◊  Actinomycotic infections are polymicrobial!

Pathogenesis:   trauma / surgery / foreign body → disruption of mucosal barrier → bacterial entry into deep tissues → fibrotic lesion spreading beyond fascial planes → abscess formation centrally → draining sinus tracts extending from abscess to skin / adjacent organs

Spread:

(a)  contiguous: production of proteolytic enzymes allow crossing of normal anatomic barriers

(b)  hematogenous

No lymphatic spread ← size of organism!

At risk:   very poor dental hygiene, immunosuppressed patient, prolonged use of IUD, bisphosphonate therapy

Location:   mandibulofacial > intestinal > lung

Clinical types:

(1)  Mandibulo- / cervicofacial actinomycosis (50–65%)

Origin:   odontogenic

At risk:   poor dental hygiene, recent dental extraction, dental caries, oromaxillofacial trauma, chronic tonsillitis, otitis, mastoiditis, osteonecrosis from irradiation / bisphosphonate therapy

•  draining cutaneous sinuses

•  “sulfur granules” in sputum / exudate = colonies of organisms arranged in circular fashion = mycelial clumps with thin hyphae 1–2 mm in diameter

√  destruction of mandible (most frequent bone involved) around tooth socket = osteomyelitis of mandible

Site:  angle of jaw, submandibular region, cheek, submental space, masticator space, temporomandibular joint

√  no new-bone formation

√  spread into soft tissues at angle of jaw + into neck ignoring normal fascial planes

√  no / few reactive regional lymph nodes

–  acute form:

√  soft-tissue swelling / painful pyogenic abscess / mass

–  subacute to chronic form:

√  painless indurated mass ± spread to skin often accompanied by draining sinus tracts

(2)  Pleuropulmonary / thoracic actinomycosis (15–30%)

Predisposed:   alcoholics

Histo:   masses of PMN leukocytes containing round actinomycotic / sulfur granules surrounded by a rim of granulation tissue

@   Lung

•  draining chest wall sinuses ← spread through fascial planes

Predisposed:   areas of parenchymal destruction and bronchiectasis ← prior TB / other organisms (= tendency of actinomyces for invasion of devitalized tissue)

√  enhancing extensive transfissural chronic segmental airspace consolidation:

√  hypoattenuating areas + peripheral enhancement (= lung necrosis)

√  often adjacent pleural thickening

Site:   usually unilateral + lower lobe predominance

√  multiple small cavitary lesions with ringlike enhancement (= abscesses)

√  fibrotic pleuritis

√  chronic pleural effusion / empyema (in > 50%)

√  rarely acute airspace pneumonia ← postobstructive endobronchial actinomycosis

DDx:   carcinoma, TB, bacterial / fungal pneumonia

@   Vertebra + ribs

√  destruction of vertebra with preservation of disk + small paravertebral abscess without calcification (DDx to tuberculosis: disk destroyed, large abscess with calcium)

√  thickening of cervical vertebrae around margins

√  destruction / thickening of ribs

(3)  Abdominopelvic / ileocecal / abdominal actinomycosis (20%)

Cause:   appendicitis, colonic diverticulitis; penetrating trauma, gut surgery; prolonged IUD use > 2 years (25% of IUDs become eventually colonized with serious infections in 2–4%)

Location:   initially localized to cecum / appendix

•  fever, leukocytosis, mild anemia

•  weight loss, nausea, vomiting, lower abdominal pain

•  chronic sinus in groin, vaginal discharge

•  yellow / brown sulfur granules on cervical Papanicolaou smear

√  concentric bowel wall thickening:

√  adjacent cystic / solid mass

√  surrounding invasive soft-tissue strands

√  strong enhancement of solid portions ← extensive dense fibrosis = hallmark of actinomycosis

√  fold thickening + ulcerations (resembling Crohn disease)

√  rupture of abdominal viscus (usually appendix)

√  fistula formation

√  rarely regional lymphadenopathy

√  usually no / minimal ascites

@   Tubular bones of hands

√  destructive lesion of mottled permeating type

√  cartilage destruction + subarticular erosive defects in joints (simulating TB)

@   CNS (2–3%), skin, pericardium

Dx:   anaerobic culture; species-specific antibodies

Rx:   high doses of penicillin G + surgical débridement

DDx:   malignancy, chronic granulomatous disease (TB, fungal infection)

ADAMANTINOMA

=  (MALIGNANT) ANGIOBLASTOMA

=  rare locally aggressive / low-grade malignancy of bone

Risk factors for malignant course:

male sex, young age at presentation, short duration of symptoms, pain at initial presentation, local recurrence

Histo:   zonal architecture of neoplastic epithelial cells (reactive to cytokeratins) concentrated centrally in osteofibrous stroma that forms peripherally columnar cells in a palisade pattern; prominent vascularity; resembles ameloblastoma of the jaw

Age:   25–50 (range, 3–74) years, commonest in 2 ^nd –3 ^rd decade

Prevalence:   < 0.5% of malignant bone tumors

•  frequently history of trauma; local swelling ± pain

Location:   middle ⅓ of tibia (90%), fibula, ulna, carpals, metacarpals, humerus, shaft of femur

Size:   average length of 10 cm

√  eccentric round osteolytic lesion with sclerotic margin

√  multiple additional foci (= multicentricity) in continuity with major lesion (CHARACTERISTIC) in 27%

√  longitudinally oriented along anterior tibial diaphysis

√  narrow zone of transition, may show mottled density

√  slight bone expansion (frequent)

√  cortical breakthrough in 15%

√  synchronous fibular involvement in 5–10%

MR:

√  intermediate signal intensity relative to muscle on T1WI

√  intensity similar to fat on T2WI

√  marked homogeneous enhancement

Prognosis:   tendency to recur after local excision (19%); after several recurrences pulmonary metastases may develop; 13% mortality rate

DDx:   fibrous dysplasia (in child < 10 years of age, painless enlargement of tibia, anterior bowing, pathologic fracture, eccentric bubbly cortical lucency and expansion with spontaneous regression)

AINHUM DISEASE

=  DACTYLOLYSIS SPONTANEA

[ainhum, Brazilian tribal language = fissure, saw, sword]

Etiology:   unknown

Histo:   hyperkeratotic epidermis with fibrotic thickening of collagen bundles below; chronic lymphocytic inflammatory reaction may be present; arterial walls may be thickened with narrowed vessel lumina

Frequency:   up to 2%

Age:   usually in males in 4^th + 5^th decades; Blacks (West Africa) + their American descendants; M > F

•  deep soft-tissue groove forming on medial aspect of plantar surface of proximal phalanx with edema distally

•  painful ulceration may develop

Location:   mostly 5^th / 4^th toe (rarely finger); near interphalangeal joint; mostly bilateral

√  sharply demarcated progressive bone resorption of distal / middle phalanx with tapering of proximal phalanx to complete autoamputation (after an average of 5 years)

√  osteoporosis

Rx:   early surgical resection of groove with Z-plasty

AMYLOIDOSIS

=  extracellular deposition of a chemically diverse group of protein polysaccharides in body tissues (abnormal folding + assembly of β2-microglobulin); tends to form around capillaries + endothelial cells of larger blood vessels causing ultimately vascular obliteration with infarction

β₂-microglobulin = low-molecular-weight serum protein not filtered by standard dialysis membranes

Incidence:   6–10÷100,000 annually in USA + western Europe

Path:   stains with Congo red

At risk:   patients on long-term hemodialysis

•  bone pain (eg, shoulder pain)

•  periarticular rubbery soft-tissue swelling + stiffness (shoulders, hips, fingers):

•  carpal-tunnel syndrome (commonly bilateral)

•  Bence-Jones protein (without myeloma)

Amyloid Arthropathy

=  synovial-articular pattern of amyloidosis

Associated with:  chronic hemodialysis, plasma cell dyscrasia, rheumatoid arthritis, familial Mediterranean fever, chronic osteomyelitis

Location:  cervical spine, hip, shoulder, elbow, knee, wrist; bilateral

√  juxtaarticular soft-tissue masses (amyloid deposited in synovium, joint capsule, tendons, ligaments) ± extrinsic osseous erosion

√  mild periarticular osteopenia

√  subchondral cysts + well-defined sclerotic margin

√  joint effusion

√  joint space preserved until late in course of disease

√  subluxation of proximal humerus + femoral neck

MR:

√  extensive deposition of abnormal soft tissue of low to intermediate SI on T1WI + T2WI covering synovial membrane, filling subchondral defects, extending into periarticular tissue

√  low SI on T1WI + T2WI subjacent to vertebral endplates in lower cervical > thoracic / lumbar spine

√  joint effusion

DDx:  inflammatory arthritis, PVNS

Diffuse Amyloid Marrow Deposition

√  generalized osteoporosis

√  coarse trabecular pattern (DDx: sarcoidosis)

√  pathologic collapse of vertebral body may occur

Amyloidoma

=  localized destructive lesion of amyloidosis (rarest form)

Location:  appendicular > axial skeleton

√  focal medullary lytic lesion with endosteal scalloping (± secondary invasion + erosion of articular bone)

Cx:     pathologic fracture

ANEURYSMAL BONE CYST

=  expansile pathologically benign lytic lesion of bone containing thin-walled cystic cavities filled with chronic blood products; name derived from roentgen appearance

Incidence:   1.4–2.3% of primary bone tumors

Etiology:

(a)  primary ABC (65–99%):

›  local circulatory disturbance ← trauma

›  improper repair of traumatic subperiosteal hemorrhage

(b)  secondary ABC (29–35%) hemorrhage into a preexisting bone lesion → venous obstruction / arteriovenous fistula:

›  common: giant cell tumor (19–39%), osteoblastoma, angioma, chondroblastoma

›  uncommon: fibrous dysplasia, fibrous histiocytoma, chondromyxoid fibroma, xanthoma (= nonossifying fibroma), eosinophilic granuloma, telangiectatic osteosarcoma, metastatic carcinoma, solitary bone cyst

Histo:   lack of anaplasia

(a)  “intraosseous arteriovenous malformation” with cystic honeycombed spaces filled with blood separated by spindle cell stroma + osteoclast-like giant cells and osteoid / bone production; mineralized chondroidlike material in ¹/ ³; areas of free hemorrhage

(b)  solid variant of ABC in 5–7%: proliferation of spindle cells

Types:

1.   INTRAOSSEOUS ABC

=  primary cystic / telangiectatic tumor of giant cell family, originating in bone marrow cavity, slow expansion of cortex; rarely related to history of trauma

2.   EXTRAOSSEOUS ABC

=  posttraumatic hemorrhagic cyst; originating on surface of bones, erosion through cortex into marrow

Peak age:   peak age 16 (range, 10–30) years; in 75% < 20 years; F > M

•  pain of relatively acute onset with rapid increase of severity over 6–12 weeks; ± history of trauma

•  neurologic signs (radiculopathy to quadriplegia) if in spine

Location:

@   spine (3–20%): thoracic (34%), lumbar (31%), cervical spine (22%), sacrum (13%); involvement of posterior elements with extension into vertebral body (75%); may involve two contiguous vertebrae (25%) / intervertebral disk / ribs / paravertebral soft tissues

@   long bones: eccentric in metaphysis of femur, tibia, humerus, fibula

@   pelvis

√  purely lytic eccentric radiolucency

√  aggressive expansile ballooning lesion of “soap-bubble” pattern + thin internal septations + trabeculations

√  rapid progression within 6 weeks to 3 months

√  sclerotic inner portion

√  almost invisible thin cortex (CT shows integrity)

√  tumor respects epiphyseal plate

√  no periosteal reaction (except when fractured)

CT:

√  “blood-filled sponge” = fluid-fluid / hematocrit levels ← blood sedimentation (in 10–35%)

√  ± mineralized chondroidlike material when abundant

MR:

√  multiple cysts of different SI representing different stages of blood by-products:

√  heterogeneous fluid-fluid levels within loculations ← hemorrhage with sedimentation

√  ↑ signal intensity on T1WI ← methemoglobin

√  low-SI rim ← intact thickened periosteal membrane

√  heterogeneous enhancement:

√  smooth enhancement of internal septa

NUC:

√  “doughnut” sign = moderate to intense radiotracer accumulation at lesion periphery (64%)

Angio:

√  hypervascularity in lesion periphery (in 75%)

Prognosis:   20–30% recurrence rate

Rx:       preoperative embolotherapy; complete resection; radiation therapy (subsequent sarcoma possible)

ANGIOMATOSIS

=  diffuse infiltration of bone / soft tissue by hemangiomatous / lymphangiomatous lesions

Age:   first 3 decades of life

May be associated with:

chylothorax, chyloperitoneum, lymphedema, hepatosplenomegaly, cystic hygroma

A.  OSSEOUS ANGIOMATOSIS (30–40%)

•  indolent course

Location:   femur > ribs > spine > pelvis > humerus > scapula > other long bones > clavicle

√  osteolysis with honeycomb / latticework (“hole-within-hole”) appearance

√  may occur on both sides of joint

DDx:   solitary osseous hemangioma

B.  CYSTIC ANGIOMATOSIS

=  extensive involvement of bone

Histo:   endothelium-lined cysts in bone

Peak age:   10–15 years (range, 3 months to 55 years)

Location:   long bones, skull, flat bones

√  size of 1–2 mm to several cm

√  multiple osteolytic metaphyseal lesions with fine sclerotic margins + relative sparing of medullary cavity

√  may show overgrowth of long bone

√  endosteal thickening

√  sometimes associated with soft-tissue mass ± phleboliths

√  chylous pleural effusion suggests fatal prognosis

DDx:   (other polyostotic diseases like) histiocytosis X, fibrous dysplasia, metastases, Gaucher disease, congenital fibromatosis, Maffucci syndrome, neurofibromatosis, enchondromatosis

C.  SOFT-TISSUE ANGIOMATOSIS (60–70%)

=  VISCERAL ANGIOMATOSIS

•  poor prognosis

D.  ANGIOMATOUS SYNDROMES
Maffucci, Osler-Weber-Rendu, Klippel-Trénaunay-Weber, Kasabach-Merritt, Gorham

ANGIOSARCOMA

=  aggressive vascular malignancy, frequently with local recurrence + distant metastases; M÷F = 2÷1

Origin:   endothelial + mesenchymal cells

Histo:   vascular channels surrounded by hemangiomatous / lymphomatous cellular elements with high degree of anaplasia

Associated with:   Stewart-Treves syndrome = angiosarcoma with chronic lymphedema developing in postmastectomy patients

Location:   skin (33%); soft tissue (24%); bone (6%): tibia (23%), femur (18%), humerus (13%), pelvis (7%)

◊  Most commonly in right atrium > retroperitoneum (IVC)

√  heterogeneously enhancing mass expanding involved vessel

DDx:   hemangioendothelioma, hemangiopericytoma

Soft-Tissue Angiosarcoma

Risk factors:   chronic lymphedema, previous radiation therapy, foreign bodies, immunosuppression

Associated with:   NF1, Klippel-Trénaunay-Weber syndrome, Maffucci syndrome

Age:     any age; peak incidence in 7^th decade

MR:

√  intermediate signal intensity on T1WI

√  areas of high SI on T1WI ← hemorrhage

√  high SI on T2WI (← tumor necrosis + methemoglobin)

√  aggressive infiltration of adjacent tissue

√  intratumoral low SI on all pulse sequences ← high flow

√  intratumoral high SI on T2WI ← low flow

√  contrast enhancement ± central areas of necrosis

ANTERIOR TIBIAL BOWING

=  WEISMANN-NETTER SYNDROME

[Robert-Julius Weismann-Netter (1894–1980)]

=  congenital painless nonprogressive bilateral anterior leg bowing

Age:   beginning in early childhood

•  may be accompanied by mental retardation, goiter, anemia

√  anterior bowing of tibia + fibula, bilaterally, symmetrically at middiaphysis

√  thickening of posterior tibial + fibular cortices

√  minor radioulnar bowing

√  kyphoscoliosis

√  extensive dural calcification

DDx:   Luetic saber shin (bowing at lower end of tibia + anterior cortical thickening)

APERT SYNDROME

=  ACROCEPHALOSYNDACTYLY TYPE I

[Eugène Charles Apert (1868–1940), médecin des hôpitaux Hôtel-Dieu and at the Hôpital des Enfants-Malades]

Frequency:   5.5÷1,000,000 neonates

Etiology:   autosomal dominant with incomplete penetrance; sporadic (in majority)

Associated with CNS anomalies:

megalocephaly, gyral abnormalities, hypoplastic white matter, heterotopic gray matter, frontal encephalocele, corpus callosal agenesis, Kleeblattschädel, cleft palate, ventriculomegaly (? related to skull base hypoplasia, rarely progressive)

•  IQ varies depending on CNS anomalies (in 50% normal)

•  otitis media (high prevalence)

•  bifid uvula

•  conductive hearing loss (common ← external + middle ear malformations)

@   Skull

•  downturned mouth

√  brachycephalic skull (← coronal craniosynostosis) + flat occiput

√  widened metopic + sagittal sutures extending from glabella to posterior fontanel (closing between 2–4 years)

√  hypoplastic / retruded midface:

√  hypertelorism

√  shallow orbits with proptosis

√  underdeveloped paranasal sinuses

√  underdeveloped maxilla with prognathism

√  high pointed arch of palate

√  prominent vertical crest in middle of forehead (← increased intracranial pressure)

√  V-shaped anterior fossa ← elevation of lateral margins of lesser sphenoid

√  ± enlargement of sella

√  stylohyoid ligament calcification (38–88%)

√  cervical spine fusion (in up to 71%), commonly of 5^th and 6^th vertebrae

√  choanal stenosis

@   Hand & feet

√  severe symmetric syndactyly = fusion of distal portions of phalanges, metacarpals / carpals (most often of 2^nd, 3^rd + 4^th digit)

√  absence of middle phalanges

√  missing / supernumerary carpal / tarsal bones

√  pseudarthroses

@   GU (10%)

•  cryptorchidism

√  hydronephrosis

√  polycystic kidneys (rare)

√  bicornuate uterus (rare)

ARTERIOVENOUS FISTULA OF BONE

Location:   lower extremity most frequent

√  soft-tissue mass

√  presence of large vessels

√  phleboliths (DDx: long-standing varicosity)

√  accelerated bone growth

√  cortical osteolytic defect (= large-vessel pathway into medulla)

√  increased bone density

ARTHROGRYPOSIS

=  ARTHROGRYPOSIS MULTIPLEX CONGENITA

=  nonprogressive congenital syndromic complex characterized by poorly developed + contracted muscles, deformed joints with thickened periarticular capsule and intact sensory system

Pathophysiology:

congenital / acquired defect of motor unit (anterior horn cells, nerve roots, peripheral nerves, motor end plates, muscle) early in fetal life with immobilization of joints at various stages in their development

Cause:   ? neurotropic agents, toxic chemicals, hard drugs, hyperthermia, neuromuscular blocking agents, mytotic abnormalities, mechanical immobilization

Frequency:   0.03% of newborn infants; 5% risk of recurrence in sibling

Path:   diminution in size of muscle fibers + fat deposits in fibrous tissue

Associated with:

(1)  neurogenic disorders (90%)

(2)  myopathic disorders

(3)  skeletal dysplasias

(4)  intrauterine limitation of movement (myomata, amniotic band, twin, oligohydramnios)

(5)  connective tissue disorders

Distribution:   all extremities (46%), lower extremities only (43%), upper extremities only (11%); peripheral joints >> proximal joints; symmetrical

•  clubfoot; claw hand; congenital dislocation of hip

•  diminished muscle mass; skin webs

√  flexion + extension contractures

√  osteopenia ± pathologic fractures

√  congenital dislocation of hip

√  carpal coalition

√  vertical talus

√  calcaneal valgus deformity

ASPHYXIATING THORACIC DYSPLASIA

=  JEUNE DISEASE

=  autosomal recessive dysplasia characterized by short narrow thorax and short limbs

Prevalence:   1÷100,000 to 1÷130,000 live births

Associated with:   renal anomalies (hydroureter), PDA

•  respiratory distress ← reduced thoracic mobility (abdominal breathing) + frequent pulmonary infections

•  progressive renal failure + hypertension

@   Chest

√  markedly narrow + elongated bell-shaped chest:

√  chest diameter significantly decreased compared with that of the abdomen

√  short horizontal ribs + flared irregular bulbous costochondral junction

√  normal size of heart leaving little room for lungs

√  “handle-bar clavicles” = horizontal clavicles at level of C6

@   Pelvis

√  trident morphology of acetabular roof ← retardation of ossification of triradiate cartilage

√  small iliac wings flared + shortened in cephalocaudal diameter (“wineglass” pelvis)

√  narrow sacrosciatic notches

√  short ischial + pubic bones

√  reduced acetabular angle + acetabular spurs

√  premature ossification of capital femoral epiphysis

@   Extremities

√  metaphyseal irregularity

@   thigh & arm

√  rhizomelic brachymelia (humerus, femur) = long bones shorter + wider than normal

√  proximal humeral + femoral epiphyses ossified at birth (frequently)

@   hand & foot

√  postaxial hexadactyly (occasionally)

√  shortening of distal phalanges

√  cone-shaped epiphyses

@   Visceral involvement

√  nephronophthisis (= medullary cystic renal disease) = enlarged kidneys with linear streaking on nephrogram → progressive renal failure (in adulthood)

√  pancreatic cysts

√  intrahepatic bile duct dilatation

√  intestinal malrotation

√  situs anomalies

OB-US:

√  proportionate shortening of long bones

√  small thorax with decreased circumference

√  increased cardiothoracic ratio

√  occasionally polydactyly

√  polyhydramnios

Prognosis:   neonatal death in 80% (respiratory failure + infections)

DDx:   Ellis-van Creveld syndrome

AVASCULAR NECROSIS

=  AVN = OSTEONECROSIS = ASEPTIC NECROSIS

=  consequence of reduced / completely interrupted blood supply to bone with death of cellular elements

Terminology (now often used interchangeably):

(1)  Osteonecrosis = ischemic bone death ← sepsis

(2)  Ischemic necrosis / avascular necrosis / aseptic necrosis = necrosis of epiphyseal + subarticular bone

(3)  Bone infarction = necrosis of metaphyseal + diaphyseal bone

Cause:   [common causes are underlined]

◊  NO predisposing factors in 25%!

A.  Trauma / thermal injury → interruption of arteries

√  typically unilateral

@   Femoral head:

1.   Femoral neck fracture (60–75%)

2.   Dislocation of hip joint (25%)

3.   Slipped capital femoral epiphysis (15–40%)

@   Carpal scaphoid:
4–6 months after fracture (in 10–15%), in 30–40% of nonunions of scaphoid fracture

Site:   proximal fragment (most common)

@   humeral head (infrequent)

@   talus (after talar neck fracture)

B.  Nontraumatic

√  bilateral (in 70–80%)

(a)  Occlusion / embolization of artery

1.   Thrombus: thromboembolic disease, sickle-cell disease (SS + SC hemoglobin), polycythemia rubra vera, pheochromocytoma (microscopic thrombotic disease)

2.   Nitrogen bubbles: Caisson disease, astronauts

3.   Fat: pancreatitis (intramedullary fat necrosis from circulating lipase), alcoholism

4.   Thromboembolism, arteriosclerosis

5.   Pregnancy

(b)  Vessel wall disease:

1.   Collagen-vascular disease: SLE, rheumatoid arthritis, polyarteritis nodosa, sarcoidosis

2.   Infectious vasculitis

3.   Arteriosclerosis

(c)  Vascular compression by abnormal deposition of:

1.   Fat: corticosteroid therapy (eg, renal transplant, Cushing disease), diabetes

2.   Blood: hemophilia, trauma (fractures, dislocations)

3.   Inflammatory cells: osteomyelitis, infection, Langerhans cell histiocytosis

4.   Tumor cells: leukemia, lymphoma

5.   Edema: radiation therapy, hypothyroidism, frostbite

6.   Substances: Gaucher disease (vascular compression by lipid-filled histiocytes), gout

(d)  Direct cell toxicity

1.   Drug therapy: immunosuppressives, cytotoxics, biphosphonates

2.   Radiation therapy

(e)  Idiopathic

1.   Spontaneous osteonecrosis of knee

2.   Legg-Calvé-Perthes disease

3.   Freiberg disease (repetitive microtrauma)

4.   Hypopituitarism

mnemonic:   PLASTIC RAGS ^{x 2}

Pancreatitis, Pregnancy

Legg-Perthes disease, Lupus erythematosus

Alcoholism, Atherosclerosis

Steroids, Sickle-cell disease

Trauma, Thermal injury

Idiopathic (Legg-Perthes disease), Infection

Caisson disease, Collagen disease (SLE)

Rheumatoid arthritis, Radiation treatment

Alcoholism, Amyloid

Gaucher disease, Gout

Sickle cell disease, Spontaneous osteonecrosis of knee

mnemonic:   GIVE INFARCTS

Gaucher disease

Idiopathic (Legg-Calvé-Perthes, Köhler, Chandler)

Vasculitis (SLE, polyarteritis nodosa, rheumatoid arthritis)

Environmental (frostbite, thermal injury)

Irradiation

Neoplasia (-associated coagulopathy)

Fat (prolonged corticosteroid use increases marrow)

Alcoholism

Renal failure + dialysis

Caisson disease

Trauma (femoral neck fracture, hip dislocation)

Sickle cell disease

Path:

(a)  Stage of cell death: cellular ischemia / anoxia → death of hematopoietic cells (in 6–12 hours) > adipocytes > bone cells = osteoclasts and osteoblasts + osteocytes (in 12–48 hours)

◊  Chondrocytes are adapted to relatively low oxygen tension and do not become devitalized!

(b)  Stage of ↑ vascularity / reparative phase (osteoclasis): trabecular resorption ← inflammatory fibrovascular infiltration + proliferation ← hyperemia mixed with areas of relatively increased trabecular density ← osteonecrosis

(c)  Stage of substitution / reactive phase (= osteogenesis): mesenchymal cells differentiate to osteoblasts on surface of dead trabeculae synthesizing new bone layer → trabecular thickening + osteoclastic resorption of devitalized bone (= creeping zone of substitution)

@   metadiaphyseal osteonecrosis: rim of sclerosis is frequently of undulating / serpentine morphology

@   epiphyseal osteonecrosis: increased bone resorption at junction of reactive zone and subchondral bone plate + weight-bearing → early fracture of overlying cartilage

Age:   4^th–6^th decades of life; M÷F = 4–8÷1

•  asymptomatic (majority of patients)

•  reduced range of motion; pain ← increase in intramedullary pressure ← medullary bone marrow edema

Location:   femoral head (most common), humeral head, femoral condyles, proximal tibia, distal femoral metadiaphysis, distal tibial metadiaphysis, scaphoid, lunate, talus

Radiography (positive only after several months of symptoms):

√  preservation of joint space (DDx: arthritis)

√  patchy areas of lucency and sclerosis:

√  dense osteonecrotic bone ← lack of resorption relative to healthy osteopenic bone + new bone laid down over necrotic trabeculae:

√  sclerosis of serpentine / undulating morphology characteristically about lesion rim (more common in metadiaphyseal lesions)

√  early areas of articular collapse (in epiphyseal osteonecrosis) typically at junction of serpentine sclerotic rim and articular surface

√  radiolucent rim around area of osteonecrosis ← absorption around necrotic bone:

√  “crescent” sign = crescentic subchondral lucency = subchondral structural collapse of necrotic segment parallel to articular surface in weight-bearing portion with separation from overlying cartilage and attached subchondral bone plate (in epiphyseal osteonecrosis)

√  later findings:

√  flattening of articular surface ← articular fragmentation + progressive articular collapse, secondary osteoarthritis

√  increased bone density ← compression of osseous trabeculae ← microfracture of nonviable bone + calcification of dendritic marrow + creeping substitution = deposition of new bone

CT (less sensitive than MRI / NUC):

◊  May be utilized for staging of known disease

√  staging upgrades in 30% compared with plain films

√  serpentine / undulating sclerotic margin (late stage)

√  useful for detecting location of articular collapse + extent in epiphyseal osteonecrosis!

NUC (80–85% sensitivity in early stages):

◊  Bone marrow imaging (with radiocolloid) more sensitive than bone imaging (with diphosphonates)

◊  More sensitive than plain films in early AVN ← evidence of ischemia seen as much as 1 year earlier

◊  Less sensitive than MR except for SPECT

Technique:   imaging improved with double counts, pinhole collimation

√  diffuse increased radionuclide activity in epiphyseal involvement with articular collapse + 2^ndary osteoarthritis

√  very early: cold = photopenic defect on bone scan (blood flow, blood pool, static phase) + bone marrow scan ← interrupted blood supply

√  late: “doughnut” sign = cold spot surrounded by increased radionuclide uptake ← chronic reparative processes:

(a)  capillary revascularization + new-bone synthesis

(b) degenerative osteoarthritis

MR:

Cx:   Malignant transformation to sarcoma (exceedingly rare, exclusive to metaphysis / metadiaphysis): malignant fibrous histiocytoma (69%), osteosarcoma (17%), angiosarcoma (9%)

Cortical Infarction

◊  Requires compromise of
(a) nutrient artery and (b) periosteal vessels!

Age:     particularly in childhood where periosteum is easily elevated by edema

√  avascular necrosis = osteonecrosis

√  osteochondrosis dissecans

Medullary Infarction

◊  Nutrient artery is the sole blood supply for diaphysis!

Location:   distal femur, proximal tibia, iliac wing, rib, humerus

 (a)  Acute phase:

√  NO radiographic changes without cortical involvement

√  area of rarefaction

√  infarcted area T1 hypointense + T2 hyperintense

√  bone marrow scan: diminished uptake in medullary RES for long period of time

√  bone scan: photon-deficient lesion within 24–48 hours; increased uptake after collateral circulation established

 (b)  Healing phase (complete healing / fibrosis / calcification):

√  demarcation by zone of serpiginous / linear calcification + ossification parallel to cortex

√  dense bone indicating revascularization

√  focal lesion with fatty marrow SI centrally + surrounding hypointense rim (= reactive / sclerotic bone)

Avascular Necrosis / Adult Osteonecrosis of Hip

Incidence:  10,000–20,000 new cases annually in USA

◊  Involvement of one hip increases risk to contralateral hip to 70%!

Age:     20–50 years

Zonal anatomy (from articular surface to center of head):

›  zone of cell death

›  reactive interface / creeping zone of substitution

›  zone of reinforcing trabecular bone

›  zone of reactive marrow

›  zone of normal marrow

Classification (Steinberg):

•  hip / groin / thigh / knee pain; limited range of motion

MR (90–100% sensitive, 85% specific for symptomatic disease):

Prevalence of clinically occult disease:  6%

◊  MR imaging changes reflect the death of marrow fat cells (not death of osteocytes with empty lacunae)!

◊  Sagittal images particularly useful!

⇒  EARLY AVN:

√  decreased Gd-enhancement on short-inversion-recovery (STIR) images (very early)

√  bone marrow edema: extensive even when area of infarction is small (early)

√  low-SI band with sharp inner interface + blurred outer margin on T1WI within 12–48 hours (= mesenchymal + fibrous repair tissue, amorphous cellular debris, thickened trabecular bone) seen as

(a)  band extending to subchondral bone plate

(b)  complete ring (less frequent)

√  “double-line” sign on T2WI (in 80%) [MORE SPECIFIC] = juxtaposition of inner hyperintense band (vascularized granulation tissue) + outer hypointense band (chemical shift artifact / fibrosis and sclerosis)

⇒  ADVANCED AVN:

√  “pseudohomogeneous edema pattern” = large inhomogeneous areas of mostly decreased SI on T1WI

√  hypo- to hyperintense lesion on T2WI

√  contrast-enhancement of interface + surrounding marrow + within lesion

⇒  SUBCHONDRAL FRACTURE:

√  predilection for anterosuperior portion of femoral head (SAG images!)

√  cleft of low SI running parallel to the subchondral bone plate within areas of fatlike SI on T1WI

√  hyperintense band (= fracture cleft filled with articular fluid / edema) within the intermediate- or low-signal-intensity of necrotic marrow on T2WI

√  lack of enhancement within + around fracture cleft

⇒  COLLAPSE OF ARTICULAR SURFACE:

√  focal depression of subchondral bone with low SI on T2WI = fibrotic changes in infarcted bone marrow

√  loss of normal spherical contour of bone

√  incongruity of articular surfaces

Predisposition:   increased thickness of reparative zone, increasing volume of joint effusion, presence of prominent surrounding edema, patient age > 40 years, body mass index ≥ 24 kg/m²

Cx:     early osteoarthritis through collapse of femoral head + joint incongruity in 3–5 years if left untreated

Best predictor:   volume of femoral head involved; collapse in 43–87% with > 25–50% + in 0–5% with < 25–30% involvement of femoral head volume

Blount Disease

[Walter Putnam Blount (1900–1992), professor of orthopedics at Marquette Medical School, Milwaukee, Wisconsin]

=  TIBIA VARA

=  avascular necrosis of medial tibial condyle

Age:     > 6 years

•  limping, lateral bowing of leg

√  medial tibial condyle enlarged + deformed (DDx: Turner syndrome)

√  irregularity of metaphysis (medially + posteriorly prolonged with beak)

Calvé-Kümmel-Verneuil Disease

=  VERTEBRAL OSTEOCHONDROSIS = VERTEBRA PLANA

=  avascular necrosis of vertebral body

Age:     2–15 years

√  uniform collapse of vertebral body into flat thin disk

√  increased density of vertebra

√  neural arches NOT affected

√  disks are normal with normal intervertebral disk space

√  intravertebral “vacuum cleft” sign (PATHOGNOMONIC)

DDx:  eosinophilic granuloma, metastatic disease

Freiberg Disease

[Albert Henry Freiberg (1868–1940), orthopedic surgeon in Cincinnati, Ohio]

=  osteochondrosis of head of 2^nd (3^rd / 4^th) metatarsal

Age:     10–18 years; M÷F = 1÷3

•  metatarsalgia, swelling, tenderness

Early:

√  flattening, increased density, cystic lesions of metatarsal head

√  widening of metatarsophalangeal joint

Late:

√  osteochondral fragment

√  sclerosis + flattening of metatarsal head

√  increased cortical thickening

Kienböck Disease

=  LUNATOMALACIA

[Robert Kienböck (1871–1953), radiologist in Vienna, Austria]

=  avascular necrosis of lunate bone

Predisposed:   individuals engaged in manual labor with repeated / single episode of trauma

Age:     20–40 year old males

Associated with:   ulna minus variant (short ulna) in 75%

•  progressive pain + soft-tissue swelling of wrist

Location:   uni- > bilateral (usually right hand)

Classification (Lichtman):

Radiographs:

√  initially normal radiograph

√  osteonecrotic fracture of carpal lunate

√  increased density + altered shape + collapse of lunate

CT:

√  coronal fracture creating a dorsal and volar half

√  multiple lunate fragments

MR:

√  diffusely decreased T1 SI involving entire lunate

√  variable T2 / STIR signal intensity

Cx:     scapholunate dissociation, ulnar deviation of triquetrum, degenerative joint disease in radiocarpal / midcarpal compartments

Rx:     ulnar lengthening / radial shortening, lunate replacement

Köhler Disease

[Alban Köhler (1874–1947), radiologist in Wiesbaden, Germany and co-founder of Deutsche Röntgengesellschaft in Berlin]

=  avascular necrosis of tarsal scaphoid

Age:     3–10 years; boys

√  irregular outline

√  fragmentation

√  disklike compression in AP direction

√  increased density

√  joint space maintained

√  decreased / increased uptake on radionuclide study

Legg-Calvé-Perthes Disease

=  COXA PLANA

[Arthur Thornton Legg (1874–1939), orthopedic surgeon in Boston]

[Jacques Calvé (1875–1954), orthopedic surgeon at Fondation Franco-Americaine de Berck, France]

[Georg Clemens Perthes (1869–1927), head of the surgical clinic in Tübingen, Germany]

=  idiopathic avascular necrosis of femoral head in children; one of the most common sites of AVN; in 10–15% almost always metachronously bilateral

Incidence:  1÷10,000 children; increased with lower socioeconomic status, low birth weight, delayed skeletal maturation

Cause:  trauma in 30% (subcapital fracture, epiphyseolysis, esp. posterior dislocation), closed reduction of congenital hip dislocation, prolonged interval between injury and reduction

Pathophysiology:

insufficient femoral head blood supply (epiphyseal plate acts as a barrier in ages 4–10; ligamentum teres vessels become nonfunctional; blood supply is from medial circumflex artery + lateral epiphyseal artery only); articular cartilage continues to grow ← supplied with nutrients from synovium

Stages:

•  1 week–6 months (mean 2.7 months) duration of symptoms prior to initial presentation: limp, knee pain

•  decreased range of hip motion concerning abduction and internal rotation

NUC (may assist in early diagnosis):

√  decreased uptake (early) in femoral head = interruption of blood supply

√  increased uptake (late) in femoral head

(a)  revascularization + bone repair

(b)  degenerative osteoarthritis

√  increased acetabular activity associated with degenerative joint disease

X-RAY:

Early signs:

√  femoral epiphysis smaller than on contralateral side (96%) = epiphyseal growth deficit

√  sclerosis of femoral head epiphysis ← sequestration + compression (82%)

√  slight widening of joint space ← thickening of cartilage, failure of epiphyseal growth, presence of joint fluid, joint laxity (60%)

√  ipsilateral bone demineralization (46%)

√  alteration of pericapsular soft-tissue outline ← atrophy of ipsilateral periarticular soft tissues (73%)

√  radiolucency of lateral + medial metaphyseal areas of femoral neck

N.B.:   NEVER destruction of articular cortex as in bacterial arthritis

Late signs:

√  delayed osseous maturation of a mild degree

√  “radiolucent crescent line” of subchondral fracture = small archlike subcortical lucency (32%)

√  subcortical fracture on anterior articular surface (best seen on frog leg view)

√  lateral subluxation of femoral head = lateral collapse of ossific nucleus

√  femoral head fragmentation

√  femoral neck cysts (from intramedullary hemorrhage in response to stress fractures)

√  loose bodies (only found in males)

Regenerative signs:

√  coxa plana = flattened collection of sclerotic fragments (over 18 months)

√  coxa magna = remodeling of femoral head to become wider + flatter in mushroom configuration to match widened metaphysis + epiphyseal plate

CT:

√  loss of “asterisk” sign (= starlike pattern of crossing trabeculae in center of femoral head) with distortion of asterisk and extension to surface of femoral head

MR (gold standard):

√  “asterisk” sign of marrow edema = normal marrow SI of femoral epiphysis replaced by low T1-SI + high T2-SI

√  low signal intensity on T1WI and T2WI = necrotic portion of superior epiphysis

√  “double-line” sign (80%) = sclerotic nonsignal rim between necrotic + viable bone edged by a hyperintense rim of granulation tissue

√  “crescent” sign ← subchondral fracture

√  prominent involvement of anterosuperior + lateral femoral head (often best seen on SAG images)

√  thickening of epiphyseal cartilage

√  synovial hypertrophy, joint effusion

√  fluid within fracture plane

√  absent enhancement of femoral head epiphysis

√  early increased diffusivity in affected femoral epiphysis

√  hip joint incongruity: lateral femoral head uncovering, labral inversion, femoral head deformity

NUC (3-phase bone scan):

√  initially no uptake of radiopharmaceutical on early dynamic images

√  increased activity in lateral pillar ← revascularization phase

√  increased activity at epiphyseal base near physis ← transphyseal neovascularization

US:

√  joint effusion, synovitis

Cx:     severe degenerative joint disease in early adulthood

Rx:     bed rest, abduction bracing (to reduce stress on infarcted head), physical therapy

Metadiaphyseal Osteonecrosis

√  well-defined serpentine hypointense rim surrounding a central region of fat SI on T1WI

√  “double line” sign = bands of low + high SI that course together in parallel surrounding a central region of low SI (= necrotic bone) on T2WI (virtually PATHOGNOMONIC)

Panner Disease

[Hans Jessen Panner (1871–1930), head of roentgenological clinic at Rikshospitalet, Copenhagen, Denmark]

(NOT osteonecrosis)

=  benign self-limited disorder of fragmented ossification in epiphysis of humeral capitellum

Age:     children 7–12 years of age

Preiser Disease

[Georg Karl Felix Preiser (1876–1913), orthopedic surgeon in Hamburg, Germany]

=  nontraumatic spontaneous osteonecrosis of entire scaphoid

Scaphoid Osteonecrosis

=  OSTEONECROSIS OF PROXIMAL POLE OF SCAPHOID

Cause:  fracture through waist / proximal pole and nonunion

Incidence of proximal pole osteonecrosis:

(a)  in > 60% of fracture nonunions of proximal ¹/³ of scaphoid

(b)  in ~ 20% of midscaphoid fractures

X-RAY:

√  increased density of proximal scaphoid fracture fragment compared with distal scaphoid / adjacent carpal bones

√  often sclerotic rounded fracture margins (= nonunion)

√  frequently surrounding lucencies (= cysts)

NUC (bone scan):

√  decreased uptake in proximal pole

CT:

√  increased sclerosis + lack of normal trabeculae in proximal third of scaphoid

MR:

√  homogeneously decreased SI (≤ SI of skeletal muscle) at T1WI in proximal pole of scaphoid (71% sensitive, 74% specific)

√  < 20% enhancement in proximal pole (86% sensitive, 96% specific)

√  complete absence of enhancement in proximal pole (54–76% sensitive)

Cx:     scaphoid nonunion advanced collapse (= persistent fracture nonunion, radioscaphoid joint space narrowing, sclerosis, osteophytes, potentially proximal pole collapse)

Spontaneous Osteonecrosis of Knee

=  SONK

Cause:  ? meniscal tear (78%), trauma with resultant microfractures, vascular insufficiency, degenerative joint disease, severe chondromalacia, gout, rheumatoid arthritis, joint bodies, intraarticular steroid injection (45–85%)

Age:     7^th decade (range, 13–83 years)

•  acute onset of pain

Location:   weight-bearing medial condyle more toward epicondylus (95%), lateral condyle (5%), may involve tibial plateau

√  radiographs usually normal (within 3 months after onset)

√  positive bone scan within 5 weeks (most sensitive)

√  flattening of weight-bearing segment of medial femoral epicondyle

√  radiolucent focus in subchondral bone + peripheral zone of osteosclerosis

√  horizontal subchondral fracture (within 6–9 months) + osteochondral fragment

√  periosteal reaction along medial side of femoral shaft (30–50%)

Cx:     osteoarthritis

Talar Avascular Necrosis

◊  Fractures involving the talar body have a higher prevalence of AVN

Risk of AVN:

(a)  nondisplaced fracture

–  talar neck fracture (Hawkins type I)  0–15%

(b)  fracture with dislocation / subluxation of:

›  subtalar joint (Hawkins type II)  20–50%

›  ankle + subtalar joints (Hawkins type III)  almost 100%

›  subtalar + tibiotalar + talonavicular joints (Hawkins type IV fracture)  100%

√  increase in talar dome opacity / sclerosis

√  deformity + articular collapse + bone fragmentation

√  absent Hawkins sign = thin subchondral radiolucent line along talar dome (← disuse osteopenia) indicates an adequate blood supply

BASAL CELL NEVUS SYNDROME

=  NEVOID BASAL CELL CARCINOMA (BCC) SYNDROME = GORLIN-GOLTZ SYNDROME

=  syndrome of autosomal dominant inheritance characterized by

(1)  multiple cutaneous basal cell carcinomas during childhood

(2)  odontogenic keratocysts of mandible

(3)  ectopic calcifications

(4)  skeletal anomalies (midface hypoplasia, frontal bossing, prognathism)

Mean age:   19 years

•  up to hundreds of skin-colored pink / tan dome-shaped papules resembling benign nevi; aggressive after puberty; may metastasize

Distribution:   nose, mouth, chest, back; affected by solar + ionizing radiation

•  shallow pitlike defects in palms + soles = deficient stratum corneum (85%)

•  mental retardation

Genetics:   mutation of patched 1 (PTCH) gene that codes for regulatory receptor in the important Sonic hedgehog signaling pathway + acts as a tumor suppressor gene in BCC + medulloblastoma

Association:   high incidence of medulloblastoma in children (4–5%); ovarian fibroma (in 17%); cardiac fibroma (in 14%)

√  multiple aggressive uni- / multiloculated mandibular > maxillary cystic lesions = odontogenic keratocyst / keratocystic odontogenic tumor (in 75%)

√  anomalies of upper 5 ribs:

√  forked = bifid rib (most commonly 4^th rib) in 26%

√  agenesis / supernumerary ribs

√  fusion of adjacent ribs

√  hypo- / dysplastic distorted splayed ribs

√  bifid spinous processes, spina bifida

√  scoliosis (cervical + upper thoracic)

√  hemivertebrae + block vertebrae

√  Sprengel deformity (scapula elevated, hypoplastic, bowed)

√  deficiency of lateral clavicle

√  brachydactyly

√  extensive early calcification of falx + tentorium (65%)

√  ectopic calcifications of subcutaneous tissue, ovaries, sacrotuberous ligaments, mesentery

√  bony bridging of sella turcica

√  macrocephaly

BATTERED CHILD SYNDROME

=  CAFFEY-KEMPE SYNDROME = CHILD ABUSE = PARENT -INFANT TRAUMATIC STRESS SYNDROME = NON-ACCIDENTAL TRAUMA

◊  Most common cause of serious intracranial injuries in children < 1 year of age; 3^rd most common cause of death in children after sudden infant death syndrome + true accidents

Prevalence:   1.7 million cases reported + 833,000 substantiated in USA in 1990 (45% neglected, 25% physically abused, 16% sexually abused children); resulting in 2,500–5,000 deaths per year; 5–10% of children seen in emergency rooms

Age:   usually < 2 years

•  skin burns, bruising, lacerations, hematomas (SNAT = suspected nonaccidental trauma)

@   Skeletal trauma (50–80%)

Site:   multiple ribs, costochondral / costovertebral separation, acromion, skull, anterior-superior wedging of vertebra, tibia, metacarpus

Unusual sites:   transverse fracture of sternum, lateral end of clavicles, scapula, vertebral compression, vertebral fracture dislocation, disk space narrowing, spinous processes

Other clues:   bilateral acute fractures, fractures of lower extremities in children not yet walking

√  multiple asymmetric fractures in different stages of healing (repeated injury = HALLMARK)

√  exuberant callus formation at fracture sites

√  avulsion fracture of ligamentous insertion; frequently seen without periosteal reaction

@   Epiphysis

√  separation of distal epiphysis

@   Metaphysis

√  marked irregularity + fragmentation of metaphyses (DDx: osteochondritis stage of congenital syphilis; infractions of scurvy)

√  “corner” fracture (11%) = “bucket-handle” fracture = avulsion of an arcuate metaphyseal fragment overlying the lucent epiphyseal cartilage

Cause:   sudden twisting motion of extremity (periosteum easily pulled away from diaphysis but tightly attached to metaphysis)

Location:   knee, elbow, distal tibia, fibula, radius, ulna

@   Diaphysis

√  isolated spiral fracture (15%) of diaphysis ← external rotatory force applied to femur / humerus

√  extensive periosteal reaction from large subperiosteal hematoma apparent after 7–14 days following injury (DDx: scurvy, copper deficiency)

√  cortical hyperostosis extending to epiphyseal plate (DDx: not in infantile cortical hyperostosis)

@   Head trauma (13–25%)

◊  Most common cause of death + physical disability!

(1)  Impact injury with translational force: skull fracture (flexible calvaria + meninges decrease likelihood of skull fractures), subdural hematoma, brain contusion, cerebral hemorrhage, infarction, generalized edema

(2)  Whiplash injury with rotational force: shearing injuries + associated subarachnoid hemorrhage

•  bulging fontanels, convulsions

•  ocular lesions, retinal detachment

Skull film (associated fracture in 1%):

√  linear fracture > comminuted fracture > diastases (conspicuously absent)

CT:

√  subdural hemorrhage (most common): interhemispheric location most common

√  subarachnoid hemorrhage

√  epidural hemorrhage (uncommon)

√  cerebral edema: focal, multifocal, diffuse

√  acute cerebral contusion as ovoid collection of intraparenchymal blood with surrounding edema

MR:

◊  More sensitive in identifying hematomas of differing ages

√  white matter shearing injuries as areas of prolonged T1 + T2 at corticomedullary junction, centrum semiovale, corpus callosum

@   Visceral trauma (3%)

◊  Second leading cause of death in child abuse

Cause:   crushing blow to abdomen (punch, kick)

Age:   often > 2 years

√  small bowel / gastric rupture

√  hematoma of duodenum / jejunum

√  contusion / laceration of lung, pancreas, liver, spleen, kidneys

√  traumatic pancreatic pseudocyst

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