Oral Exam - MSK Flashcards
Bone scan tips
- Increased uptake between ribs on bonescan is concerning for osteosarcoma lung metastases
- Heterotopic ossification after surgery can be difficul tto distinguish on bone scan from tumor recurrence
- Postsurgical change can show increased bone uptake on bone scan
- New uptake in area of benign lesions could represent fracture or malignant transformation
Malignant Hot lesions ddx:
Chondrosarcoma, Ewing sarcoma, osteosarcoma,
metastases, adamantinoma
Malignant cold lesions ddx:
Multiple myeloma; metastases - purely lytic
Benign hot lesions ddx:
Paget disease, osteoblastoma, chondroblastoma,
aneurysmal bone cyst, osteoid osteoma, giant cell tumor
Iso or mild lesions ddx
Fibrous dysplasia, fibrous cortical
defect, nonossifying fibroma, enchondroma
Adamantinoma findings
– Anterior tibial cortex
– Low-grade malignant lesion – Focal increased uptake
Osteoid osteoma
– Cortically based lesion most commonly in femur, tibia,
spine, hands, and feet
– Double density sign - intense central uptake, & moderate uptake in surrounding area
– Delayed uptake in nidus secondary to presence of
osteoblasts
Fibrous dysplasia
– Medullary lesion
– Monostotic: Femur, ribs, tibia, facial bones, & humerus – Polyostotic: Femur, tibia, pelvis, feet, ribs, facial bones,
& lumbar spine
Giant cell tumors
– Epiphyseal in location
– Distal femur, proximal tibia, distal radius, sacrum, &
proximal humerus
– Increased tracer uptake peripherally with photopenia
centrally (doughnut sign)
Aneurysmal bone cyst
– Eccentrically in medullary cavity
– Posterior elements of spine
– Metaphysisoflongbones
– Upper & lower limbs, spine, & sacrum
– Can show diffuse homogeneous uptake or peripheral
uptake & central photopenia
Enchondroma
– Typically solitary lesions in central medullary cavity
– If solitary, more common in hand
– Multiple lesions (Ollier disease & Maffucci syndrome)
– Femur, tibia, humerus, hands, & feet
– Mildly increased uptake in lesions that are large
enough for gamma camera detection
– Fractures can show change in uptake when following
these lesions
– Bone scan cannot reliably differentiate low-grade
chondrosarcoma from enchondroma
Bone island
– Medullary in location
– Can occur anywhere, but more often in pelvis, femurs,
and ribs
– Osteopoikilosis: Multiple enostoses near joints &
predominantly in appendicular skeleton
– Most bone islands have no uptake on bone scan;
larger lesions may show very mild uptake
Chondroblastoma
– Well-defined,osteolyticlesionwiththinscleroticrim
located in epiphysis or apophyses of long bone
– Femur,tibia,humerus,patella,andtarsalbones
– Skeletallyimmaturepatient
– Bonescanshowsfocalincreaseduptake
Osteochondroma
– Most common benign bone tumor
– Most commonly in long bones of upper & lower
extremity: Femur, tibia, humerus
– Uptake on bone scan is directly correlated with degree of enchondral bone formation
Solitary bone lesion
○ Only 15% of solitary lesions on bone scan are metastases (spine is most common site)
– Exception: 80%of solitary sternal lesions in breast
cancer patients are metastatic
– Vertebrae: Asymmetric, focal uptake (not confined to
endplate), involvement of pedicle suggestive of
metastasis
Rib metastasis findings
○ Solitary rib lesion often benign (~10%metastases)
– Ribs: Long, linear uptake suggestive of metastasis, may be expansile
Ddx photopenic metastases
Lytic metastases (RCC, thyroid, myeloma, poorly differentiated anaplastic tumours) +/- lung, breast, NB
Radiation
Bone infarct
AVN
Superscan findings
Disseminated bone lesions with diffusely increased skeletal activity, relative absence of renal and soft tissue activity
○ Breast and prostate cancers most common
DDX mets
Degenerative changes, arthropathies
Healing fractures
Physiologic activity
Primary bone tumour (benign and malignant)
AVN, osteonecrosis, infarct
Metabolic bone disease, infection/inflammation
Fibrous dysplasia associated abnormalities
• Associated abnormalities
○ Calvarial and facial asymmetry, exophthalmos
○ Femur
– Coxavara(shepherd’scrook)
○ McCune-Albright syndrome – FD – Café au lait spots – Endocrinopathy □ Precociouspuberty □ Hyperthyroidism □ Acromegaly □ Cushingsyndrome
○ Mazabraud syndrome
– Single or multiple intramuscular myxomas with
fibrous dysplasia; rare
○ Associatedwithaneurysmalbonecysts(ABC)
FD ddx
Benign/Malignant bone tumours
Paget’s
Neurofibromatosis
Paget’s findings
Intense activity expansile appearance of entire affected bone on bone scan
• Pelvis(30-75%)>vertebra(30-75%)>skull(25-65%)> proximal long bones (esp. femur)
– Typically involves whole bone
– Inactive or quiescent phase should show no increased
uptake
– Osteoporosis circumscripta may show uptake at
margins of lesion
○ Angiographic images from 3-phase bonescan show
increased blood flow with intensity closely correlating
with level of disease activity
Paget’s ddx
Mets
Primary bone tumour (radiographs to separate)
Fibrous dysplasia (ribs, skull, femur), spine and pelvis less common than Paget’s
BMD - when to report z score
Z-scores are reported for premenopausal women and men under age of 50
○ Z-scoreof-2.0 or lower is belowexpectedrangeforage
○ Z-score above -2.0 is within expected range for age
Prosthetic joint loosening
- Major causes include micromotion over time and osteolysis (e.g., particle disease)
- 3-phase bone scan: Variable activity on first 2 phases, focal activity at bone-prosthesis site of motion on delay phase
– Activity at tip of prosthesis in cemented hip prosthesis 1 year after placement suggests loosening
– Diffuse periprosthetic uptake of tracer suggests osteolysis from infection or loosening
○ All prosthesis initially show increased activity
– 2-3 years after placement, negative study (periprosthetic activity ≤ surrounding nonarticular bone) has very high negative predictive value
○ Hip arthroplasty
– 10% show increased activity at 2years
- periprosthetic activity in non-cemented arthroplasty 2-3 yrs after placement = loosening
– Activity tip of prosthesis in cemented hip prosthesis 1 year after placement = loosening
○ Knee arthroplasty
– Tibial component > femoral component; increased
activity frequently persists for years
Prosthetic Joint Infection
- Infection rate <1% in primary joint replacement, increased to as high as 15% in revision shoulder arthroplasty
- Vast majority occur < 90 days postoperation but may occur > 2 years delay
- 3-phase bonescan: Diffuse increased activity on all phases in early infections; may be more focal in later presentation
– Loosening vs. infection: Delayedphaseimaging only or 3-phase imaging cannot reliably differentiate aseptic loosening from infection
– In-111 leukocyte imaging with Tc-99m sulfur colloid
provides most specific and accurate assessment for
joint infection and is diagnostic test of choice
– Diffuse periprosthetic uptake of tracer suggests
osteolysis from infection or loosening
– On SPECT, osteomyelitis is likely when uptake of In- 111 WBC localizes to bone on 2 or more adjacent tomographic slices
– False-negative results occur in chronic infections
– False-positive results occur in aseptic inflammation
Periprosthetic Soft Tissue Complications
• Pseudotumor (e.g.,particledisease), periprosthetic effusions, synovitis/bursitis
○ Bonescan may be positive in first 2 phases but weakly
increased or absent in 3rd phase; usually diagnosed by
CTorMR
• Snapping hip syndrome: Iliopsoas tendon may be evaluated dynamically with fluoroscopic tenography
Heterotopic Ossification
- Bone formation in periprosthetic soft tissues commonly seen post operation due to liberation of primitive bone- forming cells
- 3-phase bone scan: Focal mildly increased activity in soft tissues with corresponding new bone on radiograph
Joint infection protocol
– According to SNMMI, 15% window at 140-keV Tc-99m peak and a 15% window at 247-keV In-111 photopeak are used if Tc-99m dose is injected on day 1 before In- 111 leukocyte imaging
– 10% or 15% window at 173-keV In-111 photo peak for delayed In-111 leukocyte images obtained on day 2 (18–30 h) after Tc-99m dose has been injected
3 Phases of Bone Scan
- Angiographic phase - 2 sec planar images for 60 seconds in anterior and posterior projections. Assesses hypervascularity
- Blood pool phase - static planar images over area of interest. Assesses tissue hyperemia.
- Delayed phase +/- SPECT/CT. Assesses bone formation.
Osteomyelitis ddx
- Arthropathy (OA, Rheumatoid, Gout, neuropathic)
- Post-traumatic
- Paget’s
- Osteoid osteoma
• RecommendI n-111 WBC with Tc-99m SC after abnormal 3- phase bone
Septic arthritis findings
Activity on both sides of joint
Primary hyperparathyroidism findings
– Normal bone scan in 80%
– Foci of increased uptake: Calvarium, mandible,
sternum, acromioclavicular joint, lateral humeral
epicondyles, hands
– Increased uptake in brown tumors
– Extraskeletal uptake
□ Lungs, kidneys, stomach most common
□ Myocardium, spleen, diaphragm, thyroid, skeletal
muscle in severe disease
Secondary hyperparathyroidism findings
– Superscan
– Diffuse lung uptake in 60%
– Brown tumors: Less common than in primary HPT
– Uptake increased in vertebrae, distal 3rd of long
bones, rib
Osteomalacia findings
○ Generalized increased uptake in axial skeleton
○ Increased uptake at ends of multiple ribs, with beading
appearance along rib cage (rachitic rosary sign)
– In contrast to linear orientation of metastasis along
single rib
○ Increased sternum uptake common
○ Pseudofractures (Looser zone or Milkman fractures)
occur in ribs, lateral scapula, clavicles, pubic rami,
Renal osteodystrophy
○ Can have very high bone: soft tissue ratio,s imilar to
superscan
– Typically most striking appearance of metabolic bone
diseases excluding Paget disease
– Lack of bladder activity can help differentiate from
metastatic superscan
○ Signs of secondary HPT
○ More diffuse and symmetric than secondary HPT,which
may show focal uptake from cystic changes and brown
tumors
Heterotopic ossification classification
- Acquired: Ectopic ossification, myositis ossificans circumscripta/traumatica
- Hereditary: Atraumatic HO, fibrodysplasia ossificans progressiva (FOP)/myositis ossificans progressiva (MOP), Münchmeyer disease
