Version May 2024
INTRODUCTION — Nonmalignant bone tumors in children range from static lesions, such as nonossifying fibromas, which remain essentially unchanged throughout childhood, to locally aggressive lesions, such as aneurysmal bone cysts, which continue to expand until treated. (See 'Nonossifying fibroma' below and 'Aneurysmal bone cyst' below.)
Most benign bone tumors have characteristic radiographic features and can be diagnosed with radiographs. It is important to be familiar with the radiographic appearance of the most common benign bone tumors. Benign bone tumors often are discovered incidentally, and recognition of benign lesions on radiographs can avoid unnecessary advanced imaging and invasive diagnostic studies.
An overview of the presentation, clinical and radiographic features, and management of the most common nonmalignant pediatric bone lesions will be presented below. Malignant bone tumors (Ewing sarcoma and osteosarcoma) are discussed separately. (See "Clinical presentation, staging, and prognostic factors of Ewing sarcoma" and "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)
OVERVIEW
Clinical evaluation — Nonmalignant bone tumors often are asymptomatic and discovered incidentally during evaluation for trauma or another condition [1]. When they are symptomatic, nonmalignant bone tumors may present with localized pain, swelling, deformity, or pathologic fracture. In most cases, the differential diagnosis of these lesions can be narrowed based upon the age of the child, the involved bone, the location of the lesion within the bone, and other general radiographic characteristics (table 1) [2].
History — Certain aspects of the history may be helpful in narrowing the differential diagnosis of a benign-appearing bone tumor. These include (table 1) [1]:
●Age – Most nonmalignant bone tumors typically present during the second decade. However, ossifying fibroma (osteofibrous dysplasia) typically presents in the first five years of life, and Langerhans cell histiocytosis of bone presents in the first decade of life.
●Pain – Pain that quickly resolves (within 20 to 25 minutes) with nonsteroidal anti-inflammatory medications is characteristic of osteoid osteoma. Nonaggressive nonmalignant bone lesions (eg, simple bone cyst, nonossifying fibroma) usually are asymptomatic but may cause pain in association with pathologic fracture, bursa formation, or neurovascular compression [1]. Aggressive nonmalignant bone lesions (eg, aneurysmal bone cyst, chondroblastoma, chondromyxoid fibroma) may cause pain that is mild, dull, slowly progressive, and worse at night [3]. The pain associated with malignant bone tumors may awaken the child from sleep but is more rapidly progressive than the pain of aggressive nonmalignant bone tumors.
●Systemic symptoms – Associated systemic symptoms (eg, fever, malaise) may indicate malignancy, rheumatologic disease, or osteomyelitis [3].
Examination — Important aspects of the examination in a child with a bone tumor include [1,3]:
●Growth parameters – Patients with hereditary multiple osteochondromas may have short stature.
●Head, eyes, ears, nose, and throat – Signs of chronic/refractory otitis media (eg, scarring of the tympanic membrane) and proptosis may indicate Langerhans cell histiocytosis. (See "Clinical manifestations, pathologic features, and diagnosis of Langerhans cell histiocytosis", section on 'Clinical manifestations'.)
●Musculoskeletal – During the musculoskeletal examination, it is important to determine the location and size of the lesion(s) and to assess bone tenderness, bone or joint swelling, deformity (patients with hereditary multiple osteochondromas or enchondromas may have angular deformities of the upper or lower extremities), joint range of motion, neurologic function, and vascular function (neurovascular compromise may indicate an aggressive tumor). Osteochondromas and periosteal chondromas may be palpable.
●Skin – Café-au-lait macules (picture 1) may indicate polyostotic fibrous dysplasia (McCune-Albright syndrome) or neurofibromatosis. Polyostotic fibrous dysplasia with soft tissue myxomas may indicate Mazabraud syndrome [4]. Multiple enchondromas with vascular malformations may suggest Maffucci syndrome (picture 2). Overlying erythema, warmth, and soft tissue swelling may suggest underlying infection (eg, osteomyelitis).
●Lymph nodes – Regional lymphadenopathy may indicate infection or a systemic process.
Radiologic evaluation — Collaboration between the clinician and radiologist is essential [5]. Most benign bone tumors have characteristic radiographic features and can be diagnosed with radiographs that are interpreted by a clinician with expertise in pediatric bone lesions. It is important to be familiar with the radiographic appearance of the most common benign bone tumors (table 1). Benign bone tumors often are discovered incidentally, and recognition of benign lesions on radiographs may avoid unnecessary advanced imaging (eg, computed tomography [CT], magnetic resonance imaging [MRI]) and invasive diagnostic studies (eg, biopsy).
Radiographs — Radiographs are the best initial modality for evaluation of primary bone lesions [1,2]. The evaluation should include views in two planes [1]. The diagnosis of nonmalignant bone tumors can be made with radiographs alone in most cases [3]. If the lesion is clearly benign on radiographs, advanced imaging techniques should not be necessary for diagnosis but may be warranted for treatment planning [2,3].
Tumors of the pelvis or scapula can be difficult to see on radiographs. Advanced imaging techniques (eg, CT, MRI) may be necessary to fully characterize bone tumors in these locations [3].
Radiographs should be reviewed systematically by considering the following questions [1,6]:
●Where is the tumor? (Long bone or flat bone? Epiphysis, metaphysis, or diaphysis (figure 1)? Medulla, cortex, or surface?)
●What is the tumor doing to the bone? Is the tumor destroying or replacing existing bone? If so, what is the pattern?
●What is the bone doing to the tumor? Is there periosteal or endosteal reaction? If so, is it well developed? Is it sharply defined? What is the type of periosteal reaction: reinforcing, spiculated, solid, interrupted?
●Are there intrinsic characteristics that suggest histology? Is there osteoid or chondral matrix? Is there dystrophic calcification? Is the lesion completely radiolucent?
Radiographic characteristics of nonmalignant bone lesions include (table 2) [1,2,6,7]:
●Well-defined or sclerotic border
●Sharp zone of transition from normal to abnormal bone
●Absence of periosteal reaction
●Confinement by natural barriers (eg, growth plate, cortex)
●Lack of destruction of the cortex
●Lack of extension into the soft tissue
Radiographic characteristics of more aggressive lesions include [2,7]:
●Poorly defined borders
●Cortical destruction ("moth-eaten" or permeative pattern (image 1))
●Periosteal reaction (eg, spiculated, interrupted, wedge-shaped [ie, Codman triangle] (image 2)); however, the absence of these findings does not exclude an aggressive lesion [8]
●Extension into the soft tissue
Advanced imaging — Advanced imaging techniques (CT or MRI) may be necessary for bone lesions that are not clearly benign on radiographs. Advanced imaging also may be necessary to detect tumors in the spine, scapula, ribs, or pelvis [3].
CT may be helpful in evaluating areas of the body that are difficult to see with radiographs (eg, pelvis, scapula, spine) [2]. Compared with radiographs, CT can better define the location of the lesion within the bone (eg, periosteal, cortex, medullary), more accurately evaluate changes in the cortex (eg, focal destruction or endosteal scalloping), and can better delineate underlying matrix mineralization. It also may be helpful in guiding therapy (eg, localization of the nidus in osteoid osteoma). However, the benefit of the supplementary information must be weighed against the additional radiation exposure.
MRI is the modality of choice when a malignant bone tumor is suspected [2]. It is the most sensitive modality for evaluation of medullary changes and defining the extent of the lesion, and provides the best contrast resolution for demonstrating soft tissue masses and invasion of adjacent structures. Radiographs should be obtained before MRI to exclude benign etiologies that do not need MRI assessment. MRI provides supplementary diagnostic information to the radiographs. Sedation may be required for MRI.
Bone scintigraphy may be helpful in evaluating metastatic disease or a multifocal process [2]. However, it is nonspecific and lacks anatomic detail, which limits its use in the initial evaluation of a single bone lesion.
Management — Some benign bone tumors can be managed with reassurance and no routine follow-up imaging is necessary. Others may need observation (eg, serial examination and radiographs). Symptomatic or aggressive nonmalignant tumors (osteoblastoma, periosteal chondroma, chondroblastoma, chondromyxoid fibroma, aneurysmal bone cyst, and giant cell tumor) usually are treated with curettage and bone grafting or excision. The management of specific tumors is discussed below.
Referral indications — Most children with bone tumors should be referred to and followed by an orthopedic surgeon familiar with these tumors, such as a tumor or pediatric specialist. Small fibromas, fibrous cortical defects, and asymptomatic osteochondromas that are detected incidentally are exceptions and may not require referral.
CLASSIFICATION — Bone tumors can be classified into several categories according to the matrix, or substance, that they produce:
●Osteoid- or bone-forming tumors, including osteoid osteoma and osteoblastoma (see 'Bone-forming lesions' below)
●Cartilage-forming tumors, including osteochondroma (exostosis), chondroma (enchondroma, periosteal chondroma), chondroblastoma, and chondromyxoid fibroma (see 'Cartilage-forming tumors' below)
●Fibrous lesions, including fibrous dysplasia, ossifying fibroma (osteofibrous dysplasia), and nonossifying fibroma (see 'Fibrous lesions' below)
●Cystic and vascular lesions, including simple bone cyst and aneurysmal bone cyst (see 'Cystic tumors' below)
BONE-FORMING LESIONS
Osteoid osteoma — Osteoid osteoma is a benign bone-forming tumor that is characterized by a small radiolucent nidus (usually <1 to 1.5 cm in diameter) [3]. The nidus produces high levels of prostaglandins [9]. In addition to prostaglandins, there is some evidence that osteoid osteomas may secrete osteocalcin [10]. Osteoid osteoma is morphologically and genetically similar to osteoblastoma and the two tumors may be different presentations of the same genetic entity [11-13]. Osteoid osteoma accounts for approximately 12 percent of benign bone tumors [14].
●Clinical features – Osteoid osteoma typically presents during the second decade, although it has been reported in children as young as 11 months old [15-19]. The lower extremity is most frequently affected; the proximal femur is the most common site [17,20]. Other common locations are the tibia, the remainder of the femur, and the spine. It is usually a solitary tumor [21]. Males are affected two to three times as often as females [16,22].
Patients with osteoid osteoma typically complain of progressively increasing pain that is worse at night and may or may not be related to activity [3,17]. The pain is relieved by nonsteroidal anti-inflammatory medications (ie, prostaglandin inhibitors), usually within 20 to 25 minutes [16,17,23,24]. Lack of relief by nonsteroidal anti-inflammatory agents should prompt consideration of other diagnoses [3].
Children with lower-extremity lesions may present with limp, swelling, muscular atrophy, leg-length discrepancy, bone deformities, muscle contractures, and local point tenderness at the site of the lesion [9,15,16]. Patients with acetabular or proximal femoral lesions may have decreased range of motion at the hip and/or a positive hip impingement sign (pain with internal rotation of the hip in 90° of flexion and slight adduction), findings that may initially suggest a diagnosis of femoroacetabular impingement [17]. (See "Evaluation of limp in children" and "Radiologic evaluation of the hip in infants, children, and adolescents", section on 'Femoroacetabular impingement'.)
Children with spine lesions may present with limp, scoliosis, localized tenderness, restriction of motion, and/or spasm of paravertebral muscles [16]. Children and adolescents with new-onset, painful scoliosis should be evaluated for osteoid osteoma. (See "Adolescent idiopathic scoliosis: Clinical features, evaluation, and diagnosis", section on 'History'.)
●Radiographic findings – On radiographs, osteoid osteoma appears as a small, round lucency (nidus) with a sclerotic margin (image 3A-B) [25]. There may be a small central sequestrum within the lucency.
Approximately 25 to 40 percent of osteoid osteomas are not obvious on radiographs, either because of their location (eg, in the spine) or because cortical thickening obscures the nidus (eg, in the shaft of a long bone such as the tibia or femur), and require computed tomography (CT) for identification (panel A of radiograph) (image 4) [17,26-29]. On magnetic resonance imaging (MRI), osteoid osteomas may cause adjacent exuberant osseous and juxta-cortical soft tissue edema which may obscure the nidus and may superficially mimic stress reaction, infection, or a malignant neoplasm. Therefore, CT is the preferred modality for advanced imaging when an osteoid osteoma is suspected based on radiographs.
●Differential diagnosis – The differential diagnosis of osteoid osteoma includes stress fracture, subacute/chronic osteomyelitis with intracortical abscess, and osteoblastoma. These conditions generally can be distinguished by their characteristic clinical and/radiographic features.
•The pain of stress fractures usually worsens with activity and is relieved with rest; on radiographs, stress fractures typically are linear and run perpendicular or at an angle to the cortex, rather than parallel to it [24]. (See "Overview of stress fractures".)
•Subacute/chronic osteomyelitis may have a tract that extends from the lesion toward the nearest growth plate [24]. (See "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Clinical features'.)
•The pain of osteoblastoma is more generalized and chronic and less responsive to nonsteroidal anti-inflammatory medications than that of osteoid osteoma. It typically has a larger nidus, although this may not be visible. (See 'Osteoblastoma' below.)
●Treatment – The treatment of osteoid osteoma depends upon the presence of symptoms. Lesions with symptoms that are tolerable or can be controlled with nonsteroidal anti-inflammatory agents may be observed with serial examinations and radiographs every four to six months.
Treatment options for symptomatic lesions (eg, intolerable pain, limp, scoliosis) include surgical resection, which may be aided by CT-guided needle localization, radiofrequency ablation (in certain institutions) (image 4) [30,31], cryoablation [32,33], or MRI-guided high-intensity focused ultrasound (in certain institutions) [34-37]. Treatment options may be limited by proximity to vital structures.
●Prognosis – Untreated osteoid osteoma spontaneously resolves over the course of several years [23,38]. Removal of the nidus generally results in resolution of pain. Recurrence is possible if the nidus is not completely removed.
Osteoblastoma — Osteoblastoma is a rare benign bone-forming tumor of unknown etiology. It is morphologically and genetically similar to osteoid osteoma and the two tumors may be different presentations of the same genetic entity [11-13]. Osteoblastoma accounts for approximately 14 percent of benign bone tumors [14].
●Clinical features – Osteoblastoma typically presents during the second decade but may be seen at any age. Males are affected more often than females.
The most common location of osteoblastoma is the posterior column of the spine (the spinous process, lamina, and pedicles) [39]. Other common locations are depicted in the figure (figure 2). Tumors in the spine may be difficult to identify on radiographs [40].
Patients with osteoblastoma typically complain of chronic pain. The pain is less responsive to nonsteroidal anti-inflammatory agents than that of osteoid osteoma [6]. Osteoblastoma uncommonly may cause systemic symptoms [41]. Children with spine lesions may present with limp or neurologic symptoms secondary to cord or nerve root compression. Children with lower extremity lesions may present with limp.
●Radiographic findings – The radiographic findings of osteoblastoma are variable, and advanced imaging (eg, CT or MRI) often is required for identification (image 5A-B). Osteoblastoma may appear similar to osteoid osteoma but is usually larger (>2 cm in diameter); it may appear as an expansive lesion (image 6), similar to an aneurysmal bone cyst, or it may have aggressive features, mimicking a malignant neoplasm [24]. Unlike more aggressive tumors, osteoblastomas rarely extend into the soft tissues.
●Differential diagnosis – The differential diagnosis of osteoblastoma includes:
•Stress fracture (see "Overview of stress fractures")
•Osteomyelitis (see "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Clinical features')
•Osteoid osteoma (see 'Osteoid osteoma' above)
•Osteosarcoma, a malignant bone tumor (see "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis")
•Aneurysmal bone cyst (see 'Aneurysmal bone cyst' below)
These conditions may require advanced radiographic imaging (eg, CT or MRI) for identification.
●Treatment – Treatment for osteoblastoma generally entails curettage and bone grafting. En block excision may be warranted for more aggressive lesions or in regions that permit excision of the bone (eg, fibula). Radiation may be required for spinal lesions when the tumor cannot be completely resected [42]. Successful treatment has also been described with image-guided cryoablation [43].
●Prognosis – Untreated osteoblastoma continues to enlarge and may damage the bone and adjacent structures [42]. It may cause progressive neurologic symptoms if it abuts the spinal canal or neural foramina. The prognosis is good if the lesion can be completely removed. The rate of recurrence is up to 20 percent if the lesion has expanded outside the bone [38].
CARTILAGE-FORMING TUMORS
Osteochondroma and hereditary multiple osteochondromas — An osteochondroma (osteocartilaginous exostosis) is a cartilage-capped bony spur arising on the external surface of a bone (image 7) [44]; the spur contains a marrow cavity that is continuous with the cavity of the underlying bone. A cartilaginous cap overlies the bony spur and is the source of growth (picture 3). The cartilage cap is thick in the child, narrows during adolescence, and generally is <1 cm in the adult [5]. Osteochondromas generally occur spontaneously but have been reported following radiotherapy [45-47]. Osteochondromas account for approximately 30 percent of benign bone tumors [14].
Hereditary multiple osteochondromas (HMO, also known as hereditary multiple exostoses [HME, MIM #133700, MIM #133701, and MIM %600209]) are characterized by two or more exostoses in the appendicular and axial skeleton (image 8). Most cases are caused by autosomal dominant inheritance of a germline mutation in the tumor suppressor genes EXT1 or EXT2 [48]. However, spontaneous mutations also occur [5]. The prevalence of HMO in the general population is approximately 1:50,000 [49-51].
●Clinical features – Osteochondromas and HMO typically present during the second decade. Males are affected more often than females [5,6,52].
Osteochondromas usually occur around the knee or the proximal humerus [52]. The distal femur is the most common location.
Osteochondromas typically present as a painless mass near a joint or on the axial skeleton, or as a painful mass associated with local trauma. Osteochondromas near the ends of long bones are palpable. Osteochondromas can cause pain, functional problems (decreased range of motion), deformity, and pathologic fracture (image 8). Deep osteochondromas (eg, in the axial skeleton) may be an incidental radiographic finding. However, osteochondromas of the ribs occasionally are associated with complications (eg, pneumothorax, hemothorax, pericardial effusion) [53-56].
Osteochondroma can affect nearby growth plates. Patients with HMO may have short stature and angular deformities (ie, varus or valgus deformities) of the upper or lower extremities. The deformities in children with involvement of the wrist and forearm may be severe. Hemiepiphysiodesis can be performed in some cases to allow gradual improvement. (See "Approach to the child with knock-knees", section on 'Other causes'.)
Although osteochondromas can involve the vertebra and may encroach on the spinal canal, most of these tumors are asymptomatic [57,58], and routine screening of the spine in asymptomatic patients with HMO is controversial [59]. Best estimates put the incidence of intracanal tumors at 1.8 percent of patients with HMO, and one in four of these osteochondromas causes neurologic symptoms [58]. Spinal lesions are associated with higher tumor burden, rib lesions, and pelvic lesions. Most experts recommend advanced spinal imaging be limited to patients with rib or pelvic lesions or neurologic symptoms.
●Radiographic findings – Radiographic features include an osseous spur (sometimes large) that arises from the surface of the cortex and usually points away from the joint (image 7). The cortex of the spur is continuous with the cortex of the underlying bone. Osteochondromas may be sessile (the base is larger than the cap) or pedunculated (the cap is larger than the base). Osteochondromas usually involve the metaphysis. Hereditary multiple osteochondromatosis can cause loss of the normal tubularization of the long bones, particularly the distal femurs.
Magnetic resonance imaging (MRI) is warranted when there is a concern for adjacent soft tissue impingement, new focal pain at site, or there is a concern for chondrosarcomatous transformation. Chondrosarcomatous transformation is extremely rare in children. On MRI, the cartilage cap is thick in the child (may be >2 cm), narrows during adolescence, and generally is <1 cm in the adult [5]. If the cartilaginous cap is >1 cm in an adult, malignant transformation to chondrosarcoma is a concern. However, in a review of 67 osteochondromas and 34 secondary chondrosarcomas in adults, no chondrosarcomas had cartilaginous caps <2 cm, and 18 percent of (benign) osteochondromas had a cartilaginous cap >1 cm [60]. Biopsy and removal of the entire osteochondroma may be warranted for lesions with a cap ≥2 cm thick when the nearby physes are nearly or completely fused.
●Differential diagnosis – The differential diagnosis of osteochondroma includes parosteal osteosarcoma (a low-grade surface osteosarcoma). Whereas the medullary canal of osteochondromas is always continuous with that of the bone, this is usually not the case with parosteal osteosarcomas. (See "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis", section on 'Parosteal osteosarcoma'.)
●Treatment – Most osteochondromas need no treatment. Patients with solitary osteochondromas and their caregivers can be educated about the rare event of malignant transformation and its signs and symptoms with follow-up as needed. Patients with HMO may need to be monitored for development of limb deformities. Caregivers should be educated about the signs and symptoms of spinal canal encroachment.
Indications for excision may include local irritation or deformity and concern for malignant transformation (cartilage cap ≥2 cm thick in an adult; increase in size after skeletal maturity; growth disturbance; new onset of symptoms; lesions of the spine, scapula, pelvis, or proximal femur) [3,5,61-63].
●Prognosis – Osteochondromas grow throughout childhood. They generally stop growing when the physes (growth plates) close and remain static throughout adulthood. There is a moderate risk of recurrence if osteochondromas are incompletely removed before the physes close [64]. Positive prognostic factors (more benign presentation and less functional limitations) include female sex, involvement of <5 sites, and HMO caused by EXT2 mutations. None of these factors was predictive of malignant transformation [65].
Osteochondromas may cause local irritation. Lesions of the proximal femur may cause arthritis of the hip joint [66].
There is a small lifetime risk of malignant transformation to chondrosarcoma, which occurs during adulthood and most commonly in patients with HMO (in as many as 5 percent of cases) [48,61,65,67]. Malignant transformation may be heralded by a change in size of an osteochondroma after skeletal maturity or new onset of symptoms [3,5,61-63]. Osteochondromas of the spine, scapula, pelvis, and proximal femur are particularly prone to malignant transformation. (See "Chondrosarcoma", section on 'Osteochondroma'.)
Enchondroma — Enchondromas are benign cartilage-forming tumors that develop in the medulla (marrow cavity) of long bones (image 9) [68,69]. They account for approximately 3 percent of benign bone tumors [14].
Enchondromatosis (a common subtype of which is Ollier disease, MIM %166000) is defined by multiple enchondromas, often with a unilateral predominance (image 10) [3,6,48]. The estimated prevalence is 1 in 100,000 [70]. Maffucci syndrome is a subtype of enchondromatosis that is characterized by multiple enchondromas and soft tissue vascular malformations (image 11 and picture 2). Most cases of enchondromatosis and Maffucci syndrome are sporadic and associated with somatic mutations in the isocitrate dehydrogenase-1 and isocitrate dehydrogenase 2 genes (IDH1 and IDH2) [71,72]. (See "Venous malformations", section on 'Maffucci syndrome'.)
●Clinical features – Enchondromas typically present during the second decade but can present at any age [68]. Enchondromatosis usually presents in children younger than 10 years [70].
Enchondromas usually occur in the long bones, particularly the long bones of the hand, followed by the humerus and femur (figure 3) [68]. They generally are central, metaphyseal lesions [6]. Enchondromas occur with equal frequency in males and females.
The signs and symptoms vary depending upon the anatomic site, extent, and distribution of involvement. Most enchondromas are asymptomatic unless a fracture is present [3]. They often are incidental findings. When symptomatic, clinical manifestations may include widening of the bone, angular deformity, and limb-length discrepancy [9]. In patients with enchondromatosis, enchondromas may arise from the skull base; clinical features include headache and cranial nerve palsy [73].
●Radiographic findings – Radiographic features of enchondromas include an oval, well-circumscribed with sclerotic or nonsclerotic margins, central lucent lesion, with or without matrix calcifications (image 9) [74]. Chondral matrix usually is not seen in children [3,6,68]. There may be endosteal scalloping of the cortex, especially when the lesion is in the hand or foot (image 10 and image 12). Multiple lesions may be present.
●Differential diagnosis – The differential diagnosis of enchondromas includes bony infarction (image 13), tuberculous dactylitis (also called spina ventosa) [75], and low-grade chondrosarcoma (image 14), which must be excluded in patients with enchondroma who have pain without fracture. (See "Chondrosarcoma", section on 'Diagnostic and staging work-up'.)
●Treatment – The treatment of enchondromas depends upon the presence of symptoms and size. Those that are asymptomatic and small enough not to increase the risk of pathologic fracture may be observed. The risk of fracture is increased when the lesions occur in a weight-bearing bone, are >25 mm in diameter, and involve >50 percent of the diameter of the cortex. The frequency of follow-up depends upon the size, location, and number of lesions.
Symptomatic chondromas are treated with curettage and bone grafting; low-grade chondrosarcoma must be excluded in patients with pain in the absence of fracture. Fractures should be permitted to heal before curettage.
●Prognosis – Solitary enchondromas usually are self-limited. However, they may continue to grow. Recurrence after curettage and bone graft is rare [6].
Enchondromas, particularly those of the long bones and pelvis, may be complicated by malignant transformation to chondrosarcoma (image 14), which usually occurs after skeletal maturity and may be heralded by the development of pain [76]. Malignant transformation of a solitary enchondroma is extremely rare (<1 percent) but has been described [76]. The risk of malignant transformation is increased (as high as 50 percent) in patients with enchondromatosis (Ollier disease) or Maffucci syndrome [48,70,77-80]. Enchondromatosis and Maffucci syndrome also are associated with nonsarcomatous extra-osseous neoplasms, including brain tumors [3,81,82].
Periosteal chondroma — Periosteal chondromas (juxtacortical chondromas) are rare, benign, cartilage-forming tumors that arise from the surface of the cortex, deep to the periosteum, and erode into the cortex [3,6,83]. A periosteal chondroma histologically and clinically resembles an enchondroma but is located on the surface of bone.
●Clinical features – Periosteal chondroma occurs in children and adults [6]. The most common site is the proximal humerus; the other long bones and small bones of the hands and feet also may be involved [3,83,84]. Clinical features may include pain at the site of the lesion and a palpable nontender hard mass that is fixed to bone.
●Radiographic features – On radiographs, periosteal chondromas appear as small, scalloped, radiolucent lesions on the outer surface of the cortex in the metaphysis or diaphysis (image 15) [3,6,83-87]. There is a rim of sclerotic bone [6]. Chondral matrix is present in approximately one-third of cases [85]. Periosteal reaction is minimal.
●Differential diagnosis – The differential diagnosis of periosteal chondroma includes [86]:
•Nonossifying fibroma (see 'Nonossifying fibroma' below)
•Soft-tissue tumors, secondarily eroding into the cortical bone
•Chondrosarcoma, a malignant tumor (see "Chondrosarcoma")
•Osteosarcoma, a malignant tumor (see "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis")
●Treatment – Periosteal chondroma usually is treated with extended curettage or en block excision to minimize the risk of local recurrence [3,6].
Chondroblastoma — Chondroblastoma is a nonmalignant cartilage-forming tumor that usually arises in the epiphyses or apophyses of long bones [74,88].
●Clinical features – Chondroblastoma typically presents during the teenage years. The most common sites are the epiphysis of the proximal humerus (image 16), distal femur (image 17), and proximal tibia (image 18); 30 percent occur around the knee (figure 4) [89,90]. Chondroblastoma is approximately 1.5 times more common in males than in females. Symptoms of chondroblastoma include low-grade joint pain (constant, unrelated to activity) and swelling [9,38]. Superficially, these epiphyseal intra-articular lesions may mimic a rheumatologic condition.
●Radiographic findings – On radiographs, chondroblastomas appear as small, well-defined epiphyseal lesions with a sclerotic border that may cross the physis (growth plate) (image 19). Chondroid matrix calcification may be seen [38].
On MRI, these lesions characteristically have central tumoral enhancement after intravenous gadolinium. Post-contrast imaging is important to differentiate a chondroblastoma, which has central enhancement, from a Brodie abscess, which characteristically demonstrates peripheral enhancement. A large joint effusion is usually present given the intra-articular location of chondroblastomas.
●Differential diagnosis – The differential diagnosis of chondroblastoma includes:
•Giant cell tumor, a nonmalignant locally aggressive skeletal tumor that occurs near the growth plate in young adults. Giant cell tumors in skeletally immature children tend to occur in the metaphysis, whereas chondroblastoma tends to occur in the epiphysis. (See "Giant cell tumor of bone".)
•Chondromyxoid fibroma. (See 'Chondromyxoid fibroma' below.)
•Avascular necrosis, an abnormality of subchondral bone in which pain is activity related. In contrast, in chondroblastoma, subchondral bone is normal and pain is constant, unrelated to activity [9]. (See "Treatment of nontraumatic hip osteonecrosis (avascular necrosis of the femoral head) in adults".)
•Aneurysmal bone cyst. (See 'Aneurysmal bone cyst' below.)
•Epiphyseal Brodie abscess related to osteomyelitis. (See "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Clinical features'.)
●Treatment – Chondroblastoma is treated with curettage and bone grafting [91]. Reconstruction may be difficult if chondroblastoma involves the articular surface.
●Prognosis – The prognosis for patients with chondroblastoma generally is good. Chondroblastoma that involves the articular surface may result in arthritis [92]. Oftentimes, the physis is involved and may lead to growth disturbance. Local recurrence rates after curettage vary, typically ranging from 0 to 10 percent [90-96]. In cases of recurrence, en bloc resection may be warranted.
Chondromyxoid fibroma — Chondromyxoid fibroma is a rare, nonmalignant, cartilage-forming tumor of the tubular long bones.
●Clinical features – Chondromyxoid fibroma usually presents in the teens or 20s [97]. Approximately one-quarter of cases occur in the proximal tibia (image 20), with the distal femur and calcaneus being the next most common sites. Males are affected approximately 1.5 times as often as females [98]. Symptoms of chondromyxoid fibroma may include pain and swelling.
●Radiographic findings – Chondromyxoid fibroma is an eccentric, intramedullary, lobulated or bubbly lesion in the metaphysis; it has a sclerotic border (image 21). It typically is lucent, with a rare chondral matrix [38,74].
●Differential diagnosis – The differential diagnosis of chondromyxoid fibroma includes:
•Nonossifying fibroma (see 'Nonossifying fibroma' below)
•Osteomyelitis (see "Hematogenous osteomyelitis in children: Clinical features and complications", section on 'Clinical features')
●Treatment – The treatment of chondromyxoid fibroma is curettage and bone grafting.
●Prognosis – The prognosis of chondromyxoid fibroma generally is good. There is a 20 percent risk of recurrence, which may require en bloc resection [6].
FIBROUS LESIONS
Fibrous dysplasia — Fibrous dysplasia is a lesion in which portions of the bone are replaced by fibrous connective tissue and poorly formed trabecular bone [6]. The process originates in the medullary cavity. It is caused by a postzygotic mutation in the guanine nucleotide stimulatory protein (GNAS1) gene. It is more of a skeletal dysplasia than a true neoplasm. Fibrous dysplasia accounts for approximately 5 to 7 percent of benign bone tumors [14].
Fibrous dysplasia may occur in single or multiple bones (monostotic and polyostotic fibrous dysplasia, respectively) [99]. The polyostotic form of fibrous dysplasia is known as McCune-Albright syndrome (or Albright syndrome, MIM #174800) and is associated with café-au-lait macules (picture 1) and endocrine abnormalities, including excess growth hormone, to which bone affected by fibrous dysplasia is more sensitive than unaffected bone [100]. Mazabraud syndrome is characterized by polyostotic fibrous dysplasia and soft tissue myxomas; it overlaps clinically with McCune-Albright syndrome [4]. (See "Definition, etiology, and evaluation of precocious puberty", section on 'McCune-Albright syndrome'.)
A detailed discussion of the evaluation and management of McCune-Albright syndrome is beyond the scope of this review, but is available in a guideline from an international consortium [101].
●Clinical features – Fibrous dysplasia most commonly presents in the teens or 20s. It may occur in any bone but is most common in the proximal femur (image 22), tibia, ribs, and skull (figure 5) [5]. Fibrous dysplasia affects slightly more males than females.
Most patients with fibrous dysplasia are asymptomatic [5]. However, fibrous dysplasia may be painful or cause swelling. It can cause repeated pathologic fractures or severe bone deformity, such as the "shepherd's crook" varus deformity of the proximal femur (image 23) [6].
●Radiographic findings – On radiographs, fibrous dysplasia appears as a lytic lesion in the metaphysis or diaphysis with a "ground glass" matrix (image 24). There is expansion of the bone and possible bowing. The cortical bone is thinned with endosteal scalloping [9]. Periosteal reaction usually is absent unless there is a pathologic fracture.
Magnetic resonance imaging is not indicated unless there is a concern for radiographically occult pathologic stress reaction or fracture.
●Differential diagnosis – The differential diagnosis of fibrous dysplasia includes:
•Nonossifying fibroma (see 'Nonossifying fibroma' below)
•Simple bone cyst (SBC) (see 'Simple bone cyst' below)
•Aneurysmal bone cyst (see 'Aneurysmal bone cyst' below)
●Treatment – The treatment of fibrous dysplasia depends upon the presence of symptoms. The need for and frequency of follow-up radiographs varies with the site of involvement and other clinical features. Fibrous dysplasia of the proximal femur or other weight-bearing bones may be associated with aggressive remodeling and fracture and warrants regular monitoring with serial radiographs.
Curettage, bone grafting, and stabilization may be warranted for fibrous dysplasia that is associated with symptoms (pain, deformity) or fracture; however, there is a high rate of recurrence. Autograft should not be used because it will be resorbed. Bisphosphonate therapy is another alternative for symptomatic patients [102,103].
●Prognosis – The deformity of fibrous dysplasia may progress with skeletal growth [6]. Fibrous dysplasia usually is static after growth ceases but may be reactivated with pregnancy [104,105]. Fibrous dysplasia often recurs after curettage and bone grafting.
Malignant transformation (eg, to osteosarcoma, fibrosarcoma) is uncommon but may occur, with a prevalence ranging from 0.4 (monostotic form) to 6.7 (McCune-Albright syndrome) percent [106-109]. The risk for malignant transformation is increased in patients with polyostotic fibrous dysplasia and radiation exposure [107]. Features associated with malignant transformation include rapidly increasing pain without trauma, rapid change in radiographic appearance, particularly osteolysis, mineralization, and cortical destruction [106,107,110,111]. (See "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)
Ossifying fibroma — Ossifying fibroma (also called osteofibrous dysplasia, intracortical fibrous dysplasia, Jaffe-Campanacci syndrome) is not a tumor, per se, but a deformity-inducing fibro-osseous lesion of the tibia and/or fibula [112,113]. The process originates in the cortex [6].
●Clinical features – Ossifying fibroma occurs in children younger than 10 years of age [112,113]. It generally affects the tibia and fibula. Clinical features include swelling and/or anterolateral bowing of the lower leg. Osteofibrous dysplasia is painful only if it associated with a pathologic fracture.
●Radiographic findings – Radiographic features of ossifying fibroma include a lytic thinning of the diaphyseal cortical bone with interspersed sclerosis, causing anterior or anterolateral bowing. There is a sharply circumscribed margin [6]. These lesions tend to be multiple and are longitudinally oriented with the bone, and may involve both the tibia and fibular shafts when the leg is affected.
●Differential diagnosis – The differential diagnosis of ossifying fibroma includes monostotic fibrous dysplasia (which originates in the medulla rather than the cortex), adamantinoma (a low-grade malignant bone tumor that occurs in older children in the second decade and adult patients), and nonossifying fibroma. (See 'Fibrous dysplasia' above and 'Nonossifying fibroma' below.)
●Treatment – The treatment of ossifying fibroma is usually observation. Asymptomatic patients may be observed every six months with serial radiographs in the rare event that the lesion may be a differentiated adamantinoma. Children with large lesions or lesions in the proximal femur or other weight-bearing bones are seen more frequently (eg, every three to four months). Excision, bone graft, and correction of bony deformity may be warranted for lesions that are symptomatic (ie, with pain or deformity) after skeletal maturity.
●Prognosis – Ossifying fibroma is noninvasive. However, it will recur if it is excised before skeletal maturity. Excision after skeletal maturity is usually successful [114,115].
Nonossifying fibroma — Nonossifying fibroma is a common benign fibrous lesion that is also known as metaphyseal cortical defect, fibrous cortical defect, and benign metaphyseal bone scar. It is a developmental defect in which areas that normally ossify are filled with fibrous connective tissue [6].
●Clinical features – Nonossifying fibroma usually is an incidental radiographic finding in teenagers. It occurs most commonly in the distal femur, followed by the distal tibia (image 25) and the proximal tibia (image 26). Females are affected as often as males [116].
Nonossifying fibroma usually is asymptomatic and discovered incidental to trauma [5]. Large lesions (eg, >50 percent of the width of the bone on coronal or sagittal view) may be associated with pathologic fracture [1,117].
●Radiographic findings – On radiographs, nonossifying fibromas appear as small, well-defined, eccentric, expansile, lytic lesions located in the metaphysis with scalloped sclerotic borders [1,6]. Multiple lesions may be present.
Nonossifying fibromas may have an atypical appearance as they fill with normal bone before they disappear [5,6]. When there is a concomitant pathologic fracture, nonossifying fibroma may have a more aggressive radiographic appearance, but it should not be mistaken for malignant tumor [5].
●Differential diagnosis – The differential diagnosis of nonossifying fibroma includes:
•Chondromyxoid fibroma (see 'Chondromyxoid fibroma' above)
•Fibrous dysplasia (see 'Fibrous dysplasia' above)
●Treatment – Small, asymptomatic nonossifying fibromas that are discovered incidentally do not require any further follow-up. Caregivers are simply counseled to bring their child in if the area becomes painful. In younger children, the lesions may grow relative to adjacent bone, increasing the risk of fracture [5].
Curettage and bone grafting may be warranted for lesions causing pain or to prevent pathologic fracture if the lesion is greater than 50 percent of the diameter of the bone or is in a high-stress area (eg, distal femoral metaphysis) [1,5].
●Prognosis – The prognosis for nonossifying fibroma generally is excellent [118]. They usually fill in during adolescence [5]. The risk of recurrence is lower than for other benign tumors.
CYSTIC TUMORS
Simple bone cyst — Simple bone cysts (SBCs; unicameral bone cysts, solitary bone cysts) are fluid-filled lesions with a fibrous lining [1].
●Clinical features – SBCs generally occur in the first 20 years of life [119]. The proximal humerus and femur are the most common locations. SBCs occur with equal frequency in males and females [5].
SBCs commonly present with a pathologic fracture. However, they may be an incidental radiographic finding. Symptoms may include localized pain, limp, or failure to use the extremity normally [1,5].
●Radiographic findings – On radiographs, SBCs appear as well-marginated lytic lesions of the metaphysis or metadiaphysis with or without reactive sclerosis [1,5] (image 27). The lesion usually involves the full diameter of bone, with mild endosteal scalloping [6].
SBCs with pathologic fractures may be indicated by the "fallen fragment" or "fallen leaf" sign, in which a fragment of bone falls to the bottom of the cyst (image 28) [9,120]. SBCs may have septations as sequelae from a previous pathologic fracture.
●Differential diagnosis – The differential diagnosis of SBC includes aneurysmal bone cyst and fibrous dysplasia. SBCs may have internal septations and fluid-fluid levels when they are imaged by magnetic resonance imaging (MRI), superficially mimicking an aneurysmal bone cyst. As a general rule, unlike aneurysmal bone cysts, the maximal axial diameter of an SBC is never larger than the greatest diameter of the involved bone. (See 'Aneurysmal bone cyst' below and 'Fibrous dysplasia' above.)
●Treatment – The treatment of SBCs is observation with serial radiographs every four to six months. Activity restrictions are often necessary to avoid pathologic fracture. Alternatively, if the clinician is concerned about fracture due to the size of the lesion or the child's activity level, SBCs may be aspirated and injected with methylprednisolone or bone marrow aspirate [121-124]. Although it has never been conclusively proven, some authors believe that glucocorticoid injection may hasten the resolution of the cyst and thus allow patients to return to normal activities. Other alternatives include percutaneous or open curettage and placement of demineralized bone matrix, calcium sulfate, or bone marrow aspirate with or without placement of metal implants.
In general, open curettage and bone grafting rarely are required and should be reserved or large lesions that compromise the structural integrity of the bone [125,126].
●Prognosis – SBCs spontaneously improve in all patients. However, regression may not occur until after skeletal maturity [127]. Although few lesions remain clinically significant, it is uncertain whether these lesions ever completely resolve. Pending spontaneous regression, fractures may occur through larger cysts.
Aneurysmal bone cyst — Aneurysmal bone cysts are nonmalignant expansile vascular lesions that consist of blood-filled channels [6,9]. They may grow rapidly and destroy bone. Aneurysmal bone cysts generally are solitary [1]. They may be primary or related to other nonmalignant bone lesions (eg, giant cell tumor, osteoblastoma, chondroblastoma) [2,5,6]. They account for approximately 9 percent of benign bone tumors [14].
●Clinical features – Aneurysmal bone cysts generally occur in adolescents. They may be found in any bone but are most common in the posterior spinal elements, femur, and tibia (figure 6) [128]. In long bones, they most commonly affect the metaphyses. Aneurysmal bone cysts are slightly more common in females than in males [5].
Aneurysmal bone cysts typically cause localized pain and swelling [129]. They may present with pathologic fracture, limp, or swelling as the lesion increases in size [1,5]. Lesions in the spine may be associated with neurologic symptoms [130]. Lesions that cross the growth plate may cause growth arrest [9].
●Radiographic findings – On radiographs, aneurysmal bone cysts appear as aggressive, expansile, lytic metaphyseal lesions with an "eggshell" sclerotic rim (image 29) [131]. Pathologic fracture or periosteal reaction may be present (image 30). The lesions are sharply circumscribed. They may have a "soap bubble" appearance secondary to the reinforcement of the remaining trabeculae that support the bone structure [6]. The cortex is usually intact, although it may be thin.
By MRI, fluid-filled cavities with a fluid level may be identified with multiple septations. After the administration of contrast, thin septal and wall enhancement may be seen. If there is a pathologic fracture, perilesional osseous and soft tissue edema may be seen.
●Differential diagnosis – The differential diagnosis of aneurysmal bone cyst includes:
•Simple bone cyst. (See 'Simple bone cyst' above.)
•Giant cell tumor, a nonmalignant locally aggressive skeletal tumor that occurs in young adults. (See "Giant cell tumor of bone".)
•Telangiectatic osteosarcoma, a malignant bone tumor. Unlike aneurysmal bone cysts, telangiectatic osteosarcomas demonstrate soft tissue and tumoral enhancement on MRI. (See "Osteosarcoma: Epidemiology, pathology, clinical presentation, and diagnosis".)
•Osteoblastoma (in the spine). (See 'Osteoblastoma' above.)
•Chondroblastoma (if they cross the growth plate). (See 'Chondroblastoma' above.)
●Treatment – Aneurysmal bone cysts are treated with excision, curettage, and bone grafting [126,132]. Chemical cauterization or cryotherapy may be required. Preoperative embolization of the aneurysmal bone cyst may be performed to ameliorate operative bleeding during excision. Medical treatment with denosumab, a monoclonal antibody that inhibits bone resorption may be indicated in areas that are difficult to treat surgically (eg, the spine or pelvis) [133-135].
●Prognosis – Aneurysmal bone cysts are locally aggressive and destructive [6]. They continue to expand until treated and may recur after excision (in 10 to 50 percent of cases) [1,5].
OTHER BONE TUMORS
Langerhans cell histiocytosis of bone — Langerhans cell histiocytosis (LCH) of bone is a benign form of LCH that is localized to bone. Patients may present with a solitary lesion (monostotic) or multiple sites of involvement (polyostotic). LCH of bone is discussed separately. (See "Clinical manifestations, pathologic features, and diagnosis of Langerhans cell histiocytosis", section on 'Lytic bone lesions'.)
Giant cell tumor — Giant cell tumor of bone is a relatively rare, nonmalignant locally aggressive osteolytic skeletal neoplasm of young adults. It is discussed separately. (See "Giant cell tumor of bone".)
SUMMARY
●Evaluation – Benign bone tumors often are discovered incidentally during evaluation of trauma or another condition. Symptoms of benign bone tumors, when they occur, may include localized pain, swelling, deformity, or pathologic fracture. (See 'Clinical evaluation' above.)
Most benign bone tumors can be diagnosed with radiographs. Characteristic clinical and radiographic features are summarized in the table (table 1). (See 'Radiologic evaluation' above.)
●Management – Most benign bone tumors are managed with serial examinations and radiographs. Symptomatic or aggressive nonmalignant tumors may be treated with curettage and bone grafting or excision. (See 'Management' above.)
●Classification – Nonmalignant bone tumors of childhood can be classified according to the matrix, or substance, that they produce: osteoid- or bone-forming tumors, cartilage-forming tumors, fibrous lesions, and cystic tumors. (See 'Classification' above.)
•Osteoid- or bone-forming lesions include:
-Osteoid osteoma (image 3A-B) (see 'Osteoid osteoma' above)
-Osteoblastoma (image 6) (see 'Osteoblastoma' above)
•Cartilage-forming tumors include:
-Osteochondroma (image 7) and hereditary multiple osteochondromas (see 'Osteochondroma and hereditary multiple osteochondromas' above)
-Solitary enchondroma (image 9), enchondromatosis (Ollier syndrome) (image 10), and Maffucci syndrome (image 11 and picture 2) (see 'Enchondroma' above)
-Periosteal chondroma (image 15) (see 'Periosteal chondroma' above)
-Chondroblastoma (image 19) (see 'Chondroblastoma' above)
-Chondromyxoid fibroma (image 20) (see 'Chondromyxoid fibroma' above)
•Fibrous lesions include:
-Fibrous dysplasia (image 22) and polyostotic fibrous dysplasia (McCune-Albright syndrome) (see 'Fibrous dysplasia' above)
-Ossifying fibroma (see 'Ossifying fibroma' above)
-Nonossifying fibroma (image 25) (see 'Nonossifying fibroma' above)
•Cystic and vascular lesions include:
-Simple bone cyst (image 28) (see 'Simple bone cyst' above)
-Aneurysmal bone cyst (image 29) (see 'Aneurysmal bone cyst' above)
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