Cystic Masses of the Knee: Magnetic Resonance Imaging Findings

doi:10.1067/j.cpradiol.2005.04.002

Current Problems in Diagnostic Radiology

Volume 34, Issue 4, July–August 2005, Pages 143-159

https://doi.org/10.1067/j.cpradiol.2005.04.002 Get rights and content

Cystic masses of the knee comprise a diverse group of pathologic entities ranging from simple cysts to complications of underlying disease to tumors. Although their presentations may be similar, the appropriate treatment and patient management can differ greatly. In this article, we review radiographic and magnetic resonance imaging characteristics of both common and uncommon cystic masses of the knee.

Section snippets

Paraarticular Ganglion or Synovial Cyst

Both the paraarticular ganglion and the synovial cyst present with focal pain and/or a palpable mass around the knee and are easily seen on MRI. These entities can also be diagnosed via an ultrasound-guided needle aspiration, which reveals a high concentration of hyaluronic acid. The histology, however, does differ between the two. A ganglion cyst is lined by connective tissue, contains mucinous material, and rarely communicates with the joint itself. In contrast, a synovial cyst is lined by

Synovitis

Inflammatory synovitis encompasses a variety of inflammatory processes; the most notable of these is rheumatoid arthritis (RA). Synovitis may be reversible with nonsteroidal antiinflammatory drugs (NSAIDs) or may progress with persistent inflammation leading to irreversible articular damage, osseous erosion, and periarticular soft-tissue destruction.⁴ Early in the disease process, radiographs may be unremarkable. Progression of the disease typically leads to such radiographically evident

Subchondral Cyst (Geode)

Subchondral cysts are commonplace features of osteoarthritis (OA) along with osteophytes, sclerosis, and loss of joint space.⁴ The cysts may be fluid-filled or they may contain fibrous tissue, whereupon they are then referred to as “geodes.”

Two theories of subchondral cyst pathogenesis exist: the synovial breach theory and the bone contusion theory. A synovial breach is thought to develop in the articular cartilage, allowing the passage of synovial fluid into the subchondral bone. Subsequent

Baker’s (Popliteal) Cyst

In 1840, Adams described an enlarged bursa that is normally found beneath the medial head of the gastrocnemius muscle and that communicates with the joint via a valve mechanism.⁶ Almost 37 years later, Baker concluded that synovial fluid could extend out of the knee and into this bursa, forming a synovial cyst in patients with knee joint effusions.⁷ Today, we know the Baker’s or popliteal cyst as the most common cystic structure occurring in the region of the knee often associated with a number

Pes Anserine Bursitis

The pes anserine bursa is located between the pes tendons (consisting of the gracilis, sartorius, and semitendinosus tendons) and the tibial insertion of the tibial collateral ligament along the medial aspect of the lower knee. Pes anserine bursitis presents with swelling and tenderness inferior to the anteromedial aspect of the proximal tibia. It may mimic a medial meniscal tear or injury to the medial collateral ligament.³ Risk factors for developing pes anserine bursitis include obesity,

Prepatellar/Pretibial Bursitis

The prepatellar bursa is located superficial to the distal patella and the proximal patellar tendon, while the pretibial bursa is located superficial to the tibial tubercle. The deep infrapatellar bursa lies between the anterior tibial plateau and the posterior aspect of the distal patellar tendon.

Prepatellar bursitis is commonly referred to as “housemaid’s knee” and presents with pain and swelling secondary to trauma or repetitive pressure. Pretibial bursitis is commonly referred to as

Semimembranosus Tibial Collateral Ligament Bursitis

The semimembranosus tibial collateral ligament bursa incorporates a deep and superficial component that unites to form an inverted “U” shape across the anterosuperior edge of the semimembranosus tendon. The bursa acts to protect the tendon lying between the medial tibial condyle and the tibial collateral ligament. Additionally, the bursa extends to the joint line but does not establish actual continuity with the joint. This is in contrast to the pes anserine bursa, which, although located in a

Cruciate Ligament Ganglion

A cruciate ligament ganglion is a cystic structure lined by flat spindle-shaped cells and containing a combination of mucin and fluid. Although ganglion cysts are common findings in the hands and wrists, they are relatively unusual in the knee. They typically arise from the alar folds that overlie either the infrapatellar fat pad or the cruciate ligaments. Although the pathogenesis is uncertain, the three following hypotheses do exist: (1) mucinous degeneration of connective tissue; (2)

Meniscal Cyst

A meniscal cyst is an encapsulated collection of synovial fluid located in the medial or lateral joint that is continuous with the meniscus. It is highly suggestive of an associated meniscal tear, but has been reported in the absence of a detectable tear (most likely due to a previously healed meniscal tear). It is thought to result from extrusion of joint fluid through a meniscal tear into the adjacent tissues, enlarging via a one-way valve effect.2, 3

The clinical presentation is that of a

Osteomyelitis

Osteomyelitis is typically classified by onset, route of infection, causative organism, and age of patient. Acute cases often present clinically with fever, pain, and/or pseudoparalysis of the affected limb. In contrast, chronic cases may present with drainage from a sinus tract and/or a low-grade fever. Acute infection is characterized by bone marrow edema, cellular infiltration, and vascular engorgement while chronic infection is notable for a loss of blood supply with subsequent development

Abscess

By definition, an abscess is a localized collection of necrotic tissue, inflammatory cells, and bacteria that is generated by suppuration in a confined space. They can involve a wide range of tissues and anatomic spaces including intramuscular and/or subcutaneous spaces as well as bone marrow or cortex. Possible routes of inoculation include directly through areas of disrupted skin surface (ie, following trauma), hematogenously, or contiguous spread. If the abscess involves or is adjacent to a

Pigmented Villonodular Synovitis

Pigmented villonodular synovitis (PVNS) is a benign, monoarticular process of unknown etiology that typically occurs in the third or fourth decade of life, often in patients with a history of antecedent trauma. It is thought to result from proliferation of synovium in the affected joint, bursa, or tendon sheath. Localized or nodular forms are referred to as giant cell tumors of the tendon sheath and arise, as their name implies, from tenosynovium. Diffuse forms arise from intraarticular

Lipoma Arborescens

Lipoma arborescens is a rare and benign intraarticular process involving the synovium whose etiology is unclear. The knee is most commonly affected, but involvement of the wrist, ankle, and shoulder has also been reported. This entity has been associated with other processes such as repetitive trauma, degenerative joint disease, and rheumatoid arthritis but the causative pathologic mechanism remains unknown. Histologically, it is characterized by replacement of the collagenous subintima of the

Synovial Chondromatosis/Osteochondromatosis

Synovial chondromatosis refers to a rare monoarticular arthropathy of unknown etiology characterized by benign cartilaginous metaplasia of the synovium and formation of multiple intraarticular cartilaginous bodies or nodules that may later ossify (osteochondromatosis) or calcify. Histologically, fibroblasts in the subintimal layer of the synovium undergo cartilaginous metaplasia generating multiple nodules of hyaline cartilage. These nodules are typically circular and well circumscribed and are

Hematoma

In general, blood products degrade in a systematic fashion and have a certain appearance based on the age of the hematoma. With regard to the MRI appearance, blood less than 48 hours typically has an isointense quality on T1-weighted images and a dark appearance on T2-weighted images. On both sequences, one will note layering of the more dense blood products with a well-demarcated interface between layers (Fig 17). In the subacute, or 3- to 7-day time frame, there will be high signal intensity

Lipohemarthrosis

Lipohemarthrosis is seen following osseous trauma or trauma to the joint itself and is indicative of an intraarticular fracture (possibly occult) or severe capsuloligamentous injury. It is characterized by three fluid layers consisting of red blood cells, serum, and fat; this is often referred to as the “Neapolitan ice cream” appearance. The fat component originates from the bone marrow (enters the joint space via an osseous fracture), synovial membrane, capsuloligamentous structures, or from

Telangiectatic Osteosarcoma

A telangiectatic osteosarcoma is a highly aggressive and relatively uncommon morphological variant of osteosarcoma (in addition to conventional, multifocal, and juxtacortical) that occurs predominately in patients under the age of 30 years. Radiographically, these tumors present as radiolucent osseous lesions, often with an appearance similar to aneurysmal bone cysts (Fig 21A). They may or may not be well defined on conventional radiography and rapidly growing tumors are commonly associated

Myxoid Liposarcoma

A myxoid liposarcoma is a large, slow-growing mesenchymal tumor that is usually soft and nontender to palpation. Most are located in the deep tissues of the body with only a small percentage occurring in the subcutaneous tissues. The lower extremities are most commonly involved, principally the thigh. In general, patients are typically a decade younger than those afflicted with other liposarcoma subtypes such as well-differentiated, round-cell, and pleomorphic. Well-differentiated tumors tend

Conclusion

Cystic masses of the knee are common findings and have a diverse array of etiologies with different prognoses and therapeutic options. A detailed history and physical examination in combination with an accurate, well-organized, and comprehensive imaging report is critical to ensuring the most appropriate patient care. Careful attention to the nuances of MRI findings as described in this article should optimize the likelihood of successful therapeutic intervention.

References (16)

E. Steiner et al.
Ganglia and cysts around joints
Radiol Clin North Am
(1996)
R. Ptasznik
Musculoskeletal ultrasoundultrasound in acute and chronic knee injury
Radiol Clin North Am
(1999)
J.T. Dearborn et al.
Orthopedicsthe evaluation and initial management of arthritis
Prim Care
(1996)
J.G. Waldschmidt et al.
Osteoarthritismagnetic resonance imaging of osteoarthritis
Rheum Dis Clin North Am
(1999)
N.A. Kothari et al.
Pediatric musculoskeletal radiologyimaging of musculoskeletal infections
Radiol Clin North Am
(2001)
D.L. Janzen et al.
Cystic lesions around the knee jointMR imaging findings
AJR
(1994)
R. Adams
Arthritis, chronic rheumatic, of the knee joint
Dublin J Med Sci
(1840)
W.M. Baker
On the formation of synovial cysts in the leg in connection with disease of the knee-joint (from Baker WM. On the formation of synovial cysts in the leg in connection with disease of the knee-joint. St Bartholomew’s Hospital Report 1877;13:245)
Clin Orthop Related Res
(1994)

There are more references available in the full text version of this article.

Cited by (17)

Giant infrapatellar ganglion cyst of Hoffa's fat pad
2019, European Journal of Radiology Open
Citation Excerpt :
Cysts and cystic-appearing soft-tissue lesions in and around the knee are common and can create a diagnostic dilemma if one is not aware of the potential diagnoses and pitfalls. Most of these lesions are benign and are related to the collection of fluid in bursae, herniation of synovium from the joint, or ganglia arising from tendons and ligaments [1–4]. Ganglia are myxoid lesions of unknown cause which are characterised by dense connective tissue filled with gelatinous fluid rich in hyaluronic acid and other mucopolysaccharides.
We present the case of a 36-year-old woman who works as a kindergarten teacher, often she is kneeling on her knees due to the nature of the job. Since a year ago, she noticed that her right knee was swelling. She had an orthopaedic examination when she could no longer bend her knee. Inspection and palpation revealed the swelling of the anterior and anterior-lateral aspect of the knee. MRI imaging revealed a large, sharply defined, lobulated lesion of the infrapatellar fat pad. After the surgical incision, a lobular lesion was found and surgically removed. Histological analysis confirmed a ganglion cyst.
Magnetic Resonance Imaging of Cysts, Cystlike Lesions, and Their Mimickers Around the Knee Joint
2018, Canadian Association of Radiologists Journal
While interpreting routine magnetic resonance imaging (MRI) of the knee joint, a radiologist may encounter various cystic lesions such as ganglion, synovial, and meniscal cysts, among others. In some cases, MRI may demonstrate cystlike lesions around the knee due to fluid distention of normal bursa and recesses, the diagnosis of which should not be difficult if a radiologist is familiar with their characteristic location and MRI appearance. In addition, there are cyst mimickers such as hematomas, abscesses, vascular lesions, and neoplasms around knee joint that may pose a diagnostic challenge on routine MRI. Due to their atypical location and variable morphology, contrast administration is helpful as the enhancement pattern aids to differentiate them from cysts and cystlike lesions. This pictorial essay aims to classify cysts, cystlike lesions, and cyst mimickers in and around the knee joint based on their anatomic location and highlight their characteristic MRI features.
Lorsqu'il interprète un examen d'imagerie par résonance magnétique (IRM) de routine de l'articulation du genou, le radiologiste peut détecter diverses lésions kystiques, comme des ganglions, des kystes synoviaux et des kystes méniscaux, entre autres. Dans certains cas, l'examen d’IRM montre des lésions kystiques autour du genou causées par la distension des fluides normalement contenus dans les bourses et les niches, une affection facile à diagnostiquer si le radiologiste est au fait de son siège caractéristique et de son apparence sur un examen d’IRM. De plus, il peut y avoir des lésions qui ressemblent à des kystes – comme des hématomes, des abcès, des lésions vasculaires et des néoplasmes – près de l'articulation du genou, ce qui rend difficile le diagnostic au moyen d'un examen d’IRM de routine. En raison de l'emplacement atypique et de la morphologie variable de ces lésions, l'administration d'un agent de contraste peut s'avérer utile, car le profil de rehaussement aide à distinguer les kystes des lésions kystiques. Cet essai illustré vise à classer les kystes, les lésions kystiques et les lésions ayant l'apparence de kystes dans l'articulation du genou et autour de celle-ci en fonction de leur siège anatomique, ainsi qu’à faire ressortir leurs caractéristiques d'imagerie.
Neoplastic and paraneoplastic synovitis
2011, Rheumatic Disease Clinics of North America
Citation Excerpt :
T1-weighted images typically show multiple areas of signal void corresponding with incompletely calcified nodules. Complete cartilaginous nodules appear isointense to the muscle on T1-weighted images, whereas T2-weighted images show high signal enhancement corresponding with joint effusion and synovial proliferation.12,19,20 Pathologic changes include cartilaginous metaplasia of the intimal layer in a solid matrix without myxoid change.
Cyst-like lesions of the knee joint and their relation to incident knee pain and development of radiographic osteoarthritis: The MOST study
2010, Osteoarthritis and Cartilage
Citation Excerpt :
These represent a wide variety of entities that include meniscal and Baker’s (popliteal) cysts; intra-articular and extra-articular ganglia; intraosseous cysts at the insertion of the cruciate ligaments and meniscotibial attachments; and cysts adjacent to the proximal tibiofibular joint (PTFJ)1–5. Cyst-like lesions arising from bursae include anserine, prepatellar, superficial and deep infrapatellar, suprapatellar, iliotibial, and tibial collateral ligament bursitis1–5. Discrete fluid collections within bursae can be detected by knee MRI, but may not necessarily be clinically significant due to their high prevalence in asymptomatic subjects6,7.
To determine whether intra- and periarticular cyst-like lesions of the knee are associated with incident knee pain and incident radiographic knee osteoarthritis (OA).
The Multicenter Osteoarthritis (MOST) Study is a cohort of individuals who have or are at high risk for knee OA. Using a nested case-control study design, we investigated the associations of cyst-like lesions (Baker’s, meniscal and proximal tibiofibular joint (PTFJ) cysts, and prepatellar and anserine bursitides) with (1) incident pain at 15- or 30-month follow-up and (2) incident radiographic OA at 30-month follow-up. Baseline cyst-like lesions were scored semiquantitatively using the Whole Organ Magnetic Resonance Imaging Score (WORMS). Conditional logistic regression models were used to assess the relation between these lesions and the outcomes, adjusting for potential confounding factors (i.e., cartilage loss, meniscal damage, bone marrow lesions, synovitis and joint effusion, which were also scored using WORMS).
Incident knee pain study included 157 cases and 336 controls. Prevalence of meniscal and PTFJ cysts in the case group was twice that in the control group [9 (6%) vs 9 (3%) and 9 (6%) vs 10 (3%), respectively]. Incident radiographic OA study included 149 cases and 298 controls. Prevalence of grade 2 Baker’s cysts and PTFJ cysts in the case group was approximately four times that in the control group [16 (11%) vs 9 (3%) and 6 (4%) vs 3 (1%), respectively]. However, none of the cyst-like lesions was associated with incident pain or radiographic OA after fully adjusted logistic regression analyses and correction of P-values for multiple comparisons.
None of the analyzed lesions was an independent predictor of incident knee pain or radiographic OA. Intra- and periarticular cyst-like lesions are likely to be a secondary phenomenon seen in painful or OA-affected knees, rather than a primary trigger for incident knee pain or radiographic OA.
MR Imaging of Cysts, Ganglia, and Bursae About the Knee
2007, Radiologic Clinics of North America
Citation Excerpt :
PCL ganglia tend to be located at the femoral or tibial insertion of the PCL, rarely surround the ligament, and do not communicate with a meniscal tear, should one be present [55]. Patients typically present with symptoms including swelling, a palpable mass, pain and tenderness, or limited mobility [1,29,55], although asymptomatic cysts may be detected as well [30]. Lateral meniscal cysts present as palpable masses more commonly than medial meniscal cysts [17,51], likely because of the relatively scant amount of fatty soft tissue present in the lateral aspect of the knee [51].
Cystic lesions around the knee comprise a diverse group of entities, ranging from benign cysts to complications of underlying diseases such as infection, arthritis, and malignancy. Their diverse causes result in varied prognoses and therapeutic options. Although the presentation of cystic masses may be similar, their management may differ, thus highlighting the importance of appropriate categorization. MR aids in the characterization of lesions by first localizing them, and then defining their relationship with adjacent structures and identifying any additional abnormalities. For the purpose of this article, the authors limit the scope of their discussion to benign cysts, ganglia, and bursae about the knee.
MR Imaging of Cysts, Ganglia, and Bursae About the Knee
2007, Magnetic Resonance Imaging Clinics of North America
Citation Excerpt :
Inflammation may result in focal pain along the posteromedial knee at the level of the knee joint line. The MR appearance is that of a fluid collection oriented along the plane of the semimembranosus tendon, which may drape over or surround the tendon [29]. This bursa does not communicate with the knee joint or other medial knee bursa, although multifocal bursitis may coexist.
Cystic lesions around the knee comprise a diverse group of entities, ranging from benign cysts to complications of underlying diseases such as infection, arthritis, and malignancy. Their diverse causes result in varied prognoses and therapeutic options. Although the presentation of cystic masses may be similar, their management may differ, thus highlighting the importance of appropriate categorization. MR aids in the characterization of lesions by first localizing them, and then defining their relationship with adjacent structures and identifying any additional abnormalities. For the purpose of this article, the authors limit the scope of their discussion to benign cysts, ganglia, and bursae about the knee.

View all citing articles on Scopus

View full text

Cystic Masses of the Knee: Magnetic Resonance Imaging Findings

Section snippets

Paraarticular Ganglion or Synovial Cyst

Synovitis

Subchondral Cyst (Geode)

Baker’s (Popliteal) Cyst

Pes Anserine Bursitis

Prepatellar/Pretibial Bursitis

Semimembranosus Tibial Collateral Ligament Bursitis

Cruciate Ligament Ganglion

Meniscal Cyst

Osteomyelitis

Abscess

Pigmented Villonodular Synovitis

Lipoma Arborescens

Synovial Chondromatosis/Osteochondromatosis

Hematoma

Lipohemarthrosis

Telangiectatic Osteosarcoma

Myxoid Liposarcoma

Conclusion

Radiol Clin North Am

Radiol Clin North Am

Prim Care

Rheum Dis Clin North Am

Radiol Clin North Am

Cystic lesions around the knee jointMR imaging findings

AJR

Arthritis, chronic rheumatic, of the knee joint

Dublin J Med Sci

On the formation of synovial cysts in the leg in connection with disease of the knee-joint (from Baker WM. On the formation of synovial cysts in the leg in connection with disease of the knee-joint. St Bartholomew’s Hospital Report 1877;13:245)

Clin Orthop Related Res