Articular and periarticular tumors, Differential diagnosis using magnetic resonance imaging
Most patients with articular or periarticular tumors present with chronic monoarthritis and nonspecific alterations on laboratory tests; thus, it is important to know the changes on magnetic resonance imaging (MRI) that can suggest their diagnosis and the differential diagnosis of these tumors.
MRI defines the anatomic origin and the tissue characteristics of articular and periarticular tumors, making it possible to reach a specific diagnosis in most cases. It is important to evaluate the MRI findings together with the plain-film findings because this helps in the characterization of mineralized tumors.
Articular and periarticular tumors represent one of the most common manifestations of a wide variety of neoplastic—both benign and malignant—and non-neoplastic lesions. The differential diagnosis is wide and the clinical diagnosis complicated because most lesions present as chronic monoarthritis or with signs, symptoms and nonspecific laboratory findings.1
Plain radiography remains the primary modality in the study of articular and periarticular tumors. In some cases, radiographs demonstrate calcifications that are very suggestive and characteristic of a specific diagnosis and help to assess the associated bone abnormalities such as remodeling, periosteal reaction or bone destruction.1, 2
In the present paper, we examine the MRI findings of bone and soft tissue lesions that arise from joints or periarticular tissues, and we present representative images of benign neoplastic lesions, malignant tumors and non-neoplastic lesions.Bone lesions
Bone lesions, both benign and malignant, may have an intraarticular or periarticular origin (Table 1).
Table 1. Classification of bone lesions located in joints or periarticular soft tissues.
|Intraarticular||Cystic lesions||Subchondral cystIntraosseous ganglion|
|Periarticular||Benign extraskeletal chondroid tumors||Soft tissue chondroma|
|Benign bone chondroid tumors||Periosteal chondroma|
|Malignant bone tumors||Primary bone lymphoma|
The radiolucent subchondral lesions found on plain radiographs are usually termed subchondral cysts. However, this term is not accurate because such lesions are not lined by epithelium nor are they uniformly fluid-filled.5
Subchondral cysts are the most common intraarticular bone lesions, usually having a degenerative origin and are characteristic of osteoarthritis. They result from pressure on the subchondral trabeculae and are usually multiple, of variable size, and with or without communication with the articular space.
Subchondral cysts have also been associated with trauma, calcium pyrophosphate deposition disease, rheumatoid arthritis, and avascular necrosis.5
Radiographically, cysts present as radiolucent lesions with a surrounding sclerotic rim. Articular space loss, sclerosis and bone proliferation are accompanying features.6
On MR images, they appear as subchondral lesions with bulging of the articular surface, intraarticular involvement and variable—depending on their content—signal intensity on T2-weighted images (Figure 1).6
Figure 1. Intraarticular bone lesion, 57-year-old man who presents with degenerative arthropathy and mechanical pain in right knee. Sagittal gradient echo (GE) T2-weighted MR image shows a subchondral cyst with homogeneous high signal intensity (arrows), degeneration and tear of the internal meniscus, subchondral hyposignal (arrowhead) and articular effusion (asterisk).Intraosseous ganglia
Intraosseous ganglia are solitary cystic lesions found at the epiphysis of long bones, although they can also be found at the carpal or tarsal bones. Intraosseous ganglia of the knee are characterized by mucoid degeneration of the cruciate ligaments.5, 6 Most patients are asymptomatic, although they may present with pain, knee block or functional impairment.
MR images show well-defined, uni- or multilocular lesions that normally occur in non-pressure areas of a joint (Figure 2). They are usually larger than subchondral cysts and may communicate with the joint or show cortical disruption and soft-tissue mass.6
Figure 2. Intraarticular bone lesion, 49-year-old woman who presents with pain in right ankle. Coronal turbo gradient echo (TGE) T2-weighted image shows a subchondral lesion in the astragalus (arrows), with homogeneous and very high signal intensity, well-defined margins and hypointense septa. There is no loss of articular space or evidence of degenerative arthropathy. The lesion was treated by excision and curettage. The histologic diagnosis was intraosseous ganglion.Periarticular bone lesions Benign extraskeletal chondroid tumors
The only tumor included by the World Health Organization (WHO) in the group of extraskeletal chondroid tumors is soft tissue chondroma.7
Soft tissue chondromas are the least common variant of extraskeletal chondromas. They arise from the articular capsule or the connective tissue adjacent to the capsule. Clinically these chondromas present as slow-growing soft tissue masses that may be painful.8
The MR images show a lobulated mass with intermediate signal on T1-weighted sequences, and high signal intensity with punctate areas of low signal on T2-weighted sequences.8 They may show areas of signal similar to that of bone marrow on all sequences and eccentric erosion of the adjacent bone (Figure 3). The predominantly peripheral enhancement following intravenous administration of gadolinium and the correlation between MRI and radiographic findings help to demonstrate the mineralized cartilaginous matrix.8, 9
Figure 3. (A–D) Periarticular bone lesion, 80-year-old woman who presents with pain and a slow-growing mass adjacent to the patella. (A) Sagittal turbo spin echo (TSE) T1-weighted image shows a mass in Hoffa's fat pad that erodes the lower margin of the patella (arrowhead), with heterogeneous intermediate signal intensity and areas of hypointensity (arrow) and hyperintensity (dotted arrow). (B) Axial TSE T2-weighted image shows intensity similar to that of the subcutaneous tissue with areas of low and very high intensity (arrows). (C) The dynamic contrast-enhanced subtraction and selective fat-suppressed MR image shows heterogeneous and peripheral enhancement of the mass (dotted arrows). (D) Lateral radiograph shows ossification of the mass and erosion of the lower margin of the patella (arrowhead). The histologic diagnosis was Hoffa's fat pad chondroma.Benign skeletal chondroid tumors
Periosteal chondroma is a very uncommon (1% of bone tumors) benign tumor of chondroid origin that occurs more frequently in men younger than 30years. It is typically found at the metaphysis and at the sites of tendon and ligament attachment in the long bones of hands and feet.10
Periosteal chondromas have characteristic radiographic features: (Figure 4A) a soft-tissue mass that erodes the cortex and is often associated with subjacent sclerosis.10, 11 This soft-tissue mass may contain cartilage, calcifications or ossifications. On occasions, a thin and compact periosteal new bone formation may be seen surrounding the soft-tissue mass.
Figure 4. (A–C) Periarticular bone lesion, 40-year-old woman who presents with a 1-year history of right knee pain. (A) Anteroposterior radiograph shows a periosteal lesion with soft-tissue density (arrow) that erodes the cortex and is associated with a compact periosteal reaction (dotted arrow). (B) The mass shows homogeneous and very high signal intensity and a peripheral rim of low intensity on proton density weighted sequence with selective fat suppression. (C) On the axial contrast-enhanced TSE-T1 image, the mass shows thick peripheral enhancement (arrow). The histologic diagnosis was periosteal chondroma.
The MR images show a subperiosteal lobulated mass that is usually well defined, with intermediate to low signal intensity on T1-weighted sequences, and very high signal intensity, with a peripheral rim of low signal, on T2-weighted sequences (Figure 4B). Periosteal chondroma can also be associated with erosion and remodeling of the adjacent bone cortex.11 Enhancement after intravenous contrast administration and radiographic findings help in the differentiation with cystic masses (Figure 4C).11, 12Malignant bone tumors
Metastatic spread to the joints of malignant bone tumors is rare, while direct spread from primary bone tumors or from adjacent soft tissues is much more common.
Primary bone lymphoma is an uncommon malignancy (less than 5% of all primary bone tumors) that usually occurs in long bones of lower extremities and in the pelvis.13
Diagnosis of this tumor may be difficult because of its variable radiographic appearance. On plain radiographs, the lesion may appear virtually normal or as a permeative and highly destructive lesion with involvement of adjacent soft tissues.13, 14
Signal intensity of primary bone lymphoma is variable and unspecific. Most of them show low signal intensity on T1-weighted sequences, high signal intensity on T2-weighted sequences, and variable enhancement on contrast-enhanced images. Involvement of soft tissue is usually extensive, infiltrating and disproportionate in relation to the lesser involvement of the bone marrow cavity13 (Figure 5).
Figure 5. (A–C) Periarticular bone lesion, 24-year-old man who presents with a 2-year history of left hip pain, and a palpable mass adjacent to the left iliac bone. (A) Plain radiograph shows a bone lesion in the left iliac bone with cortical expansion and breakthrough (arrows). (B) Coronal TSE T1-weighted image shows a mass of intermediate signal intensity in the left iliac bone that causes cortical breakthrough (arrows), displaces the iliopsoas muscle (dotted arrows), and infiltrates the iliac bone marrow (asterisk). (C) Coronal TGE T1-weighted image with selective fat suppression after intravenous contrast administration shows heterogeneous enhancement of the mass and iliac bone marrow. The histological analysis after percutaneous biopsy revealed non-Hodgkin lymphoma.
MRI findings suggestive of primary bone lymphoma are extensive soft-tissue involvement with minimal or nonexistent cortical destruction15 and a near normal plain radiograph.13, 15 These characteristics may be due to the spread of tumor cells through small vessels that run through the cortex into the adjacent soft tissue without destructing the cortex.13Soft tissue lesions
The location of soft tissue lesions can be intraarticular, periarticular or both intraarticular and periarticular (Table 2). Most soft tissue lesions are benign, cystic or solid.
Table 2. Classification of soft tissue lesions that may be located in joints or in periarticular soft tissues.
|Intraarticular||Cystic lesions||Meniscal cysts|
|Proliferative synovial lesions||Lipoma arborescens|
|Synovitis nodular focal|
|Vascular lesions||Synovial hemangioma|
|Proliferative synovial lesions||GCT of the tendon sheath|
|Neurogenic tumors||SchwannomasNeurofibromasNeural fibrolipoma|
|Myxoid tumors||Periarticular myxoma r|
|Infectious lesions||Cat-scratch disease|
|Deposit diseases||Chronic tophaceous gout|
|Intra- and periarticular||Cystic lesions||Synovial cysts|
|Proliferative synovial lesions||Synovial osteochondromatosis|
|Primary malignant tumors||Degenerate PVS|
PVS, pigmented villonodular synovitis; GCT, giant cell tumor.
Most intraarticular soft tissue lesions are benign and can be classified as cystic (meniscal cyst), synovial proliferations (lipoma arborescens, pigmented villonodular synovitis, localized nodular synovitis) and vascular malformations (hemangiomas).Cystic lesions Meniscal cysts
A meniscal cyst is a collection of synovial fluid located within or adjacent (parameniscal) to the meniscus. The etiology of these cysts includes traumatic and degenerative origin. They become symptomatic when their size is sufficient to determine the occurrence of a mass in the articular interface, their characteristic presentation.
Figure 6. (A and B) Cystic soft tissue lesion of intraarticular location, 35-year-old man who presents with right knee trauma and pain in the medial compartment. Consecutive coronal fat-suppressed PD sequences show tear of the posterior horn of the medial meniscus (arrow) and a multiseptated parameniscal cyst (asterisks) that communicates with the meniscal tear. The treatment involved partial medial meniscectomy and excision of the parameniscal cysts.Synovial proliferative lesions Lipoma arborescens
Lipoma arborescens is a rare intraarticular lesion characterized by the replacement of the subsynovial connective tissue by hyperplasic proliferation of mature fat tissue giving rise to villous proliferations and is associated with chronic effusion.3 This condition most often occurs in middle-aged (50–60years) men that present with a long-standing swelling of the joint with effusion, pain and functional impairment.
Lipoma arborescens is usually monoarticular and associated with degenerative arthropathy, and less commonly, with inflammatory arthropathy. Most lesions have an intraarticular location within the knee, but they have also been observed in the periarticular bursae.18 The treatment of choice is synovectomy.3, 18
MR imaging are diagnostic and demonstrate a frondlike mass with signal behavior similar to that of fat on all sequences (Figure 7).18 The subsynovial inflammation may show enhancement following intravenous contrast administration.3, 19
Figure 7. Intraarticular soft tissue proliferation, 45-year-old man who presents with a several-year history of pain and functional impairment of right knee. Sagittal TSE T1-weighted sequence shows polylobulated swelling of the suprapatellar bursa, with frondlike appearance and signal intensity similar to that of fat (arrows) and joint effusion (asterisk). After synovectomy, the histological analysis confirmed the diagnosis of lipoma arborescens.
The frondlike appearance of lipoma arborescens helps to differentiate this entity from other lesions that also show high signal intensity on T1-weighted sequences, such as synovial lipoma, tendinous sheath lipoma, meniscal ossicle and synovial osteochondromatosis.19Pigmented villonodular synovitis
Pigmented villonodular synovitis represents an idiopathic, benign proliferative process characterized by focal or diffuse hypertrophy of the synovium with intraarticular hemosiderin deposition.20 This condition affects men and women equally and typically presents in the third and fourth decades. The knee is the most common location. Clinical manifestations include mechanical pain that may be associated with swelling and functional impairment. The treatment of choice is synovectomy and recurrences are not uncommon.21
MRI findings include joint effusion and localized nodular (Figure 8) or diffuse (Figure 9) thickening of the synovium, with low signal intensity on T1-weighted sequences, and very low signal on gradient-echo T2-weighted sequences, more prominent after intravenous contrast administration.20, 21 The tendency to hemorrhage of these lesions may explain the joint effusion caused by repeated hemarthrosis and the characteristic low signal intensity secondary to hemosiderin deposition.21
Figure 8. (A and B) Intraarticular soft tissue proliferation, 28-year-old woman who presents with recurrent join effusion of the left knee. (A) Lateral radiograph shows suprapatellar bursa effusion (asterisk). (B) Sagittal TGE T2-weighted sequence shows a suprapatellar mass of heterogeneous signal intensity with high and low signal intensity areas (arrow) and associated joint effusion. The patient underwent synovectomy and the histologic diagnosis was localized pigmented villonodular synovitis.
Figure 9. Intraarticular soft tissue proliferation, 30-year-old man who presents with mechanical pain and functional impairment in left knee. Sagittal TGE T2-weighted sequence shows diffuse synovial proliferation with very low signal intensity (arrows) that reveals hemosiderin deposition. The histological analysis performed after synovectomy confirmed the diagnosis of diffuse pigmented villonodular synovitis.
Differential diagnosis includes other forms of synovitis with hemosiderin deposition, such as hemophiliac arthropathy.20 The clinical setting and abnormal laboratory findings will help establish the diagnosis.Localized nodular synovitis
Localized nodular synovitis is an intraarticular lesion characterized by benign localized synovial proliferation. Localized nodular synovitis and pigmented villonodular synovitis are similar histologically, but with a different natural history of less risk of recurrence.22, 23 Localized nodular synovitis is usually found in the knee, predominantly in the infrapatellar fat pad. Symptoms are unspecific and include pain, swelling and joint block.23
Although MR findings are variable, typically, they show a well-defined, oval or polylobulated lesion, with intermediate or high signal intensity on T1-weighted sequences and heterogeneous signal on T2-weighted sequences, containing hypointense nodular or linear regions in the interior. These lesions also show intense and heterogeneous enhancement after intravenous contrast administration (Figure 10).22, 23
Figure 10. (A and B) Intraarticular soft tissue proliferation, 52-year-old woman who presents with pain and right knee block. Sagittal TSE T1-weighted (A) and axial TGE T2-weighted (B) images. Oval and well-defined lesion (arrows) in the infrapatellar fat pad with intermediate signal intensity on T1-weighted sequences and high signal intensity with some linear areas of low signal intensity on T2-weighted sequences. Arthroscopy confirmed the presence of a well-defined nodule in the infrapatellar fat pad. The histologic diagnosis was localized nodular synovitis.
The MRI findings suggestive of localized nodular synovitis and that help differentiate this entity from pigmented villonodular synovitis are well-defined margins, higher signal intensity due to the small amount of hemosiderin and the absence of hemorrhagic effusion.23Vascular lesions Synovial hemangioma
Synovial hemangioma is a rare (less than 1% of all hemangiomas) benign vascular lesion that usually affects children and young adults. Patients usually present with pain, swelling, and spontaneous hemarthrosis. Synovial hemangioma occurs predominantly in the knee.3 Most lesions are intraarticular and only 30% are located in the juxta-articular bursae.
MRI findings are usually diagnostic. Synovial hemangioma presents as a polylobulated diffuse mass or as a pedunculated mass of intermediate signal intensity on T1-weighted sequences, marked hyperintensity on T2-weighted sequences, containing linear fibrous septa of low signal intensity. Heterogeneous enhancement may be seen after intravenous contrast administration (Figure 11). It may show areas of hyperintensity on T1-weighted sequences caused by slow blood flow or the presence of fat.3 Sometimes these lesions infiltrate the marrow of adjacent bones and extend to periarticular tissues.24 The repetitive hemarthrosis of these lesions may give the appearance of pigmented villonodular synovitis and hemophiliac arthropathy.3
Figure 11. (A–C) Intraarticular soft tissue proliferation, 35-year-old man who presents with swelling and repetitive right knee effusion. (A) Axial TSE T1-weighted and (B) TGE T2-weighted MT (magnetization transfer) sequences show a mass in the medial recess (arrows) that invades the anterior and inner portions of the adjacent condyle (arrowheads), with intermediate signal and areas of hyperintensity on T1-weighted and areas of hyperintensity on T2 sequences. (C) Sagittal TGE T2-weighted sequence shows the mass extending to the suprapatellar bursa (asterisk) and invading the patellar bone marrow (arrowhead). The histologic diagnosis was synovial hemangioma.Periarticular soft tissue lesions
Periarticular soft tissue lesions can be classified as cystic (bursitis), synovial proliferative (giant cell tumor of the tendon sheath), benign neoplastic (lipomas, neurogenic tumors, myxoid tumors), infectious (cat-scratch disease) and deposit diseases (chronic tophaceous gout).Cystic lesions Bursitis
Periarticular bursae are small cavities around the joints that are composed of synovium-lined fibrovascular tissue. They function to reduce friction between osteomuscular structures.
Inflammatory bursitis, usually due to trauma, chronic overuse or more rarely infection, produces accumulation of fluid in the bursa that results in pain.25
On MR images, they are seen as cystic lesions in a specific anatomical location, with low signal intensity on T1-weighted sequences, hyperintensity on T2-weighted, and peripheral wall enhancement after intravenous contrast administration. When caused by trauma, they may show heterogeneous signal associated with hemorrhage25 (Figure 12).
Figure 12. (A and B) Periarticular soft tissue cystic lesion, 46-year-old man who presents with right knee pain after blunt trauma. (A) Sagittal TGE T2-weighted and (B) axial TGE fat-suppressed T1-weighted images show hemorrhagic prepatellar bursitis with heterogeneous hyperintensity (arrows) on T2-weighted sequence and peripheral enhancement (arrowheads) after intravenous contrast administration.
Distended bursae may contain dystrophic calcification that occurs in the setting of metabolic conditions, hemodialysis patients and scleroderma. In hydroxyapatite deposition disease, calcification usually occurs on the extensor surfaces of joints.26
Dystrophic calcification, more conspicuous on radiographs, contributes to the complex aspect, predominantly hypointense, seen on MR images (Figure 13).
Figure 13. Periarticular soft tissue cystic lesion, 40-year-old woman diagnosed with scleroderma that presents with a palpable juxtapatellar mass. Sagittal TGE T2-weighted image shows superficial prepatellar and infrapatellar bursitis containing heterogeneous low signal intensity areas (arrows) corresponding to dystrophic calcificacion.Synovial proliferations Giant cell tumor of the tendon sheath
Giant cell tumor of the tendon sheath, also known as nodular tenosynovitis or tenosynovial giant cell tumor, represents the extraarticular localized form of pigmented villonodular synovitis, being one of the most common soft tissue lesions of the hand.20 It typically affects adult women (30–50years) that usually present with a slow-growing, painless soft tissue mass. In the hand, this lesion usually affects the volar aspect of the fingers.20, 22
Plain radiographs show a soft tissue mass that may be associated with pressure erosions.20
MR images show a lobulated and well-defined mass adjacent to a tendon that is iso- or hypointense relative to muscle on T1-weighted sequences, and heterogeneous with intermediate or low signal on T2-weighted sequences, depending on the hemosiderin content. Most lesions show intense enhancement after intravenous contrast administration (Figure 14).20, 22
Figure 14. (A and B) Periarticular soft tissue proliferation, 47-year-old woman who presents with a palpable nodule on the dorsum of the second digit of the right hand. (A) Axial TSE T1-weighted sequence shows polylobulated lesion of heterogeneous intermediate signal intensity (arrows) located adjacent to the extensor digitorum tendon of the right hand. Axial contrast-enhanced TSE T1-weighted sequence (B) shows heterogeneous and hyperintense signal (arrows). After lesion excision, the histological analysis confirmed the diagnosis of giant cell tumor of the tendon sheath.Benign neoplasms
The most common periarticular benign neoplasms are lipomatous and neurogenic tumors. Less commonly, myxoid tumors can also be found in the periarticular soft tissues.Lipomatous benign tumors
Lipomas are the periarticular solid tumors most commonly found in adults and usually arise from the subcutaneous tissue or the muscle. They are more frequent in women and are usually located in the deep tissue of the extremities. The periarticular location is also frequent.27
Clinical manifestations depend on the size and location of the lesion, and its relationship with adjacent structures. Lipomas are usually asymptomatic and are incidentally discovered; sometimes they present as a painless palpable mass or as a painful mass with swelling and functional impairment secondary to compression of adjacent nervous structures.19, 27
On MR images, lipomas show homogeneous signal, similar to that of subcutaneous tissue on all sequences, and show no enhancement after intravenous contrast administration unless the lesion has a peripheral capsule or contains septa (Figure 15).19, 27 These septa may be thick and show nodules of non-fatty tissue, indistinguishable from well-differentiated liposarcomas.19
Figure 15. Periarticular benign soft tissue neoplasm, 65-year-old woman who presents with right hip pain radiating to the back of the thigh. Axial TSE T1-weighted image shows a well-defined mass in the right gluteus minimus muscle that extends through the sciatic notch, with signal intensity similar to that of adipose tissue, with a peripheral capsule of hypointensity (arrows) containing thin septa of low signal intensity (arrowhead). The histological analysis performed after partial excision was encapsulated lipoma.
Hibernoma is a rare tumor that usually occurs in areas with vestigial brown adipose tissue, such as the axilla.27 Hibernomas are more frequent in women aged 30–50years. Most lesions are asymptomatic and present as a palpable mobile mass of hard consistency.
MR images show a well-defined mass of heterogeneous signal, with areas of signal similar to that of adipose tissue on all sequences and areas of hypointensity that correspond to vascular branches (Figure 16).19, 27
Figure 16. (A–C) Periarticular benign soft tissue neoplasm, 77-year-old man with right shoulder pain. (A) Coronal TSE T1-weighted image shows a well-defined mass in the left axilla (arrow), with signal similar to that of subcutaneous tissue containing linear areas of hypointensity. (B) Axial fat-suppressed TSE T2-weighted image shows the hyperintense mass containing some areas of hypointensity (arrowheads). (C) Axial TGE T1-weighted image with fat suppression during the dynamic study using intravenous contrast shows linear structures that correspond with small vessels. The histological diagnosis after total excision was a hibernoma.
Differential diagnosis of hibernoma includes conventional form of lipoma with mature fat tissue and well-differentiated liposarcomas. Enhancement after intravenous contrast administration may be helpful in distinguishing hibernoma from conventional lipomas.19 The presence of thick septa or nodules is suggestive of well-differentiated liposarcoma.28Neurogenic tumors
Schwannomas and neurofibromas are peripheral nerve sheath tumors that may be found in the periarticular soft tissue.
Schwannomas, or neurilemomas, and neurofibromas most frequently affect patients 20–50years of age and account for 5% of all benign soft-tissue tumors. They present as a painless, slow-growing mass or patients may present with radiating pain caused by tumor compression. Unlike neurofibromas, the schwannoma is usually separable from the affected nerve within the epineurium.29
On MR images, neurogenic tumors present as unspecific solid masses, with low signal intensity on T1-weighted sequences, very high signal intensity on T2-weighted sequences, and homogeneous and intense enhancement after intravenous contrast administration (Figure 17). A fusiform morphology that follows the course of the nerve is suggestive of this type of tumors (Figure 17B).
Figure 17. (A and B) Periarticular benign soft tissue neoplasm, 58-year-old woman who presents with right knee pain that radiates to the leg. (A) Axial TGE T2-weighted MT sequence shows a well-defined mass in the popliteal fossa with homogeneous and high signal intensity (arrowheads). (B) Sagittal TGE T2-weighted sequence shows the fusiform morphology and the thickened nerve (dotted arrow). The patient underwent complete surgical excision. The histologic diagnosis was popliteal schwannoma.
Another sign that may help in the diagnosis is the “target sign” that consists of a central area of hypointensity with a peripheral ring of high signal intensity on T2-weighted sequences (Figure 18). This finding corresponds to a fibrous tissue centrally and myxoid tissue peripherally. The “target” sign can be seen in neurofibromas and schwannomas.29
Figure 18. Periarticular benign soft tissue neoplasm, 49-year-old woman who presents with a nodule in the soft tissue of right elbow and radiating pain upon palpation. Axial TSE T2-weighted image shows a well-defined mass in the neurovascular bundle of the knee (arrows) with very high signal intensity and a central area of hypointensity. Surgery confirmed association with the fascicles of the median nerve. After complete surgical excision, the histological analysis confirmed the diagnosis of neurofibroma.
Neural fibrolipoma or fibrolipomatous hamartoma is a rare benign neurogenic tumor that affects peripheral nerves and infiltrates the space surrounding the nerve fascicles.29, 30 Young males and females are usually affected and present with a mass in the volar aspect of the wrist or forearm, or with carpal tunnel symptoms, since the most common location is the median nerve.
MR images show longitudinal tubular structures of low signal intensity that correspond to nerve fascicles, surrounded by an area of signal intensity similar to that of fat on all sequences that corresponds with the fatty component of the tumor (Figure 19). These findings are diagnostic of neural fibrolipoma.30
Figure 19. Periarticular benign soft tissue neoplasm, 46-year-old women that presents with carpal tunnel syndrome. Coronal TSE T1-weighted image shows an elongated lesion in the right carpus with signal intensity similar to that of subcutaneous tissue (arrows) containing longitudinal areas of hypointensity (arrowhead). Surgery revealed a mass encompassing the median nerve. Biopsy and nerve decompression were performed, as microsurgical excision was not feasible without damaging the nerve. The histologic diagnosis was median nerve fibrolipoma.
In some cases, neural fibrolipoma is associated with macrodactyly29 and should be differentiated from other causes of macrodactyly such as macrodystrophia lipomatosa. In neural fibrolipoma only the space between nerve fascicles is involved, while in macrodystrophia lipomatosa there is diffuse lipomatous infiltration of the space between fascicles, bone marrow, periostium, muscles and subcutaneous tissue.31Myxoid tumors
Soft tissue tumors with myxoid matrix can be benign and malignant. Benign tumors are more commonly found in the intramuscular compartment of extremities.32
Periarticular myxoma is a rare benign tumor that arises near a joint and may cause pressure erosions in the adjacent bone.33
The high mucin and low collagen content of these tumors accounts for a MR behavior similar to that of cysts.34 They show low signal intensity on T2-weighted sequences (Figure 20A).32, 34 The heterogeneous enhancement after intravenous contrast administration is a reflection of their true solid nature and helps to differentiate these tumors from other cystic lesions (Figure 20B).12
Figure 20. (A and B) Periarticular benign soft tissue neoplasm, 55-year-old woman who presents with long-standing right carpal pain and functional impairment. (A) Coronal TGE T2-weighted sequence shows a polylobulated mass of hyperintensity that surrounds and infiltrates (dotted arrows) the carpal bones. (B) Sagittal contrast-enhanced TSE T1 sequence shows the mass with intermediate signal (asterisks) on T1-weighted sequence and homogeneous and intense enhancement (crosses). Surgery revealed that the lesion extended to the articular space eroding the carpal bones. After surgical biopsy and partial resection, the histologic diagnosis was periarticular myxoma.Infectious lesions
Cat-scratch disease is a regional lymphadenitis of infectious etiology caused by Bartonella henselae and associated with cat scratches. It affects young patients and manifests as a painful epitrochlear or axillary lymphadenopathy that goes into remission spontaneously or after antibiotic theraphy.35
MR findings include ill-defined subcutaneous nodules of homogeneous intermediate signal intensity on T1-weighted sequences, heterogeneous high signal intensity on T2-weighted sequences, and moderate to intense enhancement after intravenous contrast administration (Figure 21).35, 36 Its ill-defined appearance and edema of adjacent soft tissue help to differentiate this entity from metastatic lymph nodes and sarcomas, which present as well-defined nodules without associated edema.36
Figure 21. (A and B) Periarticular infectious soft tissue lesion, 20-year-old man who presents with a painful erythematous nodule adjacent to the right epitrochlea. Axial TSE T1-weighted (A) and TSE T2-weighted (B) sequences show an ill-defined subcutaneous nodule in the right epitrochlear region (arrows) of homogeneous and low signal intensity on T1-weighted sequence, heterogeneous high signal intensity on T2-weighted sequence with hyperintense reticulation of the adjacent subcutaneous tissue (dotted arrow). The skin lesion and the nodule went into remission after antibiotic therapy. These findings are compatible with cat-scratch disease.Deposit diseases Chronic tophaceous gouty arthritis
Gout is a metabolic disorder more frequent in men (30–50years) that is characterized by hyperuricemia, and results from an overproduction and/or diminished uric acid renal excretion.
Focal deposition of monosodium urate is called tophi and these are characteristic of chronic gouty arthritis, which usually presents several years after prior episodes of gout. Gouty tophi are located in the periarticular soft tissues of feet, hands, wrists, elbows and knees.3, 37
On plain radiographs, tophi present as periarticular nodules that cause eccentric bone erosions with sclerotic margins. The joint space is preserved and it is not affected until advanced stages of the disease. The lack of osteopenia3 helps to differentiate gout from other erosive arthropathies (Figure 22A).
Figure 22. (A–C) Periarticular deposit disease, 72-year-old man with right knee pain and block, diagnosed with long-standing gouty arthritis. (A) Lateral radiograph shows a soft tissue density lesion in the joint space (asterisks) and cortical erosion in the tibia (dotted arrow). Sagittal TSE T1-weighted (B) and axial TGE T2-weighted (C) sequences show a mass (arrows) of intermediate intensity with areas of hypointensity on T1-weighted sequences with areas of very low signal intensity on the T2-weighted sequence.
On MR images, most tophi show intermediate signal intensity on T1-weighted sequences (Figure 22B), and greatly variable (intermediate, hypointense or hyperintense) signal intensity on T2-weigthed sequences (Figure 22C).3, 37
This variability in signal intensity on T2-weighted sequences is related to the proportion of proteins, fibrous tissue, crystals and hemosiderin. Tophi usually show homogeneous and intense enhancement after intravenous contrast administration.37 Abnormal laboratory values, articular distribution and the correlation with radiographic findings help to establish the diagnosis.Intra and periarticular soft tissue lesions
Soft tissue lesions affecting both intraarticular and periarticular tissues may be classified as cystic (synovial cysts, ganglia), synovial proliferations (synovial osteochondromatosis) and primary malignant tumors (pigmented villonadular synovitis, synovial sarcoma)Cystic lesions Synovial cysts
Synovial cysts are fluid collections that may, or may not, communicate with the joint, and may extend in any direction. The presence of a synovial lining distinguishes them from other periarticular fluid collections.3
They are often incidentally discovered, but the presence of clinical manifestations depends on their size, location and relationship with adjacent structures. Patients may present with pain, swelling, functional impairment, or symptoms secondary to compression of adjacent nerves or with a palpable mass.3, 17
On MR images, these cysts typically present as a lesion of low signal intensity on T1-weighted sequences (Figure 23A) and high signal intensity on T2-weighted or STIR sequences. Sometimes, they may contain septa (Figure 23B) or loose bodies17 or may show hyperintensity on T1-weighted sequences secondary to hemorrhage or high proteinaceous component. Synovial cyst may also show wall and septal enhancement after intravenous contrast administration.
Figure 23. (A and B) Intra- and periarticular cystic lesion, 30-year-old man who presents with a palpable lesion in the upper third of right leg. Sagittal TSE T1-weighted (A) and TGE T2-weighted (B) sequences show a polylobulated synovial cyst in the subcutaneous tissue adjacent to the knee (arrows) with low signal intensity on T1-weighted sequences and high signal intensity with hypointense septa (arrowheads) on T2-weighted sequences.Ganglia
A ganglion is a cystic lesion of unknown origin, surrounded by dense connective tissue filled with gelatinous fluid rich in mucopolysaccharides.3
On MR images, ganglia present as cystic lesions indistinguishable from synovial cysts. They may show rim enhancement following contrast administration. The relevance of the diagnosis results from their location and relationship with adjacent structures. They may be periarticular, intraarticular or periosteal.38
Periarticular and periosteal ganglia are associated with erosions and remodeling of the adjacent cortical bone caused by extrinsic pressure (Figure 24). Sometimes periarticular ganglia may result in compressive neuropathy (Figure 25).3, 38 If nerve compression is long-standing may result in muscle atrophy (Figure 26).
Figure 24. (A and B) Intra- and periarticular cystic lesion, 24-year-old woman who presents with a palpable nodule adjacent to the posterior aspect of the radius. (A) Lateral plain radiograph of right carpus shows cortical remodeling and erosion of radial metaphysis (arrow). (B) Sagittal TSE T2-weighted sequence shows a well-defined mass in the posterior carpal region eroding the adjacent radial cortex (arrowheads), with homogeneous and high signal intensity (asterisk). Surgery revealed a hard nodule in close contact with the radial metaphysis. The histologic diagnosis was periosteal ganglion.
Figure 25. Intra- and periarticular cystic lesion. Axial TSE T2-weighted sequence shows a polylobulated lesion of very high signal intensity (arrows) containing septa of hypointensity (arrowhead) along the course of the right peroneal nerve. After lesion excision, the histologic diagnosis was ganglion of peroneal nerve sheath.
Figure 26. (A and B) Intra- and periarticular cystic lesion. Oblique coronal TSE T2-weighted sequences show a suprascapular ganglion of high signal intensity (arrows) containing hypointense septa and diffuse high signal intensity of the infraspinatus muscle that results from denervation secondary to compressive neuropathy (asterisks). A gelatinous fluid was obtained by ultrasound-guided percutaneous aspiration and corticosteroids injected for lesion sclerosis.
Intraarticular ganglia are usually located adjacent to ligaments or articular capsule, or can be intraosseous. On MR images, those ganglia associated with ligaments present as cystic lesions of fusiform morphology located among the ligament fibers, or as rounded lesions adjacent to the ligament surface.5, 6, 38Proliferative synovial lesions Synovial osteochondromatosis
Synovial osteochondromatosis is a chondroid metaplasia of the synovium that generates nodules of hyaline cartilage. It presents as an articular or periarticular mass or conglomerate that may erode the adjacent bone, especially in joints with a thick capsule such as the wrist or the hip.
In the initial phase (non-mineralized synovial osteochondromatosis), there is active chondroid metaplasia but no intraarticular chondroid fragments. Plain radiographs are usually normal or show subtle changes. MR findings are diagnostic and characterized by an isointense or somewhat hyperintense mass on T1-weighted sequences, and with very high signal intensity on T2-weighted sequences.9 The lesion may contain hypointense septa (Figure 27). Increased signal following intravenous contrast administration helps to differentiate synovial osteochondromatosis from cystic lesions.12
Figure 27. Intra- and periarticular proliferative lesion, 57-year-old man who presents with left knee pain and block. Sagittal TSE T2-weighted sequence shows a large and well-defined synovial mass of homogeneous and very intense signal intensity (crosses). Following synovectomy, the histologic diagnosis was non-mineralized synovial osteochondral metaplasia.
In the second phase (mineralized synovial osteochondromatosis), synovial chondroid nodules and intraarticular chondral fragments are present. In this phase, MR images show multiple intraarticular nodules or a lobulated mass of intermediate signal intensity on T1-weighted sequences, and of high signal intensity on T2-weighted sequences containing areas of hypointensity in the interior on all sequences (Figure 28).3, 9
Figure 28. (A and B) Intra- and periarticular proliferative lesion, 62-year-old man who presents with right knee pain and a palpable mass in the popliteal fossa. Sagittal TSE T1-weighted (A) and TGE T2-weighted (B) images reveal a lobulated mass adjacent to the posterior cruciate ligament with intermediate signal intensity on T1-weighted and high signal intensity on T2-weighted, containing multiple small areas of hypointensity (arrows). Joint effusion and signs of degenerative arthropathy are also visible. Following synovectomy, the histological analysis confirmed the diagnosis of mineralized synovial osteochondral metaplasia.
In the last phase (ossified synovial osteochondromatosis), there are intraarticular chondral fragments without active synovial disease. On MR images, it appear as intraarticular nodules of signal intensity similar to that of the bone marrow on all sequences, with a peripheral halo of hypointensity corresponding to foci of endochondral ossification that are usually visible on plain radiographs or CT.9
Synovial osteochondromatosis should not be confused with other causes of osteocartilaginous loose bodies (secondary osteochondromatosis) that may be associated with trauma, degenerative arthropathy, osteonecrosis or neuropathic arthropathy39Primary malignant tumors Degenerate pigmented villonodular synovitis
Degenerate pigmented villonodular synovitis, albeit rare, is the most common primary malignant neoplasia of the joints. It represents the malignant form (3%) of diffuse pigmented villonodular synovitis, being the knee the most common location.20
MR findings of malignant pigmented villonodular synovitis may be indistinguishable from the benign form (Figure 9). Findings suggest that malignant transformation are extensive bone marrow invasion, extraarticular extensions (Figure 29) and metastases.20, 40
Figure 29. (A–C) Intra- and periarticular primary malignant tumor, 57-year-old woman who presents with long-standing left knee pain and block. Saggittal TSE T1-weighted (A) and TGE T2-weighted (B) sequences show a large mass (arrows) in the left knee of heterogeneous intermediate signal intensity on T1-weighted sequence, and heterogeneous with hyperintense and hypointense areas on T2-weighted sequences. There is bone marrow erosion and infiltration (dotted arrows) of femur and tibia and extension to periarticular soft tissues. (C) Axial contrast-enhanced fat-suppressed dynamic study shows heterogeneous and intense enhancement of the mass (crosses). Following percutaneous biopsy, the histological diagnosis was malignant pigmented villonodular synovitis.Synovial sarcoma
Synovial sarcomas usually present as a painful periarticular soft tissue mass that may extend to the adjacent joint.41 Most tumors arise in an extraarticular location and extend to the adjacent joint. Purely articular involvement is rare.42
The most common findings on MR are a polylobulated lesions of tissue mass, usually well-defined—although it may be infiltrative—with heterogeneous intermediate signal intensity on T1-weighted sequences, and heterogeneous high signal intensity on T2-weighted sequences (Figure 30).40, 41 The most characteristic finding, albeit rare, is the triple sign (Figure 30B) where intermediate signal intensity (solid elements), hyperintensity (hemorrhage and necrosis) and hypointensity (fibrosis or calcification) coexist.41
Figure 30. (A and B) Intraarticular primary malignant tumor, 57-year-old woman who presents with a painful mass in the left popliteal fossa that appears hard at palpation. (A) Sagittal TSE T1-weighted image shows a large well-defined mass in the soft tissues adjacent to the posterior aspect of the femur (asterisk), of heterogeneous intermediate signal intensity. (B) Axial TSE T2-weighted image shows the heterogeneous mass with hypointense (dotted arrow), intermediate and hyperintense (arrow) areas. The mass was resected completely and the histologic diagnosis confirmed synovial sarcoma.
Small tumors (<5cm) may present as well-defined masses or nodules of homogeneous signal on all sequences and simulate a non-malignant process. A usual manifestation is the slow growth of synovial sarcomas, even after several years of progression, in spite of their malignant nature (Figure 31).40, 41
Figure 31. (A and B) Periarticular primary malignant tumor, 34-year-old woman who presents with palpable nodule in the retromaleolar area. Sagittal TSE T1-weighted (A) and axial TSE T2-weighted (B) images show a well-defined nodule (arrows) in close contact with the tendon of the flexor digiturum longus (dotted arrows), of homogeneous and intermediate signal intensity on T1-weighted sequences, and heterogeneous and high signal intensity on T2-weighted sequence. The histologic diagnosis was synovial sarcoma.Conclusions
Plain radiography should be the primary imaging technique in the study of articular and periarticular tumors as it helps in the characterization of mineralized masses and provides information that may be useful in the characterization of lesions affecting adjacent bones.
In most cases, an MRI study is also required as this technique can accurately determine the anatomic origin of lesions and it can be used to plan the treatment.
In most cases, MR can suggest or determine a definite diagnosis based on the location and signal features of articular and periarticular tumors.Authorship
RSF has been instrumental in this work partnering with CMD in data acquisition, analysis, interpretation and design. ARP, AMC and ARR have done the bibliographic search and content writing. All of them have contributed equally to the study conception and approval of the work. Exclusively CMD and RSF contributed to the development of the work and especially took care of the critical review of the manuscript.Conflict of interest
The authors declare not having any conflict of interest.
☆ Please cite this article as: Rodríguez Pan A, et al. Tumores articulares y periarticulares: diagnóstico diferencial con resonancia magnética. Radiología. 2012;54:21–44.
Received 14 September 2010
Accepted 22 January 2011
Corresponding author. firstname.lastname@example.org
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