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Benign and locally aggressive bone lesions

Fibrous dysplasia, adamantinoma and non-ossifying fibroma with their radiographic appearances.

57 questions 9 source pages 1 fact-check flags

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Q1Describe the X-ray findings in fibrous dysplasia.▸

Expansile lesion at the metaphyseal region with cortical thinning
Intramedullary with a narrow transition zone
Ground-glass matrix, no periosteal reaction
Mild varus deformity of the proximal femur (shepherd crook deformity)
Ddx: bone cyst/ enchondroma (if matrix less ground glass), infection, brown tumour, haematological, metastasis in older patients

Q2What is the pathophysiology of fibrous dysplasia?▸

Localised dysfunction of osteoblast differentiation (via increased cAMP signalling) and maturation
Failure of lamellar bone formation (failure of lamella bone formation); bone is replaced by fibrous tissue
Mutation of Ch 20q23 (GNAS), not inherited

Q3What syndromes are associated with fibrous dysplasia?▸

McCune-Albright syndrome (McCune Albright syndrome): polyostotic FD, cafe au lait spots (coast of Maine), hyperfunctioning endocrine disease (precocious puberty, hyperT4, acromegaly)
Scoliosis; GNAS mutation
Mazabraud syndrome: polyostotic FD + soft tissue intramuscular myxoma

Q4What is the histology and risk of malignant transformation in fibrous dysplasia?▸

Histology: alphabet soup appearance - trabeculae of osteoid within fibrous stroma
Malignant transformation 1% (osteosarcoma/fibrosarcoma); 5-10% in polyostotic disease (per notes)
Nocturnal pain suggests malignant transformation

Q5What are the indications and principles of surgery in fibrous dysplasia?▸

Indications: pathological fracture, enlarging lesion, recurrent fracture/deformity, high stress area (femoral neck)
Polyostotic: mainly deformity correction and fracture prevention
Monostotic: curettage; monostotic -> aim to remove tumor (curative)
Curettage, allograft (autograft transforms into fibrous tissue), stable titanium IM nail +/- osteotomy

Q6What medical treatment is used in fibrous dysplasia?▸

Bisphosphonate for symptomatic polyostotic patients: pain relief, decrease fracture, partial resolution of lesion
Denosumab - ongoing study (J Bone Miner Res 2021)

Q7Which patients and bones are affected by fibrous dysplasia?▸

Can involve any bone
More common in females

Q8What deformities can fibrous dysplasia cause?▸

Mono-ostotic vs polyostotic disease
Coxa vara with Trendelenburg gait
Blindness with skull involvement

Q9What natural history of fibrous dysplasia must patients be counselled about?▸

Progression of the existing lesion + appearance of new lesions
Old lesions will not mature - problem of remodelling: decreased cellularity, increased collagen deposition, persistent woven bone, no compressive/tensile trabeculae -> progressive deformity
Progressive deformity until maturity, but may progress again with maturity

Q10What investigations are performed in fibrous dysplasia?▸

Inflammatory markers, ALP, LDH - increase suggests malignant transformation
Skeletal survey to rule out polyostotic disease (if polyostotic, screen for syndromes)
If mono-ostotic: consider biopsy for diagnosis (monoostotic: consider biopsy for Dx)

Q11What are the aims of treatment in fibrous dysplasia?▸

Decrease pain, prevent fracture +/- correct deformity

Q12What intraoperative difficulties are anticipated in fibrous dysplasia surgery?▸

Lesions can be very vascular - prepare blood
Choose the correct implant with the right NSA

Q13Describe the X-ray findings in eosinophilic granuloma.▸

Well-defined intramedullary lytic lesion in the diaphysis of the right femur
Laminated periosteal reaction with thinning of the cortex
Highly destructive with a well-defined border
Ddx: Ewing sarcoma, infection, haematological

Q14What is Hand-Schuller-Christian disease?▸

Triad: multiple lytic lesions, diabetes insipidus, exophthalmos
Chronic disseminated Langerhans histiocytosis with visceral involvement, >3 years old

Q15What is the histology of eosinophilic granuloma?▸

Langerhans cells (antigen-presenting): pale staining, coffee bean nuclei, eosinophilic, Birbeck granules
Giant cells present
No atypia; normal nuclear/cytoplasmic ratio

Q16What investigations are needed in eosinophilic granuloma?▸

Bloods; local imaging with MRI
Systemic staging: CT thorax + bone scan
Tissue diagnosis (biopsy)

Q17How is spinal deformity in eosinophilic granuloma managed?▸

Bracing first line: corrects 90% of deformity and regains 50% of vertebral height
Failed (10%) -> low-dose radiotherapy
Curettage + BG +/- steroid if nonoperative treatment fails or for a solitary lesion close to an articular surface
HSC: vinblastine + steroid

Q18What are the clinical features of eosinophilic granuloma?▸

Pain + limp
Progressive kyphotic posture

Q19What is the natural history of eosinophilic granuloma?▸

Self-limiting benign histiocytic lesion
Monostotic bone disease
Highly destructive with a well-defined border
Biopsy alone may be sufficient treatment

Q20What are the sites of involvement in eosinophilic granuloma?▸

Skull, ribs, clavicle, scapula, mandible
Spine especially thoracic (vertebral plana)
Diaphyseal regions of long bones and the pelvis

Q21What is the spectrum of histiocytosis X (Langerhans cell histiocytosis)?▸

A reticuloendothelial system pathology
Eosinophilic granuloma (monostotic)
Hand-Schuller-Christian disease: chronic disseminated with visceral involvement, >3 years old
Letterer-Siwe disease: <3 years old, fatal

Q22What is vertebra plana and what is its differential?▸

Single level vertebral collapse
Ddx: post-TB, post-fracture, haematogenous
Compare with platyspondyly (diffuse) in SED/osteomalacia

Q23What is the great mimicker differential of eosinophilic granuloma?▸

Osteomyelitis, leukaemia, lymphoma
Fibrous dysplasia, Ewing sarcoma

Q24Describe the X-ray findings of osteoid osteoma.▸

Osteolytic lesion over the intertrochanteric region with surrounding sclerosis
+/- homogenous cortical thickening
+/- radiolucent nidus
+/- solid periosteal reaction
Ddx: Brodie's abscess, stress/healing fracture, fibrous cortical defect, Ewing sarcoma

Q25What is the classic clinical presentation of osteoid osteoma?▸

Night pain, worse after alcohol, relieved by NSAIDs
Flexion contracture of the knee
Painful scoliosis

Q26What is the double-density sign on bone scan?▸

A small focus of intense radioactivity in the nidus
Superimposed on a larger area of lower, but still increased, radioactivity

Q27How is nidus size used to distinguish osteoid osteoma from osteoblastoma?▸

CT delineates the nidus: <1.5cm = osteoid osteoma
>1.5cm = osteoblastoma (typically 3-4cm)

Q28What are the management options for osteoid osteoma?▸

Conservative NSAIDs: 50% treated with NSAID alone; sole treatment in spinal involvement without scoliosis; self-resolves in 3 years
CT-guided radiofrequency ablation: failed conservative or juxta-articular lesions with contracture; controversial in spine as close to neural elements, need 1cm safe zone in spine; 85% success
RFA complications: skin burn, stress riser at long bone; allows concomitant biopsy
Surgery (marginal excision): failed conservative when RFA not possible, painful scoliosis; CT navigation adjunct

Q29What are the differences between osteoid osteoma and osteoblastoma?▸

Nidus size: <1.5cm (osteoid osteoma) vs >1.5cm/typically 3-4cm (osteoblastoma)
Location: proximal femur > tibia > spine vs posterior elements of the spine > proximal femur
Course: self-limiting vs progressive; NSAID relief yes vs no
Surgery: +/- vs yes; osteoblastoma has more giant cells histologically

Q30What is the pathophysiology of pain in osteoid osteoma?▸

Nidus of central woven bone with osteoblastic rimming surrounded by a reactive zone
Pain due to prostaglandin E2 concentration and COX1/2 expression
Increased unmyelinated nerve endings within
Spontaneous bleeding within

Q31What is the histology of osteoid osteoma?▸

Distinct border between the osteoid nidus and reactive bone
Nidus of immature osteoid + osteoblastic rim
Increased mitotic figures with normal NC ratio
Osteoblastoma = more giant cells

Q32What investigations are performed for a suspected osteoid osteoma?▸

Blood test to rule out infection
X-ray: reactive bone with a radiolucent nidus
CT to delineate the size of the nidus
Bone scan: double-density sign

Q33Describe the CT findings in this patient.▸

Axial cut showing a lytic lesion over the facet
Expansile, with no cortical breakage and no periosteal reaction
No definite narrowing of the spinal canal
Ddx: osteoblastoma, ABC, GCT, exostosis, chondrosarcoma

Q34What is the differential diagnosis of an anterior spinal tumour?▸

Metastasis, haemangioma, multiple myeloma
Eosinophilic granuloma, chordoma
Osteosarcoma, chondrosarcoma, Ewing sarcoma

Q35What is the assessment of osteoblastoma?▸

Hx/PE: dull pain not relieved by NSAIDs, neurological symptoms
Tumour markers including SPE
X-ray: expansile lytic lesion with reactive bone; CT to delineate nidus
Bone scan hot; MRI if neurological complication

Q36What is the histology and management of osteoblastoma?▸

Similar to osteoid osteoma but with more giant cells
Nidus of immature osteoid surrounded by osteoblasts, increased mitotic figures but no atypia
Marginal excision; recurrence 10-20%

Q37Describe the deformities shown in the clinical photo.▸

Genu valgum; right knee flexed and internally rotated posture
No gross leg length discrepancy
Forearm radial bowing + ulnar deviation of the hand
Prominent radial styloid; ulnar shortened; +/- radial head subluxation

Q38What negative findings are documented?▸

No absent ray
No gross joint swelling
No skin changes or stigmata

Q39What upper limb features are present?▸

Radial bowing with ulnar deviation of the hand
Prominent radial styloid
Ulnar shortening
+/- radial head subluxation

Q40Describe the X-ray findings in adamantinoma.▸

Skeletally mature patient
Multiple lucent lesions separated by septa of bone with a soap bubble appearance
Cortical lesion at the anterior cortex of the proximal tibia with cortical thickening
Wide transition zone, no increase in anterior bowing, no obvious periosteal reaction

Q41What is adamantinoma?▸

Low grade malignancy of unknown origin
Usually 20-40 years old, located nearly always at the anterior tibia
May metastasize to lung (25%)

Q42What are the differentials for adamantinoma?▸

Osteofibrous dysplasia, ossifying fibroma, osteoid osteoma
Brodie's abscess, fracture callus
Haematological malignancy

Q43What is the assessment and biopsy appearance in adamantinoma?▸

Hx: insidious pain; PE: anterior bowing deformity, palpable mass
CXR: lung mets 25%; MRI: decrease in T1 signal
Biopsy: fibrous and epithelial +/- glandular tissue in a gland-like pattern (glandular tissue in gland like pattern)

Q44What is the management of adamantinoma?▸

Wide margin excision + reconstruction
RT/chemotherapy not used due to slow growth

Q45Describe the X-ray findings in chondroblastoma.▸

Lytic lesion in the epiphysis of a skeletally immature patient
no obvious matrix seen; narrow transition zone with sclerotic border
Not expansile; no periosteal reaction; the physis has been breached

Q46What are the differentials for an epiphyseal lytic lesion?▸

Telangiectatic osteosarcoma, infection, metabolic disease
GCT and clear cell chondrosarcoma in older patients
Can have a secondary ABC

Q47What is the natural history of chondroblastoma?▸

Majority <25 years, common around 12
Usually epiphyseal, can cross the physis; most common around the knee, also proximal humerus/femur
<1% benign metastasis to lung; CXR shows lung mets in 2% (per notes)

Q48What is the biopsy appearance and treatment of chondroblastoma?▸

Biopsy: cobblestone, chickenwire appearance, scattered multinucleated giant cells, chondroid matrix
Intralesional curettage +/- adjuvant therapy (phenol or cryotherapy); 10-15% recurrence
Excision in patients with lung metastasis

Q49What assessment is performed for chondroblastoma?▸

Hx/PE: pain and tenderness
CXR for lung mets (2%)
Blood test; MRI
Biopsy

Q50What is a non-ossifying fibroma and who does it affect?▸

Most common benign bone tumour in childhood (5-15 years)
Metaphysis/meta-diaphyseal junction
Pathogenesis: abnormal osteoclastic resorption at the subperiosteal level during metaphyseal remodelling

Q51Describe the X-ray findings in non-ossifying fibroma.▸

Meta-diaphyseal junction
Eccentric
Bubbly lytic lesion surrounded by a sclerotic rim

Q52What conditions are associated with non-ossifying fibroma?▸

ABC, neurofibromatosis
Jaffe-Campanacci syndrome: multiple NOF, cafe au lait pigmentation, mental retardation, heart/eyes/gonads involvement

Q53What is the histology and treatment of non-ossifying fibroma?▸

Fibroblastic spindle cells in a storiform pattern (whorls of elongated spindle cells)
Treatment: always conservative
Ddx: UBC, ABC, fibrous dysplasia, infection

Q54What are the differentials and MRI findings in CMF?▸

Ddx: NOF, ABC, chondroblastoma with breaching of the physis
MRI: T1 hypointense, T2 hyperintense

Q55What is the biopsy appearance of chondromyxoid fibroma?▸

Hypercellular fibrous matrix
Hypocellular chondroid matrix
Stellate spindle cells in a myxoid matrix

Q56What is the management and recurrence rate of CMF?▸

Intra-lesional curettage + bone graft/cement
Recurrence up to 30%

Q57Describe the X-ray findings in chondromyxoid fibroma.▸

Skeletally immature patient
Lytic lesion at the proximal tibial metaphysis
Eccentrically located with cortical expansion and destruction
Narrow zone of transition
No periosteal reaction or soft tissue swelling
Dx: CMF

Fact check

Malignant transformation in fibrous dysplasia is 1%, rising to 5-10% in polyostotic disease — Overstated for polyostotic disease — Published series report ~0.4-1% overall and up to ~4% in McCune-Albright/familial cases; 5-10% is higher than most sources — (medium confidence) — source

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Benign and locally aggressive bone lesions

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