Benign Bone Tumours
Orthopaedics · Bone Tumours · lean revision notes
Benign Bone Tumours
Benign bone tumours are a favourite NEET PG topic because each lesion has a near-pathognomonic combination of age, location, and radiology. Master the "where, when, and what it looks like" of each, plus the few with malignant potential, and you can crack almost every question.
Classification by Tissue of Origin
Benign bone tumours are best remembered by the matrix/tissue they produce. This single table organises the entire chapter.
| Tissue of origin | Benign tumour | Malignant counterpart |
|---|---|---|
| Bone-forming (osteogenic) | Osteoid osteoma, Osteoblastoma, Osteoma | Osteosarcoma |
| Cartilage-forming (chondrogenic) | Osteochondroma, Enchondroma, Chondroblastoma, Chondromyxoid fibroma | Chondrosarcoma |
| Fibrous | Non-ossifying fibroma, Fibrous dysplasia | Fibrosarcoma |
| Giant cell | Giant cell tumour (locally aggressive) | (Rarely metastasising GCT) |
| Cystic / reactive | Simple (unicameral) bone cyst, Aneurysmal bone cyst | — |
| Vascular | Haemangioma | Angiosarcoma |
| Marrow | (Eosinophilic granuloma — histiocytic) | — |
High-yield: Osteochondroma is the single most common benign bone tumour overall. Giant cell tumour is the most common bone tumour around the knee in a 20–40 year-old with an epiphyseal lesion, and although classed "benign", it is locally aggressive and is the favourite "borderline" lesion.
A useful screening rule before details: lesions that are eccentric vs central, epiphyseal vs metaphyseal vs diaphyseal, and age narrow the diagnosis dramatically.
| Location within bone | Classic lesion |
|---|---|
| Epiphysis (skeletally immature) | Chondroblastoma |
| Epiphysis/metaphysis (after physeal closure) | Giant cell tumour |
| Metaphysis | Osteochondroma, NOF, simple bone cyst, osteosarcoma |
| Diaphysis | Ewing sarcoma, fibrous dysplasia, adamantinoma |
Osteochondroma (Exostosis)
The commonest benign bone tumour; really a developmental outgrowth of a displaced physeal cartilage rest rather than a true neoplasm.
Etiology/pathophysiology: A cartilage-capped bony projection arising from the external surface of bone. The lesion's medulla and cortex are continuous with the parent bone — this continuity is the diagnostic radiological hallmark. Hereditary multiple exostoses (Multiple Osteochondromatosis / Diaphyseal Aclasis) is autosomal dominant, linked to EXT1/EXT2 gene mutations, and carries a much higher malignant risk.
Clinical features: Painless hard swelling near a joint in adolescents/young adults, classically around the knee (distal femur, proximal tibia) and proximal humerus. May cause mechanical irritation, bursa formation, or nerve/vessel compression.
Radiology: Sessile or pedunculated bony outgrowth pointing away from the nearby joint (because the growing physis "pushes" it away). Cartilage cap is best assessed on MRI.
High-yield: Malignant transformation (to chondrosarcoma) occurs in <1% of solitary lesions** but in **5–25% of hereditary multiple exostoses**. Warning signs: **pain after skeletal maturity**, sudden growth, and a **cartilage cap >2 cm (>1.5–2 cm) thick on imaging.
Management: Observe if asymptomatic. Excise if symptomatic, cosmetically troubling, or showing features of malignancy — remove with the entire cartilage cap and perichondrium to prevent recurrence.
Osteoid Osteoma
A small benign osteoblastic lesion (<1.5–2 cm) with a classic clinical story that is asked almost every year.
Clinical features (the classic triad to memorise):
- Young patient (typically 10–25 years, male predominance).
- Night pain — intense, boring, worse at night.
- Dramatic relief with aspirin / NSAIDs (pain is prostaglandin-mediated — the nidus is rich in prostaglandins and COX-2).
Common sites: proximal femur and tibial diaphysis. A spinal lesion classically causes painful scoliosis (lesion on the concave side).
Radiology / Investigation of choice: Radiograph shows a small radiolucent nidus (<1.5 cm) surrounded by dense reactive sclerosis.
High-yield: CT is the investigation of choice to demonstrate the nidus (the actual tumour), which is the key to diagnosis and the target for treatment. Bone scan shows a "double density" sign. If the lesion is >2 cm, think osteoblastoma (essentially a "giant osteoid osteoma" — larger, less night pain, less aspirin response, commoner in the spine posterior elements).
Flow of diagnosis: Adolescent with night pain → relieved by aspirin → X-ray shows lucent nidus with sclerosis → CT confirms nidus → treat.
Management: Many regress spontaneously over years on NSAIDs. Definitive: CT-guided radiofrequency ablation (RFA) of the nidus is the treatment of choice; surgical en-bloc excision of the nidus is curative if RFA is unsuitable. Incomplete nidus removal → recurrence.
Osteoblastoma
The "big brother" of osteoid osteoma — same osteoblastic tissue but larger.
- Size >2 cm; dull pain that is less night-predominant and less aspirin-responsive.
- Predilection for the posterior elements of the spine (pedicles, lamina) and long bones.
- Locally more aggressive than osteoid osteoma; managed by curettage or marginal excision.
Enchondroma
A benign intramedullary cartilage tumour, the most common tumour of the hand bones.
Clinical features: Usually an incidental finding; commonest in the small tubular bones of the hands and feet (proximal phalanx). Often presents as a pathological fracture after trivial trauma.
Radiology: Central, well-defined lytic lesion with "popcorn", "rings-and-arcs" or stippled/punctate calcification; cortical thinning/expansion in phalanges.
Syndromes (high-yield eponyms):
| Syndrome | Features | Malignant risk |
|---|---|---|
| Ollier disease | Multiple enchondromas (enchondromatosis), unilateral predominance | ↑ chondrosarcoma |
| Maffucci syndrome | Multiple enchondromas + soft-tissue haemangiomas | Highest risk of malignant transformation (also visceral malignancies) |
High-yield: A solitary hand enchondroma rarely turns malignant, but an enchondroma in a long bone (e.g., femur) with pain is suspicious — distinguishing a benign enchondroma from a low-grade chondrosarcoma is a classic dilemma; endosteal scalloping >2/3 cortex, cortical destruction, soft-tissue mass and pain favour chondrosarcoma. Maffucci > Ollier for malignant transformation risk.
Management: Asymptomatic — observe. Symptomatic / fracture — curettage and bone grafting.
Chondroblastoma (Codman tumour)
- Arises in the EPIPHYSIS of a skeletally immature patient (most consistent epiphyseal lesion in this age group) — distal femur, proximal tibia, proximal humerus.
- Presents with joint pain, effusion, decreased range of movement.
- Radiology: well-defined lytic epiphyseal lesion that may cross the physis, with fine calcification.
- Histology: "chicken-wire" calcification, chondroblasts, scattered giant cells.
- Treatment: curettage and grafting.
Chondromyxoid Fibroma
- Rarest cartilage tumour; metaphysis of proximal tibia typical.
- Eccentric, lobulated, lytic lesion with a sclerotic scalloped margin.
- Curettage; can recur.
Non-Ossifying Fibroma (NOF) / Fibrous Cortical Defect
- The most common incidental benign lesion in children — often a "do-not-touch" finding.
- Eccentric, metaphyseal, cortically based lytic lesion with a thin sclerotic ("soap-bubble") rim, classically distal femur/tibia.
- Most regress spontaneously; treat (curettage) only if large (>50% diameter) with fracture risk.
- Jaffe-Campanacci syndrome: multiple NOFs + café-au-lait spots.
Fibrous Dysplasia
Developmental anomaly where normal bone is replaced by fibro-osseous tissue (failure of maturation of woven bone), caused by a post-zygotic GNAS gene mutation.
- Monostotic (commonest) or polyostotic.
- Radiology: "ground-glass" matrix, lytic-expansile lesion; "shepherd's crook" deformity of the proximal femur from repeated microfractures.
- McCune-Albright syndrome: polyostotic fibrous dysplasia + café-au-lait macules (irregular "coast of Maine" borders) + precocious puberty/endocrinopathy.
High-yield: Ground-glass matrix + shepherd's crook femur = fibrous dysplasia. Bisphosphonates help pain; surgery for deformity/fracture.
Simple (Unicameral) Bone Cyst — SBC
A fluid-filled benign cystic lesion, usually centrally located.
- Age: 5–15 years; site: proximal humerus and proximal femur (metaphysis, abutting the physis).
- Often asymptomatic until a pathological fracture.
- Central, well-defined lytic lesion; the "fallen fragment / fallen leaf" sign (a fractured cortical fragment falling to the dependent part of the fluid-filled cyst) is pathognomonic.
- Management: aspiration + intralesional steroid (methylprednisolone) injection; curettage/grafting if recurrent. Many heal after fracture.
Aneurysmal Bone Cyst — ABC
A locally destructive, blood-filled, expansile lesion (often with USP6 gene rearrangement); may be primary or secondary to another lesion (GCT, chondroblastoma, fibrous dysplasia).
- Age: 10–20 years; metaphysis of long bones and posterior spinal elements.
- Eccentric, "blown-out"/ballooned, expansile lytic lesion that markedly thins and expands the cortex.
- MRI: multiple fluid–fluid levels (from settled blood) — characteristic but not exclusive (also seen in telangiectatic osteosarcoma, so always confirm histologically).
- Management: curettage + bone grafting ± adjuvant (phenol, cryotherapy); selective arterial embolisation for spinal/pelvic lesions.
High-yield: Simple bone cyst = central + "fallen fragment" sign, whereas aneurysmal bone cyst = eccentric + expansile + fluid-fluid levels. This pair is a classic two-option MCQ.
Giant Cell Tumour (Osteoclastoma)
Benign but locally aggressive; the most clinically important lesion of the chapter.
Clinical features: Age 20–40 years (after physeal closure), slight female predominance. Site: epiphyseo-metaphyseal end of long bones, classically around the knee (distal femur > proximal tibia) and distal radius. Pain, swelling, sometimes pathological fracture.
Radiology: Eccentric, expansile, "soap-bubble" lytic lesion reaching up to the subchondral bone / articular surface with no reactive sclerosis and no matrix mineralisation.
Histology: Sheets of mononuclear stromal cells with uniformly distributed multinucleated osteoclast-like giant cells. (Mutation in H3F3A / histone H3.3 gene.)
High-yield: GCT is graded by Campanacci grading (I–III). It can give benign pulmonary metastases in ~1–3% and undergo malignant transformation, especially after radiotherapy — so radiotherapy is avoided. Denosumab (RANKL inhibitor) is used for inoperable/recurrent/spinal GCT and as a neoadjuvant.
Management: Extended intralesional curettage + adjuvant (phenol/liquid nitrogen/high-speed burr) + cement (PMMA) or graft for most; wide resection ± reconstruction for extensive/recurrent disease. High recurrence with simple curettage alone.
Stepwise Clinical Approach to a Bone Lesion
A reproducible framework that examiners love:
1. Age → narrows the field (chondroblastoma/SBC in children; GCT after fusion). → 2. Location (epiphysis/metaphysis/diaphysis; central vs eccentric). → 3. Radiological "aggressiveness" — Lodwick grading: geographic (well-defined) = benign; moth-eaten/permeative = aggressive/malignant. → 4. Periosteal reaction — solid/buttressed = benign; lamellated ("onion-skin"), sunburst, Codman triangle = aggressive. → 5. Matrix — ground-glass (fibrous dysplasia), rings-and-arcs (cartilage), cloud-like (bone). → 6. Biopsy for confirmation when in doubt (always after imaging, never before).
High-yield: A well-defined geographic lesion with a sclerotic rim = benign; a wide zone of transition, cortical breach, soft-tissue mass and aggressive periosteal reaction = malignant. The zone of transition is the single best radiographic predictor of aggressiveness.
Quick Differentiation of the "Classic Five"
| Lesion | Age | Location | Hallmark |
|---|---|---|---|
| Osteochondroma | 10–20 | Metaphysis, away from joint | Cortex/medulla continuous with bone |
| Osteoid osteoma | 10–25 | Femur/tibia diaphysis | Night pain, aspirin relief, CT nidus |
| Enchondroma | 10–40 | Hand small bones | Rings-and-arcs calcification |
| Simple bone cyst | 5–15 | Proximal humerus/femur | Central, fallen-fragment sign |
| Aneurysmal bone cyst | 10–20 | Metaphysis/spine | Eccentric, fluid-fluid levels |
Key Differentials & Look-alikes
- Osteoid osteoma vs Brodie's abscess (subacute osteomyelitis): both lytic with sclerosis; clinical infective features and a sequestrum favour Brodie's abscess.
- Enchondroma vs low-grade chondrosarcoma: pain, deep endosteal scalloping, cortical destruction → chondrosarcoma.
- SBC vs ABC: central/fallen fragment vs eccentric/expansile/fluid-fluid levels.
- GCT vs ABC vs brown tumour of hyperparathyroidism: all giant-cell-rich, expansile, lytic — always check serum calcium/PTH to exclude brown tumour before labelling a "GCT".
- ABC vs telangiectatic osteosarcoma: both show fluid-fluid levels; biopsy mandatory.
Complications
- Pathological fracture (SBC, enchD, fibrous dysplasia, GCT).
- Malignant transformation: osteochondroma → chondrosarcoma; enchondromatosis (Ollier/Maffucci) → chondrosarcoma; fibrous dysplasia → rare sarcoma; GCT → malignancy (esp. post-radiotherapy).
- Local recurrence after inadequate excision/curettage (GCT, ABC, chondromyxoid fibroma).
- Nerve/vessel compression, bursa formation, deformity (osteochondroma, fibrous dysplasia).
Recently Asked / Exam Angle
- "Most common benign bone tumour" → Osteochondroma.
- Night pain relieved by aspirin + small nidus on CT → Osteoid osteoma; investigation of choice = CT; treatment = RFA.
- Epiphyseal lytic lesion in a skeletally immature patient → Chondroblastoma (chicken-wire calcification on histology).
- Eccentric lytic lesion reaching subchondral bone in a 30-year-old around the knee → Giant cell tumour; drug for inoperable GCT = denosumab; avoid radiotherapy.
- Fallen-fragment sign → Simple bone cyst; treatment = intralesional steroid.
- Fluid-fluid levels on MRI → Aneurysmal bone cyst (remember the telangiectatic osteosarcoma trap).
- Multiple enchondromas + soft-tissue haemangiomas → Maffucci syndrome (highest malignant risk).
- Café-au-lait + precocious puberty + polyostotic ground-glass lesions → McCune-Albright (fibrous dysplasia, GNAS).
- Cartilage cap >2 cm / new pain after maturity in osteochondroma → suspect chondrosarcoma.
- Gene associations: EXT1/EXT2 (hereditary multiple exostoses), GNAS (fibrous dysplasia), USP6 (ABC), H3F3A (GCT) — increasingly tested.
Rapid Revision
- Osteochondroma = commonest benign bone tumour; cortex/medulla continuous; grows away from the joint.
- Osteoid osteoma = night pain + aspirin relief + nidus <1.5 cm; CT is investigation of choice, RFA is treatment.
- Osteoblastoma = osteoid osteoma >2 cm, spine posterior elements, less aspirin response.
- Enchondroma = commonest tumour of the hand; rings-and-arcs/punctate calcification.
- Ollier = multiple enchondromas; Maffucci = enchondromas + haemangiomas (highest malignant risk).
- Chondroblastoma = epiphysis of immature bone; chicken-wire calcification (Codman tumour).
- Simple bone cyst = central, proximal humerus, fallen-fragment sign; treat with intralesional steroid.
- Aneurysmal bone cyst = eccentric, expansile, fluid-fluid levels; USP6 gene.
- Giant cell tumour = 20–40 yrs, epiphyseo-metaphyseal, soap-bubble, subchondral, locally aggressive; denosumab for inoperable, avoid radiotherapy, Campanacci grading.
- Fibrous dysplasia = ground-glass matrix + shepherd's crook femur; GNAS; McCune-Albright triad.
- NOF = incidental eccentric metaphyseal lesion with sclerotic rim; Jaffe-Campanacci with café-au-lait.
- Aggressiveness clue: narrow zone of transition + sclerotic rim = benign; wide zone, cortical breach, Codman triangle/sunburst = malignant — always exclude brown tumour (check calcium/PTH) in giant-cell lesions.