Systemic approach to bone tumor radiology

In this presentation, systemic approach to bone tumor diagnosis by radiology procedures is explained. it is based on radiology assistant website

1. Systemic approach to bone tumor radiology Ramin Sadeghi , MD

2. Introduction The most important determinators in the analysis of a potential bone tumor are: The morphology of the bone lesion on a plain radiograph Well-defined osteolytic ill-defined osteolytic Sclerotic The age of the patient The plain radiograph is the most useful examination for differentiating these lesions.  CT and MRI are only helpful in selected cases.

3. The most reliable indicator in determining whether these lesions are benign or malignant is the zone of transition between the lesion and the adjacent normal bone

4. Infections, a common tumor mimic, are seen in any age group. Infection may be well-defined or ill-defined osteolytic , and even sclerotic. EG and infections should be mentioned in the differential diagnosis of almost any bone lesion in patients Many sclerotic lesions in patients > 20 years are healed, previously osteolytic lesions which have ossified, such as: NOF, EG, SBC, ABC and chondroblastoma .

5. Zone of transition The zone of transition is the most reliable indicator in determining whether an osteolytic lesion is benign or malignant.   The zone of transition only applies to osteolytic lesions since sclerotic lesions usually have a narrow transition zone.

6. A small zone of transition results in a sharp, well-defined border and is a sign of slow growth. In patients In patients > 30 years, and particularly over 40 years, despite benign radiographic features, metastasis or plasmacytoma also have to be considered NOF, SBC and ABC

7. Wide zone of transition An ill-defined border with a broad zone of transition is a sign of aggressive growth Infection and EG should always be considered and DDx

8. Age is one of the most important clues for correct diagnosis of bone tumors

9. A periosteal reaction is a non-specific reaction and will occur whenever the periosteum is irritated by a malignant tumor, benign tumor, infection or trauma. There are two patterns of periosteal reaction: a benign and an aggressive type. A Codman's triangle refers to an elevation of the periosteum away from the cortex, forming an angle where the elevated periosteum and bone come together.

10. Benign periosteal reaction Malignant lesions never cause a benign periosteal reaction. A benign type of periosteal reaction is a thick, wavy and uniform callus formation resulting from chronic irritation. Image: An OO

11. Aggressive periosteal reaction This type of periostitis is multilayered, lamellated or demonstrates bone formation perpendicular to the cortical bone. left: Osteosarcoma with interrupted periosteal reaction and Codman's triangle proximally. middle: Ewing sarcoma with lamellated and focally interrupted periosteal reaction. (blue arrows) right: Infection with a multilayered periosteal reaction. Notice that the periostitis is aggressive, but not as aggressive as in the other two cases. Fibrous dysplasia, Enchondroma , NOF and SBC are common bone lesions. They will not present with a periosteal reaction unless there is a fracture. If no fracture is present, these bone tumors can be excluded.

12. Cortical destruction Cortical destruction is a common finding, and not very useful in distinguishing between malignant and benign lesions.  Complete destruction may be seen in high-grade malignant lesions, but also in locally aggressive benign lesions like EG and osteomyelitis.  More uniform cortical bone destruction can be found in benign and low-grade malignant lesions.  Endosteal scalloping of the cortical bone can be seen in benign lesions like FD and low-grade chondrosarcoma .

13. The images on the left show irregular cortical destruction in an osteosarcoma (left) and cortical destruction with aggressive periosteal reaction in Ewing's sarcoma.

14. In ballooning the destruction of endosteal cortical bone and the addition of new bone on the outside occur at the same rate, resulting in expansion. This ' neocortex ' can be smooth and uninterrupted, but may also be focally interrupted in more aggressive lesions like GCT. left: Chondromyxoid fibroma A benign, well-defined, expansile lesion with regular destruction of cortical bone and a peripheral layer of new bone. right: Giant cell tumor A locally aggressive lesion with cortical destruction, expansion and a thin, interrupted peripheral layer of new bone. Notice the wide zone of transition towards the marrow cavity, which is a sign of aggressive behavior.

15. In the group of malignant small round cell tumors which include Ewing's sarcoma, bone lymphoma and small cell osteosarcoma, the cortex may appear almost normal radiographically , while there is permeative growth throughout the Haversian channels. These tumors may be accompanied by a large soft tissue mass while there is almost no visible bone destruction. The image on the left shows an Ewing's sarcoma with permeative growth through the Haversian channels accompanied by a large soft tissue mass. The radiograph does not shown any signs of cortical destruction.

16. Location within the skeleton The location of a bone lesion within the skeleton can be a clue in the differential diagnosis. The illustration on the left shows the preferred locations of the most common bone tumors. In some locations, such as in the humerus or around the knee, almost all bone tumors may be found.

17. Location of the tumors in the skeleton Hemangioma   spine , ribs, craniofacial bones, femur, tibia Lymphoma  femur, tibia, humerus , iliac bone, vertebra Metastases  vertebrae, ribs, pelvis, femur, humerus Non Ossifying Fibroma  tibia, femur, fibula, humerus Osteoid osteoma   femur, tibia, spine, tarsal bone, phalanx Osteoblastoma   spine, tarsal bone ( calc ), femur, tibia, humerus Osteochondroma   femur, humerus , tibia, fibula, pelvis Osteomyelitis  femur, tibia, humerus , fibula, radius Osteosarcoma  femur, tibia, humerus , fibula, iliac bone Solitary Bone Cyst  proximal humerus , proximal femur, calcaneal bone , iliac bone Aneurysmal Bone Cyst  tibia, femur, fibula, spine, humerus Adamantinoma tibia shaft, mandible Chondroblastoma   femur, humerus , tibia, tarsal bone ( calc ), patella Chondromyxoid fibroma  tibia, femur, tarsal bone, phalanx foot , fibula Chondrosarcoma   femur, rib, iliac bone, humerus , tibia Chordoma   sacrococcygeal , spheno -occipital , cervical, lumbar, thoracic Eosinophilic Granuloma  femur, skull , iliac bone, rib, vertebra Enchondroma   phalanges of hands and feet , femur, humerus , metacarpals , rib Ewing's sarcoma  femur, iliac bone , fibula, rib, tibia Fibrous dysplasia  femur, tibia, rib, skull , humerus Giant Cell Tumor  femur, tibia, fibula, humerus , distal radius

18. Epiphysis Only a few lesions are located in the epiphysis, so this could be an important finding. In young patients it is likely to be either a chondroblastoma or an infection. In patients over 20, a giant cell tumor has to be included in the differential diagnosis. In older patients a geode, i.e. degenerative subchondral bone cyst must be added to the differential diagnosis. Look carefully for any signs of arthrosis . Metaphysis NOF, SBC, CMF, Osteosarcoma, Chondrosarcoma , Enchondroma and infections. Diaphysis Ewing's sarcoma, SBC, ABC, Enchondroma , Fibrous dysplasia and Osteoblastoma .

19. Centric in long bone SBC , eosinophilic granuloma, fibrous dysplasia, ABC and enchondroma are lesions that are located centrally within long bones. Eccentric in long bone Osteosarcoma, NOF , chondroblastoma , chondromyxoid fibroma, GCT and osteoblastoma are located eccentrically in long bones. Cortical Osteoid osteoma is located within the cortex and needs to be differentiated from osteomyelitis. Juxtacortical Osteochondroma . The cortex must extend into the stalk of the lesion. Parosteal osteosarcoma arises from the periosteum . SBC: central diaphyseal NOF: eccentric metaphyseal SBC: central diaphyseal Osteoid osteoma : cortical Degenerative subchondral cyst: epiphyseal ABC: centric diaphyseal

20. Matrix Calcifications or mineralization within a bone lesion may be an important clue in the differential diagnosis. There are two kinds of mineralization: a chondroid matrix in cartilaginous tumors like enchondromas and chondrosarcomsa and an osteoid matrix in osseus tumors like osteoid osteomas and osteosarcomas. 

21. Chondroid matrix Calcifications in chondroid tumors have many descriptions: rings-and-arcs, popcorn, focal stippled or flocculent. left: Enchondroma , the most commonly encountered lesion of the phalanges. middle: middle: Peripheral chondrosarcoma , arising from an osteochondroma ( exostosis ). right: Chondrosarcoma of the rib.

22. Osteoid matrix Mineralization in osteoid tumors can be described as a trabecular ossification pattern in benign bone-forming lesions and as a cloud-like or ill-defined amorphous pattern in osteosarcomas. Sclerosis can also be reactive, e.g. in Ewing’s sarcoma or lymphoma. left Cloud-like bone formation in osteosarcoma. Notice the aggressive, interrupted periosteal reaction (arrows). right Trabecular ossification pattern in osteoid osteoma . Notice osteolytic nidus (arrow).

23. Polyostotic lesions Polyostotic lesions   NOF, fibrous dysplasia, multifocal osteomyelitis, enchondromas , osteochondoma , leukemia and metastatic Ewing' s sarcoma.  Multiple enchondromas are seen in Morbus Ollier .  Multiple enchondromas and hemangiomas are seen in Maffucci's syndrome. Polyostotic lesions > 30 years   Common: Metastases, multiple myeloma, multiple enchondromas .  Less common: Fibrous dysplasia, Brown tumors of hyperparathyroidism, bone infarcts. Mnemonic for multiple oseolytic lesions: FEEMHI :  Fibrous dysplasia, enchondromas , EG, Mets and myeloma, Hyperparathyroidism, Infection.

24. Polyostotic Fibrous Dysplasia. Multiple osteolytic lesions in femur

25. Spine lesions

26. 1-Hemangioma . 2-Metastasis . 3-Multiple myeloma. 4-Plasmocytoma : vertebra plana . This 'Mini Brain ' appearance of plasmacytoma in the spine is sufficiently pathognomonic to obviate biopsy

27. Ill defined osteolytic tumors

28. Infection is seen in all ages. Ill-defined borders in GCT is seen in a locally aggressive lesion. Chondrosarcoma is usually well-defined, but high grade chondrosarcoma can be ill-defined. Metastases and myeloma are also usually well-defined, but sometimes ill-defined.

29. A partially ill-defined osteolytic lesion with endosteal scalloping. There are cloud-like calcifications indicating a chondroid matrix. These imaging findings and the size of the lesion favor the diagnosis of a chondrosarcoma . Most commonly presents as a well-defined lesion, but uncommonly it can be encountered as an ill-defined lytic lesion. Calcifications can be seen when there is a large myxoid component within the tumor, but they are not essential for the diagnosis.

30. Two other lesions that proved to be a chondrosarcoma . Notice that calcifications are not essential in chondrosarcoma .

31. A lobulated partially ill-defined lytic lesion of the proximal humerus . The presence of calcifications suggest that this is a chondroid tumor. The lytic parts with cortical involvement and expansion should raise the suspicion of a high grade chondrosarcoma

32. Eosinophilic granuloma EG is like osteomyelitis a great mimicker of benign and malignant bone tumors. Must be included in the differential diagnosis of almost any ill-defined osteolytic bone lesion in patients under the age of 30. May also present as a well-defined lesion. EG can be excluded in patients > 30 years. Commonly found in the skull, mandible, spine and long bones, but can occur anywhere.

33. examples of EG with ill-defined borders. There are single or multiple layered periosteal reactions.

34. a typical presentation of EG in the skull as an ill-defined osteolytic lesion

35. Ewing’s sarcoma Most common presentation : ill-defined osteolytic lesion with multiple small holes in the diaphysis of a long bone in a child with a large soft tissue mass. Presentation with pain, mass, fever, anemia and leukocytosis. Most common location : femur, iliac bone, fibula, rib, tibia. Differential diagnosis : Osteosarcoma, lymphoma, infection and EG. Frequently aggressive type of periosteal reaction, but never a benign type.

36. An ill-defined lytic lesion in the femur of a young patient. There is a permeative destruction pattern with irregular cortical destruction. There is an aggressive periosteal reaction (arrow). This is also called sunburst appearance

37. a patient with a Ewing's sarcoma in the femur. Notice the ill-defined osteolysis . There is an aggressive periosteal reaction

38. an ill-defined lytic lesion of the right iliac bone in a young patient which can easily be overlooked. Final diagnosis: Ewing's sarcoma

39. Giant cell tumor Giant cell tumor is a benign lesion, but can be locally aggressive. A well-defined margin is associated with a locally less aggressive biologic behavior. In many cases the margin is ill-defined (figure). These tumors often thin the cortex and may expand into the soft tissues surrounding the bone. Most commonly seen in age 20-40 years. In the age group > 40 years, metastasis and plasmacytoma have to be included in the differential diagnosis.

40. On the left a giant cell tumor of the distal radius with ill-defined margins, destruction of the subchondral bone plate and extension towards the soft tissues. On the right a giant cell tumor in the proximal tibia with somewhat better defined margin and non-interrupted cortical bone.

41. Lymphoma Primary non-Hodgkin's lymphoma of bone is rare. Presentation: usually pain and palpable mass. Preferential sites: femur and humerus . Radiographic appearance may differ from virtually normal to severely permeative . Differential diagnosis: Ewing's sarcoma, however, lymphoma usually in higher age group Metastasis and plasmacytoma in age > 40y.

42. An ill-defined lytic lesion of the humerus diaphysis. Notice tunneling of the cortical bone (red arrows). On the MR notice the linear abnormalities within the cortical bone and the circumferential soft tissue mass. Differential diagnosis (depending on age): Ewing's sarcoma, osteomyelitis and bone lymphoma. Biopsy revealed Non-Hodgkin lymphoma

43. metastases Most common malignancy in bone. Must be considered in the differential diagnosis of any bone lesion in a patient > 40 years. May present as well-defined osteolytic , ill-defined osteolytic and also as sclerotic bone lesion. Majority of osteolytic metastases originate from breast, lung, kidney, colon, melanoma and thyroid.

44. A 60 year old patient with a known malignancy. There is a lesion in the distal femur, that you could easily overlook and think that it was focal osteopenia. The lesion presents as a large ill-defined osteolytic mass extending into the epiphysis and almost abuttting the articular surface. In a patient 20-40 years of age GCT would be a possible diagnosis. It proved to be a metastasis.

45. Multiple myeloma plasmacytoma Multiple myeloma must be included in the differential diagnosis of any lytic bone lesion, either well-defined or ill-defined in age > 40. Most common presentation: multiple lytic 'punched out' lesions. A solitary presentation is referred to as plasmacytoma . Usually no increased uptake on bone scan. The most common location is in the axial skeleton (spine, skull, pelvis and ribs) and in the diaphysis of long bones (femur and humerus ).

46. Osteomyelitis Broad spectrum of radiographic features. May occur at any age, no typical location. Radiographic appearance : predominant reactive changes, including periosteal reaction, sclerosis and edema. Periosteal reaction and permeative pattern may mimic malignant process: Ewing's sarcoma, osteosarcoma, lymphoma, leukemia. In the pediatric age group eosinophilic granuloma may also mimic osteomyelitis. Pediatric osteomyelitis: most commonly in central metaphysis, may cross to epiphysis. Adult osteomyelitis: most commonly in central metaphysis or diaphysis. May be highly permeative with cortical breakthrough, abcesses and fluid along fascia on MR imaging.

47. a subacute form of osteomyelitis. There is an eccentric ill-defined lesion seen on both sides of the physeal plate in the proximal tibia. This is highly suggestive for osteomyelitis. Other lesions do not cross the growth plate in general. On the right coronal T1-weighted MR image reveals a well-defined epi-metaphyseal lesion. There is a dark peripheral zone of reactive sclerosis, and extensive edema with low signal Intensity in the metaphysis.

48. an ill-defined osteolytic lesion in the proximal metaphysis of the tibia with extensive reactive sclerosis and solid periosteal reaction.

49. osteosarcoma Hallmark of osteosarcoma is the production of bony matrix, which is reflected by the sclerosis seen on the radiograph. Usually typical malignant features including permeative-motheaten pattern of destruction, irregular cortical destruction and aggressive (interrupted) periosteal reaction. Occasionally an osteosarcoma may present as a lytic or mixed lytic-sclerotic lesion. Completely lytic osteosarcoma may represent telangiectatic subtype, composed of multiple cavities filled with blood (may resemble aneurysmal bone cyst!).

50. a mixed osteolytic and sclerotic lesion in the proximal humerus with irregular cortical destruction. There is an aggressive periosteal reaction and a soft tissue mass.

51. well-defined osteolytic tumors and tumor-like lesions These lesions are sometimes referred to as benign cystic lesions, which is a misnomer since most of them are not cystic, except for SBC and ABC.  It is true that in patients under 30 years a well-defined border means that we are dealing with a benign lesion, but in patients over 40 years metastases and multiple myeloma have to be included in the differential diagnosis.

52. In patients In patients > 40 years metastases and multiple myeloma are by far the most common well-defined osteolytic bone tumors . Patients with Brown tumor in hyperparathyroidism should have other signs of HPT or be on dialysis. Differentiation between a benign enchondroma and a low grade chondrosarcoma can be impossible based on imaging findings only. Infection is seen in all ages.

53. Mnemonic

54. Fibrous dysplasia Fibrous dysplasia is a benign disorder characterized by tumor-like proliferation of fibro- osseus tissue and can look like anything. FD most commonly presents as a long lesion in a long bone. FD is often purely lytic and takes on ground-glass look as the matrix calcifies. In many cases there is bone expansion and bone deformity. The ipsilateral proximal femur is invariably affected when the pelvis is involved. When FD in the tibia is considered, adamantinoma should be in the differential diagnosis. Discriminator : If periosteal reaction or pain is present, exclude fibrous dysplasia, unless there is a fracture .

55. Fibrous dysplasia: various presentations with or without sclerotic margin, with groundglass appearance, with calcifications or ossifications

56. Enchondroma In the phalanges of the hand it frequently presents with a fracture.  It is the most common lesion in the phalanges, A well-defined lytic lesion in the hand is almost always an enchondroma . In some locations it can be difficult to differentiate between enchondroma and bone infarct.  It is almost impossible to differentiate between enchondroma and low grade chondrosarcoma based on radiographic features alone . Ollier's disease is multiple enchondromas . Maffucci's syndrome is multiple enchondromas with soft tissue hemangiomas . Features that favor the diagnosis of a low-grade chondrosarcoma : Higher age Size > 5 cm Activity on bone scan Fast enhancement on dynamic contrast enhanced MR series Endosteal scalloping of the cortical bone Discriminators  : Must have calcification except in phalanges. No periostitis .

57. left Fat suppressed coronal PD-image of the knee. Typical enchondromas in the femur and tibia as seen frequently as coincidental finding in MR-examinations. middle Well-defined lytic lesion in the rib with cortical thinning. right Well-defined lytic lesion with a sclerotic margin and without calcifications in the end phalanx.

58. Eosinophilic granuloma EG is a non-neoplastic proliferation of histiocytes and is also known as Langerhans cell histiocytosis .  It should be included in the differential diagnosis of any sclerotic or osteolytic lesion, either well-defined or ill-defined, in patients under the age of 30. The diagnosis EG can be excluded in age > 30. EG is usually monostotic , but can be polyostotic . 

59. left Osteolytic lesion arising from the neurocranium with associated soft tissue swelling. middle Mixed lytic-sclerotic lesion, not well-defined with solid periosteal reaction. right Sharply defined osteolytic lesion of the skull. There is no 'button sequestrum ', which is more or less pathognomonic.

60. Button sequestrum Pathognomic of EG

61. Giant cell tumor Giant cell tumor is a lesion with multinucleated giant cells. In most cases it is a benign lesion. Malignant GCT is rare and differentiation between benign or malignant GCT is not possible based on the radiographs. GCT is also included in the differential diagnosis of an ill-defined osteolytic lesion, provided the age and the site of the lesion are compatible. Discriminators : Epiphyses must be closed. Must be an epiphyseal lesion and abut the articular surface. Must be well-defined and non-sclerotic margin. Must be eccentric.

62. Giant cell tumor in the tibia abuts the articular surface

63. NOF A benign well-defined, solitary lesion due to proliferation of fibrous tissue. It is the most common bone lesion .  NOF is frequently a coincidental finding with or without a fracture.  NOF usually has a sclerotic border and can be expansile . They regress spontaneously with gradual fill in . NOF may occur as a multifocal lesion.  The radiographic appearance is almost always typical, and as such additional imaging and biopsy is not warranted. Discriminators : Must be under age 30. No periostitis or pain.

64. Osteoblastoma Osteoblastoma is a rare solitary, benign tumor that produces osteoid and bone. Consider osteoblastoma when ABC is in the differential diagnosis of a spine lesion (figure). A typical osteoblastoma is larger than 2 cm, otherwise it completely resembles osteoid osteoma . Discriminator : Mention when ABC is mentioned.

65. Metastases Metastases are the most common malignant bone tumors . Metastases must be included in the differential diagnosis of any bone lesion, whether well-defined or ill-defined osteolytic or sclerotic in age > 40. Bone metastases have a predilection for hematopoietic marrow sites: spine, pelvis, ribs, cranium and proximal long bones: femur, humerus . Metastases can be included in the differential diagnosis if a younger patient is known to have a malignancy, like neuroblastoma , rhabdomyosarcoma , retinoblastoma. Most common osteolytic metastases: kidney, lung, colon and melanoma. Most common osteosclerotic metastases: prostate and breast. Discriminator : Must be over age 40.

66. Multiple Myeloma Multiple myeloma must be included in the differential diagnosis of any lytic bone lesion, whether well-defined or ill-defined in age > 40. The most common location is in the axial skeleton (spine, skull, pelvis and ribs) and in the diaphysis of long bones (femur and humerus ). Most common presentation: multiple lytic 'punched out' lesions.  Multiple myeloma doe not show any uptake on bone scan. Discriminator : Must be over age 40 . Differential diagnosis: multiple lesions: metastases. solitary lesion: chondrotumor , GCT and lymphoma.

67. On the left a CT-image of a patient with multiple myeloma. Notice the numerous osteolytic lesions and permeative cortical destruction pattern. In the left sacral wing there is a larger lesion with a high density due to replacement of fatty bone marrow by myeloma (red arrow).

68. Aneurysmal Bone Cyst ABC is a solitary expansile well-defined osteolytic bone lesion, that is filled with blood. It is named aneurysmal because it is expansile . ABC is thought to be the result of a reactive process secondary to trauma or increased venous pressure. Sometimes an underlying lesion like GCT, osteoblastoma or chondroblastoma can be found. ABC can occur almost anywhere in the skeleton. Discriminators: Must be under age 30. Must be expansile

69. ABC of the proximal fibula: well-defined, expansile osteolytic lesion with thin peripheral bone shell

70. Solitary Bone Cyst Solitary bone cyst, also known as unicameral bone cyst, is a true cyst.  Many well-defined osteolytic lesions are often called cystic, but this is a misnomer.  SBC frequently presents with a fracture.  Sometimes a fallen fragment is appreciated.  Predilection sites: proximal humerus and femur .  Usually less expansion compared with ABC.  Differential diagnosis: ABC, FD when cystic .  SBC may migrate from metaphysis to diaphysis during growth of the bone. Discriminators: Must be under age 30. Must be centric

71. SBC: well-defined osteolytic lesion without expansion of the proximal meta-diaphysis of the humerus with pathologic fracture

72. Hyperparathyroidism Brown tumors can occur in any bone and present as osteolytic lesions with sharp margins.  Septa and ridges may be seen.  Differential diagnosis: ABC, metastases and GCT depending on location and age . Discriminators: Must have other signs of HPT.

73. a patient who had a nefrectomy for renal cell carcinoma and who was on dialysis. Multiple well-defined osteolytic lesions were found on a follow up CT scan. The differential diagnosis included metastases and Brown tumors in hyperparathyroidism. Biopsy revealed Brown tumor.

74. Infection Infection or osteomyelitis is the great mimicker of bone tumors.  It has a broad spectrum of radiographic features and occurs at any age and has no typical location.  In the chronic stage it can mimic a benign bone tumor ( Brodies abscess).  In the acute stage it can mimic a malignant bone tumor with ill-defined margins, cortical destruction and an aggressive type of periostitis .  Only when there is a thick solid periosteal reaction we can recognize the non-malignant underlying process. Discriminators: None.

75. Chondroblastoma The patella, carpal and tarsal bones can be regarded as epiphysis concerning the differential diagnosis.  On the left a chondroblastoma located in the patella. Discriminators  : must be under age 30. must be in the epiphysis.

76. Chondroblastoma : notice extensive edema (middle) and fluid-fluid level due to secondary ABC.

77. Chondromyxoid Fibroma Chondromyxoid Fibroma is a rare lesion. CMF resembles NOF. Preferential sites: proximal tibia and foot.   Although the name suggests that CMF is a chondroid lesion, calcifications are usually not seen. Discriminators   : Mention when an NOF is mentioned.

78. CMF There is an eccentric osteolytic lesion in the metaphysis of the proximal tibia. On the inner side there is a sclerotic margin. On the outer side there is a regular cortical destruction with peripheral bone layer. The MR also shows a sclerotic margin with low signal intensity.

79. Sclerotic bone tumors and tumor-like lesions

80. Bone infarction Typical presentation: central lesion in metaphysis or diaphysis with a well defined serpentiginous border. May resemble cartilaginous tumors . Causes: corticosteroid use, sickle cell disease, trauma, Gaucher's disease, renal transplantation. The term bone infarction is used for osteonecrosis within the diaphysis or metaphysis. If the osteonecrosis is located in the epiphysis, the term avascular osteonecrosis is used . Differentiating a bone infarct from an enchondroma or low-grade chondrosarcoma on plain films can be difficult or even impossible. Cartilaginous tumors in particular chondrosarcoma may show endosteal scalloping , while a bone infarct does not. Chrondroid tumors are more frequently encountered than bone infarcts.

81. On MR imaging bone infarcts are characterized by irregulair serpentiginous margins with low signal intensity on both T1 and T2 WI and with intermediate to high fat signal in the center part. Enhancement after i.v. Gadolinium is usually minimal or absent (see right image). At the periphery of the infarct a zone of relative high signal intensity on T2WI may be found.

82. Bone island Benign lesion consisting of well-differentiated mature bone tissue within the medullary cavity. Also known as enostosis The shape is usually round or oval. Frequently encountered as a coincidental finding and can be found in any bone. Occasionally slowly enlargement can be seen. Bone islands can be large at presentation. Bone scan shows no high activity, opposed to low-grade intraosseous osteosarcoma

83. Chondroblastoma Typical presentation: well-defined osteolytic lesion in tarsal bone , patella or epiphysis of a long bone in a 20-year old with pain and swelling in a joint. Abundant edema is almost always present. DD: Ganglion cyst, osteomyelitis, GCT, ABC, enchondroma .

84. a lesion located in the epi - and metaphysis of the proximal humerus . The lesion is predominantly calcified. Coronal T1W image shows lobulated margins and peripheral low SI due to the calcifications.

85. Chondrosarcoma Most common malignant bone tumor, which is almost always low-grade Primary sites of origin: proximal long bones, around knee, pelvis and shoulder girdle, usually central and metaphyseal Radiological hallmark: formation of a chondroid ( cartilagenous ) matrix, which presents as punctuated, stippled or popcorn-like calcifications. The chondroid matrix is of a variable amount from almost absent to dens compact chondroid matrix. Disappearane of calcifications in a pre-existing enchondroma should raise the suspicion of malignant transformation.

86. a calcified lesion in the proximal tibia without suspicious features. This could very well be an enchondroma . There were other features that favored the diagnosis of a low-grade chondrosarcoma like a positive bone scan and endosteal scalloping of the cortical bone on an MRI (not shown). A chondrosarcoma was diagnosed at biopsy.

87. a 44-year old male with a mixed lytic and sclerotic mass arising from the fifth metacarpal bone. There are calcified strands within the soft tissues. T2-weighted axial MR image demonstrates high signal intensity of the tumor in the metacarpal bone with extension of a lobulated soft tissue mass. Diagnosis: chondrosarcoma grade 2

88. a chondrosarcoma of the left iliac bone. Because of the large dimensions with soft tissue extension on plain radiograph and axial T2-weighted MR image, a high grade chondrosarcoma was suspected. Biopsy showed grade 2 chondroarcoma .

89. two other lesions in different patients that proved to be chondrosarcoma . The sclerotic lesion in the humeral head could very well be a benign enchondroma based on the imaging findings. Symptoms are usually absent, however, in adult patients with a chondroid lesion in a long bone, particularly of larger size, always consider low-grade chondrosarcoma .

90. Plain radiograph and coronal T1-weighted contrast-enhanced fat-suppressed MR image of a mixed lytic and sclerotic lesion of the distal femoral diaphysis. Notice the homogeneous thickening of the cortical bone. There are no calcifications. The MR image shows that the lesion has lobulated contours and nodular enhancement. The homogeneous enhancement in the upper part with edema and cortical thickening are not typical for a low-grade chondrosarcoma . A high grade chondrosarcoma must be considered in the differential diagnosis. Biopsy revealed dedifferentiated chondrosarcoma .

91. Peripheral chondrosarcoma Accounts for 8% of all chondrosaromas . Prevalence of 3-5% in patients with hereditary multiple osteohondromas . Development in centrally located osteochondromas like the pelvis, hip and shoulder is most common. Consider peripheral chondrosaroma in growing osteochondromas with or without pain after closure of the physeal plate. Radiographic or CT features that suggest malignancy: growth of osteohondroma in skeletally mature patients irregular or indistinct surface of lesions erosion or destruction of adjacent bone soft tissue mass with scattered or irregular calcifications Use MRI with water-sensitive sequence (T2 FS) to determine cartilage cap thickness. Consider progression of osteohondroma to chondrosarcoma when cartilage cap measures > 10 mm.

92. Periosteal or juxtacortical chondrosarcoma A juxtacortical chondrosarcoma has be considered in the differential diagnosis when a mineralized lesion adjacent to the cortical bone is seen.

93. Here a partially calcified mass against the proximal humerus with involvement of the cortical bone on an axial CT image. T2-weighted MR image reveals a lobulated mass with high signal intensity. The bone marrow compartment is not involved which is important for the surgical strategy. A periosteal chondroma may have the same imaging characteristics, however, these are almost always much smaller.

94. Plain radiograph in another patient shows irreglar mineralized lesion with elevation of the periosteum and cortical involvement. On the right T2-WI with FS of same patient.. The juxtacortical mass has a high SI and lobulated contours. DD: juxtacortical chondrosarcoma , parosteal osteosarcoma.

95. Enchondroma Most commonly encountered bone tumor in the small bones of the hand and foot. Enchondroma is a fairly common benign cartilaginaous lesion which may present as an entirely lytic lesion without any calcification, as a dense calcified lesion or as a mixed lesion with osteolysis and calcifications. Enchondromas as well as low-grade chondrosarcomas are frequently encountered as coincidental findings in patients who have a MRI or bone scan for other reasons.

96. Eosinophilic granuloma Typically presents as a lytic lesion in a flat bone, vertebra or diaphysis of long bone. May show extinction and become  sclerotic  and indolent,. MR usually shows a large amount of reactive changes in bone and soft tissue. In the active phase there is multilaminar periosteal reaction and bone and soft tissue edema. Eosinophilic granuloma like osteomyelitis, can be a serious mimicker of malignancy (particularly Ewing sarcoma). Should be included in the differential diagnosis of young patient with multiple lucent lesions ( Langerhans cell histiocytosis ).

97. a 20 year old patient with a sclerotic expansile lesion in the clavicle. Notice that there are small areas of ill-defined osteolysis . In an older patient one should first consider an osteoblastic metastasis. If the patient had fever and a proper clinical setting, osteomyelitis would be in the differential diagnosis.

98. Fibrous dysplasia FD is often purely lytic, but may have a groundglass appearance as the matrix calcifies. Ossifications or calcifications can be present in variable amounts.

99. a rather wel -defined eccentric lesion which is predominantly sclerotic. The differential diagnosis includes: Fibro-osseous lesion like fibrous dysplasia. Non-ossifying fibroma which has been filled in. Adamantinoma in case of a sclerotic lesion with several lucencies of the tibia in a young patient.

100. Here a well-defined mixed sclerotic-lytic lesion of the left iliac bone. The diagnosis was fibrous dysplasia. DD: old SBC. Bone scintigraphy can be either negative or show limited uptake. The signal intensity on MR depends on the amount of calcifications and ossifications and fibrous tissue (low SI) and cystic components (high SI on T2). Fibrous dysplasia can be monostotic or polyostotic . Usually it is a lesion of childhood or young adults. Not infrequently encountered as coincidental finding at later age. Central location most common with some expansion and cortical thinning

101. Melorrheostosis is a dysplasia of the bone, characterized by apposition of mature bone on the outer or inner surface of cortical bone. Usually one bone is involved. The epiphysis, metaphysis and diaphysis may be involved. Usually new bone is added to one side of the cortex only. Complete envelopment may occur. Here Melorrheostosis of the ulna with the appearance of candle wax. A surface osteosarcoma could be considered in the differential diagnosis Axial T1-weighted MR image shows homogeneous low signal intensity due to the compact bone apposition.

102. Metastases Sclerotic osteoblastic metastases must be included in the differential diagnosis of any sclerotic bone lesion in a patient > 40 years. Most commonly originate from prostate and breast cancer and less frequently from lung cancer, lymphoma or carcinoid. In breast cancer, metastases may present as lytic lesions that may become sclerotic expressing a favourable response to chemotherapy.

103. a patient with prostate cancer. Notice the numerous predominantly osteoblastic metastases.

104. a patient with breast cancer. There is a metastasis, which presents as a subtle sclerotic lesion in the humerus metaphysis. This could be an osteoblastic metastasis or an osteolytic metastasis that responded to chemotherapy.

105. a radiograph of the pelvis with a barely visible osteoblastic metastasis in the left iliac bone (blue arrow). Notice that CT depicts these lesions far better (red arrows).

106. CT-images of a patient with prostate cancer. Notice the numerous ill-defined osteoblastic metastases.

107. Non-ossifying fibroma Non-ossifying fibroma (NOF) can be encoutered occasionally as a partial or completely sclerotic lesion. Typically a NOF presents as an eccentric well-defined lytic lesion, usually found as a coincidental finding. These lesions usually regress spontaneously and may then become sclerotic. Other benign lesions, like solitary bone cyst, fibrous dysplasia, chondroblastoma and other benign bone tumors may become inert and may also become sclerotic.

108. on the left a typical osteolytic NOF with a sharp sclerotic border. The image on the right is of a different patient who has an old NOF that shows complete fill in.

109. an incidental finding of several eccentric sclerotic lesions of the distal femur. These are inert filled-in non-ossifying fibromas. No further examination is needed.

110. Osteochondroma Osteochondroma is a bony protrusion covered by a cartilaginous cap. Growth of the osteochondroma takes place in the cap, corresponding with normal enchondral growth at the growth plates. Accordingly, growth of osteochondromas is allowed until a patient reaches adulthood and the physeal plates are closed. Growth of osteochondromas at adult ages, which is characterized by a thick cartilaginous cap ( high SI on T2WI ) should raise the suspicion of progression to a peripheral chondrosarcoma .

111. a patient with a broad-based osteochondroma . Notice that the cortical bone extends into the lesion. This feature differentiates it from a juxtacortical tumor.

112. a patient with a broad-based osteochondroma with extension of the cortical bone into the stalk of the lesion. Notice the lytic peripheral part with subtle calcifications. This part corresponds to a zone of high SI on T2-WI with FS on the right. This represents a thick cartilage cap. This is an example of progression of an osteochondroma to a peripheral chondrosarcoma .

113. Malignant transformation Radiographic features that should raise the suspicion of malignant transformation on plain radiographs or CT include: Growth of osteochondroma in skeletally mature patient Irregular or indistinct surface of lesions focal lucent regions in interior of lesions erosion or destruction of adjacent bone presence of soft tissue mass with scattered or irregular calcifications

114. Oteoid Osteoma Small osteolytic lesion (up to 1.5 cm) with or without central calcification. Surrounded by a prominent zone of reactive sclerosis due to a periosteal and endosteal reaction, which may obscure the central nidus . In juxta -articular localisation , the reactive sclerosis may be absent. Localisation : femur, tibia, hands and feet, spine (arch). Axial imaging for differentiation from Brodie abscess, osteoblastoma , stress fracture

115. Here the reactive sclerosis is the most obvious finding on the X-ray. There is reactive sclerosis with a nidus that is barely visible on the radiograph (blue arrow), but clearly visible on the CT (red arrows). CT scan is usually very helpful in detecting the nidus and differentiating osteoid osteoma from other sclerotic lesions like osteoblastoma , osteomyelitis, arthritis, stress fracture and enostosis . MRI also may detect the nidus , combined with abundant bone marrow and soft tissue edema.

116. In most cases of osteoid osteoma the radiographic appearance is determined by the reactive sclerosis. In some cases however the osteolytic nidus can be visible on the radiograph (figure).

117. Osteoma consists of densely compact bone. It is most commonly located in the outer table of the neurocranium or in a paranasal sinus .

118. Osteomyelitis Osteomyelitis is a mimicker of various benign and malignant bone tumors and reactive processes that may be accompanied by reactive sclerosis. Acute osteomyelitis is characterised by osteolysis . Sclerosis  is usually the most prominent finding in  subacute and chronic osteomyelitis . A periosteal reaction with or without layering may be present. Sometimes a more solid periosteal reaction is present combined with cortical thickening and broadening of the bone.

119. an image of a patient with chronic osteomyelitis. Centrally there is an ill-defined osteolytic area. The major part of the lesion consists of reactive sclerosis.

120. Osteosarcoma 2nd most common primary bone tumor and highly malignant. 50% around the knee. Presentation: pain, mass, pathologic fracture. Sclerosis is present from either tumor new bone formation or reactive sclerosis. Age: most commonly seen in 10-25 years, but may occur in older patients. Plain films typically reveal lesions with moth-eaten or permeative pattern of the transition zone with irregular cortical destruction and an interrupted periosteal reaction with soft tissue extension. A periosteal reaction known as  Codman's triangle appears as tumor elevates periosteum from underlying bone. Cortical soft tissue extension may produce radiating spicules of bone called  sunray appearance .

121. images of an osteosarcoma in the right femur. It is barely visible within the bone, but an agressive periostitis is seen (arrow). Continue with the MR-images.

122. The sagittal T1WI and Gd -enhanced T1W-image with fatsat show a large tumor mass infiltrating a large portion of the distal femur and extending through the cortex into the soft tissues.

123. Parosteal osteosarcoma Parosteal osteosarcoma is a sarcoma that has it's origin on the surface of the bone. It grows primarily into the surrounding soft tissues, but may also infiltrate into the bone marrow. It is most commonly located on the posterior side of the distal meta-diaphysis of the femur. Ossification in parosteal osteosaroma is usually more mature in the center than at the periphery . This is opposed to myositis ossificans which may present very close to the cortical bone, but maturation develops from the center to the periphery.

124. Radiograph. Small homogeneous mass adjacent to the cortex of the diaphysis of the femur MRI Juxtacortical mass with enhancement of the periphery. Bone marrow and cortiical bone are otherwise normal. Notice absence of reactive changes around the lesion.

125. Paget disease is a chronic disorder of unknown origin with increased breakdown of bone and formation of disorganized new bone. The most common appearance is the mixed lytic-sclerotic. In this case we see the pathognomonic triad of bone expansion, cortical thickening and trabecular bone thickening in the mixed lytic and sclerotic phase of Paget's disease of right hemipelvis .

126. Myositis ossificans Here a patient with a mineralized mass in the soft tissues. Notice that the mineralization is predominantly in the periphery of the mass and that there is a lucent zone between the mass and the cortical bone. Contrast-enhanced T1-weighted MR image demonstrates heterogeneous enhancement of the mass with extensive surrounding edema. This is consistent with the diagnosis of a reactive process like myositis ossificans .

127. Stress fractures occur in normal (fatigue fractures) or metabolically weakened (insufficiency fractures) bones. Usually stress fractures are easy to recognize. Uncommonly it can be difficult to differentiate a stress fracture from a pathologic fracture, that occurs at the site of a bone tumor.

128. Uncommonly it can be difficult to differentiate a stress fracture from a bone tumor like an osteoid osteoma or from a pathologic fracture, that occurs at the site of a bone tumor.

129. an example of a patient with a stress fracture of the distal fibula. Coronal MR image demonstrates subtle low intensity line representing the fracture. Differential diagnosis based on the periosteal reaction and the extensive edema: Osteomyelitis Eosinophilic granuloma

130. Posttraumatic calcifications Here a patient with a juxtacortical sclerotic mass of the proximal humerus (left). This proved to be a reactive calcification secondary to trauma. Notice the resemblance to a juxtacortical mass in another patient (right), which was a biopsy proven parosteal osteosarcoma. This shows that differentiating a tumor from a reactive proces scan be quite difficult in some cases. When a reactive process is more likely based on history and imaging features, follow-up is sometimes still needed.

131. Subungual exostoses Subungual exostoses are bony projections which arise from the dorsal surface of the distal phalanx, most commonly of the hallux. These lesions are not osteochondromas , but consist of reactive cartilage metaplasia. The radiographic appearance and location are typical.

132. Nora's lesion Here two patients with a bizar parosteal osteochondromatous proliferation (BPOP), also called Nora's lesion. This benign reactive process is most commonly found adjacent to the cortex of phalanges of hands or feet (75%). The cortical bone and bone marrow compartment are not involved. Rapid growth of the mineralized mass is not uncommon.

133. Chondrosarcoma Malignant bone tumor that produces cartilage . usually central and metaphyseal Typical presentation: large osteolytic lesion with scalloping of the inner cortex and rings-and-arcs or popcorn calcifications in an elderly person with a painful swelling. Secundary chondrosarcoma is most common and arises from enchondroma or osteochondroma . Patients with multiple enchondromas like in Ollier's disease and Mafucci's syndrome are at risk. Low grade tumor can usually not be differentiated from enchondroma based on imaging findings alone. High grade tumor may present as aggressive ill-defined lesion with extention into the soft tissues.

134. Chondrosarcoma On plain radiographs the differential diagnosis with enchondroma can be difficult. Think of chondrosarcoma instead of enchondroma if there is one or more of the following features: Elderly patient Location in long bones Size > 5 cm Uptake on bone scan Endosteal scalloping on MRI Cortical involvement Early enhancement on dynamic contrast enhanced series Disappearane of calcifications in a pre-existing enchondroma should raise the suspicion of malignant transformation.

135. The differential diagnosis on the plain radiographs in all these three cases is enchondroma . Additional MR imaging and bone scintigraphy may be helpful to make the diagnosis of chondrosarcoma more or less likely.