Bubbly Lesions of Bone

Residents Section Pattern of the Month w79 08.18.09 Eisenberg Residents Section Pattern of the Month Residents inradiology Ronald L. Eisenberg 1 Eisenberg RL Keywords: bubbly lesions, fegnomashic, skeletal radiograph DOI:10.2214/AJR.09.2964 Received April 27, 2009; accepted after revision May 1, 2009. 1 Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave., Boston, MA 02215. Address correspondence to R. L. Eisenberg (rleisenb@ bidmc.harvard.edu). WEB This is a Web exclusive article. AJR 2009; 193:W79 W94 Bubbly lesions of bone are common findings on skeletal radiographs. The long, otherwise difficult-to-recall differential diagnosis has led to the development of the classic mnemonic fegnomashic, which some have preferred to rearrange as fog machines. The entities in the following list account for more than 95% of the conditions that produce bubbly lesions of bone: Fegnomashic Fibrous dysplasia Enchondroma Eosinophilic granuloma Giant cell tumor Nonossifying fibroma Osteoblastoma Metastases Myeloma Aneursymal bone cyst Simple bone cyst Hyperparathyroidism (brown tumor) Infection Chondroblastoma Chondromyxoid fibroma 0361 803X/09/1932 W79 American Roentgen Ray Society A Fig. 1 Fibrous dysplasia. Views of humerus (A) and ischium (B) in two different patients show expansile lesions containing irregular bands of sclerosis, giving them multilocular appearance. B AJR:193, August 2009 W79

Fibrous Dysplasia Fibrous dysplasia (Fig. 1) is a proliferation of fibrous tissues in the medullary cavity, usually beginning during childhood. Involving a single bone in 70 80% of cases, fibrous dysplasia most commonly affects the long bones (femur, tibia), ribs, and skull. It is the most common cause of an expansile focal rib lesion. Fibrous dysplasia is associated with endocrinopathy in 2 3% of patients, especially in girls who experience precocious puberty. Malignant degeneration is extremely rare. Fibrous dysplasia appears radiographically as a well-defined lucent area, which varies from completely radiolucent to homogeneous ground-glass density depending on the amount of fibrous or osseous tissue deposited in the medullary cavity. Often there is local expansion of bone with endosteal erosion of the cortex that predisposes to pathologic fractures. In severe and long-standing disease, affected bones may be bowed or deformed ( shepherd s crook deformity of the femur). Enchondroma Enchondroma (Figs. 2 and 3) is a common benign cartilaginous tumor that is most frequently found in children and young adults. It is usually asymptomatic and discovered either incidentally or when a pathologic fracture occurs. The development of severe pain or radiographic growth of the lesion with loss of marginal definition, cortical disruption, and local periosteal reaction suggests malignant degeneration. The incidence of this complication increases the closer the tumor is to the axial skeleton. Multiple enchondromatosis is termed Ollier s disease. Typically involving a small bone of the hands and feet, an enchondroma appears radiographically as a well-marginated lucency arising in the medullary cavity, usually near the epiphysis. It expands bone locally and often causes thinning and endosteal scalloping of the cortex. This may lead to pathologic fracture with minimal trauma. Characteristic calcifications, which may vary from minimal stippling to large, amorphous areas of increased density, develop in the lucent matrix. Fig. 2 Enchondroma. A, Well-demarcated tumor (arrow) expands bone and thins cortex. B, Pathologic fracture (arrow). A B W80 AJR:193, August 2009

Eisenberg Fig. 3 Multiple enchondromatosis. View of both hands shows multiple globular and expansile lucent filling defects involving all metacarpals and proximal and middle phalanges. Eosinophilic Granuloma Eosinophilic granuloma (Fig. 4) is the benign form of Langerhans histiocytosis that predominantly affects the skull, pelvis, femur, and spine. This condition almost always occurs before 30 years of age and most affected patients are under 20. Eosinophilic granuloma usually appears radiographically as a well-defined medullary lucency, often with endosteal scalloping and local or extensive periosteal reaction. Rapidly growing lesions may have indistinct, Fig. 4 Eosinophilic granuloma. Bubbly osteolytic lesion in femur, with scalloping of endosteal margins and thin layer of periosteal response. AJR:193, August 2009 W81

Fig. 5 Giant cell tumor. Typical eccentric lucent lesion in distal femoral metaphysis extends to immediate subarticular cortex. Surrounding cortex, though thinned, remains intact. Fig. 6 Malignant giant cell tumor. Tumor has caused cortical disruption, extends outside host bone, and has ill-defined margin. hazy borders. A characteristic finding is a peculiar beveled contour of the lesion that produces a hole-within-a-hole effect. In the skull, eosinophilic granuloma typically produces one or more small punched-out areas that originate in the diploic space, expand and perforate both the inner and outer tables, and often contain a central bone density (button sequestrum). In the spine, generally spotty destruction in a vertebral body may proceed to collapse the vertebra into a thin flat disk (vertebra plana). Giant Cell Tumor Giant cell tumor (Figs. 5 and 6) is a lytic lesion that develops in the end of a long bone of a young adult after epiphyseal closure. It primarily involves the knee (distal femur, proximal tibia) and wrist (distal radius, ulna). Although usually asymptomatic, a giant cell tumor may be associated with intermittent dull pain and a palpable tender mass and predispose to pathologic fracture. Approximately 20% of giant cell tumors are malignant, although there is much overlap in the radiographic appearance of benign and malignant lesions. The malignant nature of a lesion is best seen as tumor extension through the cortex and an associated soft-tissue mass on CT. Giant cell tumor classically appears radiographically as an eccentric lucent metaphyseal lesion that may extend to the immediate subarticular cortex of a bone but does not involve the joint. Expansion toward the shaft produces a well-demarcated lucency, often with cortical expansion but without a sclerotic shell or border. Aggressive lesions cause cortical destruction, though this can be seen in benign lesions. Nonossifying Fibroma A nonossifying fibroma (Fig. 7) results from a fibrous cortical defect (discussed later), a common process that develops in up to 40% of normal children. Although most of these defects regress spontaneously and disappear by the time of epiphyseal closure, a persistent and growing lesion with continued proliferative activity in an older child or young adult is termed a nonossifying fibroma. The lesion most frequently occurs in the distal portions of the femur and tibia. A nonossifying fibroma appears radiographically as a multilocular, eccentric lucency that causes cortical thinning and expansion. It generally is sharply demarcated by a thin, scalloped rim of sclerosis. W82 AJR:193, August 2009

Eisenberg Fig. 7 Nonossifying fibroma. Multilocular, eccentric lucency with sclerotic rim in distal femur. Osteoblastoma Osteoblastoma (Figs. 8 and 9) is a rare bone neoplasm that most often arises in adolescence. Approximately one half involve the vertebral column, most frequently the posterior elements (neural arches and processes). Most of the remainder of these neoplasms affect the long bones or the small bones of the hands and feet. Although predominantly lytic, an osteoblastoma occasionally has internal calcification and an aggressive appearance simulating a malignant lesion. It may be difficult to differentiate histologically from an osteoid osteoma, but it is usually much larger (> 2 cm) and thus the term giant osteoid osteoma is often applied to the sclerotic form of this lesion. An osteoblastoma usually appears radiographically as a well-circumscribed, eccentric, and expansile lucency. It may break through the cortex to produce a soft-tissue component surrounded by a thin calcific shell. Fig. 8 Osteoblsatoma. Sharply defined erosive lesion (arrows) involves superior margin of lower cervical spinous process. Fig. 9 Osteoblastoma. Expansile, eccentric mass in proximal humerus causes thinning of cortex (arrows). AJR:193, August 2009 W83

Fig. 10 Metastasis (lung cancer). Frontal (A) and lateral (B) views show large, purely lytic lesion with substantial soft-tissue component. (Courtesy of Jim Wu, Boston, MA) A Fig. 11 Metastasis (thyroid carcinoma). Large area of entirely lytic, expansile destruction (arrows) involves left ilium. Metastases Most lytic metastases (Figs. 10 and 11) are irregular, poorly defined, and multiple. However, a single large metastatic focus may occasionally appear as an expansile, trabeculated lesion. Termed a blowout metastasis, it typically is secondary to a highly vascular carcinoma of the kidney or thyroid. Myeloma A single plasma cell tumor (Fig. 12) may infrequently present as an apparently solitary destructive bone lesion with no evidence of the major disease complications usually associated with multiple myeloma. It generally develops into typical multiple myeloma (diffuse lytic lesions) within 1 2 years (Fig. 13). A solitary plasmacytoma typically appears radiographically as an expansile, often trabeculated lucency that predominantly involves the ribs, long bones, and pelvis. A highly destructive tumor may expand or balloon bone before it breaks through the cortex. In the spine, an affected vertebral body may collapse or be destroyed. B W84 AJR:193, August 2009

Eisenberg A Fig. 12 Myeloma. Frontal views (A and B) of both femurs show multiple small lytic lesions. (Courtesy of Jim Wu, Boston, MA) Fig. 13 Myeloma (solitary plasmacytoma). Highly destructive tumor has obliterated virtually entire left half of pelvis. Aneurysmal Bone Cyst Rather than a true neoplasm or cyst, an aneurysmal bone cyst (Fig. 14) is composed of numerous blood-filled arteriovenous communications. It most frequently occurs in children and young adults, presenting with mild pain of several months duration, swelling, and restriction of movement. Aneurysmal bone cysts primarily involve the metaphyses of long bones (especially the femur and tibia) and the posterior elements of vertebrae. The lesion may extend beyond the axis of the host bone and form a visible soft-tissue mass that, when combined with a cortex so thin that it is invisible on radiographs, may be mistaken for a malignant bone tumor. An aneurysmal bone cyst appears radiographically as an expansile, eccentric, cystlike lesion causing marked ballooning of thinned cortex. Light trabeculation and septation in the lesion may produce a multiloculated appearance. Periosteal reaction may develop. B AJR:193, August 2009 W85

Fig. 14 Aneurysmal bone cyst. Expansile, eccentric, cystic lesion of tibia with multiple fine internal septa. Because severely thinned cortex is difficult to detect, tumor resembles malignant process. Fig. 15 Simple bone cyst. Lesion in proximal humerus has oval configuration, with its long axis parallel to that of host bone. Note thin septa that produce multiloculated appearance. Simple Bone Cyst A simple bone cyst (Figs. 15 and 16) is a true fluid-filled cyst with a wall of fibrous tissue. It begins adjacent to the epiphyseal plate and appears to migrate down the shaft, although in reality it is the epiphysis that has migrated away from the cyst. Bone cysts arise in children and adolescents and most commonly involve the proximal humerus and femur. They often present as a pathologic fracture, which may show the fallen fragment sign (fragments of cortical bone that are free to fall to the dependent portion of the fluid-filled cyst, unlike a bone tumor that has a firm tissue consistency). Radiographically, a simple bone cyst appears as an expansile lucent lesion that is sharply demarcated from adjacent normal bone. It may contain thin septa (scalloping of underlying cortex) that produce a multiloculated appearance. A simple bone cyst tends to have an oval configuration, with its long axis parallel to that of the host bone. W86 AJR:193, August 2009

Eisenberg Fig. 16 Simple bone cyst (fallen fragment sign). After pathologic fracture, cortical bone fragment (arrow) lies free in subtrochanteric bone cyst. (Reprinted with permission from Reynolds J. Fallen fragment sign in diagnosis of unicameral bone cysts. Radiology 1969; 92:949 953) Hyperparathyroidism Patients with hyperparathyroidism (Fig. 17) (especially the primary type) may develop socalled brown tumors, which are true cysts representing intraosseous hemorrhage. In most cases, there is other radiographic evidence of hyperparathyroidism. A large lesion may simulate malignancy or lead to pathologic fractures and bizarre deformities. Brown tumors appear radiographically as single or multiple focal lytic areas that are generally well demarcated and often cause expansion of bone. They most commonly involve the mandible, pelvis, ribs, and femur. Fig. 17 Hyperparathyroidism (brown tumors). Multiple lytic lesions in pelvis (A) and about knee (B). A B AJR:193, August 2009 W87

Infection Focal areas of lytic destruction, often with sclerosis and periosteal reaction, may occur with various infectious processes (Fig. 18). In fungal disease (coccidioidomycosis; blastomycosis), the lesions are often multiple. A large central radiolucent area associated with endosteal scalloping and expansion, which may have cortical breakthrough and a soft-tissue mass, is one appearance of echinococcal cyst involving the skeleton. This condition is usually monostotic and predominantly involves the pelvis, spine, and long bones. A rare manifestation of disseminated tuberculosis in children is single or multiple small oval lucencies with well-defined margins lying in the long axis of a bone, primarily the skull, shoulder, pelvic girdle, and axial skeleton. Fig. 18 Infection (coccidioidomycosis). Typical well-marginated, punched-out lytic defect in head of third metacarpal (arrows). (Reprinted with permission from McGahan JP, Graves DS, Palmer PE, Stadalnik RC, Dublin AB. Classic and contemporary imaging of coccidiodomycosis. AJR 1981; 136:393 404) W88 AJR:193, August 2009

Eisenberg Chondroblastoma Chondroblastoma (Fig. 19) is the classic epiphyseal lesion, which occurs in children and young adults before enchondral bone growth ceases. It also may involve the greater trochan ter of the femur and the greater tuberosity of the humerus. This rare, benign cartilaginous tumor typically appears radiographically as an eccentric, round or oval epiphyseal lucency that often has a thin sclerotic rim and may contain flocculent calcification. Fig. 19 Chondroblastoma. Osteolytic lesion containing calcification (arrows) in epiphysis. Note open epiphyseal line. (Reprinted with permission from Edeiken J. Roentgen diagnosis of diseases of bone. Baltimore: Williams and Wilkins, 1981) Chrondromyxoid Fibroma Chrondromyxoid fibroma (Fig. 20) is an uncommon benign bone tumor originating from cartilage-forming connective tissue and predominantly occurring in young adults. Calcification is infrequent (unlike chondroblastoma and other cartilaginous bone lesions). Approximately 50% of chondromyxoid fibromas involve the tibia, with the remainder affecting the pelvis and other bones of the extremities). A chondromyxoid fibroma typically appears radiographically as an eccentric, round or oval lucency arising in the metaphysis of a long bone. The overlying cortex is usually bulging and thinned, and the inner border is generally thick and sclerotic, often with scalloped margins. Fig. 20 Chondromyxoid fibroma. Ovoid, eccentric metaphyseal lucency with thinning of overlying cortex and sclerotic inner margin. AJR:193, August 2009 W89

Additional Lesions Among other lesions that may infrequently appear as bubbly lesions are the following (in alphabetical order): Adamantinoma Angiomatous lesion Central chondrosarcoma Epidermoid inclusion cyst Fibrous cortical defect Glomus tumor Hemangioma Hemophilic pseudotumor Intraosseous ganglion Lipoma Lymphoma Ossifying fibroma Pigmented villonodular synovitis Sarcoidosis Fig. 21 Adamantinoma. Multiloculated eccentric, expansile, well-circumscribed lesion in characteristic location in midportion of tibia. Fig. 22 Angiomatous lesion (hemangioendothelioma). Expansile lucency containing delicate bony trabeculation. W90 AJR:193, August 2009

Eisenberg Adamantinoma Adamantinoma (Fig. 21) is a rare tumor that primarily affects adolescents and young adults and classically involves the tibia. It often recurs and may metastasize. Radiographically, an adamantinoma typically appears as a large loculated, expansile lucent mass in the midportion of the tibia. Angiomatous Lesion An angiomatous lesion (Fig. 22) is a rare congenital malformation consisting of endotheliumlined structures that may be lymphatic channels (lymphangiomatosis) or blood vascular channels (hemangiomatosis). Usually there is widespread involvement of multiple long bones, flat bones, and the skull. It typically appears as multiple (less commonly single) lucent metaphyseal lesions that often have a sclerotic margin and are sometimes associated with a soft-tissue mass. Central Chondrosarcoma Central chondrosarcoma (Fig. 23), a malignant tumor of cartilaginous origin, may originate de novo or in a preexisting cartilaginous lesion (osteochondroma, enchondroma). The tumor is about half as common as osteogenic sarcoma, develops at a later age (half the patients are more than 40 years old), grows more slowly, and metastasizes later. Central chondrosarcoma may also appear as an aggressive, poorly defined osteolytic lesion that blends imperceptibly with normal bone and can expand to replace the entire medullary cavity (this may simply be a later phase of the first, benign-appearing type). Radiographically, central chondrosarcoma appears as a localized lucent area of osteolytic destruction in the metaphyseal end of a bone. When the rate of tumor growth exceeds that of bone repair, the margins of the lesion become irregular and ill defined and the tumor extends to cause cortical destruction and invasion of soft tissues. The cartilaginous tissue in a chondrosarcoma can be easily recognized by the amorphous punctate, flocculent, or snowflake calcifications that are seen in approximately two thirds of central tumors. Fig. 23 Central chondrosarcoma. Irregular and illdefined lytic lesion of lower ilium. Fig. 24 Fibrous cortical defect. Multilocular, eccentric lucency in distal tibia. Note thin, scalloped rim of sclerosis. AJR:193, August 2009 W91

Epidermoid Inclusion Cyst An epidermoid inclusion cyst appears radiographically as a well-circumscribed lucency in a terminal phalanx. It may cause thinning, expansion, or even loss of the cortical margin. Unlike an enchondroma, there is usually a history of penetrating trauma and no stippled calcification. Fibrous Cortical Defect Fibrous cortical defect (Fig. 24) is not a true neoplasm, but rather a benign and asymptomatic small focus of cellular fibrous tissue causing an osteolytic lesion in the metaphyseal cortex of a long bone (most frequently the distal femur). One or more fibrous cortical defects develop in up to 40% of all healthy children. Most regress spontaneously and disappear by the time of epiphyseal closure. A persistent and growing lesion is termed nonossifying fibroma. A fibrous cortical defect is generally a small, often multilocular, eccentric lucency that causes cortical thinning and expansion and is sharply demarcated by a thin, scalloped rim of sclerosis. Initially round, the defect soon becomes oval with its long axis parallel to that of the host bone. Glomus Tumor A glomus tumor appears radiographically as a central well-circumscribed lucency that primarily involves the distal aspect of the terminal phalanx of a finger. A glomus tumor may mimic an enchondroma, but is generally painful. A subungual glomus tumor may cause pressure erosion at that site. Hemangioma A hemangioma (Fig. 25) can rarely appear as a lucent area with delicate bony trabeculation, most commonly near the end of a tubular or flat bone. Much more commonly, a skeletal hemangioma produces multiple coarse linear striations running vertically in a demineralized vertebral body or a sunburst pattern of osseous spicules radiating from a central lucency in the skull. Fig. 25 Hemangioma (vertebral body). Multiple coarse, linear striations run vertically in demineralized vertebral body. Fig. 26 Lipoma. Expansile lucency with thinned cortex in characteristic location in calcaneus. (Courtesy of Jim Wu, Boston, MA) W92 AJR:193, August 2009

Eisenberg Hemophilic Pseudotumor In patients with hemophilia, an extensive local area of intraosseous hemorrhage may involve the femur, pelvis, tibia, and small bones of the hands. It appears radiographically as a central or eccentric lucent lesion, often with a large adjacent soft-tissue hemorrhage. There may be cortical erosion suggesting a sarcoma. Intraosseous Ganglion An intraosseous ganglion appears radiographically as a well-defined lucency with a sclerotic margin adjacent to the articular surface. It most commonly involves the proximal tibia (near the attachment of the cruciate ligaments), the head and neck of the femur, and the medial malleolus. Lipoma Lipoma (Fig. 26) is a rare bone tumor that arises in the calcaneus, skull, ribs, or extremities. It appears radiographically as an expansile lucency with a thinned cortex. The lesion may break through the cortex and have an adjacent soft-tissue component. Lymphoma Lymphoma (Fig. 27) may produce single or multiple lytic defects, often with endosteal scalloping of the cortex. A mottled pattern of destruction and sclerosis may simulate hematogenous metastases. Fig. 27 Lymphoma. Focal lytic defect with endosteal scalloping of cortex. AJR:193, August 2009 W93

Ossifying Fibroma Ossifying fibroma is a rare tumor that may be associated with reactive bone sclerosis or calcification of the tumor matrix. It typically presents radiographically as a smooth, round, or expansile mass involving the skull, face, or mandible. Pigmented Villonodular Synovitis Protrusion of proliferative synovium in this condition infrequently produces a synovial cystic mass that can mimic a giant cell tumor and present as a lucent lesion extending to the articular surface. Sarcoidosis Perivascular granulomatous infiltration of sarcoidosis (Fig. 28) in the haversian canals of bone may destroy the fine trabeculae and produce a mottled or lacelike coarsely trabeculated pattern. Radiographically, this appears as single or multiple sharply circumscribed, punchedout areas of lucency, primarily involving the small bones of the hands and feet. There may be cortical thinning, expansion, or destruction. Fig. 28 Sarcoidosis. Multiple osteolytic lesions throughout phalanges with typical punched-out appearance. Apparent air density in soft tissues is photographic artifact. W94 AJR:193, August 2009