**Abstract**

Benign bone tumors in the pediatric population can have varied clinical presentations ranging from asymptomatic to nonspecific pain, swelling, or pathological fracture. A systemic imaging approach should be utilized to evaluate for focal bone abnormalities. Radiologists must be aware of salient imaging features of pediatric benign bone tumors, as it helps to guide clinicians for further management and help decreasing patient anxiety and unnecessary medical intervention.

**Keywords:** Pediatric benign bone tumors, Osteoid Osteoma, Enchondroma, Non-Ossifying Fibroma

### **1. Introduction**

Primary benign bone tumors are more common than malignancies in children. The patient's age and lesion location are two critical factors when evaluating for a bone tumor. The initial imaging modality to evaluate for a bone tumor is radiography. Radiographs confirm the presence and location of a tumor, assist in the formulation of differential diagnosis, characterize the tumor, and guide in selecting further imaging. Cross-sectional imaging is helpful for tissue characterization and for evaluating the extent of the lesions. The patient's age helps to narrow down the differential diagnosis.

#### **2. Classification**

Pediatric benign bone tumors based on the peak age of occurrence: Child (0–10 years). Eosinophillic Granuloma. Simple bone cyst. Adolescent (10–20 years). Aneurysmal bone cyst. Chondroblastoma. Chondromyxoid fibroma. Fibrous dysplasia. Osteochondroma. Nonossifying fibroma/fibrous cortical defect. Osteoblastoma. Periosteal chondroma. Simple bone cyst.

Adult: Enchondroma. Giant cell tumor. Osteoblastoma. Brown Tumor (Hyperparathyroidism). The location of the lesion in the bone can help narrow down the differential diagnosis.

Cystic lesions: Unicameral (simple) bone cyst, aneurysmal bone cyst. Osteoid matrix lesions: Enostosis, osteoma, osteoid osteoma, osteoblastoma. Chondroid matrix: Enchondroma, chondroblastoma, chondromyxoid fibroma,

Fibro-osseous lesions: Nonossifying fibroma, fibrous dysplasia, osteofibrous

A simple bone cyst is also called a solitary cyst or unicameral bone cyst (UBC). A simple bone cyst is a common benign nonneoplastic lucent bony lesion mainly seen in childhood and typically asymptomatic. Approximately 85% of unicameral bone cysts occur in children and adolescents [1]. There is 2–3:1 male predominance [2]. During the active phase, the cyst increases in size and remains close to the physis. The latent phase cysts are found farther from the physis and usually do not continue to grow. Cysts may appear to migrate into diaphysis, but actually, it is the growth plate that migrates away from the cyst. The lesions are usually asymptomatic and found incidentally, although the adjacent joint's pain, swelling, and stiffness can also occur. The most frequent

complication is a pathologic fracture, and this is usually the cause of presentation. 75% of patients come in with a pathologic fracture [3]. Pathologically, the cysts contain clear serosanguineous fluid surrounded by fibrous membranous lining. The proximal humerus is the most common location (in 50–60% of cases) [4]. The second most common location is the

On radiography, bone cysts are located centrally in the medullary cavity within the metaphysis. Most cysts are less than 3 cm in short-axis diameter but

Computed Tomography (CT) scan and Magnetic Resonance Imaging (MRI) can help exclude other entities that can potentially mimic a simple bone cyst such as an intraosseous lipoma, fibrous dysplasia, eosinophilic granuloma, giant cell tumor, nonossifying fibroma, or aneurysmal bone cyst. The CT scan helps to delineate the cyst and confirms a fallen fragment. MRI confirms the cystic nature of the lesion. The fluid contents are low signal on T1 and high signal on T2-weighted imaging (**Figure 1B** and **C**). In contrast, the cyst lining enhances, but the contents do not (**Figures 1D, 2C**). Occasionally, when presenting with intralesional hemorrhage from fracture, fluid–fluid levels may

be seen representing internal degraded blood products. The internal hemorrhage may evolve into septations that can be demonstrated on MRI

may be much larger in the long axis. The cyst wall is well-defined and sclerotic; the overlying cortex is thinned, and the lesion may be mildly expansile (**Figures 1A, 2A**). Following a fracture, a fragment of bone may be seen dependently within the cyst, called a fallen fragment sign, considered

pathognomonic for a simple bone cyst [5] (**Figure 3A**).

osteochondroma, juxtacortical chondroma.

Vascular malformations: Hemangioma. Giant cell tumors: Giant cell tumor. Others: Langerhans cell histiocytosis.

**3. Primary benign bone tumors by tissue type**

Fat containing lesions: Lipoma.

*Imaging of Pediatric Benign Bone Tumors DOI: http://dx.doi.org/10.5772/intechopen.99021*

Cystic bone lesions:

1.Simple bone cyst:

proximal femur.

(**Figure 2B**).

**25**

dysplasia.

Pediatric benign bone tumors based on location in the long bones:

Epiphysis: Chondroblastoma. Giant cell tumor. Metaphysis: Aneurysmal bone cyst. Chondromyxoid fibroma. Enchondroma. Nonossifying fibroma/fibrous cortical defect. Osteochondroma. Simple bone cyst. Diaphysis: Fibrous dysplasia. Nonossifying fibroma/fibrous cortical defect. Osteochondroma. Osteofibrous dysplasia. Simple bone cyst. Aneurysmal bone cyst. Enchondroma.

Some lesions are solitary, and others are multifocal at presentation. The following are the examples of multifocal pediatric benign bone lesions:

Brown tumors (hyperparathyroidism). Cystic angiomatosis/lymphangiomatosis. Enchondroma (Ollier disease, Maffucci syndrome). Fibrous dysplasia (McCune-Albright syndrome). Infiltrate myofibromatosis. Langerhans cell histiocytosis. Nonossifying fibroma (Jaffe-Campanacci Syndrome). Osteochondroma (Diaphyseal Aclasis). Chronic recurrent multifocal osteomyelitis (CRMO).

The following features are characteristic for nonaggressive benign bone lesions and help differentiate from aggressive malignant bone lesions:

Well-defined margins with a narrow zone of transition.

Expansion of bone from slow growth.

Smooth periosteal new bone formation.

Absence of an associated soft tissue mass.

Some benign bone tumors are adequately defined by radiographs and do not require any further imaging for diagnosis or treatment. However, most bone tumors require additional imaging; this may be in the form of CT, MRI, scintigraphy, PET scanning, and rarely ultrasound. The choice of imaging for a given tumor depends on the differential diagnostic considerations, possible treatment options, and whether the lesion is aggressive or nonaggressive.

Classification of pediatric bone tumors according to matrix or tissue type:

*Imaging of Pediatric Benign Bone Tumors DOI: http://dx.doi.org/10.5772/intechopen.99021*

Cystic lesions: Unicameral (simple) bone cyst, aneurysmal bone cyst. Osteoid matrix lesions: Enostosis, osteoma, osteoid osteoma, osteoblastoma. Chondroid matrix: Enchondroma, chondroblastoma, chondromyxoid fibroma, osteochondroma, juxtacortical chondroma.

Fibro-osseous lesions: Nonossifying fibroma, fibrous dysplasia, osteofibrous dysplasia.

Fat containing lesions: Lipoma. Vascular malformations: Hemangioma. Giant cell tumors: Giant cell tumor. Others: Langerhans cell histiocytosis.
