eMedicine Specialties > Radiology > Musculoskeletal

Baker Cyst

Liem T Bui-Mansfield, MD, Associate Professor, Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland
Rush A Youngberg, MD, Chief of Musculoskeletal Radiology, Department of Radiology, Madigan Army Medical Center

Updated: Sep 18, 2009

Introduction

Background

The most common mass in the popliteal fossa, Baker cyst, also termed popliteal cyst, results from fluid distention of the gastrocnemio-semimembranosus bursa. The eponym honors the work of Dr William Morrant Baker. In 1877, Baker described 8 cases of periarticular cysts caused by synovial fluid that had escaped from the knee joint and formed a new sac outside the joint.^{[1 ]}The common underlying conditions were osteoarthritis and Charcot joint.^{[2 ]}

Axial, T2-weighted magnetic resonance image of the knee shows effusion, synovial proliferation (white arrowhead), and a Baker cyst that contains debris (black arrowhead).

Contrast-enhanced, axial computed tomography (CT) scan of the knee shows multiple gaslike lucencies within a Baker cyst and synovial enhancement.

Anteroposterior radiograph of the knee shows uniform joint-space loss in the medial and lateral knee compartments without osteophytosis. A Baker cyst is seen medially (arrowhead).

Pathophysiology

A Baker cyst may serve as a protective mechanism for the knee. Intrinsic intra-articular disorders cause joint effusion. The knee effusion is displaced into the Baker cyst, thus reducing potentially destructive pressure in the joint space. Jayson and Dixon postulated that joint effusion and fibrin are pumped from the knee joint into the Baker cyst but not in the reverse direction, because of a valvelike communication, such as a ball valve or a Bunsen valve (see Image below and Image 1 in Multimedia).^{[5 ]}

Valvular mechanism of Baker cyst. Effusion and fibrin are pumped (large arrows) into the Baker cyst (long, thin arrows). In the Bunsen-valve mechanism, the enlarging Baker cyst exerts mass effect (feathered arrow) on the slitlike communication between the joint and the cyst, trapping effusion. In the ball-valve mechanism, fibrin serves as a 1-way valve that prevents the effusion's return to the knee joint. Trapped effusion is reabsorbed through the semipermeable membrane (short, thin arrows), leaving behind concentrations of fibrin. (MFC: medial femoral condyle; MTP: medial tibial plateau; G: medial head of gastrocnemius muscle; SM: semimembranosus muscle)

• A primary, or idiopathic, cyst has a valvular connection with the joint cavity. Membranes, synovial bands, and folds were seen in all valvular cases in Rauschning and Lindgren's study. Scarring and irritation may create these folds in primary cysts. Alternatively, the synovial bands may be remnants of connective tissue interposed between the joint and bursal cavity. Idiopathic cysts usually are seen in young patients without symptoms. Cyst contents usually are viscous.
• A secondary, or symptomatic, cyst communicates freely with the knee joint and contains synovial fluid of normal viscosity. Secondary cysts reveal underlying articular disorders, which was demonstrated in 14 of 41 patients (34%) with Baker cysts in Rauschning and Lindgren's study. Associated articular disorders in the study included osteoarthritis, rheumatoid arthritis (RA), psoriatic arthritis, nonspecific synovitis, meniscal tears, and chondromalacia patellae.

Frequency

United States

The prevalence of Baker cysts depends on patient population and imaging modality, as shown in Tables 1 and 2 (see below).

Table 1. Prevalence of Baker Cysts Based on Diagnostic Modalities

Table 2. Prevalence of Baker Cysts Based on Patient Populations

Mortality/Morbidity

Refer to Special Concerns for a detailed discussion.

Race

No racial predilection exists.

Sex

No sex predilection exists.

Anatomy

Refer to Pathophysiology for a detailed discussion.

Presentation

Table 3 lists the most common symptoms in patients with a Baker cyst, as found in a study of 38 patients by Bryan and colleagues.^{[7 ]}

Table 3.  Symptoms of Baker Cyst

In the study, a popliteal mass was the most common presenting complaint or symptom. A significant number of patients (13%) had pseudothrombophlebitis, a syndrome in which symptoms simulate those of deep venous thrombosis (DVT). Therefore, DVT should be excluded in patients with Baker cyst and leg swelling.

Medical conditions associated with Baker cysts, in descending order of frequency, are as follows:

• Arthritides
  • Osteoarthritis
  • RA
  • Juvenile RA
  • Gout
  • Reiter syndrome
  • Psoriasis
  • Systemic lupus erythematosus
• Internal derangement (meniscal tears, anterior cruciate ligament [ACL] tears, osteochondral fractures)
• Infection (septic arthritis, tuberculosis)
• Chronic dialysis
• Hemophilia
• Hypothyroidism
• Pigmented villonodular synovitis
• Sarcoidosis

Arthritis is the most common condition associated with Baker cysts, with osteoarthritis probably being the most frequent cause among the arthritides.^{[8 ]}Although the prevalence of Baker cysts in patients with inflammatory arthritis is higher than in patients with osteoarthritis, osteoarthritis is much more common than inflammatory arthritis. Using ultrasonography, Fam and colleagues found that 21 of 50 patients (42%) with osteoarthritis had Baker cysts.^{[9 ]}Bilateral cysts were seen in 8 patients (16%). The occurrence of Baker cysts relates directly to the presence of knee effusion and the severity of the osteoarthritis.

In 99 consecutive patients with RA, Andonopoulos and coauthors demonstrated Baker cysts on ultrasonograms of 47 patients (48%).^{[10 ]}Twenty of the 99 patients (20%) had bilateral cysts. Of 198 knees, 67 (34%) had Baker cysts, yet only 29 cysts (43%) were diagnosed clinically.

Baker cysts appear much less frequently in children than in adults. The prevalence of Baker cysts in asymptomatic children examined ultrasonographically was 2.4%. The prevalence of Baker cyst in children undergoing MRI examination of the knee was 6.3%. None of the children with Baker cyst demonstrated an associated ACL or meniscal tear. Four patients (8%) had osteochondritis dissecans (n = 2), septic arthritis (n = 1), or juvenile RA (n = 1). In most children with Baker cysts (82%), the cysts disappeared without intervention (84%) or caused no symptoms (16%). However, in children with arthritis, Baker cysts are common.

In a study of 44 children with knee arthritis, ultrasonography detected a Baker cyst in 27 children (61%), most of whom (80%) had juvenile RA.^{[11 ]}The remaining causes of arthritis in the study included spondyloarthropathy, psoriatic arthritis, septic arthritis, and systemic lupus erythematosus. Cysts were followed prospectively with serial ultrasonography for 18-24 months. Cysts resolved with the resolution of suprapatellar effusion. Reports of Baker cyst associated with gout, Reiter syndrome, psoriasis, and systemic lupus erythematosus exist. The common underlying pathology for these medical conditions is synovial proliferation with effusion.

Arthrography is more sensitive than ultrasonography in detecting Baker cysts. In 24 patients with a possible Baker cyst, arthrography of both knees was performed immediately after ultrasonography. The latter detected a cyst in 19 of the 48 knees (40%), while arthrography demonstrated a cyst in 22 knees (46%). The increased sensitivity of arthrography is probably the result of its ability to distend the bursa.

Guerra and colleagues found a 30% incidence of popliteal bursa in cadaveric anatomic dissection of older patients.^{[12 ]}Using diagnostic arthroscopy, Johnson and coauthors demonstrated a 37% incidence of popliteal bursa.^{[13 ]}The incidence of Baker cysts detected through MRI of the knee varies (5-18%) according to the patient population. Initially, Fielding and colleagues reported an association between Baker cyst and tear of the medial meniscus or complete tear of the ACL.^{[14 ]}Stone and colleagues demonstrated that 84% of Baker cysts detected on magnetic resonance images had meniscal tears.^{[15 ]}Most tears were observed in the posterior horn of the medial meniscus.

Subsequently, Miller and coauthors confirmed a significant association of Baker cyst with effusion, meniscal tears, and degenerative arthropathy.^{[16 ]}The probability of a Baker cyst in the presence of any 1 variable (ie, association) is P = 0.08-0.10, of any 2 variables is P = 0.19-0.21, and of all 3 variables is P = 0.38. However, no association was found between Baker cyst and ACL tear.

Sansone and colleagues reviewed the incidence of associated intra-articular disorders in a series of 1001 adult patients undergoing MRI of the knee.^{[17 ]}They found that the most common associated lesions were meniscal tears, chondral lesions, and ACL tears.

Treatment

The treatment of Baker cysts is conservative and includes the use of nonsteroidal anti-inflammatory agents, ice, and assisted weight bearing, in addition to the correction of underlying intra-articular disorders. Internal derangements of the knee can be treated with therapeutic arthroscopy.^{[18 ]}Total knee arthroplasty is reserved for severe osteoarthritis.^{[19,20 ]}

Radioactive synoviorthesis can be used to treat inflammatory arthritides and hemophilia. Prior to this treatment, arthrography should be performed to exclude a leaking Baker cyst (see Image below and Image 19 in Multimedia). A leaking Baker cyst would release radionuclide agent outside the knee joint, which is a contraindication to radioactive synoviorthesis.

Arthrography of the knee performed prior to radioactive synoviorthesis shows leakage of contrast (arrow) just superior to the sinus (arrowhead and "BB" marker).

Preferred Examination

Imaging evaluation of a Baker cyst begins with conventional radiography to detect a soft-tissue mass (see Image below and Image 2 in Multimedia), internal calcifications, displacement of an atherosclerotic popliteal artery, and the unusual case of adjacent bony involvement from a large and/or long-standing cyst.^{[8 ]}

Anteroposterior radiograph of the knee shows uniform joint-space loss in the medial and lateral knee compartments without osteophytosis. A Baker cyst is seen medially (arrowhead).

Transverse ultrasonographic image of the knee in a patient who had recent arthroscopy shows a complex, cystic mass (arrow) in the medial aspect of popliteal fossa. The mass communicates with the knee joint (arrowhead), which is consistent with a Baker cyst.

Longitudinal ultrasonographic image of a Baker cyst in a patient who underwent recent knee arthroscopy.

Color Doppler imaging can confirm the absence of vascular flow within the mass to exclude a popliteal artery aneurysm or cystic adventitial degeneration of a popliteal artery (see Images below and Image 5, Image 6 in Multimedia).^{[21 ]}Ultrasonography can concomitantly exclude a coexisting DVT created by subjacent mass effect. The weakness of ultrasonography is related to the difficulty in establishing a true connection to the joint space proper, which is essential for discriminating between a Baker cyst and other potentially harmful conditions in the differential diagnosis (see the discussion on magnetic resonance evaluation, below).

Transverse ultrasonographic image of the popliteal fossa shows a complex, cystic mass (arrowhead).

Transverse color Doppler ultrasonographic image of the popliteal fossa shows multiple cysts surrounding a normal-sized popliteal artery (A), which is consistent with cystic adventitial degeneration.

The communication with the joint by way of the gastrocnemio-semimembranosus bursa is deep within the popliteal space, adjacent to the dense posterior femoral cortex.  The ultrasonography probe is placed over the popliteal skin surface, and because this thin, necklike connection to the joint is anterior to the cyst, the mere presence of a large or complex Baker cyst may obscure the visualization of this connection.

Previously, Baker cysts were commonly detected by conventional arthrography or by computed tomography (CT) scanning. Arthrography demonstrates the cyst only if the iodinated contrast material that is injected into the joint during arthrography communicates with the cyst under the pressure of the injection. CT scanning can delineate a low to intermediate attenuation mass, which normally measures from 20 to -10 Hounsfield units, in the posteromedial popliteal space. CT scanning can easily delineate secondary findings, such as intracystic osseous fragments, mass effect, wall thickening, and bony erosion.

In current radiologic practice, Baker cysts are often detected on MRI evaluations of the knee (performed for any indication).  Sansone and colleagues studied 1001 randomly selected patients who were submitted for a knee MRI examination; the authors reported the frequency of Baker cysts to be 4.7%, but the frequency in the literature varies.  The advantages of MRI are derived from the superior soft-tissue contrast resolution that it affords and from the modality's multiplanar capability, which help to determine the extent and composition of the Baker cyst.

However, one of the most important benefits of employing MRI is the ability to use the axial plane to establish positive identification of the high – signal intensity, fluid-filled neck of the cyst that connects the cyst to the joint space (see Image below and Image 7 in Multimedia).  This makes it possible to discriminate between a benign Baker cyst and one of the uncommon, but clinically important, types of cystic tumors, such as myxoid liposarcoma, that can occur in the popliteal fossa.

Axial, T2-weighted magnetic resonance image with fat saturation reveals a Baker cyst connected to the knee joint by way of a narrow neck between the tendons of the medial head of the gastrocnemius and semimembranosus muscles.

Differential Diagnoses

Deep Venous Thrombosis, Lower Extremity

Other Problems to Be Considered

Vascular masses

• Popliteal artery aneurysm - Most common in the popliteal fossa
• Cystic adventitial degeneration of the popliteal artery - Erdheim mucoid degeneration

Nonvascular masses

• Simple Baker cyst
• Complicated Baker cyst - Characterized by internal debris (see Image 12, Image 17, Image 18 in Multimedia), septations (see Image 16 in Multimedia), or MRI signal intensity atypical for simple cyst
  • Inflammatory arthritides
  • Septic arthritis
  • Postoperative changes - Seroma, hematoma, or abscess
  • Hemorrhage within a cyst
  • Hemophilic arthropathy
• Soft-tissue tumor
  • Benign - Peripheral nerve sheath tumors (neurilemmoma)
  • Malignant - myxoid liposarcoma (adults), lipoblastoma (children, especially < 5 y)
• Meniscal cyst - Occurs more often laterally, but medial cysts have been identified
• Ganglion cyst
• Traumatic tear of the gastrocnemius muscle

Radiography

Findings

Imaging evaluation of a popliteal mass begins with conventional radiography to detect a soft-tissue mass, calcifications, and bony involvement. A Baker cyst appears as a soft-tissue mass in the posteromedial knee joint (see Image below and Image 2 in Multimedia).

Anteroposterior radiograph of the knee shows uniform joint-space loss in the medial and lateral knee compartments without osteophytosis. A Baker cyst is seen medially (arrowhead).

Anteroposterior radiograph of the knee shows calcifications (arrowhead) overlying the medial tibial plateau.

Lateral radiograph of the knee shows multiple calcified bodies (arrowhead) posterior to the knee, which is consistent with synovial osteochondromatosis.

Lateral radiograph of the knee shows a calcified body (arrowhead), which appears to be a large fabella, posterior to the knee.

Anteroposterior radiograph of the knee shows that a calcified body (arrowhead) is overlying the medial femoral condyle, making a fabella highly unlikely. The calcified, loose body is in a Baker cyst.

Computed Tomography

Contrast-enhanced, axial computed tomography (CT) scan of the knee shows multiple gaslike lucencies within a Baker cyst and synovial enhancement.

Findings

On a CT scan, a Baker cyst appears as a fluid-containing mass located behind the medial femoral condyle and between the tendons of the medial head of the gastrocnemius and semimembranosus muscles. A space-occupying lesion in the posteromedial knee suggests the diagnosis but is not always sufficient to exclude other etiologies, for which MRI or ultrasonography is more specific.

Degree of Confidence

CT scanning is not as sensitive as MRI in detecting an internal derangement, which may be the cause of a Baker cyst. In addition, the definitive diagnosis of a Baker cyst may not be made without the injection of air and/or iodinated contrast material into the knee joint.

Magnetic Resonance Imaging

Findings

On MRI, a Baker cyst appears as a homogeneous, high – signal intensity, cystic mass behind the medial femoral condyle; a thin, fluid-filled neck interdigitates between the tendons of the medial head of the gastrocnemius and semimembranosus muscles (see Image below and Image 7 in Multimedia).^{[22 ]}
 

Axial, T2-weighted magnetic resonance image with fat saturation reveals a Baker cyst connected to the knee joint by way of a narrow neck between the tendons of the medial head of the gastrocnemius and semimembranosus muscles.

In addition, intravenously administered gadolinium can detect synovial enhancement (see Images below and Image 12, Image 13 in Multimedia) and pannus formation in RA in the cyst and in the joint space proper, prior to the radiographic detection of well-known signs of RA much later in the course of the disease (erosion, uniform joint space loss without marked osteophytosis, periarticular osteopenia, soft-tissue swelling).

Axial, T2-weighted magnetic resonance image of the knee shows effusion, synovial proliferation (white arrowhead), and a Baker cyst that contains debris (black arrowhead).

Axial, T1-weighted magnetic resonance image of the knee after the intravenous administration of gadolinium shows synovial enhancement (arrowhead).

Sagittal, T2-weighted magnetic resonance image with fat saturation of the knee shows a large knee effusion and a Baker cyst.

Sagittal, T2-weighted magnetic resonance image with fat saturation of the knee, lateral to the view in Image above, shows a complete rupture of the anterior cruciate ligament.

Sagittal, T2-weighted magnetic resonance image shows a Baker cyst containing hypointense, loose bodies.

Axial, T2-weighted magnetic resonance image with fat saturation shows a Baker cyst containing hypointense, loose bodies.

Ultrasonography

Findings

Ultrasonography is a very helpful imaging technique in the evaluation of a popliteal mass.^{[23,24,25 ]} The modality can be used to determine whether the popliteal mass is a cyst or a solid mass. A simple Baker cyst appears as an anechoic mass with posterior acoustic enhancement that communicates with the knee joint. Findings on an ultrasonogram relate to the criteria of a simple cyst, which include an anechoic mass, a sharply defined posterior wall, and posterior acoustic enhancement. A complex Baker cyst has internal echoes within the hypoechoic mass (see Images below and Image 3, Image 4 in Multimedia). Calcified, loose bodies within a Baker cyst appear as mobile, intraluminal, echogenic foci with distal acoustic shadowing, an appearance similar to that of cholelithiasis in a gallbladder. An additional advantage of ultrasonography is that it can exclude a coexisting DVT.

Transverse ultrasonographic image of the knee in a patient who had recent arthroscopy shows a complex, cystic mass (arrow) in the medial aspect of popliteal fossa. The mass communicates with the knee joint (arrowhead), which is consistent with a Baker cyst.

Longitudinal ultrasonographic image of a Baker cyst in a patient who underwent recent knee arthroscopy.

Transverse ultrasonographic image of the popliteal fossa shows a complex, cystic mass (arrowhead).

Transverse color Doppler ultrasonographic image of the popliteal fossa shows multiple cysts surrounding a normal-sized popliteal artery (A), which is consistent with cystic adventitial degeneration.

Degree of Confidence

This is the fastest, most cost-effective manner in which to diagnose a Baker cyst.

False Positives/Negatives

A cyst that is too large or complex may obscure visualization of the fluid-filled connection to the joint space proper, leading to a false-positive diagnosis.

Intervention

Special Concerns

• Potential complications of Baker cysts that have been reported in the medical literature are as follows:
  • Pseudothrombophlebitis syndrome (rupture, dissection)
  • DVT
  • Pulmonary embolism
  • Hemorrhage
  • Leaking
  • Infection
  • Posterior compartment syndrome
  • Trapped calcified bodies
• The most common complication of Baker cyst is the rupture or dissection of fluid into the adjacent proximal gastrocnemius muscle belly, which results in a pseudothrombophlebitis syndrome mimicking symptoms of DVT. The incidence of Baker cyst rupture is 3.4-10%. A ruptured Baker cyst may present as an enlarging mass in the calf.
• Among patients with symptoms of DVT, the incidence of Baker cysts is 3.1-4.1%; the incidence of patients with a Baker cyst who have coexistent DVT is 0.2-11%. Therefore, a differential diagnosis of Baker cyst should be considered in patients presenting with symptoms that are suggestive of DVT. Once DVT is excluded, the popliteal fossa should be carefully evaluated for a ruptured Baker cyst. Alternatively, if a Baker cyst is observed incidentally on a venous duplex examination, the authors suggest that the radiologist should then search carefully for a coexistent DVT.
• Because of their anatomic location, Baker cysts can be a risk factor for DVT. Most commonly, the Baker cyst is located between the tendons of the medial head of the gastrocnemius and the semimembranosus bursa. Occasionally, the Baker cyst can be found between the heads of the gastrocnemius muscles. In a series of patients with Baker cyst simulating DVT, all patients demonstrated lateral deviation of the popliteal vein, and 30% of patients revealed compression of the popliteal vein. A report exists of a patient who developed a pulmonary embolism after receiving a diagnosis of Baker cyst and DVT.
• Posterior compartment syndrome usually is caused by trauma. Rarely, dissection or rupture of a Baker cyst can increase pressure within the deep posterior compartment of the leg, causing posterior compartment syndrome.^{[26 ]}Dissection of Baker cysts can also cause anterior compartment syndrome, depending on the direction of dissection. A Baker cyst usually dissects through the muscles, primarily below the knee. There is evidence that almost one third of dissections are into the thigh.
• An infected Baker cyst is rare; review of the literature disclosed only 3 occurrences. The infected patients had either fever, an increased white blood cell (WBC) count, or an elevated erythrocyte sedimentation rate.
• An entity that may mimic an infected Baker cyst is a Baker cyst that contains gaslike lucencies. Only 2 patients have been reported with a gas-containing, noninfected Baker cyst. Both patients had diabetes mellitus and RA. The authors did not suggest a mechanism for the appearance of the gaslike lucencies in the Baker cyst.
• Jayson and Dixon studied the valvular mechanisms in juxta-articular cysts and postulated that joint effusion and fibrin are pumped from the knee joint into the Baker cyst but—because of a valvelike communication (either a Bunsen or ball valve)—not in the reverse direction (see Image 1).^{[5 ]}The effusion can be readily reabsorbed through the synovial membrane, leaving behind concentrations of fibrin, which on radiographs may appear as gaslike lucencies. In our experience, 1 patient had a noninfected Baker cyst with gaslike lucencies (see Images below), along with diabetes mellitus and RA. Because gaslike lucencies in a Baker cyst are rare and an infected Baker cyst is a serious condition, the former diagnosis must be one of exclusion; a CT scan with appropriate window settings allows discrimination between air and fibrin.

Anteroposterior radiograph of the knee shows multiple tiny lucencies superior to the medial femoral condyle (arrowhead).

Lateral radiograph of the knee shows multiple tiny lucencies (arrowhead) posterior to the knee.

Contrast-enhanced, axial computed tomography (CT) scan of the knee shows multiple gaslike lucencies within a Baker cyst and synovial enhancement.

• Radiographic findings of calcified bodies posterior to the knee joint can be confusing. The differential diagnosis includes soft-tissue neoplasms with calcification (eg, extraskeletal soft-tissue sarcoma), a popliteal artery aneurysm, vascular malformations, and loose, calcified bodies trapped in a Baker cyst. Calcified bodies in Baker cysts are common, with an incidence of 6% in one series.
• Calcified bodies may derive from trauma (ie, loose bodies resulting from osteochondral fractures), arthropathy (ie, loose bodies associated with joint surface disintegration, such as that related to osteoarthritis, infection, and neuropathic joints), or synovial chondromatosis (that is, calcified or noncalcified bodies resulting from chondrometaplasia of synovial tissue) (see Image 8, Image 9 in Multimedia).
• Distal migration of loose bodies supports the diagnosis of a dissecting Baker cyst. Rarely, a solitary, calcified, loose body in a Baker cyst may simulate a fabella on the lateral view of conventional radiography of the knee (see Image 10, Image 11 in Multimedia). However, on the frontal view, a fabella is located in the lateral head of the gastrocnemius muscle, while a calcified, loose body in a Baker cyst is located medially.

Multimedia

Media file 1: Valvular mechanism of Baker cyst. Effusion and fibrin are pumped (large arrows) into the Baker cyst (long, thin arrows). In the Bunsen-valve mechanism, the enlarging Baker cyst exerts mass effect (feathered arrow) on the slitlike communication between the joint and the cyst, trapping effusion. In the ball-valve mechanism, fibrin serves as a 1-way valve that prevents the effusion's return to the knee joint. Trapped effusion is reabsorbed through the semipermeable membrane (short, thin arrows), leaving behind concentrations of fibrin. (MFC: medial femoral condyle; MTP: medial tibial plateau; G: medial head of gastrocnemius muscle; SM: semimembranosus muscle)

Media file 2: Anteroposterior radiograph of the knee shows uniform joint-space loss in the medial and lateral knee compartments without osteophytosis. A Baker cyst is seen medially (arrowhead).

Media file 3: Transverse ultrasonographic image of the knee in a patient who had recent arthroscopy shows a complex, cystic mass (arrow) in the medial aspect of popliteal fossa. The mass communicates with the knee joint (arrowhead), which is consistent with a Baker cyst.

Media file 4: Longitudinal ultrasonographic image of a Baker cyst in a patient who underwent recent knee arthroscopy.

Media file 5: Transverse ultrasonographic image of the popliteal fossa shows a complex, cystic mass (arrowhead).

Media file 6: Transverse color Doppler ultrasonographic image of the popliteal fossa shows multiple cysts surrounding a normal-sized popliteal artery (A), which is consistent with cystic adventitial degeneration.

Media file 7: Axial, T2-weighted magnetic resonance image with fat saturation reveals a Baker cyst connected to the knee joint by way of a narrow neck between the tendons of the medial head of the gastrocnemius and semimembranosus muscles.

Media file 8: Anteroposterior radiograph of the knee shows calcifications (arrowhead) overlying the medial tibial plateau.

Media file 9: Lateral radiograph of the knee shows multiple calcified bodies (arrowhead) posterior to the knee, which is consistent with synovial osteochondromatosis.

Media file 10: Lateral radiograph of the knee shows a calcified body (arrowhead), which appears to be a large fabella, posterior to the knee.

Media file 11: Anteroposterior radiograph of the knee shows that a calcified body (arrowhead) is overlying the medial femoral condyle, making a fabella highly unlikely. The calcified, loose body is in a Baker cyst.

Media file 12: Axial, T2-weighted magnetic resonance image of the knee shows effusion, synovial proliferation (white arrowhead), and a Baker cyst that contains debris (black arrowhead).

Media file 13: Axial, T1-weighted magnetic resonance image of the knee after the intravenous administration of gadolinium shows synovial enhancement (arrowhead).

Media file 14: Sagittal, T2-weighted magnetic resonance image with fat saturation of the knee shows a large knee effusion and a Baker cyst.

Media file 15: Sagittal, T2-weighted magnetic resonance image with fat saturation of the knee, lateral to the view in Image above, shows a complete rupture of the anterior cruciate ligament.

Media file 16: Sagittal, T2-weighted magnetic resonance image with fat saturation shows a complicated Baker cyst containing multiple internal septations.

Media file 17: Sagittal, T2-weighted magnetic resonance image shows a Baker cyst containing hypointense, loose bodies.

Media file 18: Axial, T2-weighted magnetic resonance image with fat saturation shows a Baker cyst containing hypointense, loose bodies.

Media file 19: Arthrography of the knee performed prior to radioactive synoviorthesis shows leakage of contrast (arrow) just superior to the sinus (arrowhead and "BB" marker).

Media file 20: Anteroposterior radiograph of the knee shows multiple tiny lucencies superior to the medial femoral condyle (arrowhead).

Media file 21: Lateral radiograph of the knee shows multiple tiny lucencies (arrowhead) posterior to the knee.

Media file 22: Contrast-enhanced, axial computed tomography (CT) scan of the knee shows multiple gaslike lucencies within a Baker cyst and synovial enhancement.

References

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Keywords

Baker cyst, Baker's cyst, popliteal cyst, popliteal bursa, gastrocnemio-semimembranosus bursa, gastrocnemio-semimembranous bursa, gastrocnemiosemimembranosus bursa, gastrocnemiosemimembranous bursa

Contributor Information and Disclosures

Author

Liem T Bui-Mansfield, MD, Associate Professor, Department of Radiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland
Liem T Bui-Mansfield, MD is a member of the following medical societies: American Roentgen Ray Society, Radiological Society of North America, and Society of Skeletal Radiology
Disclosure: Nothing to disclose.

Coauthor(s)

Rush A Youngberg, MD, Chief of Musculoskeletal Radiology, Department of Radiology, Madigan Army Medical Center
Disclosure: Nothing to disclose.

Medical Editor

David S Levey, MD, PhD, Orthopedic/Spine MRI TeleRadiologist, Radsource, LLC
David S Levey, MD, PhD is a member of the following medical societies: American Roentgen Ray Society, Radiological Society of North America, and Texas Medical Association
Disclosure: Nothing to disclose.

Pharmacy Editor

Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand
Disclosure: Nothing to disclose.

Managing Editor

Javier Beltran, MD, Chair, Department of Radiology, Maimonides Medical Center
Disclosure: Nothing to disclose.

CME Editor

Robert M Krasny, MD, Resolution Imaging Medical Corporation
Robert M Krasny, MD is a member of the following medical societies: American Roentgen Ray Society and Radiological Society of North America
Disclosure: Nothing to disclose.

Chief Editor

Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington
Felix S Chew, MD, MBA, EdM is a member of the following medical societies: American Roentgen Ray Society, Association of University Radiologists, and Radiological Society of North America
Disclosure: Nothing to disclose.

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Finnish Medical Society Duodecim - Professional Association. 2000 Apr 18 (revised 2007 Jan 11). Various pagings. NGC:005501

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