Girl, 13, With a Bump on Her Leg

A girl, age 13 years, 4 months, presented to her primary care provider’s office for a well visit. Among her concerns, she mentioned a “bump” she had had on her right leg “for the past six months, maybe longer.” The area felt irritated when touched or when the patient “ran too much.” She had seen no change in the bump since she first noticed it. The patient knew of no trauma or other preceding factors. She denied any fever or warmth, redness, or ecchymosis to the area.

Medical history was unremarkable except for familial short stature and myopia. The patient was the fifth of eight children born to nonconsanguinous parents. She denied any surgical history or hospitalizations and was premenarcheal. She was up to date on all age-appropriate vaccines, with her meningococcal vaccine administered at that visit.

The patient’s blood pressure was 99/58 mm Hg with an apical pulse rate of 82 beats/min. Her growth parameters were following her curve. Her height was 55” (0.3 percentile); weight, 81 lb (7.5 percentile); and BMI, 18.8 (48.6 percentile).

The physical exam was normal with the exception of the musculoskeletal exam. Examination of the lower extremities revealed a palpable, 4 cm x 5 cm lesion at the right distal medial thigh just proximal to the knee. The lesion could not be visualized but on palpation was tender and firm. There was some question as to whether the lesion itself or inflamed soft tissue overlying the lesion was mobile. No overlying warmth, induration, erythema, or ecchymosis was noted.

Passive and active range of motion was intact at the hip and knee. No lesions to the upper extremities were evident, and no scoliosis was seen.

Blood work was done to rule out certain diagnoses. Results from a complete blood count with differential, lactate dehydrogenase (LDH), parathyroid hormone, lipid profiles, thyroid function, and a comprehensive metabolic profile were unremarkable. A low level of vitamin D 25-OH was detected: 21.7 ng/mL (normal range, 32 to 100 ng/mL).

Distal femur x-rays with posteroanterior, lateral, and oblique views were ordered. The imaging revealed a 3 cm x 3 cm lesion projecting from the “distal, somewhat medial” femur, which was diagnosed as a benign femoral osteochondroma. Significant inflammation to the surrounding soft-tissue structures was observed. A questionable old fracture of the osteochondroma was noted. The remaining bony structures and joints appeared normal.

An ultrasound of the lesion was also ordered to investigate soft-tissue swelling. This revealed a hypoechoic collar around the distal end of the osteochondroma, which could represent a fluid collection, hematoma from trauma, or bursitis. The soft tissues were deemed normal.

Because of the extent of inflammation, the radiologist recommended MRI without contrast to rule out bursitis or trauma to the osteochondroma.

DISCUSSION
Osteochondromas, which may be present in up to 3% of the general population, are the most common benign bone tumors.^1-3 An osteochondroma is a cartilage-capped bony projection that arises on the external surface of the bone; it contains a marrow cavity that is continuous with the underlying bone.^2,4 The majority of osteochondromas are solitary, accounting for perhaps 85% to 90% of all such lesions, and they are typically nonhereditary; the remaining 10% to 15% of osteochondromas are hereditary multiple osteochondromas or exostoses^1,2 (see “Definition of Multiple Exostoses Syndrome”^2,5,6,7).

Most lesions are painless and slow growing, and they usually occur in children and adolescents.² They typically stop growing at skeletal maturity with the closure of the growth plates.^3,8,9 There is no predilection for males or females in single lesions.²

Solitary osteochondromas typically appear in the lower extremities and at long tubular bone metaphyses,^1-3,10 especially on the femur, humerus, tibia, spine, and hip. Any part of the skeleton can be affected, but 30% of lesions occur on the femur and 40% at either the proximal metaphysis of the tibia or the distal metaphysis of the femur.^2,11

Most osteochondromas are asymptomatic and are found incidentally.^1,3 However, some patients present with local pain as a result of irritation to adjacent structures, limitation of joint motion, growth disturbance, or fracture of the pedicle.^3,4,9,11,12 A very small proportion of patients (no more than 1%) with solitary osteochondromas experience malignant transformation.^2,3,6,7 No particular blood work is recommended for patients with solitary osteochondromas.²

Differential Diagnosis
In addition to osteochondromas, several other lesions should be considered in the patient with musculoskeletal lesions (see Table 1^5,6,13-19).

Cartilaginous tumors. Chondrosarcomas are malignant cartilaginous tumors.^20-22 They commonly affect long bones, including the humerus and femur, and some flat bones, such as the pelvic bones.^13,22 They are most commonly seen in adults, and have no predisposition by gender.¹³

Chondrosarcomas can be primary (ie, arising de novo) or secondary (developing on preexisting benign cartilaginous neoplasms, including osteochondromas). The majority of chondrosarcomas are slow growing, and they rarely metastasize. It is difficult to differentiate between a benign lesion (such as an osteochondroma) and a chondrosarcoma by either histology or radiology. However, reliable predictors for malignancy include size exceeding 5 cm and location in the axial skeleton.²⁰

Bone tumors.Osteosarcomas are the most common malignant bone tumors in children and adolescents, with 400 to 560 US patients in this age-group diagnosed each year.^14-16 Osteosarcomas are uncommon in children younger than 10; their incidence peaks during the early teenage years (median peak age, 16), then declines rapidly among older patients. They are more common in males than females.¹⁵

Osteosarcomas commonly develop during periods of rapid bone turnover, such as the adolescent growth spurt. Common sites include the distal femur, proximal humerus, and proximal tibia,^15,16 particularly near the knee.¹³ Usually, osteosarcomas present with nonspecific symptoms, including strain-related pain of several months’ duration, which may disrupt sleep.¹⁶ Laboratory findings in affected patients may include elevations in LDH, alkaline phosphatase, and/or ESR.^15,23

Physical exam reveals a visible or palpable mass in the affected area, along with decreased joint motion; localized warmth or erythema may also be present. Late signs of osteosarcoma include weight loss, general malaise, and fever. First-line imaging for the patient with a suspected osteosarcoma is x-ray, which will show ill-defined borders, osteoblastic and/or osteolytic features, and an associated soft tissue mass. Advanced imaging, such as MRI, is warranted.¹⁶

Ewing sarcoma, the second most common bone tumor in children and adolescents, is an aggressive form of childhood cancer.^14,18 Approximately 25% of all Ewing sarcomas arise in soft tissues rather than bones.¹⁸ They are more common in whites than in other ethnic groups and have a slight male predominance.^13,18 The median age at diagnosis is 15.¹³ The most common presenting symptoms are tumor related, such as pain or a noticeable mass. While x-rays are usually ordered first, MRI is preferred.¹⁸

Soft tissue tumors and masses.Rhabdomyosarcomas are malignancies that account for more than half of the soft tissue sarcomas in children and adolescents. Less than one-fifth of cases occur in the extremities, and most occur in children younger than 10. These lesions have a slight male predominance and are more common in whites than in other patients.^14,17,24

Approximately 6% of childhood soft tissue tumors are adipose tissue tumors, which may be benign (eg, lipomas) or malignant (eg, liposarcomas). Lipomas in children account for nearly 4% of all soft tissue tumors and can be classified as superficial (which are often diagnosed clinically) or deep (frequently requiring imaging).²⁵

Lymphomaaccounts for 7% of cancers in US children and adolescents and more than 25% of newly diagnosed cancers in patients between 15 and 19, making it the most common malignancy in adolescents and the third most common in children.^26,27 Non-Hodgkin lymphoma is the fourth leading type of malignancy in US adolescents.²⁷ Rarely, lymphomas present with primary event soft tissue involvement.²⁸

Myositis ossificans (MO) is a rare benign disorder involving formation of heterotrophic bone in skeletal muscles and soft tissues.²⁹ Though possible in patients of any age, MO is most commonly seen in adolescents and young adults. Often the result of soft tissue injury (in which case it is referred to as myositis ossificans circumscripta or traumatic), MO develops in areas that are exposed to trauma, such as the anterior thighs or arms. Lesions can be diagnosed via plain x-ray or CT, although MRI and ultrasound can also be useful evaluation tools.^17,29,30

Because MO circumscripta typically presents as a painful soft tissue mass, it can be mistaken for a soft tissue sarcoma or an osteosarcoma; radiologic evaluation is required to make the proper diagnosis. Less common forms of MO are myositis ossificans progressiva and myositis ossificans without a history of trauma.²⁹

Ollier diseaseis a rare, nonfamilial disorder characterized by multiple enchondromas (or enchondromatoses), which are distributed asymmetrically with areas of dysplastic cartilage. Enchondromas are benign cartilage tumors that frequently affect long tubular bones along the metaphyses in proximity to the growth plate. The enchondromas result in significant growth abnormalities. About one in 1 million people are diagnosed yearly.^5,19 (Similarly, Maffucci syndrome is represented by multiple enchondromas in association with hemangiomas.⁵)

Ollier disease typically manifests during childhood⁵ with bone swelling, local pain, and palpable bony masses, which are often associated with bone deformities.¹⁹ Patients generally present with an asymmetric shortening of one extremity and the appearance of palpable bony masses on their fingers or toes, which may or may not be associated with pathologic fractures.^5,19 In 20% to 50% of patients with Ollier disease, enchondromas are at risk for malignant transformation into chondrosarcomas.⁵

Vascular malformations. Certain abnormalities of vascular development cause birthmarks and abnormalities of varying degree in underlying tissues.³¹ They are usually present at birth and grow proportionally to the child’s growth.^25,31 However, they can also be seen in later childhood and adolescence.

Radiologic Investigation
Plain radiography of the affected area is the first-line radiologic study to be performed.¹³ While most osteochondromas can be diagnosed by plain x-ray, cross-sectional imaging via CT or MRI is recommended in lesions with certain characteristics, such as a broad stalk or location in the axial skeleton. Because MRI involves no radiation exposure, it is a particularly good diagnostic tool for children.³²

Ultrasound is a good imaging method for evaluating for complications of osteochondromas, including bursa formation or vascular compromise.³²

Treatment and Management
Although usually asymptomatic, osteochondroma can trigger some significant symptoms. Osteochondromas are at risk for fracture and can cause body deformities, mechanical joint problems, weakness of the affected limb, numbness, vascular compression, aneurysm, arterial thrombosis, venous thrombosis, pain, acute ischemia, and nerve compression. Clinical signs of malignant transformation include pain, swelling, and increased lesion size.²

Surgical excision is recommended but should be delayed until after the patient has reached skeletal maturity in order to decrease the risk for recurrence.³³

Patient Education and Follow-up
In addition to explaining appropriate pain management (eg, NSAIDs), it is especially important for the pediatric NP or PA to encourage the patient with a solitary osteochondroma to follow up with the pediatric orthopedic surgeon. Reasons include the need to monitor growth of the lesion (which is likely to continue in a patient who has not yet reached skeletal maturity) and assess for associated functional or joint problems. Patients should also be advised to seek the specialist’s attention if such problems develop or if pain increases.

Generally, the pediatric clinician should be sufficiently informed to answer questions about this condition from the patient or family. Any follow-up laboratory work recommended by the specialist can also be performed by the pediatric NP or PA.

OUTCOME FOR THE CASE PATIENT
MRI without contrast, as recommended by the radiologist to rule out a bursa or trauma to the osteochondroma, was considered an important part of the follow-up plan. As the patient had not yet reached skeletal maturity, she was referred to a pediatric orthopedic surgeon for possible excision of the lesion, due to its size and the pain associated with running or other exertion.

CONCLUSION
Solitary osteochondromas are the most common benign bone tumors. Although they are generally asymptomatic, pain and other symptoms can arise as a result of irritation to the adjacent structures. In this case, the patient’s chief complaint was an irritating “bump” that she had had on her right leg for at least six months.

Generally, follow-up monitoring of the osteochondroma and orthopedic follow-up care are warranted, at least until the patient reaches skeletal maturity. At that point, surgical excision of the lesion is recommended.            

REFERENCES
1. Florez B, Mönckeberg J, Castillo G, Beguiristain J. Solitary osteochondroma long-term follow-up. J Pediatr Orthop B. 2008;17:91-94.

2. Kitsoulis P, Galani V, Stefanaki K, et al. Osteochondromas: review of the clinical, radiological and pathological features. In Vivo. 2008;22:633-646.

3. Ramos-Pascua LR, Sánchez-Herráez S, Alonso-Barrio JA, Alonso-León A. Solitary proximal end of femur osteochondroma: an indication and result of the en bloc resection without hip luxation [in Spanish]. Rev Esp Cir Ortop Traumatol. 2012;56:24-31.

4. Payne WT, Merrell G. Benign bony and soft tissue tumors of the hand. J Hand Surg. 2010;35:1901-1910.

5. Pannier S, Legeai-Mallet L. Hereditary multiple exostoses and enchondromatosis. Best Pract Res Clin Rheumatol. 2008;22:45-54.

6. Bovée JV. Multiple osteochondromas. Orphanet J Rare Dis. 2008;3(3).

7. Staals EL, Bacchini P, Mercuri M, Bertoni F. Dedifferentiated chondrosarcomas arising in preexisting osteochondromas. J Bone Joint Surg Am. 2007;89:987-993.

8. Singh R, Jain M, Siwach R, et al. Large para-articular osteochondroma of the knee joint: a case report. Acta Orthop Traumatol Turc. 2012;46:139-143.

9. Lee JY, Lee S, Joo KB, et al. Intraarticular osteochondroma of shoulder: a case report. Clin Imaging. 2013;37:379-381.

10. Kim Y-C, Ahn JH, Lee JW. Osteochondroma of the distal tibia complicated by a tibialis posterior tendon tear. J Foot Ankle Surg. 2012;51: 660-663.

11. Allagui M, Amara K, Aloui I, et al. Historical giant near-circumferential osteochondroma of the proximal humerus. J Shoulder Elbow Surg. 2010;19:e12-e15.

12.
Li M, Luettringhaus T, Walker KR, Cole PA. Operative treatment of femoral neck osteochondroma through a digastric approach in a pediatric patient: a case report and review of the literature. J Pediatr Orthop B. 2012;21:230-234.

13. Hogendoorn PC, Athanasou N, Bielack S, et al; ESMO/EUROBONET Working Group. Bone sarcomas: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2010;21 suppl 5:v204-v213.

14. Arndt CAS, Rose PS, Folpe AL, Laack NN. Common musculoskeletal tumors of childhood and adolescence. Mayo Clin Proc. 2012;87:475-487.

15. Ta HT, Dass CR, Choong PF, Dunstan DE. Osteosarcoma treatment: state of the art. Cancer Metastasis Rev. 2009;28:247-263.

16. Messerschmitt PJ, Garcia RM, Abdul-Karim FW, et al. Osteosarcoma. J Am Acad Orthop Surg. 2009;17:515-527.

17. Laffan EE, Ngan B-Y, Navarro OM. Pediatric soft-tissue tumors and pseudotumors: MR imaging features with pathologic correlation: Part 2. Tumors of fibroblastic/myofibroblastic, so-called fibrohistiocytic, muscular, lymphomatous, neurogenic, hair matrix, and uncertain origin. Radiographics. 2009;29:e36.

18. Balamuth NJ, Womer RB. Ewing’s sarcoma. Lancet Oncol. 2010;11(2):184.

19. D’Angelo L, Massimi L, Narducci A, Di Rocco C. Ollier disease. Childs Nerv Syst. 2009;25:647-653.

20. Gelderblom H, Hogendoorn PC, Dijkstra SD, et al. The clinical approach towards chondrosarcoma. Oncologist. 2008;13:320-329.

21. Nosratzehi T, Pakfetrat A. Chondrosarcoma. Zahedan J Res Med Sci. 2013;15:64-64.

22. Prado FO, Nishimoto IN, Perez DE, et al. Head and neck chondrosarcoma: analysis of 16 cases. Br J Oral Maxillofacial Surg. 2009;47:555-557.

23. Kim HJ, Chalmers PN, Morris CD. Pediatric osteogenic sarcoma. Curr Opin Pediatr. 2010;22:61-66.

24. Sultan I, Qaddoumi I, Yaser S, et al. Comparing adult and pediatric rhabdomyosarcoma in the surveillance, epidemiology and end results program, 1973 to 2005: an analysis of 2,600 patients. J Clin Oncol. 2009;27:3391-3397.

25. Navarro OM, Laffan EE, Ngan B-Y. Pediatric soft-tissue tumors and pseudo-tumors: MR imaging features with pathologic correlation: Part 1. Imaging approach, pseudotumors, vascular lesions, and adipocytic tumors. Radiographics. 2009;29:887-906.

26. Gross TG, Termuhlen AM. Pediatric non-Hodgkin lymphoma. Curr Hematol Malig Rep. 2008;3:167-173.

27. Hochberg J, Waxman IM, Kelly KM, et al. Adolescent non-Hodgkin lymphoma and Hodgkin lymphoma: state of the science. Br J Haematol. 2009;144:24-40.

28. Derenzini E, Casadei B, Pellegrini C, et al. Non-Hodgkin lymphomas presenting as soft tissue masses: A single center experience and meta-analysis of the published series. Clin Lymphoma Myeloma Leuk. 2012 Dec 12. [Epub ahead of print]

29. Micheli A, Trapani S, Brizzi I, et al. Myositis ossificans circumscripta: a paediatric case and review of the literature. Eur J Pediatr. 2009;168:523-529.

30. McKenzie G, Raby N, Ritchie D. Non-neoplastic soft-tissue masses. Br J Radiol. 2009;82:775-785.

31. Buckmiller LM, Richter GT, Suen JY. Diagnosis and management of hemangiomas and vascular malformations of the head and neck. Oral Dis. 2010;16:405-418.

32. Khanna G, Bennett DL. Pediatric bone lesions: beyond the plain radiographic evaluation. Semin Roentgenol. 2012;47:90-99.

33.
Rijal L, Nepal P, Baral S, et al. Solitary diaphyseal exostosis of femur, how common is it? Eur J Orthop Surg Traumatol. 2011;21:363-365.

A girl, age 13 years, 4 months, presented to her primary care provider’s office for a well visit. Among her concerns, she mentioned a “bump” she had had on her right leg “for the past six months, maybe longer.” The area felt irritated when touched or when the patient “ran too much.” She had seen no change in the bump since she first noticed it. The patient knew of no trauma or other preceding factors. She denied any fever or warmth, redness, or ecchymosis to the area.

Medical history was unremarkable except for familial short stature and myopia. The patient was the fifth of eight children born to nonconsanguinous parents. She denied any surgical history or hospitalizations and was premenarcheal. She was up to date on all age-appropriate vaccines, with her meningococcal vaccine administered at that visit.

The patient’s blood pressure was 99/58 mm Hg with an apical pulse rate of 82 beats/min. Her growth parameters were following her curve. Her height was 55” (0.3 percentile); weight, 81 lb (7.5 percentile); and BMI, 18.8 (48.6 percentile).

The physical exam was normal with the exception of the musculoskeletal exam. Examination of the lower extremities revealed a palpable, 4 cm x 5 cm lesion at the right distal medial thigh just proximal to the knee. The lesion could not be visualized but on palpation was tender and firm. There was some question as to whether the lesion itself or inflamed soft tissue overlying the lesion was mobile. No overlying warmth, induration, erythema, or ecchymosis was noted.

Passive and active range of motion was intact at the hip and knee. No lesions to the upper extremities were evident, and no scoliosis was seen.

Blood work was done to rule out certain diagnoses. Results from a complete blood count with differential, lactate dehydrogenase (LDH), parathyroid hormone, lipid profiles, thyroid function, and a comprehensive metabolic profile were unremarkable. A low level of vitamin D 25-OH was detected: 21.7 ng/mL (normal range, 32 to 100 ng/mL).

Distal femur x-rays with posteroanterior, lateral, and oblique views were ordered. The imaging revealed a 3 cm x 3 cm lesion projecting from the “distal, somewhat medial” femur, which was diagnosed as a benign femoral osteochondroma. Significant inflammation to the surrounding soft-tissue structures was observed. A questionable old fracture of the osteochondroma was noted. The remaining bony structures and joints appeared normal.

An ultrasound of the lesion was also ordered to investigate soft-tissue swelling. This revealed a hypoechoic collar around the distal end of the osteochondroma, which could represent a fluid collection, hematoma from trauma, or bursitis. The soft tissues were deemed normal.

Because of the extent of inflammation, the radiologist recommended MRI without contrast to rule out bursitis or trauma to the osteochondroma.

DISCUSSION
Osteochondromas, which may be present in up to 3% of the general population, are the most common benign bone tumors.^1-3 An osteochondroma is a cartilage-capped bony projection that arises on the external surface of the bone; it contains a marrow cavity that is continuous with the underlying bone.^2,4 The majority of osteochondromas are solitary, accounting for perhaps 85% to 90% of all such lesions, and they are typically nonhereditary; the remaining 10% to 15% of osteochondromas are hereditary multiple osteochondromas or exostoses^1,2 (see “Definition of Multiple Exostoses Syndrome”^2,5,6,7).

Most lesions are painless and slow growing, and they usually occur in children and adolescents.² They typically stop growing at skeletal maturity with the closure of the growth plates.^3,8,9 There is no predilection for males or females in single lesions.²

Solitary osteochondromas typically appear in the lower extremities and at long tubular bone metaphyses,^1-3,10 especially on the femur, humerus, tibia, spine, and hip. Any part of the skeleton can be affected, but 30% of lesions occur on the femur and 40% at either the proximal metaphysis of the tibia or the distal metaphysis of the femur.^2,11

Most osteochondromas are asymptomatic and are found incidentally.^1,3 However, some patients present with local pain as a result of irritation to adjacent structures, limitation of joint motion, growth disturbance, or fracture of the pedicle.^3,4,9,11,12 A very small proportion of patients (no more than 1%) with solitary osteochondromas experience malignant transformation.^2,3,6,7 No particular blood work is recommended for patients with solitary osteochondromas.²

Differential Diagnosis
In addition to osteochondromas, several other lesions should be considered in the patient with musculoskeletal lesions (see Table 1^5,6,13-19).

Cartilaginous tumors. Chondrosarcomas are malignant cartilaginous tumors.^20-22 They commonly affect long bones, including the humerus and femur, and some flat bones, such as the pelvic bones.^13,22 They are most commonly seen in adults, and have no predisposition by gender.¹³

Chondrosarcomas can be primary (ie, arising de novo) or secondary (developing on preexisting benign cartilaginous neoplasms, including osteochondromas). The majority of chondrosarcomas are slow growing, and they rarely metastasize. It is difficult to differentiate between a benign lesion (such as an osteochondroma) and a chondrosarcoma by either histology or radiology. However, reliable predictors for malignancy include size exceeding 5 cm and location in the axial skeleton.²⁰

Bone tumors.Osteosarcomas are the most common malignant bone tumors in children and adolescents, with 400 to 560 US patients in this age-group diagnosed each year.^14-16 Osteosarcomas are uncommon in children younger than 10; their incidence peaks during the early teenage years (median peak age, 16), then declines rapidly among older patients. They are more common in males than females.¹⁵

Osteosarcomas commonly develop during periods of rapid bone turnover, such as the adolescent growth spurt. Common sites include the distal femur, proximal humerus, and proximal tibia,^15,16 particularly near the knee.¹³ Usually, osteosarcomas present with nonspecific symptoms, including strain-related pain of several months’ duration, which may disrupt sleep.¹⁶ Laboratory findings in affected patients may include elevations in LDH, alkaline phosphatase, and/or ESR.^15,23

Physical exam reveals a visible or palpable mass in the affected area, along with decreased joint motion; localized warmth or erythema may also be present. Late signs of osteosarcoma include weight loss, general malaise, and fever. First-line imaging for the patient with a suspected osteosarcoma is x-ray, which will show ill-defined borders, osteoblastic and/or osteolytic features, and an associated soft tissue mass. Advanced imaging, such as MRI, is warranted.¹⁶

Ewing sarcoma, the second most common bone tumor in children and adolescents, is an aggressive form of childhood cancer.^14,18 Approximately 25% of all Ewing sarcomas arise in soft tissues rather than bones.¹⁸ They are more common in whites than in other ethnic groups and have a slight male predominance.^13,18 The median age at diagnosis is 15.¹³ The most common presenting symptoms are tumor related, such as pain or a noticeable mass. While x-rays are usually ordered first, MRI is preferred.¹⁸

Soft tissue tumors and masses.Rhabdomyosarcomas are malignancies that account for more than half of the soft tissue sarcomas in children and adolescents. Less than one-fifth of cases occur in the extremities, and most occur in children younger than 10. These lesions have a slight male predominance and are more common in whites than in other patients.^14,17,24

Approximately 6% of childhood soft tissue tumors are adipose tissue tumors, which may be benign (eg, lipomas) or malignant (eg, liposarcomas). Lipomas in children account for nearly 4% of all soft tissue tumors and can be classified as superficial (which are often diagnosed clinically) or deep (frequently requiring imaging).²⁵

Lymphomaaccounts for 7% of cancers in US children and adolescents and more than 25% of newly diagnosed cancers in patients between 15 and 19, making it the most common malignancy in adolescents and the third most common in children.^26,27 Non-Hodgkin lymphoma is the fourth leading type of malignancy in US adolescents.²⁷ Rarely, lymphomas present with primary event soft tissue involvement.²⁸

Myositis ossificans (MO) is a rare benign disorder involving formation of heterotrophic bone in skeletal muscles and soft tissues.²⁹ Though possible in patients of any age, MO is most commonly seen in adolescents and young adults. Often the result of soft tissue injury (in which case it is referred to as myositis ossificans circumscripta or traumatic), MO develops in areas that are exposed to trauma, such as the anterior thighs or arms. Lesions can be diagnosed via plain x-ray or CT, although MRI and ultrasound can also be useful evaluation tools.^17,29,30

Because MO circumscripta typically presents as a painful soft tissue mass, it can be mistaken for a soft tissue sarcoma or an osteosarcoma; radiologic evaluation is required to make the proper diagnosis. Less common forms of MO are myositis ossificans progressiva and myositis ossificans without a history of trauma.²⁹

Ollier diseaseis a rare, nonfamilial disorder characterized by multiple enchondromas (or enchondromatoses), which are distributed asymmetrically with areas of dysplastic cartilage. Enchondromas are benign cartilage tumors that frequently affect long tubular bones along the metaphyses in proximity to the growth plate. The enchondromas result in significant growth abnormalities. About one in 1 million people are diagnosed yearly.^5,19 (Similarly, Maffucci syndrome is represented by multiple enchondromas in association with hemangiomas.⁵)

Ollier disease typically manifests during childhood⁵ with bone swelling, local pain, and palpable bony masses, which are often associated with bone deformities.¹⁹ Patients generally present with an asymmetric shortening of one extremity and the appearance of palpable bony masses on their fingers or toes, which may or may not be associated with pathologic fractures.^5,19 In 20% to 50% of patients with Ollier disease, enchondromas are at risk for malignant transformation into chondrosarcomas.⁵

Vascular malformations. Certain abnormalities of vascular development cause birthmarks and abnormalities of varying degree in underlying tissues.³¹ They are usually present at birth and grow proportionally to the child’s growth.^25,31 However, they can also be seen in later childhood and adolescence.

Radiologic Investigation
Plain radiography of the affected area is the first-line radiologic study to be performed.¹³ While most osteochondromas can be diagnosed by plain x-ray, cross-sectional imaging via CT or MRI is recommended in lesions with certain characteristics, such as a broad stalk or location in the axial skeleton. Because MRI involves no radiation exposure, it is a particularly good diagnostic tool for children.³²

Ultrasound is a good imaging method for evaluating for complications of osteochondromas, including bursa formation or vascular compromise.³²

Treatment and Management
Although usually asymptomatic, osteochondroma can trigger some significant symptoms. Osteochondromas are at risk for fracture and can cause body deformities, mechanical joint problems, weakness of the affected limb, numbness, vascular compression, aneurysm, arterial thrombosis, venous thrombosis, pain, acute ischemia, and nerve compression. Clinical signs of malignant transformation include pain, swelling, and increased lesion size.²

Surgical excision is recommended but should be delayed until after the patient has reached skeletal maturity in order to decrease the risk for recurrence.³³

Patient Education and Follow-up
In addition to explaining appropriate pain management (eg, NSAIDs), it is especially important for the pediatric NP or PA to encourage the patient with a solitary osteochondroma to follow up with the pediatric orthopedic surgeon. Reasons include the need to monitor growth of the lesion (which is likely to continue in a patient who has not yet reached skeletal maturity) and assess for associated functional or joint problems. Patients should also be advised to seek the specialist’s attention if such problems develop or if pain increases.

Generally, the pediatric clinician should be sufficiently informed to answer questions about this condition from the patient or family. Any follow-up laboratory work recommended by the specialist can also be performed by the pediatric NP or PA.

OUTCOME FOR THE CASE PATIENT
MRI without contrast, as recommended by the radiologist to rule out a bursa or trauma to the osteochondroma, was considered an important part of the follow-up plan. As the patient had not yet reached skeletal maturity, she was referred to a pediatric orthopedic surgeon for possible excision of the lesion, due to its size and the pain associated with running or other exertion.

CONCLUSION
Solitary osteochondromas are the most common benign bone tumors. Although they are generally asymptomatic, pain and other symptoms can arise as a result of irritation to the adjacent structures. In this case, the patient’s chief complaint was an irritating “bump” that she had had on her right leg for at least six months.

Generally, follow-up monitoring of the osteochondroma and orthopedic follow-up care are warranted, at least until the patient reaches skeletal maturity. At that point, surgical excision of the lesion is recommended.            

REFERENCES
1. Florez B, Mönckeberg J, Castillo G, Beguiristain J. Solitary osteochondroma long-term follow-up. J Pediatr Orthop B. 2008;17:91-94.

2. Kitsoulis P, Galani V, Stefanaki K, et al. Osteochondromas: review of the clinical, radiological and pathological features. In Vivo. 2008;22:633-646.

3. Ramos-Pascua LR, Sánchez-Herráez S, Alonso-Barrio JA, Alonso-León A. Solitary proximal end of femur osteochondroma: an indication and result of the en bloc resection without hip luxation [in Spanish]. Rev Esp Cir Ortop Traumatol. 2012;56:24-31.

4. Payne WT, Merrell G. Benign bony and soft tissue tumors of the hand. J Hand Surg. 2010;35:1901-1910.

5. Pannier S, Legeai-Mallet L. Hereditary multiple exostoses and enchondromatosis. Best Pract Res Clin Rheumatol. 2008;22:45-54.

6. Bovée JV. Multiple osteochondromas. Orphanet J Rare Dis. 2008;3(3).

7. Staals EL, Bacchini P, Mercuri M, Bertoni F. Dedifferentiated chondrosarcomas arising in preexisting osteochondromas. J Bone Joint Surg Am. 2007;89:987-993.

8. Singh R, Jain M, Siwach R, et al. Large para-articular osteochondroma of the knee joint: a case report. Acta Orthop Traumatol Turc. 2012;46:139-143.

9. Lee JY, Lee S, Joo KB, et al. Intraarticular osteochondroma of shoulder: a case report. Clin Imaging. 2013;37:379-381.

10. Kim Y-C, Ahn JH, Lee JW. Osteochondroma of the distal tibia complicated by a tibialis posterior tendon tear. J Foot Ankle Surg. 2012;51: 660-663.

11. Allagui M, Amara K, Aloui I, et al. Historical giant near-circumferential osteochondroma of the proximal humerus. J Shoulder Elbow Surg. 2010;19:e12-e15.

12.
Li M, Luettringhaus T, Walker KR, Cole PA. Operative treatment of femoral neck osteochondroma through a digastric approach in a pediatric patient: a case report and review of the literature. J Pediatr Orthop B. 2012;21:230-234.

13. Hogendoorn PC, Athanasou N, Bielack S, et al; ESMO/EUROBONET Working Group. Bone sarcomas: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2010;21 suppl 5:v204-v213.

14. Arndt CAS, Rose PS, Folpe AL, Laack NN. Common musculoskeletal tumors of childhood and adolescence. Mayo Clin Proc. 2012;87:475-487.

15. Ta HT, Dass CR, Choong PF, Dunstan DE. Osteosarcoma treatment: state of the art. Cancer Metastasis Rev. 2009;28:247-263.

16. Messerschmitt PJ, Garcia RM, Abdul-Karim FW, et al. Osteosarcoma. J Am Acad Orthop Surg. 2009;17:515-527.

17. Laffan EE, Ngan B-Y, Navarro OM. Pediatric soft-tissue tumors and pseudotumors: MR imaging features with pathologic correlation: Part 2. Tumors of fibroblastic/myofibroblastic, so-called fibrohistiocytic, muscular, lymphomatous, neurogenic, hair matrix, and uncertain origin. Radiographics. 2009;29:e36.

18. Balamuth NJ, Womer RB. Ewing’s sarcoma. Lancet Oncol. 2010;11(2):184.

19. D’Angelo L, Massimi L, Narducci A, Di Rocco C. Ollier disease. Childs Nerv Syst. 2009;25:647-653.

20. Gelderblom H, Hogendoorn PC, Dijkstra SD, et al. The clinical approach towards chondrosarcoma. Oncologist. 2008;13:320-329.

21. Nosratzehi T, Pakfetrat A. Chondrosarcoma. Zahedan J Res Med Sci. 2013;15:64-64.

22. Prado FO, Nishimoto IN, Perez DE, et al. Head and neck chondrosarcoma: analysis of 16 cases. Br J Oral Maxillofacial Surg. 2009;47:555-557.

23. Kim HJ, Chalmers PN, Morris CD. Pediatric osteogenic sarcoma. Curr Opin Pediatr. 2010;22:61-66.

24. Sultan I, Qaddoumi I, Yaser S, et al. Comparing adult and pediatric rhabdomyosarcoma in the surveillance, epidemiology and end results program, 1973 to 2005: an analysis of 2,600 patients. J Clin Oncol. 2009;27:3391-3397.

25. Navarro OM, Laffan EE, Ngan B-Y. Pediatric soft-tissue tumors and pseudo-tumors: MR imaging features with pathologic correlation: Part 1. Imaging approach, pseudotumors, vascular lesions, and adipocytic tumors. Radiographics. 2009;29:887-906.

26. Gross TG, Termuhlen AM. Pediatric non-Hodgkin lymphoma. Curr Hematol Malig Rep. 2008;3:167-173.

27. Hochberg J, Waxman IM, Kelly KM, et al. Adolescent non-Hodgkin lymphoma and Hodgkin lymphoma: state of the science. Br J Haematol. 2009;144:24-40.

28. Derenzini E, Casadei B, Pellegrini C, et al. Non-Hodgkin lymphomas presenting as soft tissue masses: A single center experience and meta-analysis of the published series. Clin Lymphoma Myeloma Leuk. 2012 Dec 12. [Epub ahead of print]

29. Micheli A, Trapani S, Brizzi I, et al. Myositis ossificans circumscripta: a paediatric case and review of the literature. Eur J Pediatr. 2009;168:523-529.

30. McKenzie G, Raby N, Ritchie D. Non-neoplastic soft-tissue masses. Br J Radiol. 2009;82:775-785.

31. Buckmiller LM, Richter GT, Suen JY. Diagnosis and management of hemangiomas and vascular malformations of the head and neck. Oral Dis. 2010;16:405-418.

32. Khanna G, Bennett DL. Pediatric bone lesions: beyond the plain radiographic evaluation. Semin Roentgenol. 2012;47:90-99.

33.
Rijal L, Nepal P, Baral S, et al. Solitary diaphyseal exostosis of femur, how common is it? Eur J Orthop Surg Traumatol. 2011;21:363-365.

A girl, age 13 years, 4 months, presented to her primary care provider’s office for a well visit. Among her concerns, she mentioned a “bump” she had had on her right leg “for the past six months, maybe longer.” The area felt irritated when touched or when the patient “ran too much.” She had seen no change in the bump since she first noticed it. The patient knew of no trauma or other preceding factors. She denied any fever or warmth, redness, or ecchymosis to the area.

Medical history was unremarkable except for familial short stature and myopia. The patient was the fifth of eight children born to nonconsanguinous parents. She denied any surgical history or hospitalizations and was premenarcheal. She was up to date on all age-appropriate vaccines, with her meningococcal vaccine administered at that visit.

The patient’s blood pressure was 99/58 mm Hg with an apical pulse rate of 82 beats/min. Her growth parameters were following her curve. Her height was 55” (0.3 percentile); weight, 81 lb (7.5 percentile); and BMI, 18.8 (48.6 percentile).

The physical exam was normal with the exception of the musculoskeletal exam. Examination of the lower extremities revealed a palpable, 4 cm x 5 cm lesion at the right distal medial thigh just proximal to the knee. The lesion could not be visualized but on palpation was tender and firm. There was some question as to whether the lesion itself or inflamed soft tissue overlying the lesion was mobile. No overlying warmth, induration, erythema, or ecchymosis was noted.

Passive and active range of motion was intact at the hip and knee. No lesions to the upper extremities were evident, and no scoliosis was seen.

Blood work was done to rule out certain diagnoses. Results from a complete blood count with differential, lactate dehydrogenase (LDH), parathyroid hormone, lipid profiles, thyroid function, and a comprehensive metabolic profile were unremarkable. A low level of vitamin D 25-OH was detected: 21.7 ng/mL (normal range, 32 to 100 ng/mL).

Distal femur x-rays with posteroanterior, lateral, and oblique views were ordered. The imaging revealed a 3 cm x 3 cm lesion projecting from the “distal, somewhat medial” femur, which was diagnosed as a benign femoral osteochondroma. Significant inflammation to the surrounding soft-tissue structures was observed. A questionable old fracture of the osteochondroma was noted. The remaining bony structures and joints appeared normal.

An ultrasound of the lesion was also ordered to investigate soft-tissue swelling. This revealed a hypoechoic collar around the distal end of the osteochondroma, which could represent a fluid collection, hematoma from trauma, or bursitis. The soft tissues were deemed normal.

Because of the extent of inflammation, the radiologist recommended MRI without contrast to rule out bursitis or trauma to the osteochondroma.

DISCUSSION
Osteochondromas, which may be present in up to 3% of the general population, are the most common benign bone tumors.^1-3 An osteochondroma is a cartilage-capped bony projection that arises on the external surface of the bone; it contains a marrow cavity that is continuous with the underlying bone.^2,4 The majority of osteochondromas are solitary, accounting for perhaps 85% to 90% of all such lesions, and they are typically nonhereditary; the remaining 10% to 15% of osteochondromas are hereditary multiple osteochondromas or exostoses^1,2 (see “Definition of Multiple Exostoses Syndrome”^2,5,6,7).

Most lesions are painless and slow growing, and they usually occur in children and adolescents.² They typically stop growing at skeletal maturity with the closure of the growth plates.^3,8,9 There is no predilection for males or females in single lesions.²

Solitary osteochondromas typically appear in the lower extremities and at long tubular bone metaphyses,^1-3,10 especially on the femur, humerus, tibia, spine, and hip. Any part of the skeleton can be affected, but 30% of lesions occur on the femur and 40% at either the proximal metaphysis of the tibia or the distal metaphysis of the femur.^2,11

Most osteochondromas are asymptomatic and are found incidentally.^1,3 However, some patients present with local pain as a result of irritation to adjacent structures, limitation of joint motion, growth disturbance, or fracture of the pedicle.^3,4,9,11,12 A very small proportion of patients (no more than 1%) with solitary osteochondromas experience malignant transformation.^2,3,6,7 No particular blood work is recommended for patients with solitary osteochondromas.²

Differential Diagnosis
In addition to osteochondromas, several other lesions should be considered in the patient with musculoskeletal lesions (see Table 1^5,6,13-19).

Cartilaginous tumors. Chondrosarcomas are malignant cartilaginous tumors.^20-22 They commonly affect long bones, including the humerus and femur, and some flat bones, such as the pelvic bones.^13,22 They are most commonly seen in adults, and have no predisposition by gender.¹³

Chondrosarcomas can be primary (ie, arising de novo) or secondary (developing on preexisting benign cartilaginous neoplasms, including osteochondromas). The majority of chondrosarcomas are slow growing, and they rarely metastasize. It is difficult to differentiate between a benign lesion (such as an osteochondroma) and a chondrosarcoma by either histology or radiology. However, reliable predictors for malignancy include size exceeding 5 cm and location in the axial skeleton.²⁰

Bone tumors.Osteosarcomas are the most common malignant bone tumors in children and adolescents, with 400 to 560 US patients in this age-group diagnosed each year.^14-16 Osteosarcomas are uncommon in children younger than 10; their incidence peaks during the early teenage years (median peak age, 16), then declines rapidly among older patients. They are more common in males than females.¹⁵

Osteosarcomas commonly develop during periods of rapid bone turnover, such as the adolescent growth spurt. Common sites include the distal femur, proximal humerus, and proximal tibia,^15,16 particularly near the knee.¹³ Usually, osteosarcomas present with nonspecific symptoms, including strain-related pain of several months’ duration, which may disrupt sleep.¹⁶ Laboratory findings in affected patients may include elevations in LDH, alkaline phosphatase, and/or ESR.^15,23

Physical exam reveals a visible or palpable mass in the affected area, along with decreased joint motion; localized warmth or erythema may also be present. Late signs of osteosarcoma include weight loss, general malaise, and fever. First-line imaging for the patient with a suspected osteosarcoma is x-ray, which will show ill-defined borders, osteoblastic and/or osteolytic features, and an associated soft tissue mass. Advanced imaging, such as MRI, is warranted.¹⁶

Ewing sarcoma, the second most common bone tumor in children and adolescents, is an aggressive form of childhood cancer.^14,18 Approximately 25% of all Ewing sarcomas arise in soft tissues rather than bones.¹⁸ They are more common in whites than in other ethnic groups and have a slight male predominance.^13,18 The median age at diagnosis is 15.¹³ The most common presenting symptoms are tumor related, such as pain or a noticeable mass. While x-rays are usually ordered first, MRI is preferred.¹⁸

Soft tissue tumors and masses.Rhabdomyosarcomas are malignancies that account for more than half of the soft tissue sarcomas in children and adolescents. Less than one-fifth of cases occur in the extremities, and most occur in children younger than 10. These lesions have a slight male predominance and are more common in whites than in other patients.^14,17,24

Approximately 6% of childhood soft tissue tumors are adipose tissue tumors, which may be benign (eg, lipomas) or malignant (eg, liposarcomas). Lipomas in children account for nearly 4% of all soft tissue tumors and can be classified as superficial (which are often diagnosed clinically) or deep (frequently requiring imaging).²⁵

Lymphomaaccounts for 7% of cancers in US children and adolescents and more than 25% of newly diagnosed cancers in patients between 15 and 19, making it the most common malignancy in adolescents and the third most common in children.^26,27 Non-Hodgkin lymphoma is the fourth leading type of malignancy in US adolescents.²⁷ Rarely, lymphomas present with primary event soft tissue involvement.²⁸

Myositis ossificans (MO) is a rare benign disorder involving formation of heterotrophic bone in skeletal muscles and soft tissues.²⁹ Though possible in patients of any age, MO is most commonly seen in adolescents and young adults. Often the result of soft tissue injury (in which case it is referred to as myositis ossificans circumscripta or traumatic), MO develops in areas that are exposed to trauma, such as the anterior thighs or arms. Lesions can be diagnosed via plain x-ray or CT, although MRI and ultrasound can also be useful evaluation tools.^17,29,30

Because MO circumscripta typically presents as a painful soft tissue mass, it can be mistaken for a soft tissue sarcoma or an osteosarcoma; radiologic evaluation is required to make the proper diagnosis. Less common forms of MO are myositis ossificans progressiva and myositis ossificans without a history of trauma.²⁹

Ollier diseaseis a rare, nonfamilial disorder characterized by multiple enchondromas (or enchondromatoses), which are distributed asymmetrically with areas of dysplastic cartilage. Enchondromas are benign cartilage tumors that frequently affect long tubular bones along the metaphyses in proximity to the growth plate. The enchondromas result in significant growth abnormalities. About one in 1 million people are diagnosed yearly.^5,19 (Similarly, Maffucci syndrome is represented by multiple enchondromas in association with hemangiomas.⁵)

Ollier disease typically manifests during childhood⁵ with bone swelling, local pain, and palpable bony masses, which are often associated with bone deformities.¹⁹ Patients generally present with an asymmetric shortening of one extremity and the appearance of palpable bony masses on their fingers or toes, which may or may not be associated with pathologic fractures.^5,19 In 20% to 50% of patients with Ollier disease, enchondromas are at risk for malignant transformation into chondrosarcomas.⁵

Vascular malformations. Certain abnormalities of vascular development cause birthmarks and abnormalities of varying degree in underlying tissues.³¹ They are usually present at birth and grow proportionally to the child’s growth.^25,31 However, they can also be seen in later childhood and adolescence.

Radiologic Investigation
Plain radiography of the affected area is the first-line radiologic study to be performed.¹³ While most osteochondromas can be diagnosed by plain x-ray, cross-sectional imaging via CT or MRI is recommended in lesions with certain characteristics, such as a broad stalk or location in the axial skeleton. Because MRI involves no radiation exposure, it is a particularly good diagnostic tool for children.³²

Ultrasound is a good imaging method for evaluating for complications of osteochondromas, including bursa formation or vascular compromise.³²

Treatment and Management
Although usually asymptomatic, osteochondroma can trigger some significant symptoms. Osteochondromas are at risk for fracture and can cause body deformities, mechanical joint problems, weakness of the affected limb, numbness, vascular compression, aneurysm, arterial thrombosis, venous thrombosis, pain, acute ischemia, and nerve compression. Clinical signs of malignant transformation include pain, swelling, and increased lesion size.²

Surgical excision is recommended but should be delayed until after the patient has reached skeletal maturity in order to decrease the risk for recurrence.³³

Patient Education and Follow-up
In addition to explaining appropriate pain management (eg, NSAIDs), it is especially important for the pediatric NP or PA to encourage the patient with a solitary osteochondroma to follow up with the pediatric orthopedic surgeon. Reasons include the need to monitor growth of the lesion (which is likely to continue in a patient who has not yet reached skeletal maturity) and assess for associated functional or joint problems. Patients should also be advised to seek the specialist’s attention if such problems develop or if pain increases.

Generally, the pediatric clinician should be sufficiently informed to answer questions about this condition from the patient or family. Any follow-up laboratory work recommended by the specialist can also be performed by the pediatric NP or PA.

OUTCOME FOR THE CASE PATIENT
MRI without contrast, as recommended by the radiologist to rule out a bursa or trauma to the osteochondroma, was considered an important part of the follow-up plan. As the patient had not yet reached skeletal maturity, she was referred to a pediatric orthopedic surgeon for possible excision of the lesion, due to its size and the pain associated with running or other exertion.

CONCLUSION
Solitary osteochondromas are the most common benign bone tumors. Although they are generally asymptomatic, pain and other symptoms can arise as a result of irritation to the adjacent structures. In this case, the patient’s chief complaint was an irritating “bump” that she had had on her right leg for at least six months.

Generally, follow-up monitoring of the osteochondroma and orthopedic follow-up care are warranted, at least until the patient reaches skeletal maturity. At that point, surgical excision of the lesion is recommended.            

REFERENCES
1. Florez B, Mönckeberg J, Castillo G, Beguiristain J. Solitary osteochondroma long-term follow-up. J Pediatr Orthop B. 2008;17:91-94.

2. Kitsoulis P, Galani V, Stefanaki K, et al. Osteochondromas: review of the clinical, radiological and pathological features. In Vivo. 2008;22:633-646.

3. Ramos-Pascua LR, Sánchez-Herráez S, Alonso-Barrio JA, Alonso-León A. Solitary proximal end of femur osteochondroma: an indication and result of the en bloc resection without hip luxation [in Spanish]. Rev Esp Cir Ortop Traumatol. 2012;56:24-31.

4. Payne WT, Merrell G. Benign bony and soft tissue tumors of the hand. J Hand Surg. 2010;35:1901-1910.

5. Pannier S, Legeai-Mallet L. Hereditary multiple exostoses and enchondromatosis. Best Pract Res Clin Rheumatol. 2008;22:45-54.

6. Bovée JV. Multiple osteochondromas. Orphanet J Rare Dis. 2008;3(3).

7. Staals EL, Bacchini P, Mercuri M, Bertoni F. Dedifferentiated chondrosarcomas arising in preexisting osteochondromas. J Bone Joint Surg Am. 2007;89:987-993.

8. Singh R, Jain M, Siwach R, et al. Large para-articular osteochondroma of the knee joint: a case report. Acta Orthop Traumatol Turc. 2012;46:139-143.

9. Lee JY, Lee S, Joo KB, et al. Intraarticular osteochondroma of shoulder: a case report. Clin Imaging. 2013;37:379-381.

10. Kim Y-C, Ahn JH, Lee JW. Osteochondroma of the distal tibia complicated by a tibialis posterior tendon tear. J Foot Ankle Surg. 2012;51: 660-663.

11. Allagui M, Amara K, Aloui I, et al. Historical giant near-circumferential osteochondroma of the proximal humerus. J Shoulder Elbow Surg. 2010;19:e12-e15.

12.
Li M, Luettringhaus T, Walker KR, Cole PA. Operative treatment of femoral neck osteochondroma through a digastric approach in a pediatric patient: a case report and review of the literature. J Pediatr Orthop B. 2012;21:230-234.

13. Hogendoorn PC, Athanasou N, Bielack S, et al; ESMO/EUROBONET Working Group. Bone sarcomas: ESMO clinical practice guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2010;21 suppl 5:v204-v213.

14. Arndt CAS, Rose PS, Folpe AL, Laack NN. Common musculoskeletal tumors of childhood and adolescence. Mayo Clin Proc. 2012;87:475-487.

15. Ta HT, Dass CR, Choong PF, Dunstan DE. Osteosarcoma treatment: state of the art. Cancer Metastasis Rev. 2009;28:247-263.

16. Messerschmitt PJ, Garcia RM, Abdul-Karim FW, et al. Osteosarcoma. J Am Acad Orthop Surg. 2009;17:515-527.

17. Laffan EE, Ngan B-Y, Navarro OM. Pediatric soft-tissue tumors and pseudotumors: MR imaging features with pathologic correlation: Part 2. Tumors of fibroblastic/myofibroblastic, so-called fibrohistiocytic, muscular, lymphomatous, neurogenic, hair matrix, and uncertain origin. Radiographics. 2009;29:e36.

18. Balamuth NJ, Womer RB. Ewing’s sarcoma. Lancet Oncol. 2010;11(2):184.

19. D’Angelo L, Massimi L, Narducci A, Di Rocco C. Ollier disease. Childs Nerv Syst. 2009;25:647-653.

20. Gelderblom H, Hogendoorn PC, Dijkstra SD, et al. The clinical approach towards chondrosarcoma. Oncologist. 2008;13:320-329.

21. Nosratzehi T, Pakfetrat A. Chondrosarcoma. Zahedan J Res Med Sci. 2013;15:64-64.

22. Prado FO, Nishimoto IN, Perez DE, et al. Head and neck chondrosarcoma: analysis of 16 cases. Br J Oral Maxillofacial Surg. 2009;47:555-557.

23. Kim HJ, Chalmers PN, Morris CD. Pediatric osteogenic sarcoma. Curr Opin Pediatr. 2010;22:61-66.

24. Sultan I, Qaddoumi I, Yaser S, et al. Comparing adult and pediatric rhabdomyosarcoma in the surveillance, epidemiology and end results program, 1973 to 2005: an analysis of 2,600 patients. J Clin Oncol. 2009;27:3391-3397.

25. Navarro OM, Laffan EE, Ngan B-Y. Pediatric soft-tissue tumors and pseudo-tumors: MR imaging features with pathologic correlation: Part 1. Imaging approach, pseudotumors, vascular lesions, and adipocytic tumors. Radiographics. 2009;29:887-906.

26. Gross TG, Termuhlen AM. Pediatric non-Hodgkin lymphoma. Curr Hematol Malig Rep. 2008;3:167-173.

27. Hochberg J, Waxman IM, Kelly KM, et al. Adolescent non-Hodgkin lymphoma and Hodgkin lymphoma: state of the science. Br J Haematol. 2009;144:24-40.

28. Derenzini E, Casadei B, Pellegrini C, et al. Non-Hodgkin lymphomas presenting as soft tissue masses: A single center experience and meta-analysis of the published series. Clin Lymphoma Myeloma Leuk. 2012 Dec 12. [Epub ahead of print]

29. Micheli A, Trapani S, Brizzi I, et al. Myositis ossificans circumscripta: a paediatric case and review of the literature. Eur J Pediatr. 2009;168:523-529.

30. McKenzie G, Raby N, Ritchie D. Non-neoplastic soft-tissue masses. Br J Radiol. 2009;82:775-785.

31. Buckmiller LM, Richter GT, Suen JY. Diagnosis and management of hemangiomas and vascular malformations of the head and neck. Oral Dis. 2010;16:405-418.

32. Khanna G, Bennett DL. Pediatric bone lesions: beyond the plain radiographic evaluation. Semin Roentgenol. 2012;47:90-99.

33.
Rijal L, Nepal P, Baral S, et al. Solitary diaphyseal exostosis of femur, how common is it? Eur J Orthop Surg Traumatol. 2011;21:363-365.