STEPTRACKERMUSCULOSKELETAL + ONCOLOGY | PATHOLOGY | HIGH-YIELD REVIEW

Benign Bone Tumors & Cysts

Bony bumps, painful night nidus, soap-bubble lesions and cartilage islands — age and location narrow each one.

FOCUS ON

Osteochondroma: most common benign bone tumor, cartilage-capped stalk from the metaphysis. Osteoid osteoma: young man, cortical nidus, night pain relieved by NSAIDs. Giant cell tumor: women 20–40, epiphysis at the knee, soap bubble, locally aggressive. Enchondroma: hands and feet; multiple (Ollier, Maffucci) → chondrosarcoma risk.

PICTURE

LESION

ORIGIN · BEHAVIOR

FEATURES

CLUE

How to read: end of a long bone, joint at the top — epiphysis, growth plate (dashed), metaphysis, diaphysis. Other rows show the vertebra (posterior side up), a finger or the skull. Red = lesion.

Osteochondroma

most common benign

Lateral bony outgrowth with a cartilage cap, continuous with the medullary cavity; EXT1/EXT2

Males < 25; metaphysis near the knee, growing away from the joint; painless mass

Multiple = hereditary exostoses · rare → chondrosarcoma

Osteoid osteoma

Benign osteoblastic tumor < 2 cm; makes PGE₂

Young males; cortex of proximal femur/tibia; radiolucent nidus with dense sclerotic rim

Night pain relieved by NSAIDs

Osteoblastoma

Same histology, > 2 cm

Vertebrae (posterior elements); dull pain not relieved by NSAIDs

Can cause scoliosis or nerve compression

Giant cell tumor

Neoplastic stromal cells make RANKL → osteoclast-like multinucleated giant cells; H3F3A

Women 20–40; epiphysis of distal femur/proximal tibia; "soap bubble" lytic lesion

Locally aggressive, recurs · denosumab

Enchondroma

Benign hyaline cartilage in the medullary cavity

Small bones of hands and feet; often incidental or pathologic fracture

Ollier (multiple, IDH1/2), Maffucci (+ hemangiomas) → chondrosarcoma

Chondroblastoma

Immature cartilage cells

Adolescents; epiphysis, often before growth plate closure

"Chicken-wire" calcification

Unicameral (simple) bone cyst

Fluid-filled cavity of unknown cause

Children; proximal humerus or femur metaphysis; presents with pathologic fracture

"Fallen fragment" sign

Aneurysmal bone cyst

Blood-filled spaces; USP6 rearrangement

Adolescents; expansile eccentric lesion in metaphysis or vertebra; fluid-fluid levels on MRI

Can be secondary to other tumors

Nonossifying fibroma

Developmental fibrous lesion of the cortex

Children; eccentric lucent metaphyseal lesion with sclerotic scalloped border

Incidental, regresses

Langerhans cell histiocytosis

Clonal Langerhans cells (BRAF V600E)

Child with punched-out lytic skull lesion; eosinophils; Birbeck granules (tennis racket); CD1a, langerin, S100 ⁺

Can involve pituitary → DI

Mechanism — location narrows the list

EpiphysisGiant cell tumor, chondroblastoma

MetaphysisOsteochondroma, osteosarcoma, simple and aneurysmal cysts

DiaphysisEwing sarcoma, osteoid osteoma (cortex)

Hands & feetEnchondroma

Benign lesions have narrow transition zones and sclerotic rims; malignant ones are permeative with periosteal reaction.

Benign lesions by clue

LESION

AGE

SITE

X-RAY

Osteochondroma

< 25, male

Metaphysis

Stalk with cartilage cap

Osteoid osteoma

< 25, male

Cortex

Lucent nidus, sclerotic rim

Giant cell tumor

20–40, female

Epiphysis (knee)

Soap bubble

Enchondroma

Any

Hands, feet

Lucent with ring calcification

Simple cyst

Child

Proximal humerus

Fallen fragment

LCH

Child

Skull

Punched-out lytic

How it's tested

COMMON CONFUSIONOsteoid osteoma (small, cortex, NSAID-responsive) vs osteoblastoma (larger, spine, not NSAID-responsive) — same cells, different size and behavior.

THE TRAPGiant cell tumor is "benign" but locally destructive and recurs after curettage — and rarely metastasizes to lung.

YOUR APPROACHAge + sex → bone and region (epiphysis, metaphysis, diaphysis, small bones) → X-ray pattern → histology clue → syndrome (multiple lesions).

If you see… think…

Teen with painless bony bump near the knee pointing away from the joint → osteochondroma

Multiple exostoses in a family → hereditary multiple exostoses (EXT1/2)

Young man with night pain in the femur relieved by ibuprofen → osteoid osteoma

30-year-old woman, lytic soap-bubble lesion at distal femur epiphysis → giant cell tumor

Multinucleated osteoclast-like cells driven by RANKL → giant cell tumor

Lytic lesion of a finger phalanx with pathologic fracture → enchondroma

Multiple enchondromas + soft-tissue hemangiomas → Maffucci syndrome

Child with humerus fracture through a lucent metaphyseal cyst → unicameral bone cyst

Expansile blood-filled cyst with fluid-fluid levels → aneurysmal bone cyst

Child with lytic skull lesion and Birbeck granules → Langerhans cell histiocytosis