Baker’s Cyst in Imaging

Baker’s Cyst in Imaging : 

Baker’s Cyst in Imaging By: Jesly Lopez Darrian Roberson 10/12/2011

What is a Baker’s Cyst? : 

What is a Baker’s Cyst? Also known as popliteal cyst; benign swelling behind the knee of the semimembranosus , gastroc or less frequent some other bursa behind the knee. Not considered a “true” cyst because of the communication between the synovial cyst and synovial cavity [1] . Cause is thought to be related to DJD or meniscal injury to knee joint that causes effusion. Swollen synovial sac of knee then produces posterior bulge into popliteal space. When cyst swells enough it becomes palpable with patient in extension. Self limiting in children and young adults

Patient Presentation: 

Patient Presentation Signs and Symptoms. .. Pain in posterior aspect of knee Palpable cystic-like swelling seen when patient is standing in extension. Patient describes a pressure that increases with flexion. Decreased Tibiofemoral flexion AROM. Swelling and inflammation (may mimic DVT) of structures posterior to knee. Joint Effusion most prevalent in medial joint line.

Diagnosis: 

Diagnosis Diagnosis is done by physical examination. Signs, symptoms and past medical history is usually efficient in ruling in Bakers cyst. Conventional radiography is first used to detect a soft-tissue mass and/or internal calcifications, however hard body inside cyst may mimic fabella on lateral radiograph [3]. Followed-up with Magnetic Resonance Imaging which is best to confirm diagnosis. Ultrasonography and Arthrography can also be used [2].

Incidence : 

Incidence Baker’s cyst is usually prevalent in individuals with a PMH of chronic osteoarthritis (or Chopart’s joint) of the knee [1] . Also prevalent in athletic populations with previous injuries to knee that cause joint effusion. Such as: ACL, meniscus tears, etc;. Can be seen post-op arthroscopic knee surgery where residual joint effusion pushes fluid into posterior aspect of knee developing benign cyst [2] .

Functional Limitations: 

Functional Limitations Patient describes pain as dull/achy which becomes worse with prolonged standing or walking. Patient demonstrates difficulty with activities that require flexion of tibiofemoral joint, such as: -Squatting -Kneeling -Heavy lifting -Stairs In older individuals with OA as a co-morbidity it can be debilitating, oftentimes requiring assistance to complete ADL’s. In younger individuals, Baker’s cysts require them to modify or stop activity. Often times patient presents with other complications and previous insults to knee where functional and recreational abilities were already compromised.

Management of Baker’s Cyst: 

Management of Baker’s Cyst Rehabilitative process depends on severity of functional limitations of patient. In severe cases where patient’s current level of function is considerably compromised, surgical intervention to remove Baker’s cyst is indicated where fluid is aspirated to shrink cyst and resect . However, most frequently Baker’s cyst are treated conservatively. Emphasis is placed on managing pain and return to PLOF. - Cryotherapy to reduce swelling -NSAID’s (patient directed to take as labeled on bottle) - Bracing; to provide stability and compression to posterior knee. - Strengthening quads, and general stretching of LE musculature. - ROM exercises Once inflammation is reduced, with proper rehabilitation cyst diminishes.

Role of Imaging for Diagnosis of Baker’s Cyst: 

Role of Imaging for Diagnosis of Baker’s Cyst The best diagnostic indicator for Baker’s cyst is Magnetic Resonance Imaging or MRI. “The advantages of MRI are derived from the superior soft-tissue contrast resolution and from MRI’s multiplanar capability, which help to determine the extent and composition of the Baker cyst [3].”

Role of Imaging for Diagnosis of Baker’s Cyst: 

Role of Imaging for Diagnosis of Baker’s Cyst However, one of the most important benefits of using 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 the image below) [3]. This makes it possible to discriminate between a benign Baker cyst and one of the uncommon, but clinically important, types of cystic tumors that can occur in the popliteal fossa [4].

Role of Imaging for Diagnosis of Baker’s Cyst: 

Role of Imaging for Diagnosis of Baker’s Cyst A/P Radiograph. This radiograph demonstrates the presence of a Baker’s cyst posterior to the medial tibial and femoral condyles (arrowhead). Alignment: Size and anatomic form all appear normal. Bone Density: Trebeculae appear thin and coarse along lateral border of lateral femoral condyle . Subchondral Sclerosis secondary to increased bone density. Cartilage: Considerable decrease joint space relative to DJD. Sclerosis of subchondral bone. Soft Tissue: Gross inflammation of surrounding soft tissue, especially medial musculature. Cyst is seen to be causing considerable swelling and occupying space in joint space. Capsule distention can be expected.

Role of Imaging for Diagnosis of Baker’s Cyst: 

Role of Imaging for Diagnosis of Baker’s Cyst Axial, T2-weighted MRI. “Effusion is present, synovial proliferation (white arrowhead), and Baker’s cyst that contains debris (black arrowhead)” [3].

Possible Biomechanical and Physical Impairments: 

Possible Biomechanical and Physical Impairments Based on our findings of this radiograph we are able to identify possible complications and/or patient presentations clinically. Due to the substantial joint space loss we can expect that the patient to be in moderate to severe pain, because of the obliterated joint cartilage. Patient is bone on bone with no cartilage to disperse shock absorption forces. This will eventually lead to malalignment as the bone surfaces cause frictional forces that lead to further displacement. We can expect p atient will have difficulty with ambulation, stair negotiation, and functional activities that require patient to squat, or bend down which increase compressive forces on the joint surfaces.

Questions: 

Questions 1) Insults to knee that cause joint effusion is one of the causes of Baker’s cyst (excess fluid is pushed posterior); why would a patient with Chopart’s disease (chronic OA) present with a Baker’s cyst? 2) Why are Baker’s Cyst predominately found on the medial aspect of knee versus lateral?

References: 

References 1) Hellmann, DB (2005). "Chapter 20: Arthritis & Musculoskeletal Disorders". In Tierney LM, Jr., McPhee SJ, Papadakis MA. Current Medical Diagnosis & Treatment (44th ed.). Philadelphia, PA: F. A. Davis Company. 2) Guerra J Jr , Newell JD, Resnick D, Danzig LA. Pictorial essay: gastrocnemio-semimembranosus bursal region of the knee. AJR Am J Roentgenol . Mar 1981;136(3):593-6. 3) Marra MD, Crema MD, Chung M, Roemer FW, Hunter DJ, Zaim S, et al. MRI features of cystic lesions around the knee. Knee . Dec 2008;15(6):423-38. 4) Munk PL, Vellet AD, Levin MF. Leaking Baker's cyst detected by magnetic resonance imaging. Can Assoc Radiol J . Apr 1993;44(2):125-8.