# Benign Bone Lesions: When to Observe, Biopsy, or Treat

## Introduction

Benign bone lesions are frequently encountered in orthopedic practice, often as incidental findings on imaging obtained for unrelated reasons. The challenge for the orthopedic surgeon is distinguishing truly benign, "leave-alone" lesions from those that require further workup, biopsy, or treatment. A systematic approach based on clinical presentation, patient age, anatomic location, and imaging characteristics guides appropriate management and avoids unnecessary intervention.

## Latent (Stage 1) Lesions: Observe

### Non-Ossifying Fibroma (Fibrous Cortical Defect)

Non-ossifying fibroma is the **most common benign bone lesion** in children and adolescents, found in the metaphysis of long bones, typically around the knee (distal femur, proximal tibia). Its radiographic appearance is pathognomonic: an eccentric, well-defined, cortical-based lucency with a sclerotic, scalloped border. It is asymptomatic and discovered incidentally. The natural history involves spontaneous involution with skeletal maturation, replaced by normal bone. Management is observation only with no treatment, biopsy, or follow-up imaging necessary for small lesions. The exception is large lesions (greater than 50% of bone diameter) that may warrant prophylactic fixation or curettage if fracture risk is significant.

### Fibrous Dysplasia

Fibrous dysplasia is a developmental disorder in which normal bone is replaced by immature fibrous tissue and disorganized woven bone. It may be monostotic (70-80%) or polyostotic (20-30%). Polyostotic fibrous dysplasia with endocrine abnormalities and cafe-au-lait spots constitutes McCune-Albright syndrome. The radiographic appearance shows ground glass or hazy opacity within the medullary canal, and it may cause cortical expansion and deformity (shepherd's crook deformity of the proximal femur). Management is observation for asymptomatic lesions, with prophylactic fixation or osteotomy for impending fracture or progressive deformity.

### Enchondroma

Enchondroma is a benign cartilage tumor arising within the medullary canal, most common in the small bones of the hand and proximal humerus. Radiographically it appears as a well-defined lucency with chondroid matrix (rings and arcs or punctate calcification). Asymptomatic lesions require no treatment. Ollier disease (multiple enchondromas/enchondromatosis) carries a 25-30% risk of malignant transformation to chondrosarcoma. Maffucci syndrome (enchondromatosis with soft tissue hemangiomas) carries an even higher malignancy risk. Solitary enchondromas in the appendicular skeleton have negligible malignant transformation risk. Concern for chondrosarcoma arises with pain unrelated to fracture, lesion size greater than 5 cm, periosteal reaction, cortical destruction, or endosteal scalloping exceeding 2/3 of cortex.

![Plain radiographs showing classic appearances of non-ossifying fibroma, fibrous dysplasia, and enchondroma](/images/orthopedic-surgery/benign-bone-lesions-radiographs.jpg)

## Active (Stage 2) Lesions: Consider Treatment

### Unicameral Bone Cyst (Simple Bone Cyst)

Unicameral bone cysts are fluid-filled cysts in the proximal humerus or proximal femur of children (ages 5-15). Radiographically they appear as central, well-defined lucent lesions in the metaphysis and may show a **fallen fragment sign** (pathognomonic if fractured). They often present with a pathologic fracture. Management options include observation after fracture healing (the fracture itself may stimulate cyst healing), aspiration and injection of corticosteroids (methylprednisolone) or bone marrow aspirate for persistent or symptomatic cysts, curettage and bone grafting for recalcitrant lesions, and flexible intramedullary nailing for cysts in the proximal femur to prevent fracture and promote healing. Recurrence rate is 15-30% after injection and lower after curettage.

### Aneurysmal Bone Cyst (ABC)

Aneurysmal bone cysts are expansile, blood-filled, multiloculated cystic lesions most common in patients under 20 years, affecting the metaphysis of long bones and posterior spinal elements. Radiographically they appear as expansile, eccentric, lytic lesions with a thin periosteal shell ("blowout" or "soap bubble" appearance). MRI shows pathognomonic fluid-fluid levels within the cystic spaces. They can be primary or secondary (arising within another lesion such as GCT, chondroblastoma, or osteoblastoma). Management includes curettage with adjuvant treatment (high-speed burr, cryotherapy, phenol, argon beam) and bone grafting, embolization (useful as neoadjuvant or standalone for surgically inaccessible locations), and denosumab or sclerotherapy as emerging nonsurgical options. Recurrence rate is 10-30% after curettage.

### Giant Cell Tumor (GCT) of Bone

Giant cell tumor is locally aggressive (Enneking Stage 3) but rarely metastasizes (1-3% pulmonary metastases). Peak age is 20-40 years (skeletally mature). The classic location is the **epiphysis extending to the subchondral bone** of long bones around the knee (distal femur, proximal tibia). Radiographically it appears as an eccentric, lytic, expansile lesion in the epiphysis without matrix production, with no sclerotic border (geographic but non-sclerotic). MRI shows solid tissue (not cystic) with heterogeneous signal.

Management involves extended curettage with adjuvant treatment (high-speed burr, phenol, cryotherapy, cement) as the standard treatment. PMMA (cement) fills the defect, allows early weight-bearing, provides a thermal adjuvant effect, and enables easy radiographic surveillance for recurrence. Denosumab (RANKL inhibitor) is effective for locally advanced or recurrent GCT and can reduce tumor size preoperatively, though it may cause a "hardened rim" complicating curettage. En bloc resection is reserved for recurrent tumors, expendable bones, or severely destructive lesions. Recurrence rate is 15-25% after extended curettage with adjuvants.

![MRI showing fluid-fluid levels in an aneurysmal bone cyst and an epiphyseal giant cell tumor of the proximal tibia](/images/orthopedic-surgery/abc-gct-mri.jpg)

## Other Important Benign Lesions

### Osteoid Osteoma

Osteoid osteoma is a small (less than 1.5 cm), painful, bone-forming tumor most common in adolescents and young adults. The classic presentation is **night pain dramatically relieved by NSAIDs (aspirin or ibuprofen)**. It is most common in the femoral neck and tibial diaphysis. CT scan shows the characteristic nidus (small lucent center) surrounded by reactive sclerosis. Management includes NSAIDs for 2-3 years (natural regression), radiofrequency ablation (RFA) for persistent symptoms (success rate exceeding 90%), and surgical excision (en bloc or curettage) if RFA is not feasible.

### Osteoblastoma

Osteoblastoma is a larger version of osteoid osteoma (greater than 2 cm nidus) with a predilection for the posterior elements of the spine. Pain is not as reliably responsive to NSAIDs. Management is curettage or en bloc excision; recurrence is possible, especially with aggressive variants.

### Chondroblastoma

Chondroblastoma is an epiphyseal cartilage tumor in skeletally immature patients, most common in the proximal humerus, proximal femur, and proximal tibia. Radiographically it appears as a well-defined, lytic epiphyseal lesion with chondroid calcification. Management is curettage and bone grafting, taking care to avoid damaging the physis.

### Osteochondroma (Exostosis)

Osteochondroma is the **most common benign bone tumor** (or developmental growth aberration). It is a cartilage-capped bony projection arising from the metaphysis, directed away from the joint. The cortex and medullary canal are continuous with the parent bone (pathognomonic). Solitary osteochondromas have less than 1% malignant transformation risk. Multiple hereditary exostoses (MHE/HME) is an autosomal dominant condition with multiple osteochondromas and 5-10% lifetime risk of chondrosarcoma transformation. Management is observation unless symptomatic (pain, neurovascular compression, cosmesis); excision is performed if growth continues after skeletal maturity (raising concern for malignant transformation).

| Lesion | Typical Age | Classic Location | Radiographic Appearance | Management |
|--------|------------|-----------------|------------------------|------------|
| Non-ossifying fibroma | Children/adolescents | Metaphysis, around knee | Eccentric, cortical, sclerotic scalloped border | Observation (resolves spontaneously) |
| Fibrous dysplasia | Any age | Femur, tibia, ribs | Ground-glass opacity; shepherd's crook | Observation; fixation if fracture risk |
| Enchondroma | 20-50 years | Hand phalanges, proximal humerus | Central lucency with rings/arcs calcification | Observation; biopsy if painful |
| Unicameral bone cyst | 5-15 years | Proximal humerus, proximal femur | Central metaphyseal lucency; fallen fragment sign | Injection (steroids/BMAC) or curettage |
| Aneurysmal bone cyst | < 20 years | Metaphysis; posterior spine | Expansile, eccentric, fluid-fluid levels on MRI | Curettage + adjuvant; embolization |
| Giant cell tumor | 20-40 years | Epiphysis (around knee) | Eccentric, lytic, no sclerotic rim, subchondral | Extended curettage + cement (PMMA) |
| Osteoid osteoma | Adolescents/young adults | Femoral neck, tibial diaphysis | Nidus with surrounding sclerosis on CT | NSAIDs or radiofrequency ablation |
| Osteochondroma | Children/adolescents | Metaphysis (away from joint) | Cortex/medulla continuous with parent bone | Observation unless symptomatic |

## Decision Framework

The decision to observe, biopsy, or treat depends on several features. A classic benign appearance warrants observation. Pain not explained by fracture, growth after skeletal maturity, aggressive radiographic features, impending fracture risk, or diagnostic uncertainty should prompt biopsy or treatment as appropriate.

![Decision algorithm for management of incidentally discovered bone lesions](/images/orthopedic-surgery/benign-lesion-algorithm.jpg)

## Key Clinical Pearls

Non-ossifying fibroma is the most common benign bone lesion in children; its radiographic appearance is pathognomonic and no further workup is needed for typical presentations. Giant cell tumor is an epiphyseal lesion in skeletally mature patients; extended curettage with cement packing is the standard treatment, with recurrence rates of 15-25%. An enchondroma that causes pain not attributable to fracture, grows in size, or shows cortical destruction should be suspected of malignant transformation to chondrosarcoma and requires biopsy. Osteoid osteoma has a classic presentation of night pain relieved by NSAIDs and a characteristic CT nidus; radiofrequency ablation is the preferred treatment for refractory symptoms.

## References

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3. Thomas DM, Skubitz KM. Giant cell tumour of bone. *Curr Opin Oncol*. 2009;21(4):338-344.
4. Murphey MD, Choi JJ, Kransdorf MJ, Flemming DJ, Gannon FH. Imaging of osteochondroma: variants and complications with radiologic-pathologic correlation. *Radiographics*. 2000;20(5):1407-1434.