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  1. Nomenclature:
    1. Osteoid: organic molecules that form non-mineralized matrix
  2. Bone Structure:
    1. Cortex:
      1. Periosteum: (2 layers of cells, inner having osteoproductive potential)
        1. Benign periostitis
          1. Thick, wavyform, uniform
          2. Causes => venous stasis, ischemia, hypertrophic pulmonary osteoarthropathy, thyroid acropachy
      2. Haversian: (central blood vessel in haversian canal) Osteoblasts and osteoclasts change periosteum into haversian bone.
      3. Endosteum: Thin layer of inner portion between haversian system and trabecula restructures haversian system into trabecular system.
    2. Cancellous = trabecular bone
    3. Bone marrow = hematopoietic and stroma (adipocytes from same precursor as osteoblasts)
  3. Bone Lesions:
    1. Agressiveness:
      1. Expansile with sclerosis: slow growing
      2. Non-expansile, no sclerosis: aggressive
      3. Malignancy: wide transition zone, cortical destruction, periosteal reaction
    2. Benign vs. malignant
      1. Cortical destruction or thinning in benign: infection, EG, ABC, fibrous and cartilaginous lesions.
      2. Periostitis
        1. Benign = thick, dense, wavy
        2. Malignant = lamellated (onion-skinned), amorphous, sunburst.
        3. EG, ABC, OO, trauma can look malignant. If looks benign, likely to be benign.
      3. Normal periosteal reaction occurs in infants 2-6 months of age.
      4. Zone of transition: narrow vs. wide. Sclerotic is narrow. Permeative is wide (Round cell = MM, reticulum cell sarcoma (bone lymphoma), Ewing's). Other permeative is infection and EG. Aggressive not necessarily malignant.
      1. Benign by age
        1. <30: Cystic: EG, ABC, NOF, chondroblastoma, solitary bone cyst; Osteosclerotic: osteoid osteoma, osteoblastoma
      2. Malignant by age:
        1. 1-30: Ewing's sarcoma, osteosarcoma
        2. 30-40: GCT, parosteal sarcoma, fibrosarcoma, MFH, reticulum cell sarcoma
        3. >40: Chondrosarcoma, metastatic disease, myeloma
        4. Lytic lesion, old patient (MMOL): multiple myeloma, mets, osteosarcoma, lymphoma
    3. By osseous site:
      1. Epiphyseal
        1. Peds (ICE)
          1. Infection
          2. Chondroblastoma
          3. EG
        2. Adults (GMC-C)
          1. GCT
          2. Metastasis
          3. Cysts (ganglion, subchondral, geodes)
          4. Clear cell chondrosarcoma
      2. Metaphysis
        1. High-grade osteosarcoma
        2. Osteoblastoma
        3. Chondromyxoid fibroma
        4. Osteochondroma
        5. Metaphyseal enlargement (Ehrlenmeyer flask deformity)
      3. Metadiaphysis
        1. Peds
          1. Benign cortical defect/NOF
      4. Diaphysis malignant round cell (40% of Ewing's), fibrous dysplasia, NOF, simple cyst, ABC, 75% of osteoblastomas
        1. Metastases
        2. Ewings sarcoma
        3. Chondrosarcoma
    4. By Bone:
      1. Tibia: Adamantinoma, juvenile adamantinoma (ossifying fibroma), 28% of chondromyxoid fibroma, osteofibrous dysplasia.
      2. Femur and tibia: osteoid osteoma
      3. Posterior femur: parosteal osteosarcoma, cortical desmoid (avulsion injury)
      4. Post vertebral elements: osteoblastoma
      5. Calvarium, vertebra, jaws: hemangioma
      6. Mandible and maxilla: ameloblastoma
      7. Sacrum:
        1. GCT
        2. ABC
        3. Osteoblastoma
        4. Hemangioma
        5. Osteochondroma
        6. Chordoma
        7. MM
        8. Lymphoma
        9. Ewing (PNET)
        10. Chondrosarcoma
        11. Osteosarcoma
        12. Angiosarcoma
    5. Lytic:
      1. Benign (FENGOMASCHIC):
        1. <30: EG, ABC, NOF, chondroblastoma, solitary bone cyst
        2. Epiphyseal: Chondroblastoma, GCT, infection, Geode, (EG, ABC)
        3. No periostitis
          1. Fibrous dysplasia
          2. Enchondroma
          3. NOF
          4. Solitary bone cyst
            1. No calcifications on plain films (lipoma calcifies)
        4. Multiple: Fibrous dysplasia, EG, enchondroma, high PTH, infection, (mets, myeloma)
        5. Rib lesions: fibrous dysplasia, ABC, enchondroma, EG, (mets, myeloma)
      2. Malignant: Mets, Myeloma
    6. Matrix:
      1. Osteoid matrix.
        1. Benign (OBOOO)
          1. Osteoma
            1. Usually found in calvaria and paranasal sinuses
          2. Bone island (enostosis)
            1. Osteopoikilosis - multiple bone islands clustered around joints.
          3. Osteoid Osteoma
            1. Cortex of tubular bones is most common location
            2. Nidus is composed of highly vascular fibrous tissue, osteoid and immature bone
            3. Sclerotic reaction
              1. Maybe away from the lesion if nidus is intraarticular, similar to remote periosteal reaction in chondroblastoma (no periosteum in the joints)
          4. Osteoblastoma
            1. Similar to osteoid osteoma, but nidus measures > 2cm
            2. May rarely undergo malignant transformation
          5. Ossifying fibroma
            1. Found in anterior proximal tibia
            2. Diff Dx
              1. Adamantimoma
              2. Cortical fibrous dysplasia
        2. Malignant
          1. Osteosarcomas
            1. Conventional (central)
            2. Telangiectatic
              1. Fluid-fluid levels
            3. Parosteal (surface)
              1. Found in posterior distal femoral metaphysis, proximal tibia or proximal humerus
              2. Cleavage plane between tumor and adjacent bone is usually seen
            4. Periosteal (surface)
              1. Usually diaphyseal in location
              2. Causes scalloping
            5. Soft tissue osteosarcoma
      2. Cartilaginous
        1. Enchondroma (arcs and rings calcifications)
          1. Ollier's disease
          2. Mafucci's syndrome
        2. Osteochondroma (exostosis)
          1. Multiple hereditary osteochondromas
          2. Dysplasia epiphysealis hemimelica (Trevor disease)
            1. Intra-articular epiphyseal osteochondromas
        3. Juxtacortical chondroma
          1. DiffDx: periosteal osteosarcoma
        4. Chonroblastoma
          1. Found exclusively in the epiphysis with open physis
          2. In older patients, clear cell chondrosarcoma should be considered
        5. Chonromyxoid fibroma
        6. Chondrosarcoma
      3. Fibrous
        1. Fibrous dysplasia
          1. Long ground glass lesion in a long bone
          2. McCune-Albright syndrome
            1. Coast of Maine
            2. Hormonal disorder
        2. Fibrous cortical defect/NOF
          1. Bubbly lytic cortical lesion with sclerotic margin
        3. Malignant fibrous histiocytoma
          1. Can involve soft tissue or bone
      4. Marrow and mets
        1. Ewing's sarcoma
          1. Most are lytic (permeative)
          2. May have some reactive bony sclerosis (onion-skin periostitis, but can be sunburst or amorphous)
          3. Soft tissue component is not calcified
        2. Primary Lymphoma
        3. Multiple myeloma
        4. Mets
          1. Lytic: Lung, kidney, breast, thyroid, GI, neuroblastoma
          2. Blastic: Prostate, breast, bladder, GI, lung, medulloblastoma
      5. Vascular
        1. Benign: Hemangioma, lymphangioma, glomus tumor
        2. Malignant: Angiosarcoma
      6. Miscellaneous
        1. Peripheral nerve sheath tumors
        2. Morton's neuroma
        3. Giant cell tumor of tendon sheath
        4. Synovial cell sarcoma
        5. Giant cell tumor (osteoclastoma)
          1. Occur after epiphyseal closure
          2. Originates in metaphyses and extends into epiphyses
        6. Solitary bone cyst
          1. Fallen fragment sign
        7. ABC
        8. LCH
          1. Vertebra plana
        9. Brown tumor of hyperparathyroidism
          1. Local accumulations of osteoclasts
        10. Myositis ossificans
          1. Matures in the periphery first (paraosteal osteosarcoma shows denser calcification in the center)
        11. Chordoma
        12. Adamantinoma
        13. Ganglion cyst
          1. Loculated collections of viscous fluid
    7. Diffuse osteosclerosis
      1. Short list (3MSPROF)
        1. Myelofibrosis
        2. Mastocytosis
        3. Metastasis
        4. Sickle Cell Disease
        5. Pyknodysostosis
        6. Renal osteodystrophy
        7. Osteopetrosis
        8. Fluorosis
      2. Long List
        1. Metastases
        2. Myelofibrosis
        3. Mastocytosis
        4. Melorheostosis
          1. Thickened cortical bone
          2. Wax on a candle appearance
        5. Pyknodysostosis
        6. Paget
        7. Phosphorus poisoning
        8. Renal osteodystrophy
        9. Sickle cell disease
        10. Tuberous sclerosis
        11. Osteopetrosis
        12. Fluorosis
        13. Hypervitaminosis D
        14. Hypothyroidism
  4. Metabolic
    1. Fluorosis
      1. Flowing ossification of ALL
    2. Hyper Vit A
      1. Flowing ossification of ALL
      2. Hydrocephalus
      3. Periosteal new bone formation
    3. Hyper Vit D
      1. Soft tissue calcifications
      2. Cortical and trabecular thickening
      3. Periosteal new bone formation
    4. Scurvy ( low Vit C)
      1. Diffuse dimeralization, insufficiency fractures
      2. Subperiosteal hemorrhage and periosteal ossification in children
      3. Sclerotic epiphyseal rim "Wimbergers ring"
      4. Dense metaphyseal line "Frenkels sign"
      5. Metaphyseal corner fracture "Pelkins fracture"
    5. Heavy metal poisoning
      1. Increased bone density and undertubulation at metaphysis
    6. Hypothyroidism
      1. Adults - mild osteoporosis
      2. Peds - delayed skeletal age, wormian bones, bullet-shaped vertebra, epiphyseal fragmentation
    7. Thyroid acropachy
      1. Seen after treatment for thyrotoxicosis
    8. Hypoparathyroidism
      1. Osteosclerosis
      2. Suncutaneous depostion of calcium phosphate salts
    9. Pseudo- and Pseudo-Pseudohypoparathyroidism
      1. Short stature
      2. Short metacarpals/metatarsals
  5. Marrow
    1. Red to yellow marrow conversion
      1. Epiphyses and apophyses
      2. Terminal phalanges
      3. Long bones
        1. Diaphyses
        2. Metaphyses
      4. Flat bones
  6. Infection
    1. Involucrum - new bone formed around sequestrum (necrotic bone)
    2. Hematogenous spread
      1. Infants
        1. Metaphyses, epiphyses and joint
      2. Children (blood vessels do not cross physis)
        1. Metaphyses
      3. Adults (metaphyseal and epiphyseal vessels anastomose)
        1. Joint may be involved
    3. Syphillis
      1. Saber shin deformity - anterior bowing of tibia
      2. Neuropathic arthropathy in the knees
      3. Periosteal reaction in infants
      4. Wimberger sign => bilateral symmetric involvement of the proximal medial tibial metaphysis
    4. Brodie abscess
      1. Subacute or chronic osteomyelitis in a child
  7. Skull
    1. "Hair on end"
      1. Thalassemia
  8. Spine
    1. C-spine
      1. Wide predental space
        1. RA
        2. Down's syndrome
        3. Trauma
    2. Schmorls node
      1. Sclerotic margin (metastases are usually lytic or mixed)
    3. Ivory vertebrae
      1. Metastatic disease
      2. Paget disease
    4. H-shaped vertebrae (H-SG)
      1. Sickle cell disease
      2. Gaucher disease
    5. Fish mouth vertebra (Homo-HOG)
      1. Homocysteinuria
      2. (Sickle cell disease)
      3. Hyperparathyroidism
      4. Osteopenia
      5. Gaucher disease
    6. Vertebrae plana (MEMO)
      1. Mets/Multiple myeloma (adult)
      2. EG (< 30 years old)
      3. Platyspondyly => universal vertebral plana (Morquio)
      4. Osteopenia (adult)
    7. Picture-frame vertebra
      1. Paget disease
    8. Rugger-Jersey spine
      1. Hyperparathyroidism
    9. Bone within bone
      1. Osteopetrosis
    10. Increased AP diameter of vertebral body
      1. Acromegaly
    11. Posterior elements
      1. Osteoblastoma
      2. Osteoid osteoma
      3. Aneurysmal bone cyst
    12. Vertebral body
      1. Giant cell tumor
      2. EG
    13. Dagger sign
      1. Calcification of interspinous ligament in ankylosing spondylitis
    14. Shiny corner sign
      1. Ankylosing spondylitis
    15. Syndesmophytes:
      1. Ossification of Sharpey's fibers of the annulus fibrosus
      2. Marginal and symmetrical: ankylosing spondylitis, IBD
      3. Non-marginal and asymmetrical: Psoriatic Arthritis, Reiter's syndrome
    16. Marginal osteophyte
      1. Extension of vertebral endplate
      2. DJD
    17. Non-marginal osteophyte
      1. Horizontal extension of vetebral body 2-3 mm away from the end-plate
      2. DJD
      3. If large => PsA and Reiter
    18. Paraspinal osteophyte
      1. Ossification of longitudinal ligaments
      2. DISH
    19. Morquio (MPS IV)
      1. Hypoplasia or abscence of odontoid process
      2. Platyspondyly (DDx => Hurler demonstrates normal height of vertebra)
      3. Central vertebral body beaking
      4. Lumbar gibbus (kyphosis)
    20. Hurler
      1. Frontal bossing
      2. Lumbar gibbus
      3. Proximally long slender ribs, which are widened distally
      4. Widely flared iliac wings
      5. Anterior beak
  9. SI Joints
    1. Superior syndesmosis - enthesitis with resultant ossification of syndesmosis
      1. DISH, reactive arthritis, PsA, fluorosis, vit D toxicity and AS
    2. Inferior synovial joint
      1. Early erosive changes
        1. AS - symmetric
        2. PsA - asymmetric
  10. Ribs
    1. Congenital
      1. Fused ribs
      2. Bifid ribs
      3. Intrathoracic ribs
      4. Osteogenesis imperfecta
        1. Ribbon ribs
    2. Rib notching
      1. Coarctation of the aorta distal to origin of left subclavian
        1. Blood travels through subclavian, internal mammary, then intercostals and into descending aorta
        2. First two ribs are uninvolved (arise from costocervical trunk)
      2. Aortic thrombosis
      3. Takayasu's aortitis
      4. Congenital heart diseases associated with decreased pulmonary flow
        1. Intercostal arterires enlarge to supply collateral blood flow to oligemic lungs
      5. SVC obstruction
        1. Results in increased flow through intercostal veins
      6. Neurofibromas in NF type I
        1. Ribbon ribs
      7. Superior rib notching
        1. Pathogenesis: disturbance of osteoblastic and osteoclastic activity and stress from intercostal muscles
        2. Paralysis
        3. RA
        4. SLE
        5. Marked tortuosity of the intercostal arteries from severe aortic obstruction
    3. Infection
    4. Lesions
      1. Benign
        1. Monostotic fibrous dysplasia
          1. Expansile lesion with sclerotic margins in the posterior aspect of the rib
        2. Polyostotic fibrous dysplasia
        3. EG (less than 30 years of age)
          1. Expansile but do not have sclerotic margins
        4. Osteochondroma
        5. Enchondroma
        6. Osteoblastoma
      2. Malignant
        1. Chondrosarcoma
        2. Osteogenic sarcoma
        3. Fibrosarcoma
        4. Multiple myeloma
        5. Metastases
          1. Bronchogenic carcinoma
          2. Breast carcinoma
            1. Sclerotic
          3. Renal cell and thyroid carcinoma
            1. Expansile lytic metastases
          4. Prostate
            1. Sclerotic
    5. Costal cartilage ossification
      1. Female => central portion of the cartilage in the shape of finger
      2. Male => peripheral, has appearnce of two fingers
    6. Berquist triad
      1. Spine/pelvis fx
      2. Rib fx
      3. Diaphragmatic rupture
  11. Radius
    1. Radial dysplasias
  12. Wrist
    1. Kienbock's => avascular necrosis of the lunate
      1. Associated with negative lunate variance
    2. SLAC wrist
      1. Etiology
        1. Scapholunate dissociation
        2. Scaphoid non-union
        3. AVN of scaphoid (Preiser disease)
        4. Intraarticular fractures
        5. Kienbuck disease
        6. Degenerative and inflammatory arthritis (gout, CPPD)
  13. Hand
    1. Benign tumors
      1. Ganglion cyst
      2. Giant cell tumor of the tendon sheath (similar to PVNS)
        1. Bone erosion from pressure effect
        2. A portion of the tumor is dark on T1WI and T2WI (hemosiderin)
  14. Hip
    1. CHD
      1. Fibrofatty pulvinar
      2. Inverted limbus (labrum)
      3. Psoas tendon
    2. Otto pelvis
      1. Primary protrusio of the acetabulum
    3. Migration of  femoral head
      1. Superolateral migration
        1. OA
      2. Medial migration
        1. Fracture of the acetabulum
      3. Axial (superomedial) migration
        1. RA
        2. AS
        3. CPPD
    4. Normal joint space during early stages of disease (A-OPT)
      1. AVN
        1. When secondary osteoathritis develops, radiographic changes are more severe in the femoral head, compared to primary osterarthritis, where acetabulum and femoral head are equally involved.
        2. DiffDx
          1. Steriod use
          2. Trauma
          3. Caisson's disease
      2. Osteochondromatosis
        1. May see scalloping defects along the femoral neck
      3. PVNS
        1. May see scalloping defects along the femoral neck
      4. TB
  15. Soft tissues
    1. Calcifications
      1. Infectious
        1. Cistercircosis
        2. Filiariasis
    2. Necrotizing fascitis
      1. Nodular fascial enhancement