BONE PATHOLOGY

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CHAPTER 7 BONE PATHOLOGY

Bone tumors

Introduction
Osteochondroma
Enchondroma
Chondroblastoma
Chondrosarcoma
Chondromyxoid fibroma
Synovial chondromatosis
Osteoid osteoma
Osteoblastoma
Osteosarcoma
Desmoplastic fibroma of bone
Fibrosarcoma of bone
Benign fibrous histiocytoma of bone
Malignant fibrous histiocytoma of bone
Ewing’s sarcoma (see also PNET)
Giant cell tumor of bone
Chordoma
Adamantinoma
Aneurysmal bone cyst
Simple bone cyst
Fibrous dysplasia of bone
Osteofibrous dysplasia
Langerhans cell disease
Erdheim–chester disease
Chest wall hamartoma of infancy

Non-tumor pediatric osteoarticular disease

Arthritis
Osteomyelitis
Chronic recurrent multifocal osteomyelitis (CRMO)
Osteopetrosis
Myositis ossificans
Ganglion cyst

BONE TUMORS

INTRODUCTION

• In many countries, including the UK, bone tumors are diagnosed and managed by specialist tertiary centers
• In most cases the diagnosis is suspected from clinical and imaging data and hence biopsies and resection specimens will be dealt with by specialist bone tumor centers

image the appropriate handling, blocking and sectioning of such specimens requires specialist equipment and expertise

• Therefore, this section will only briefly cover the main points of entities which may be encountered in a diagnostic pediatric pathology practice and more specialist texts on bone pathology should be consulted
• In general, malignant pediatric bone tumors affect the long bones and include predominantly

image osteosarcomas

– affecting mainly metaphyses of patients in the second decade

image Ewing sarcoma

– affecting mainly diaphyses of similar aged patients

image a range of other pediatric malignancies may metastasize to bone and a bone lesion in a patient under 5 years of age is statistically more likely to be metastatic

• Most bone tumors are not associated with an underlying predisposing factor but a range of associations are reported

image Ollier disease
image Maffuci syndrome
image familial retinoblastoma syndrome
image Rothmund–Thomson syndrome
image multiple osteochondromas
image Paget’s disease of bone
image post-radiation
image other rare entities

• Bone tumors generally present with:

image pain
image swelling
image loss of function
image pathological fracture

• Radiological imaging is essential for adequate interpretation of the histopathological features, in particular:

image the site

– specific bone
– diaphysis vs metaphysis vs epiphysis

image size
image position

– central vs eccentric

image invasiveness and soft tissue involvement
image periosteal reaction
image isolated vs multiple lesions

• In surgical pathology material bone tumors are graded on the basis of cellularity and nuclear features

image see specialist texts for discussion and specific details

OSTEOCHONDROMA

Epidemiology

• First three decades

image common in children

• 15% are multiple
• Malignant transformation in <1%

image increased risk in multiple

Clinical features

• Asymptomatic, painless bony lesion
• Metaphysis of long bones of limbs

Histopathological features (Fig 7.1)

• Pedunculated lesion with cartilage cap and extension of medulla into lesion
• Outer perichondrium
• Underlying cartilage
• Underlying bone
• Endochondral ossification
• No atypia
• Well organized structure
image

Fig 7.1 Photomicrograph of a benign osteochondroma, demonstrating a well-organized structure with a cartilage cap overlying the medullary cavity.

Differential diagnoses and pitfalls

• Myxoid change, atypia, fibrous bands and disorganization may indicate malignant transformation

ENCHONDROMA

Epidemiology

• Common
• Most often present in adults

image children also affected

Clinical features

• Tubular bones

image mainly hands and feet

• Painless swellings
• Pathological fractures

Histopathological features (Fig 7.2)

• Multinodular, intramedullary well-circumscribed cartilage nodules
• Hyaline cartilage matrix
• Bland chondrocytes

image small round nuclei

• May show myxoid change
• No mitoses or atypia
• Normal marrow between nodules
image

Fig 7.2 Photograph of a benign enchondroma in a patient with Maffuci syndrome, demonstrating a nodular lesion composed of mature cartilage.

Differential diagnoses and pitfalls

Periosteal chondroma

• On bone surface

image arises from periosteum

• Long bones

image especially humerus

• Cartilage nodules do not penetrate underlying cortex

Enchondromatosis

• Ollier disease

image multiple enchondromas in childhood

• Maffuci syndrome

image also has vascular lesions of soft tissue

– especially cavernous hemangiomas

• Increased risk of chondrosarcoma

image develops in adulthood

CHONDROBLASTOMA

Epidemiology

• 10–25 years
• M > F

Clinical features

• Mainly long bones epiphyses
• Painful
• Local recurrence 10–20%

Histopathological features (Figs 7.3, 7.4)

• Lesion composed of chondroblasts

image uniform round to ovoid cells
image clear to eosinophilic cytoplasm
image nuclear grooves

– ‘coffee bean’ nuclei

• Scattered osteoclast-like giant cells
• Immature chondroid stroma
• Pericellular ‘chicken wire’ calcification
• Scattered slightly atypical nuclei are normal variant
image

Fig. 7.3

image

Figs 7.3–7.4 Photomicrographs of a chondroblastoma, demonstrating a lesion composed of chondroblasts with areas of immature chondroid stroma and scattered osteoclast-like giant cells.

Differential diagnoses and pitfalls

• Non-progressive lung ‘metastases’ reported in association with benign chondroblastomas

CHONDROSARCOMA

• Malignant mesenchymal tumor with hyaline differentiation

Epidemiology

• Mainly adults

image children reported

Clinical features

• Pelvis, long bones, hands and feet, head and neck (Gadwal et al 2000)
• Swelling, pain

Histopathological features (Figs 7.5–7.6)

• Chondroid matrix
• Lobules of cartilage

image hypercellular
image atypical chondrocytes

– hyperchromatic
– enlarged
– binucleate
– mitoses

image myxoid change
image necrosis

• Grades I–III (grade predicts prognosis)
image

Fig. 7.5

image

Figs 7.5–7.6 Photomicrographs of chondrosarcomas, confirmed on specialist review, demonstrating infiltrating lesions composed of lobules of cartilage with chondroid matrix and atypical chondrocytes.

Periosteal chondrosarcoma

• similar features but in periosteal location

Mesenchymal chondrosarcoma

• Younger age

image usually young adults

• Malignant behavior but long clinical course
• Craniofacial, ribs, vertebrae
• Biphasic pattern

image areas of undifferentiated small round cells

– similar to other SRBCTs

image nodules of hyaline cartilage

Clear cell chondrosarcoma

• Mainly adults

image adolescents also

• Epiphyses of long bones

image mainly humerus and femur

• Lobules of clear cells with distinct membranes
• Focal chondroid differentiation

Immunohistochemical staining

• S100+ in chondroid areas
• SRBCTs of mesenchymal chondrosarcoma are CD99+

Differential diagnoses and pitfalls

• Caution in diagnosing chondrosarcoma in childhood

image rare

• Caution in diagnosing chondrosarcoma in lesions of hands and feet

image in these sites enchondromas may also be hypercellular, binucleate

• Secondary chondrosarcomas develop in benign enchondroma or osteochondroma

image especially Ollier / Maffuci syndromes

• development of increased cellularity and atypia

CHONDROMYXOID FIBROMA

Epidemiology

• Rare
• M > F
• Usually 10–30 years

Clinical features

• Any site

image mainly long bones

• Pain and swelling
• Metaphyseal eccentric lucent lesion
• 15% recurrence

Histopathological features

• Well-demarcated lesions
• Microlobular pattern
• Myxoid stroma
• Stellate and spindle cells

image alternating microscopic cellular and hypocellular areas

• Pleomorphism 20–30%
• Rare mitoses

image not atypical

• With or without cartilage and calcification
• ABC like areas 10%

Immunohistochemical staining

• S100+
• Peripheral cells may be SMA+, CD34+

SYNOVIAL CHONDROMATOSIS

Epidemiology

• Usually adults

image children reported

Clinical features

• Joints

image usually knee

• Pain, swelling, locking, mass

Histopathological features

• Nodules of hyaline cartilage

image variably cellular

• Fibrous outer layer
• With or without synovium and ossification

OSTEOID OSTEOMA

Epidemiology

• Usually children
• M > F

Genetics

• Possible 17q loss

image not in diagnostic use

Clinical features

• Any site

image mainly long bones

• Pain

image especially at night
image relieved by NSAIDS

• Tender
• Swelling
• Well circumscribed cortical lesion

image associated with cortical sclerosis on radiology

Histopathological features

• <2 cm diameter
• Central connective tissue with osteoid

image forming bony trabeculae
image prominent osteoblasts

• Cartilage not usually present
• Hypervascular peripheral sclerotic bone

OSTEOBLASTOMA

Epidemiology

• Usually 10–30 years
• M > F

Clinical features

• Spine and sacrum, limbs and other sites
• Mainly medullary

image rare periosteal
image cementoblastoma in jaw

• Pain
• Swelling
• Local mechanical effects
• Lytic lesion with reactive periosteal shell
• May have ABC-like areas

Histopathological features (Figs 7.7, 7.8)

• >2cm diameter
• Well circumscribed, pushing margin
• Morphologically mimics osteoid osteoma

image randomly arranged central bony trabeculae
image covered by osteoblasts

• Vascular stroma

image ABC-like areas

image

Fig. 7.7

image

Figs 7.7–7.8 Photomicrographs of osteoblastomas, demonstrating randomly arranged bony trabeculae covered by osteoblasts.

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