Tumors and Focal Bone, Joint, and Soft-Tissue Lesions

10.1055/b-0034-87941

Tumors and Focal Bone, Joint, and Soft-Tissue Lesions

The average annual incidence rate of primary bone sarcomas is approximately 8.7 per million children younger than 20 years of age, and primary bone sarcomas occur 10 times less frequently than soft tissue sarcomas.

**Table 5.68 Tumors and focal lesions: epiphyseal lesions before closure of growth plate**
Diagnosis	Findings	Comments
Osteomyelitis Fig. 5.112a, b	Erosion in the epiphysis or well-defined lucency from an intraosseous abscess.	Bacterial infections in the epiphyses are not as common as in the metaphyses. Tuberculosis has a predilection for the ends of long bones in children.
Avascular necrosis (AVN) Fig. 5.113a, b Fig. 5.36, p. 519	Mixed sclerosis and lucency ± subchondral collapse.	MRI shows early findings of marrow edema, and bone scan shows increased uptake prior to changes on radiography.
Langerhans cell histiocytosis	Lytic (punched out) defect in the epiphysis.	Uncommon location of Langerhans cell histiocytosis.
Chondroblastoma (Codman tumor) Fig. 5.114a–d	Osteolytic lesion with a fine sclerotic rim, 25%–50% have a stippled matrix (“popcorn” calcifications), ± internal trabeculations.	Common locations: proximal humerus, distal femur, and proximal tibia.
Articular osteocondroma/dysplasia epiphysealis hemimelica (Trevor disease) Fig. 5.46, p. 526	Irregular ossification at sites of epiphyseal enchondromas. Cartilage may be seen capping the stalks of the enchondromas on MRI.	Sixty to seventy percent of patients have enchondromas at multiple epiphyses. Most common sites are the talar dome and distal tibial epiphyses.

**Fig. 5.112a, b Osteomyelitis** affecting the epiphysis. Decreased T1-weighted signal intensity (a) and enhancement in the femoral epiphysis after gadolinium (b; arrows; compare with normal ossification center in the tibia).

**Fig. 5.113a, b Avascular necrosis.** (a) Diffuse bone demineralization, faint sclerosis in the metaphyses, and growth recovery lines around the knee in a 4-year-old with acute lymphoblastic leukemia in remission. (b) T2-weighted MRI reveals the underlying AVN and bone infarcts.

**Fig. 5.114a–d Chondroblastoma** presenting as a well-marginated lucency in the proximal epiphysis of the tibia on radiography (a) and CT (b). MRI reveals increased T2-weighted signal intensity with fluid-fluid levels (c) and T1-weighted enhancement about the margins of the lesions (d). Note the normal appearance of the margins of the distal femoral epiphysis with punctate bone formation (arrow in a and b).

**Table 5.69 Tumors and focal lesions: epiphyseal lesions after closure of growth plate**
Diagnosis	Findings	Comments
AVN	Mixed sclerosis and lucency ± subchondral collapse.	MRI shows early findings of marrow edema, and bone scan shows increased uptake prior to changes on radiography.
Giant cell tumor Fig. 5.115	Osteolytic lesion with a geographic type of bone destruction. Lucent expansile lesion eccentrically located without marginal sclerosis, but narrow zone of transition. Internal trabeculations.	Abuts the subchondral bone. Typical locations: ends of the distal femur, proximal tibia, distal radius, and proximal humerus.
Fibrous dysplasia Fig. 5.116	(see Table 5.71 )
Subchondral cysts Fig. 5.117a, b	Well-marginated lucency subjacent to the subchondral bone.	May arise from herniation of synovium into the bone (synovial herniation pit).
Clear cell chondrosarcoma	Expansile lytic lesion with thinning of the cortex.	Extensive bone formation may mimic osteosarcoma.

**Fig. 5.115 Giant cell tumor** in the proximal tibial of a 15-year-old. Bubbly, lucent, and expansile lesion.

**Fig. 5.116 Polyostotic fibrous dysplasia.**

**Fig. 5.117a, b Large subchondral cyst** in a patient with trisomy 21 and inflammatory arthritis. (a) Radiograph shows a well-marginated lucent lesion with a narrow zone of transition. (b) The wall of the cystic cavity enhances, as does the inflamed and thickened synovium in the suprapatellar pouch.

**Table 5.70 Tumors and focal lesions: metaphysis**
Diagnosis	Findings	Comments
Fibrous cortical defect (metaphyseal defect) and nonossifying fibroma (NOF; nonosteogenic fibroma) Fig. 5.118a, b	Well-demarcated, eccentric, lucent defect communicating with the cortex and marginated by a thin rim of sclerosis.	Radiography is usually diagnostic. Observed in 30% of normal population < 20 y of age. Proximal and distal tibial and distal femur > proximal humerus and fibula. 1. Large lesions = NOF 2. Small lesions = fibrous cortical defect.
Distal femoral cortical defect (periosteal desmoids, avulsive cortical irregularity, distal metaphyseal femoral defect, cortical desmoid, or medial supracondylar defect) Fig. 5.119a–d, p. 576	Cortically based lesion at posterome-dial aspect of distal femur. Similar in appearance to fibrous cortical defect.	May be bilateral. Occurs in 12- to 20-y-olds. Fibrous proliferation of periosteum. Lesions resolve spontaneously. Located at posterome-dial aspect of distal femur.
Osteochondroma (osteocartilaginous exostosis) Fig. 5.120a–c Fig. 5.121, p. 578	Pedunculated: Slender osseous stalk (continuous with the medulla) that projects away from the joint. Capped with hyaline cartilage. Sessile: broad based attached to the cortex.	Very common benign bone lesion. Usually discovered before age 20 y. Knees, hips, shoulders, and ankles. Mass effect on structures. Rarely may transform into chondrosarcoma. Multiple hereditary osteochondromatosis: autosomal dominant. Features of trichorhinophalangeal (Langer-Giedion) and Potocki-Shaffer syndromes.
Aneurysmal bone cyst Fig. 5.122a, b, p. 578	Multicystic and eccentric expansile lesion encased in a thin shell of cortical bone.	May abut the metaphyseal side of the growth plate. Fluid-fluid levels on MRI or CT similar to telangiectatic osteosarcoma. Common sites: proximal tibia and femur, proximal humerus, scapula, and spine.
Unicameral bone cyst Fig. 5.123a, b, p. 579	Centrally located, well-circumscribed, lucent lesion with sclerotic margins. May contain septations. Prior to treatment or pathologic fracture, follows the signal intensity of fluid on MRI pulse sequences.	Tumorlike lesion of unknown cause. May be the result of local disturbance of bone growth. Common locations in patients < 20 y include proximal humerus and femur; > 20 y include scapula, ilium, distal femur, proximal tibia, and calcaneus. May reoccur and reabsorb surgical packing material. Fallen fragment sign: cortical fragment layering in the cyst after pathologic fracture.
Osteosarcoma Fig. 5.124a, b Fig. 5.125a–c, p. 580	(see Table 5.76 )
Enchondromatosis (including Ollier disease and Maffucci syndrome) Fig. 5.126a, b, p. 580 Fig. 5.127a–c, p. 581	(see Table 5.75 )

**Fig. 5.118a, b Fibrous cortical defect** (arrows) in the proximal tibia on radiography (a) and axial T2 fat-saturated MRI (b).

**Fig. 5.119a–d Distal femoral cortical defect.** (a) The defect is lu-cent with irregular margins on radiography (arrow). (b) Because of pain and a limp, additional imaging was performed that showed the classic appearance of the lesion on CT with a smaller cortical defect on the contralateral side. The lesion is associated with the cortex and is dark on T1-(c) and bright on T2-weighted (arrow in d) MRI.

**Fig. 5.120a–c Osteochondroma** displacing the peroneal tendons. (a) The osteochondroma (arrow) projects off the posterior aspect of the distal fibula and displaces the peroneal tendons posteriorly. (b) The cartilage cap has increased T2-weighted signal intensity (arrow). (c) The tendons are also displaced laterally (arrowhead) by the cartilage cap (arrow).

**Fig. 5.121 Osteochondroma.** Multiple hereditary exostoses.

**Fig. 5.122a, b Aneurysmal bone cyst** arising from the metaphysis. Bubbly lucent and expansile lesion (a) with fluid-fluid levels on MRI (b).

**Fig. 5.123a, b Unicameral bone cyst** at the proximal femur. Expansile lucent lesion on radiography (a) with a fluid-fluid level on fat-saturated T2-weighted MRI (b).

**Fig. 5.124a, b Osteosarcoma** arising from the distal femur with a Codman triangle (arrow), soft-tissue mass (arrowheads), and exuberant bone formation (**a, b**).

**Fig. 5.125a–c Periosteal osteosarcoma** arising from the proximal tibia. (a) Patient presented with swelling (arrowheads) after minor trauma. (**b, c**) Cortical erosion (arrows in a) on radiography prompted a subsequent MRI that showed an enhancing mass eroding the underlying bone.

**Fig. 5.126a, b Ollier disease** with diffuse enchondromatosis on radiograph (a) and STIR MRI (b). t Talus

**Fig. 5.127a–c Enchondromatosis about the knee.** (**a, b**) Radiography shows lucencies in the metaphyses. (c) T2-weighted MRI shows cartilage signal intensity.

**Table 5.71 Tumors and focal lesions: diaphyseal lesions**
Diagnosis	Findings	Comments
Subacute osteomyelitis	Mixed lucent and sclerotic lesion.
Bone infarct Fig. 5.128 Fig. 5.113, p. 573	Coarse sclerotic calcifications confined to the medulla. Serpiginous alternating bands of high and low T2-weighted signal intensity on MRI.	DD: Enchondroma, fibrous dysplasia, NOF, interosseous lipoma. Patients usually have predisposing history for infarcts (sickle cell disease, steroids, etc.). Differentiate from AVN = osteonecrosis of the subchondral bone predisposing to collapse of the joint.
Fibrous dysplasia (monostotic) Fig. 5.91, p. 558	Well-defined geographic lesion with narrow zone of transition. Appearance depends on the relative contribution of fibrous tissue and bone. More fibrous lesions have a cystic or ground-glass matrix. More osseous lesions have scattered calcifications or thick rim (rind sign) of sclerosis. Variable appearance on MRI.	Monostotic 70%–80% of case. Age 10–50 y. Replacement of cancellous bone by fibrous tissue. Common sites: midshaft of tibia, proximal femur, and ribs.
Fibrous dysplasia (polyostotic) Fig. 5.116, p. 574	Multiple lesions. Similar features as monostotic form but may appear more aggressive.	Polyostotic 20%–30% of cases. Tends to involve only one side of body. Similar locations as monostotic form plus: jaw, pelvis, forearm, hands, feet, and fibula. McCune-Albright syndrome is associated with geographic nevi and endocrine abnormality (precocious puberty). Mazabraud syndrome: fibrous dysplasia and intramuscular myxomas.
Unicameral bone cyst	(see Table 5.70 )
Osteoid osteoma	(see Table 5.76 )
Osteoblastoma	(see Table 5.76 )
Langerhans cell histiocytosis	Lesions in diaphysis may have more periosteal reaction than the lytic lesions in other sites.	Variable appearance from a punched out lytic lesion to a mixed lytic and sclerotic lesion.
Ewing sarcoma family of tumors Fig. 5.129a–c	Variable appearance. Poorly marginated lesion with permeative or moth-eaten pattern of bone destruction. Lamellated periosteal new bone formation or sunburst periosteal reaction. Large soft-tissue mass. Soft-tissue mass may cause saucerization.	Age 5–25 y. Second most common bone tumor of childhood. Long bones of lower extremity > pelvis > spine. Femur > ilium > tibia. Varying degrees of neuroectodermal differentiation (Ewing sarcome, Askin sarcoma, primitive neuroectodermal tumor [PNET]). Sclerosis in tumor may resemble osteoid formation of osteosarcoma.
Lymphoma Fig. 5.73, p. 544	Variable appearance. Tends to involve a large portion of bone. Geographic lytic destruction with moth-eaten or permeative pattern. Ivory bone (especially vertebra). Periosteal reaction and soft-tissue masses. Diffuse marrow infiltration on MRI.	Occurs in patients aged 10–70 y. Primary lymphoma of bone is very uncommon. DD: metastatic neuroblastoma, Ewing sarcoma, osteosarcoma.
Enchondroma Fig. 5.130, p. 584	Matrix of coarse sclerotic, punctate, or annular calcifications (arcs and whirls). Homogeneous high signal intensity on T2-weighted MRI with a lobular configuration.	Small lesions may appear similar to bone infarcts. Difficult to distinguish enchondroma from a low-grade chondrosarcoma (localized cortical thickening and lesions > 4 cm in length may indicated chondrosarcoma). Occurs in patients aged 15–40 y.
Benign fibrous histiocytoma (xanthofibroma or fibrous xanthoma)	Similar features as NOF but often develops at an atypical location or appears more aggressive.	Occurs in patients aged 15–60 y. Located in diaphysis or, in contrast to NOF, the articular end of a long bone, ribs, and pelvis. Locally aggressive with recurrence after resection.
Adamantinoma	Well-demarcated, elongated osteolytic lesion separated by sclerotic bone ± soap bubble lucencies. Heterogeneous signal intensity on MRI.	Rare malignant tumor mainly arising at the proximal diaphysis of the tibia >> middle humerus, proximal radius, and proximal fibula. Occurs in patients aged 10–40 y. May have satellite lesions.
Osteofibrous dysplasia	Similar in appearance to NOF and fibrous dysplasia.	Classically seen at proximal or middle third of the tibia.

**Fig. 5.128 Bone infarct** with increased sclerosis in the proximal diaphysis and characteristic bone-within-bone appearance (arrows) in sickle cell disease.

**Fig. 5.129a–c Ewing sarcoma** arising from the proximal humerus with a mottled bone architecture, wide zone of transition (arrows in a), and large soft-tissue mass (arrowheads in a). (b) The cortical destruction is demonstrated on the coned-down image from the screening chest CT. (c) The mass enhances and displaces the biceps tendons on MRI.

**Fig. 5.130 Enchondroma** with arcs and rings pattern of mineralized chondroid matrix.

**Table 5.72 Tumors and focal lesions: pelvic lesions**
Diagnosis	Findings	Comments
Fibrous dysplasia	(see Table 5.71 )
Aneurysmal bone cyst Fig. 5.131a–c	(see Table 5.70 )	Pelvis is less common site.
Ewing sarcoma	(see Table 5.71 )
Chondrosarcoma	Similar appearance to an enchondroma but more aggressive.	Rare in children. Occur in children in atypical locations and may have a poorer prognosis.

**Fig. 5.131a–c Aneurysmal bone cyst** arising in the left pubic bone. Expansile and lucent lesion (a) with fluid-fluid levels on MRI (**b, c**).

**Table 5.73 Tumors and focal lesions: scapular lesions**
Diagnosis	Findings	Comments
Round blue cell tumors Fig. 5.132, p. 586	Destructive lesion with periosteal reaction and cortical disruption usually extending throughout the entire glenoid.	Ewing sarcoma, Langerhans cell histiocytosis, and osteomyelitis may be indistinguishable on imaging.
Osseous Bankart lesion	Fracture of the anteroinferior glenoid after an anteroinferior dislocation of the humeral head.
Stress fracture Fig. 5.133a–d, p. 586	Typically occurs at the neck or body.
Inflamed bursa (snapping scapula syndrome) Fig. 5.134, p. 587	Focal region of soft-tissue thickening/fluid in the chest wall between the chest wall and undersurface of the body of the scapula (usually near the medial tip).	A snapping or clicking may be reproduced on shoulder adduction and abduction.

**Fig. 5.132 Langerhans cell histiocytosis.** Diffuse bone marrow edema and periosteal reaction involve the body and glenoid of the scapula on T2-weighted fat-saturated MRI.

**Fig. 5.133a–d Stress fracture** of the scapula may be mistaken (as was this one) for a tumor on MRI. MRI shows increased T2-weighted signal intensity (a) and enhancement about the body and glenoid (b). Screening chest CT for lung metastases (c) shows smooth periosteal reaction and reconstructed coronal images (d) confirm a healing fracture line (arrows in c and d).

**Fig. 5.134 Snapping scapula syndrome** with an inflamed bursa between the scapula and chest wall (arrow).

**Table 5.74 Tumors and focal lesions: chest wall masses**
Diagnosis	Findings	Comments
Benign (anatomic variation)	Variation in anatomy of rib, costal cartilage, tilted sternum, bifid rib, breast tissue.	(see Tables 5.1 and 5.6 )
Lipoma	Fat density on CT and follows the signal intensity of fat on all MRI pulse sequences.	May contain septations.
Ewing sarcoma and PNET Fig. 5.7, p. 497	Chest wall mass with bone destruction ± pleural effusion.	Typically involves one rib at the time of presentation. May invade lung.
Infection Fig. 5.135a–c, p. 588	Large chest wall mass with underlying bone destruction.	DD: Actinomycosis, tuberculosis, blastomycosis, cryptococcosis, nocardiosis. May be misinterpreted as a tumor.
Vascular malformation	(see Table 5.77 )	May extend from the chest wall into the neck, upper extremity, and/or mediastinum.
Rhabdomyosarcoma	Large soft-tissue mass with variable density due to cystic and solid components.	Rib involvement is uncommon, unlike Ewing sarcoma and PNET. Invasion into adjacent structures.
Chondrosarcoma	Large mass with bone destruction and scattered areas of calcification with a chondroid matrix.	Typically arises from the anterior chest wall (sternum or costochondral arches) or scapula. Rare in children.
Osteosarcoma	(see Table 5.76 )	Chest is a rare site of involvement. Arises from a rib, scapula, or clavicle. Ossification may not be visible in some patients.
Other sarcomas		Rare: synovial, malignant peripheral nerve sheath tumors (neurofibromatosis type 1), leiomyosarcoma, fibrosarcoma, hemangiopericytoma, etc.
Neuroblastoma	Soft-tissue mass ± bone destruction either a metastasis or extension from paraspinal disease.	Chest wall is an uncommon site for neuroblastoma.
Lipoblastoma	Fat containing.	Locally invasive.
Desmoid tumor	Heterogeneously enhancing mass with destruction of the ribs.

**Fig. 5.135a–c Actinomycosis mass** arising from the right chest wall displaces the scapula on radiography (a). The soft-tissue mass encases the upper chest wall (b) and causes periosteal reaction in the ribs (c).

**Table 5.75 Tumors and focal lesions: multiple lesions**
Diagnosis	Findings	Comments
Metastasis Fig. 5.136a–c Fig. 5.137a, b, p. 590	Multiple lytic or blastic lesions on radiography. Altered bone marrow signal intensity on MRI. Pathologic fractures. Bone demineralization.	Neuroblastoma, leukemia, Langerhans cell histiocytosis, rhabdomyosarcoma.
Fibrous dysplasia Fig. 5.116, p. 574	(see Table 5.71 )
Brown tumor	Well-circumscribed lucent regions in bone. May be accompanied by other findings of hyperparathyroidism: erosions, granular (salt-and-pepper) skull, etc.	Hyperparathyroidism presents as “stones, bones, and groans.” Both primary and secondary forms of hyperparathyroidism may lead to lytic lesions in bone. Tumors in the primary form are usually seen in adults. The secondary form is most often the result of chronic renal failure and lytic lesions have an increased incidence with age.
Langerhans cell histiocytosis Fig. 5.8, p. 497	Expansile and well-defined lucent lesion.	Skeletal survey may be useful to detect multiple lesions.
Multiple hereditary exostoses	(see Table 5.70 )	Growth of multiple osteochondromas around areas of active bone growth. May lead to shortening and bowing of bones and mass effect on adjacent soft tissues.
Enchondromatosis (including Ollier disease and Maffucci syndrome) Fig. 5.126, p. 580 Fig. 5.127, p. 581	Multiple enchondromas (see Table 5.71 for description of an enchondroma).	Ollier: extensive involvement of enchondromas usually unilateral and distributed in metaphyses and diaphyses most commonly in the hands. Maffucci: similar distribution of enchondromas as Ollier plus soft-tissue hemangiomas.
Angiomatosis (hemangiomatosis and lymphangiomatosis) Fig. 5.138a–c Fig. 5.139, p. 592	Osteolytic lesion rimmed by sclerosis or with a narrow zone of transition. May have a honeycomb appearance.	Occurs in patients aged 8–30 y. Diaphyses of long bones, pelvis, and spine. May rarely appear sclerotic. Gorham disease (congenital with massive destruction of bone).
Angiosarcoma	Nonspecific imaging appearance. Aggressive lytic lesion with wide zone of transition. May have a honeycomb appearance similar to angiomatosis.	Occurs in patients aged 10–60 y. More common in skin and soft tissues than bone (~6%). Long bones > pelvis.

**Fig. 5.136a–c Pre-B cell acute lymphocytic leukemia.** Multiple lesions on T1-weighted MRI (**a, b**) enhance after gadolinium administration were occult on CT imaging (c).

**Fig. 5.137a, b Blastic metastasis.** The primary osteosarcoma in the proximal right humerus (a) and blastic metastatis (arrow in b).

**Fig. 5.138a–c Lymphangiomatosis** with lytic lesions involving the sternum (arrow in a), femur (arrow in b), and pelvis (c).

**Fig. 5.139 Lymphangiomatosis** with bone involvement (Gorham disease).

**Table 5.76 Tumors and focal lesions: bone- or cartilage-forming**
Diagnosis	Findings	Comments
Benign
Enostosis (bone island) Fig. 5.101, p. 563	Well-marginated focus of cortical bone within cancellous (trabecular) bone.	Endosteal equivalent of an osteoma.
Osteoma Fig. 5.140	Dense ivorylike sclerotic mass with sharply demarcated boarder attached to the bone.	Slow-growing solid lesion after 10 y of age. Skull and jaw > long bones.
Enchondroma	Calcifications in the intramedullary space. Calcifications range from punctuate to rings. ± Endosteal scalloping and expansion.	May be difficult to distinguish between enchondroma and low-grade chondrosarcoma.
Osteoid osteoma Fig. 5.141a, b Fig. 5.142a–c, p. 594	Very thick smooth cortical thickening and a lucent center (nidus). DD: chronic osteomyelitis and cortical stress fracture.	Fifty percent have typical clinical presentation of night pain relieved with anti-inflammatory medications. Two-y delay from onset of symptoms until diagnosis.
Osteoblastoma Fig. 5.142a–c, p. 594 Fig. 5.143a, b, p. 595	Spherical or slightly oval lucent lesions marginated by sclerosis.	Four distinct types: (1) almost identical to osteoid osteoma but larger (> 2 cm diameter), (2) expansive lesion, (3) simulating an aggressive neoplasm, (4) periosteal (juxtacortical).
Heterotopic bone formation Fig. 5.144, p. 595	Soft-tissue ossification near joints.	May lead to bridging and ankylosis of the joint.
Juxtacortical myositis ossificans Fig. 5.108, p. 569	Ossified lesion abutting the cortex.	History of trauma may be difficult to elicit from a child.
Tuberous sclerosis Fig. 5.145, p. 595	Dense sclerotic lesions.	Not to be confused with an osteoblastic lesion in a patient with tuberous sclerosis.
Melorheostosis Fig. 5.9, p. 498	Intramedullary sclerosis with the appearance of dripping candle wax.	Follows dermatomes.
Malignant
Osteosarcoma primary Fig. 5.146a–c, p. 596 Fig. 5.124, p. 579	Aggressive mixed lucent and sclerotic lesion: permeative or moth-eaten bone destruction, wide zone of transition, cloudlike opacities of new bone formation, aggressive periosteal reaction (Codman triangle), soft-tissue mass.	Variable amount of bone formation. May be classified into subtypes based on World Health Organization.
Chondrosarcoma	Aggressive mixed lucent and sclerotic lesion. Calcifications range from punctuate to rings.	Clues to differentiate from enchondroma include pain, progressive destruction of the chondroid matrix, large size, and a large unmineralized component.
Secondary sarcoma Fig. 5.147a–c	May arise in area of prior intervention or disturbance.	Following extraskeletal irradiation, chemotherapy, and treatment for retinoblastoma. Malignant transformation within a benign process (Paget disease, fibrous dysplasia, bone infarct) usually occurs in adulthood.

**Fig. 5.140 Osteoma** arising offthe posterior skull.

**Fig. 5.141a, b Osteoid osteoma.** Thick periosteal reaction from osteoid osteoma on radiography (a). (b) The periosteal reaction surrounds the central nidus on CT.

**Fig. 5.142a–c Osteoblastoma** with a mixed lucent and sclerotic lesion in the left scapula (a). (b) Intense activity is seen in the nidus on bone scan. (c) A large region of bone marrow edema surrounds the nidus on the sagittal proton-density fat-saturated MRI.

**Fig. 5.143a, b Osteoblastoma** in the proximal femur of a 15-year-old (a) with lucent nidus (arrows) and thick periosteal reaction (arrowheads). (b) T1-weighted MRI shows the periosteal reaction enhancement in the nidus (arrow).

**Fig. 5.144 Chronic heterotopic bone formation** (arrow) in a 29-year-old with spina bifida and chronic hip dislocations.

**Fig. 5.145 Tuberous sclerosis** simulating a blastic metastasis.

**Fig. 5.146a–c Osteosarcoma primary.** Sunburst pattern of periosteal reaction from chondroblastic osteosarcoma (arrow in a) with corresponding appearance on (b) STIR and (c) T1-weighted post-contrast imaging.

**Fig. 5.147a–c Secondary chondrosarcoma** arising from the scapula in a patient 7 years after treatment for rhabdomyosarcoma of the axilla. (a) CT shows bone destruction and soft-tissue mass. (b) MRI shows increased T2-weighted signal intensity and enhancement of the mass (c).

**Table 5.77 Tumors and focal lesions: soft-tissue masses**
Diagnosis	Findings	Comments
Benign
Cyst or bursa Fig. 5.148a, b Fig. 5.31, p. 515	Fluid-filled cyst (anechoic on US; dark on T1- and bright on T2-weighted MRI sequences).	Rim of cyst may enhance. Examples: synovial cyst, ganglion cyst, popliteal cyst, iliopsoas bursa, etc.
Myositis ossificans Fig. 5.107, p. 568 Fig. 5.108, p. 569	Soft-tissue mass rimmed by a peripheral margin of ossification separate from the adjacent bone. May appear aggressive on MRI with increased T2-weighted signal intensity and enhancement.	History of trauma not always elicited from children. Amorphous calcifications may be seen early (1–2 wk) after trauma.
Abscess	Fluid-filled structure with a thick wall that may be hyperemic on US and enhance on MRI or CT.	Clinical signs and symptoms of infection are typically present.
Myositis/cellulitis Fig. 5.149	Soft-tissue swelling on radiography. Increased fluid signal, swelling, and enhancement on MRI.	May be focal or diffuse.
Myonecrosis Fig. 5.150	Soft-tissue mass with central necrosis.	May be seen in patients after trauma or with sickle cell disease.
Vascular malformation Fig. 5.109, p. 570	May produce periosteal reaction, chronic cortical thickening or remodeling of adjacent bone. High or low flow vascular mass on US or magnetic resonance angiography/magnetic resonance venography.	Venous malformations may contain phleboliths. Classified as capillary, venous, lymphatic, or combined malformations.
Lipoma	Usually well-defined mass that follows signal intensity of fat (T1 bright, T2 fast spin echo bright, and dark on STIR and fat-saturated pulse sequences).
Giant cell tumor of the tendon sheath	Nodular mass attached to a tendon. Characteristic low to intermediate T1- and low T2-weighted signal intensity on MRI. Variable gadolinium enhancement.	Not really a tumor, but more of a reactive lesion. Seen at tendons that have a synovial-lined tendon sheath. Localized form is usually seen at hands and feet. The diffuse form is rare, affects the lower extremities, and is the counterpart to PVNS affecting joints.
Peripheral nerve tumors Fig. 5.151a–d	Focal mass. Similar or slightly increased in intensity to adjacent muscle on T1- and T2-weighted MRI. Target sign (hyperintense rim with low central T2-weighted signal intensity).	DD: schwannoma, neurofibroma, and neurofibromatosis.
Rheumatoid nodules Fig. 5.152a–c	Subcutaneous soft-tissue masses usually 1–4 cm located near joints.	Common locations include the posterior elbow and inferior heal.
Juvenile fibromatosis	Variable appearance on MRI. Focal or infiltrative with enhancement in the cellular portions of the tumor.	Local recurrence.
Nodular fasciitis Fig. 5.153a, b	Soft-tissue mass arising from the fascia.	Rapidly growing benign mass most commonly found in the superficial fascia.
Osteoblastoma	(see Table 5.76 )	Extraskeletal osteoblastoma is a rare presentation.
Infantile digital fibroma	Enlarging soft-tissue mass ± erosion of a phalanx.	Occurs in patients aged 1–5 y. Recurrent.
Malignant
Rhabdomyosarcoma Fig. 5.154a–c	Variable appearance of a soft-tissue mass ± bone invasion.	Limb involvement is less common than in the central nervous system and genitourinary system.
Nonrhabdomyosarcoma Fig. 5.155a–c, p. 602	Variable appearance of a soft-tissue mass.	DD: synovial sarcoma, epithelioid sarcoma, liposarcoma, malignant peripheral nerve sheath tumor, clear cell sarcoma, infantile fibrosarcoma, hemangiopericytoma, leiomyosarcoma, alveolar soft part sarcoma, malignant fibrous histiocytoma, angiosarcoma, fibromyxoid sarcoma, extraskeletal myxoid chondrosarcoma, spindle-cell sarcoma, etc.
Lymphoma	Variable appearance of a soft-tissue mass.	May present with symptoms localized to the site of soft-tissue involvement, as an incidental finding on imaging for other reasons, or as part of the staging of the disease.
Myofibroma Fig. 5.156a, b
Synovial cell sarcoma Fig. 5.157a–c	Soft-tissue mass typically located in close proximity to a joint.	One of the nonrhabdomyosarcomas most commonly seen adjacent to the knee. Tissue type is unrelated to the synoviocytes that line the joint spaces.
Extraskeletal Ewing sarcoma Fig. 5.158, p. 604	Variable appearance of a soft-tissue mass.	Occurs in patients aged 3–71 y. May develop in the extremities, genitourinary and gastrointestinal tracts and central nervous system.
Extraskeletal osteosarcoma	Ill-defined heterogeneous mineralized tumor mass.	Lower extremity and buttock. May be difficult to distinguish from early myositis ossificans. High rate of meta-static disease. Rare: ~4% of all osteosarcomas. More often seen in adults. DD: calcified hematoma, nodular fasciitis, ossifying lipoma, and myositis ossificans.

**Fig. 5.148a, b Popliteal cyst.** MRI shows the fluid-filled cyst (arrow in a) with rim enhancement (b).

**Fig. 5.149 Myositis** of the left pectoralis muscles with gadolinium enhancement and swelling on MRI (arrows).

**Fig. 5.150 Osteonecrosis and myonecrosis** in a child with sickle cell disease.

**Fig. 5.151a–d Peripheral nerve tumor.** Schwannoma arising in the muscles of the forearm. (a) US shows a solid mass with blood flow. MRI shows an encapsulated mass that is intermediate in signal intensity on T1 (b), bright on T2-weighted (c), and uniform in enhancement after gadolinium administration (d).

**Fig. 5.152a–c Rheumatoid nodules** (**a–c**) in the superficial soft tissues of the heel (arrows in a and b) as demonstrated on us (a) and T2-weighted fat-saturated MRI (b) and T1-weighted postcontrast MRI (c).

**Fig. 5.153a, b Nodular fasciitis** (a) arising from the anterior compartment fascia of the proximal calf (b) enhances after gadolinium.

**Fig. 5.154a–c Rhabdomyosarcoma.** (**a–c**) A soft-tissue mass arising in the distal calf.

**Fig. 5.155a–c Cystic liposarcoma of the thigh.** The signal intensity from a tiny nodule of fat (arrow in a) on T1-weighted imaging (a) is suppressed on STIR (b) and gadolinium-enhanced T1-weighted fat-suppressed (c) imaging.

**Fig. 5.156a, b Myofibroma** arising from the proximal thigh (arrow in a) on T2-weighted fat-saturated (a) and T1-weighted fat-saturated postcontrast–enhanced (b) imaging.

**Fig. 5.157a–c Synovial sarcoma** arising from a characteristic location in the posterior proximal calf on T2-weighted (a) and T1-weighted prior to (b) and after gadolinium (c).

**Fig. 5.158 Extraskeletal Ewing sarcoma.** A 20-month-old boy with a mass on the medial side of the right upper leg. Gadolinium-enhanced MRI shows a discrete enhancing mass remote from osseous structures; histology showed an extraosseous Ewing sarcoma.

Virtually all palpable, asymptomatic anterior chest wall lesions in children are benign and related to normal variations in the chest wall bone or cartilage.

**Table 5.78 Tumors and focal lesions: joints**
Diagnosis	Findings	Comments
PVNS Fig. 5.32, p. 516	Juxta-articular soft-tissue masses with erosive changes in the underlying bone. Masses arising from the synovium have low signal intensity on both T1- and T2-weighted sequences and signal dropout on gradient echo.	Locally destructive proliferative disorder of the synovium. May affect the tendon sheath (giant cell tumor) and bursa (pigmented villonodular bursitis). Adults > children. Vary rarely calcifications may be seen.
Synovial osteochondromatosis Fig. 5.159a, b	Soft-tissue swelling and joint effusion with many radiopaque bodies, small and uniform in size.	Benign metaplastic proliferation of multiple cartilaginous nodules in the joint, bursa, or tendon sheath. Rarely polyarticular. Differentiate from secondary osteochondromatosis = caused by OA with intra-articular bodies.
JIA Fig. 5.42, p. 523	Hypertrophied synovium ± enhancement on MRI or increased blood flow on US.	May affect joint or tendon sheaths. Erosions and joint space narrowing are a later finding.
Hemarthrosis (trauma, hemophilia) Fig. 5.33, p. 517	Uniform joint space narrowing. Hemosiderin in the synovium (dark on T1- and T2-weighted MRI).	Tends to affect large joints. Patients usually already have a diagnosis of trauma or a bleeding disorder.
Synovial hemangioma	Radiographs are often normal. Phleboliths, periosteal thickening, and advanced maturation of the epiphysis may be seen. MRI may characterize the vascular components of the lesion.	Occurs in patients aged 9–49 y. Most commonly affects the knee joint > elbow, wrist, ankle, and tendon sheaths.

**Fig. 5.159a, b Synovial osteochondromatosis** of the right hip. Ossicles surround the right hip on radiography (a) and T1-weighted fat-suppressed magnetic resonance arthrogram (b) shows that the osteochondromatosis is located in the joint.

**Table 5.79 Tumors and focal lesions: infancy**
Diagnosis	Findings	Comments
Vascular malformation	(see Table 5.77 )	Thrombocytopenia from consumptive coagulopathy.
Congenital fibrosarcoma Fig. 5.160	Radiographically evident soft-tissue mass enveloping, splaying, and resorbing bones without frank bone destruction. Mixed solid and cystic mass with ± areas of necrosis on MRI and ± large draining vein.	Rapidly enlarging soft-tissue mass ± ulceration. More favorable prognosis than adult fibrosarcoma. Thrombocytopenia from disseminated intravascular coagulopathy.
Rhabdomyosarcoma	Soft-tissue mass that usually does not invade bone. Solid or partially cystic on MRI. Well-defined or infiltrative margins.	Approximately 50% arise caudally (buttock, sacrum, bladder, vagina). Approximately 50% have widespread metastatic disease.
Infantile hemangiopericytoma	Large soft-tissue mass ± bone invasion, ± calcific stippling. Vascular mass with feeding vessels but usually no draining vein.	Rapid growth. One-third occur in extremities, one-third the trunk, and one-third head and neck. Rarely metastasize.
Malignant peripheral nerve sheath tumor	Similar appearance as peripheral nerve sheath tumor but more aggressive. May displace or invade bone (see Table 5.77 ).	Rare before the age of 10 y. Associated with neurofibromatosis type 1.
Extrarenal rhabdoid tumor	Variable appearance of a rapidly enlarging soft-tissue mass.	Age < 1 y. Infrequently involves extremities.

**Fig. 5.160 Congenital fibrosarcoma** arising from the calf of a neonate on sagittal STIR MRI.

**Table 5.80 Soft-tissue alteration without mass**
Diagnosis	Findings	Comments
Infection	Increased T2-weighed signal intensity and enhancement in the superficial soft tissues (cellulitis), fascia, or muscles. Soft-tissue swelling and increased echogenicity on US.	Imaging findings that support a clinical diagnosis of necrotizing fasciitis include enhancement and thickening of fascia and gas in the soft tissues.
Muscle or tendon tear	Abnormality confined to the muscle or tendon with increased T2-weighted signal intensity and fluid. Fluid, alterations in the muscle fibers, and a tendon or muscle gap may also be seen on US.
Dermatomyositis Fig. 5.161a–c, p. 606	Increased T2-weighted signal intensity and enhancement confined to muscles. Increased echogenicity and swelling on US.	Usually distributed in muscle groups in the proximal limbs. DD: inclusion body myositis, juvenile myositis, polymyositis.
Fat necrosis Fig. 5.162a, b, p. 606	Linear regions of decreased signal intensity on non–fat-suppressed MRI that have a scarlike appearance.	Although typically localized to sites of prior trauma, patients may not always be able to recall the trauma.