular cartilage;
• ligament sprain or tear;
• synovitis — inflammation of the synovial lining of the joint;
• gout and other joint disorders;
• knee trauma;
• excessive or repetitive physical strain.

In children, a Baker’s cyst may develop without significant abnormalities inside the joint and may sometimes become smaller without treatment. The cause of the cyst and the need for treatment should be assessed by a doctor in each individual case.

What Symptoms Can a Baker’s Cyst Cause?

A small cyst may not cause any symptoms. As it becomes larger, the following symptoms may occur:

• a soft or firm lump behind the knee;
• a feeling of pressure or fullness in the popliteal area;
• pain at the back of the knee;
• stiffness after physical activity;
• difficulty bending or fully straightening the leg;
• swelling of the knee joint;
• discomfort while walking, squatting, or climbing stairs;
• clicking, locking, or instability of the knee when there is an associated meniscus injury or damage to other structures.

Symptoms may become worse after prolonged walking, running, squatting, or other activities that place stress on the knee joint.

What Does MRI Show in a Baker’s Cyst?

During an MRI examination, the radiologist assesses the cyst and all the main structures of the knee joint. The images can show:

• the exact location of the cyst;
• its length, width, and volume;
• whether it communicates with the knee joint;
• the characteristics of its fluid content;
• the presence of septa or heterogeneous material;
• signs of inflammation in the surrounding tissues;
• compression of nearby structures by a large cyst;
• signs of fluid leakage or cyst rupture;
• the amount of fluid within the knee joint;
• the condition of the menisci, ligaments, cartilage, tendons, and bones.

An important advantage of MRI is that it can identify not only the cyst but also its possible underlying cause. For example, the report may describe a meniscus tear, osteoarthritis, synovitis, cartilage damage, or a ligament injury.

What Does a Baker’s Cyst Look Like on MRI?

A typical Baker’s cyst appears as a structure with fluid signal intensity in the posteromedial part of the knee. It is located between the semimembranosus tendon and the medial head of the gastrocnemius muscle.

The cyst may have a simple single-chamber structure or a more complex multiloculated appearance. It may contain septa, thick fluid, or small internal components. If the structure has an atypical appearance, the radiologist will assess it particularly carefully and may recommend further examination.

When Is MRI Recommended for a Suspected Baker’s Cyst?

A knee MRI may be recommended when:

• a lump of uncertain origin has appeared behind the knee;
• pain and swelling persist for a prolonged period;
• restricted movement or instability develops after a knee injury;
• a meniscus, cartilage, or ligament injury is suspected;
• ultrasound has identified a cyst, but the internal structures of the joint also need to be assessed;
• symptoms return after treatment or aspiration;
• the size, structure, or possible complications of the cyst need to be clarified;
• surgery or another procedure is being planned;
• the lump has an atypical appearance and requires differential diagnosis.

MRI may also detect a small Baker’s cyst incidentally when the knee is examined for another reason. If the cyst does not cause symptoms, specific treatment may not be required.

MRI or Ultrasound for a Baker’s Cyst

Method	What it can assess
Ultrasound	Helps determine whether the lump is filled with fluid and assess its size and the surrounding superficial tissues. It can also be used to examine the veins when thrombosis is suspected.
Knee MRI	Shows the cyst and provides a detailed assessment of the menisci, cartilage, ligaments, tendons, bone marrow, synovial lining, and other structures of the knee.
X-ray	Does not show the cyst itself but may reveal osteoarthritis, narrowing of the joint space, bone deformities, or the effects of an injury.

Ultrasound may be sufficient for the initial confirmation of a simple cyst. MRI is appropriate when the underlying cause needs to be identified, associated injuries must be excluded, or a complex clinical situation requires further assessment.

Is Contrast Needed for MRI of a Baker’s Cyst?

MRI is usually performed without intravenous contrast to identify a typical Baker’s cyst and assess the structures of the knee joint.

A doctor may recommend contrast in atypical cases, for example when:

• the lesion has a heterogeneous or unusual structure;
• the cyst needs to be distinguished from another mass;
• there are signs of a significant inflammatory or infectious process;
• postoperative changes require more detailed assessment;
• the result of a previous examination was inconclusive.

The need for contrast enhancement is determined by the doctor based on the symptoms, medical referral, and results of previous examinations.

What Happens When a Baker’s Cyst Ruptures?

Sometimes the wall of the cyst ruptures and its fluid spreads between the tissues of the lower leg. This may cause:

• sudden pain behind the knee or in the calf;
• swelling of the lower leg;
• a feeling of warmth;
• redness or discolouration of the skin;
• stiffness and pain while walking;
• swelling that gradually spreads down the leg.

The symptoms of a ruptured Baker’s cyst may resemble those of deep vein thrombosis. It is not possible to distinguish between these conditions based on symptoms alone.

Seek urgent medical attention if you develop sudden swelling on one side, pain, redness, or warmth in the calf. Emergency care is required if these symptoms are accompanied by shortness of breath, chest pain, dizziness, or coughing up blood.

Does a Baker’s Cyst Need Treatment?

The treatment approach depends on the size of the cyst, the severity of the symptoms, and the underlying cause. A cyst that does not cause symptoms may only require observation.

Treatment may include:

• temporarily reducing the load on the knee;
• rehabilitation and therapeutic exercises;
• medication for inflammation prescribed by a doctor;
• treatment of osteoarthritis, arthritis, or another underlying condition;
• aspiration and removal of fluid when clinically indicated;
• intra-articular medication prescribed by a doctor;
• arthroscopic treatment of a damaged meniscus or another intra-articular abnormality;
• surgery in rare and complex cases.

Simply removing or draining the cyst without treating the underlying knee condition does not always eliminate the cause of fluid accumulation. As a result, the cyst may return.

How to Prepare for a Knee MRI

Special preparation is usually not required for a knee MRI without contrast. Before the examination, patients should:

• remove jewellery, watches, and other metal objects;
• inform the staff about implants, prostheses, metal devices, or electronic implants;
• bring a medical referral, if available;
• bring the results of previous MRI, ultrasound, or X-ray examinations;
• report any previous knee surgery;
• inform the staff in advance about pregnancy or claustrophobia.

It is important to remain still during the scan because movement can reduce image quality. The knee is positioned in a specialised coil, and a series of images is then obtained in different planes.

What Should You Do After Receiving the MRI Results?

The MRI report should be reviewed by an orthopaedic trauma specialist, rheumatologist, or the doctor who referred you for the examination. The specialist will compare the imaging findings with your symptoms, physical examination, and other test results.

Further treatment depends on more than the size of the cyst. The condition of the menisci, cartilage, and ligaments, the presence of osteoarthritis or inflammation, the severity of pain, and restricted mobility are also important.

Knee MRI in Kyiv near Shuliavska

At HBMedical Medical Centre, patients can undergo a knee MRI in Kyiv. The examination can assess a Baker’s cyst, menisci, ligaments, cartilage, tendons, bones, and other possible causes of knee pain and swelling.

The examination is performed using a 1.5 Tesla Siemens Magnetom Sempra MRI scanner. The medical centre is located at 3 Oleksandra Dovzhenka Street, Kyiv, near Shuliavska metro station.

More information about the examination, preparation, and booking is available on the Knee MRI in Kyiv page.

Book a knee MRI at HBMedical to assess a Baker’s cyst and examine the internal structures of the knee joint.

Frequently Asked Questions

Can a Baker’s cyst be seen on MRI?

Yes. MRI shows the location, size, and structure of the cyst, its connection with the knee joint, and any possible spread of fluid. It can also detect a meniscus injury, osteoarthritis, synovitis, or another possible cause of the cyst.

Is a Baker’s cyst a tumour?

No. A typical Baker’s cyst is a fluid-filled sac rather than a malignant tumour. However, any unexplained lump behind the knee should be examined by a doctor.

Which is better for diagnosing a Baker’s cyst: MRI or ultrasound?

Ultrasound clearly shows a fluid-filled structure and may be sufficient for the initial diagnosis. MRI provides more information about the menisci, cartilage, ligaments, and other internal structures of the knee joint.

Can a Baker’s cyst disappear on its own?

A small cyst may sometimes become smaller or stop causing symptoms, especially after the underlying knee condition has been treated. The decision between observation and treatment should be made by a doctor.

Can you exercise with a Baker’s cyst?

The appropriate level of physical activity depends on the symptoms and the cause of the cyst. Exercise should be stopped if pain, swelling, or restricted movement occurs. Returning to sport is recommended after examination and individual medical advice.

Is contrast required for MRI of a Baker’s cyst?

Contrast is usually not required for a typical cyst and a comprehensive assessment of the knee joint. It may be recommended if the lesion has an atypical structure or another pathological process needs to be excluded.

Which doctor should you see for a Baker’s cyst?

An orthopaedic trauma specialist is usually the first doctor to consult. If the cyst is associated with an inflammatory joint disorder, consultation with a rheumatologist may also be required.

This material is provided for informational purposes and does not replace a medical examination or consultation.