Nuclear: Skeleton Flashcards
Tc-99m MDP localizes to…
Osteoblasts, which use it to create osteoid (predominantly in cortical bone)
Arrows
Growth plates
Note: Tc-99m MDP uptake in growth plates (and osteochondral junctions) is normal as osteoblast activity is high here.
MDP uptake is dependent on…
- Osteoblastic activity
- Blood flow (less important)
Which organs has physiologic uptake of Tc-99m MDP?
- Bone (mostly cortex)
- Kidneys and bladder
- Breasts (especially in younger females)
- Soft tissues (faint uptake)
Standard dose of Tc-99m MDP for bone scan?
15-25 mCi
How long do you wait to scan after Tc-99m MDP injection?
2-4 hours
Note: This is to let the radiotracer clear from the soft tissues (so you can see the bones more clearly). If there is impaired renal function, the soft tissues may take longer to clear.
What are the 3 main ways a Tc-99m MDP study can get fucked up?
- Poor renal function (too much soft tissue uptake)
- Poor MDP labeling (gastric, thyroid, and/or salivary gland uptake)
- The flare phenomenon (pseudo-progression)
What is the most likely difference between these two Tc-99m MDP studies?
Poor renal function on the right (too much soft tissue uptake)
How could you improve this Tc-99m MDP study?
- Encourage oral hydration during the 2-6 hours between radiotracer injection and scan
- Get a 24 hour delay (tradeoff between better signal:background ratio and lower tracer signal)
What is wrong with this Tc-99m MDP study?
Radiotracer is contaminated with free technetium
Note: There shouldn’t be any gastric uptake and there is marked gastric uptake here.
What is the cause of free technetium contamination in a Tc-99m MDP study?
- Oxidation from air getting into the vial/syringe during MDP labeling
- Not enough stannous ion (rare)
Note: Normally MDP is labeled by mixing it with stannous ion and pertechnetate, but this must be done without introducing air.
Radiotracer uptake in which organs suggests there is free technetium contamination on a Tc-99m MDP study?
- Gastric uptake
- Thyroid uptake
- Salivary gland uptake
Note: These should not be visible on a Tc-99m MDP study. The most likely problem was air introduced during the labeling process causing oxidation.
What is the flare phenomenon on a Tc-99m MDP study?
Bone metastases that have been treated with chemotherapy may actually appear worse 2 weeks to 3 months after treatment due to increased bone turnover from successful treatment of the metastases
Note: On plain film the lesions should appear more sclerotic (confirming a positive response to chemotherapy). You can also repeat the study more than 3 months after treatment to confirm positive response.
Is it normal to see skull sutures on a Tc-99m MDP study?
Yes faintly, but if it is marked uptake you should think about renal osteodystrophy
Tc-99m MDP
Abnormal breast uptake
Note: Mild diffuse breast uptake is normal (especially in younger females), but focal uptake is not.
Tc-99m MDP
Abnormal focal skull uptake (think meningioma or met)
Tc-99m MDP
Renal cortical activity hotter than adjacent vertebrae, think hemochromatosis
Tc-99m MDP
Diffuse renal uptake hotter than adjacent vertebrae, think chemotherapy (or urinary obstruction)
Tc-99m MDP
Abnormal liver uptake (normally not visible):
- AL^3+ contamination
- Cancer (primary hepatoma or mets)
- Amyloidosis
- Liver necrosis
Tc-99m MDP
Focal, irregular liver uptake, think liver mass (hepatoma vs. metastasis)
Note: The liver should not be visible on MDP studies.
White arrow
Tc-99m MDP
Abnormal spleen uptake, think auto-infarction in sickle cell disease
Note: The spleen should not be visible on MDP studies.
Tc-99m MDP
Abnormal spleen uptake, think auto-infarction in sickle cell disease (uptake is due to dystrophic calcification)
Note: Look for bone infarctions (focal areas of photopenia).
Differential for lung uptake on Tc-99m MDP studies
- Metastases (classically osteosarcoma)
- Dystrophic calcification
- Fibrothorax
- Radiation changes
- Sarcoidosis
- Granulomatosis with polyangiitis
Note: Lung uptake is very nonspecific.
Abnormal uptake in thigh muscles, think rhabdomyolysis
Note: Focal uptake in the right humerus is due to a prior fracture.
Tc-99m MDP
Superscan (kidneys aren’t visible):
- Diffuse metastases (think breast or prostate cancer)
- Metaboic (hyperparathyroidism, renal osteodystrophy, Pagets disease, severe thyrotoxicosis)
- Horseshoe kidney
Note: You should look at any prior CT to make sure there isn’t a horseshoe kidney.
Sacral insufficiency fracture (think osteoporosis or prior radiation)
Note: This is the “Honda” sign.
Differential for diffusely decreased bone uptake on a Tc-99m MDP scan
- Free technetium
- Bisphosphonate therapy
When should you obtain a bone scan in a pt suspected of being a victim of elder abuse?
1 week after suspected trauma
Note: Fractures may not show up on bone scans for several days in elderly pts.
Hypertrophic osteoarthropathy, think lung cancer and get a chest radiograph or chest CT
Note: “Tramline sign” along the periosteum of long bones can also be seen in conditions of chronic hypoxia (cystic fibrosis, cyanotic heart disease, mesothelioma, pneumoconioses, etc.).
Avascular necrosis of the femoral head
Note: “Donut sign” of the femoral head (arrows).
Which primary bone tumors are hot on Tc-99m MDP scans?
- Fibrous dysplasia
- Giant cell tumor
- Osteoblastoma
- Osteoid osteoma
- Aneurysmal bone cyst
- Osteosarcoma
- Ewings sarcoma
Which primary bone tumors may show the “donut sign” on Tc-99m MDP scans (hot circle with central photopenia)?
Cystic bone lesions:
- Aneurysmal bone cyst
- Simple bone cyst
- Giant cell tumor
- Telangiectatic osteosarcoma
PSA less than _____ basically excludes the possibility of prostate cancer bone metastases
10 ng/mL
Note: PSA > 100 ng/mL is highly predictive of bone metastases.
Single area of abnormal focal uptake in a bone on a Tc-99m MDP scan…
Most likely benign 80%
Note: Bone metastases are usually (80%) multifocal.
Bone scan showing a single focal area of abnormal uptake in the sternum…
- If known breast cancer, this is likely a met
- If not breast cancer, it is likely benign (median sternotomy, trauma, etc.)
Bone scan showing a single focal area of abnormal uptake in a spinal vetebra…
- If known prostate cancer, think met (especially if rounded)
- If not prostate cancer, think fracture (especially if linear)
Why is there vertebral body uptake?
Linear vertebral body uptake is usually due to a osteoporotic compression fracture
Note: If you are still concerned about a metastasis, you can get a follow up MDP scan (if fracture, the uptake will decrease over time).
How can you differentiate rib fractures from rib metastases on a Tc-99m MDP bone scan?
Rib fractures tend to be multifocal in a linear arrangement along the ribcage
Rib metastases also tend to be multifocal, but scattered randomly throughout the ribcage (also metastases rarely go only to the ribs, so look for mets elsewhere)
Which portion of the skeleton is most likely to have metastatic lung cancer?
The appendicular skeleton
Which portion of the skeleton is most likely to have metastatic breast cancer?
Spine
Note: A solitary sternal metastasis is more specific for breast cancer.
Which portion of the skeleton is most likely to have neuroblastoma metastases?
Metaphyses of long bones
Which nuclear imaging study is best for detecting neuroblastoma metastases?
I-123/I-131 MIBG
Is a bone scan or a skeletal survey more sensitive for bone metastases?
Bone scans are way better for osteoblastic mets
Skeletal surveys are better for lytic mets
Bone scan for multiple myeloma?
No, bone scans are not very sensitive for lytic mets (skeletal survey is better)
Next step: bone scan demonstrates an “equivocal lesion” that may or may not be a met
Get a radiograph (if there is no radiographic lesion that correlates to the radio tracer uptake, this is more suspicious for metastasis and you should get an MRI)
When should you do a follow-up bone scan to determine whether bone mets have improved s/p chemotherapy?
At least 3 months after chemotherapy
Note: If you perform a bone scan within 3 months of chemotherapy, you may get the flare phenomenon (bone mets actually look worse due to increased bone turnover from successful treatment of bone mets, which can’t be differentiated from disease progression).
How do radiation changes appear on Tc-99m MDP bone scans?
Warm in the acute/early phase (peaking 2-3 months after radiation), then appearing cold (if it’s cold at 6 months you should expect it to be permanently cold)
Note: If an irradiated area was cold at 6 months and not appears hot, think recurrent disease.
Focal radiotracer uptake in a previously irradiated region of the femur (bone scan 7 months post radiation showed this region to be cold)…
Think recurrent disease
Note: If an irradiated area is cold more than 6 months after radiation, it should remain cold permanently (any new radiotracer uptake in this region is concerning for recurrent disease).
Differential for super scan
- Diffuse metastases (especially breast and prostate cancer)
- Metabolic (hyperparathyroidism, renal osteodystrophy, Pagets disease, severe thyrotoxicosis)
- Horseshoe kidney
Differential for metabolic superscan
- Hyperparathyroidism (usually the multiple choice answer)
- Renal osteodystrophy
- Pagets disease
- Severe thyrotoxicosis
Horseshoe kidney
Diffuse metastaes (super scan with faint renal uptake)
Tc-99m MDP
Think osteoid osteoma
Note: “Double density” showing a nidus of hot uptake within an area of warm uptake.
Tc-99m MDP
Think fibrous dysplasia
Note: If you see a super hot mandible, think fibrous dysplasia.
Tc-99m MDP
Think Pagets disease
Note: Super hot, enlarged femur, tibia, and skull.
Tc-99m MDP
Think Pagets disease
Note: Super hot, enlarged pelvis asymmetrically.
Osteoid osteomas are hot on which phases of a bone scan?
All three phases
Which portion of the spine is classically involved in Pagets disease?
Both the vertebral body AND posterior elements
Note: If there is more focal uptake (especially in the pedicles only), then think metastases.
Differential for photopenic bone lesions on Tc-99m MDP scans
- Late radiation changes
- Early osteonecrosis
- Bone infarction (very early or late)
- Anaplastic tumors (multiple myeloma, renal, thyroid, neuroblastoma)
- Artifact (prosthesis, pacemaker, spinal stimulator, etc.)
- Hemangioma (variably hot)
- Bone cyst (without fracture)
- Mature heterotypic ossification
Differential for photopenic bone metastases on bone scan
- Multiple myeloma
- Renal cancer
- Thyroid cancer
- Neuroblastoma
Common causes of photopenic artifacts on bone scans
- Prostheses
- Pacemakers
- Spinal stimulators
Why would you follow heterotypic ossification with serial bone scans?
To identify when the heterotypic ossification is mature (no longer active) prior to surgical resection
Note: If you resect heterotypic ossification while it is still metabolically active, it has a high rate of recurrence.
What are the two main radio tracers used for bone scans?
- Tc-99m MDP
- F-18 NaF
What type of bone scan is this?
F-18 NaF
Note: F-18 NaF bone scans appear much higher resolution than Tc-99m MDP studies. Look at how relatively shitty MDP is!
If F-18 NaF bone scans are faster with a higher resolution, why aren’t they done more often?
They are more expensive than Tc-99m MDP studies
Critical organ for Tc-99m MDP studies
Bone
Critical organ for F-18 NaF studies
Bladder
What scan is this?
F-18 FDG PET
Note: Brain uptake. There is diffuse bone uptake due to bone stimulation (erythropoietin or granulocyte colony stimulating factor treatment).
What are the 3 phases of a 3 phase bone scan?
- Flow (looks for hyperperfusion)
- Blood pool (looks for hyperemia)
- Delayed (looks for increased bone uptake)
Note: You can also do a 4th phase (extended delay) to help with localization.
Differential for focal uptake on all 3 phases of a 3 phase bone scan (i.e. 3 phase hot lesion)
- Osteomyelitis
- Fracture
- Tumor
- Osteoid osteoma
- Charcot joint
Why is it important to do a 3 phase bone scan when looking for osteomyelitis
To differentiate cellulitis and osteomyelitis:
Cellulitis (hot on flow and blood, but cold on delay)
Osteomyelitis (hot on all 3 phases)
3 phase bone scan
Cellulitis
Note: Focal uptake on flow and blood pool phases, but not on delayed phases (osteomyelitis would be 3 phase hot).
Right ulnar osteomyelitis
Note: Right ulna is 3 phase hot.
What are the best imaging modalities to look for spinal osteomyelitis?
- MRI
- Bone scan combined with a gallium scan
Reflex sympathetic dystrophy
AKA complex regional pain syndrome: persistent pain after a triggering event (stroke, trauma, or other acute illness)
How can reflex sympathetic dystrophy (complex regional pain syndrome) appear on bone scans?
Increased uptake on flow and blood pool phases with periarticular uptake on delayed phase
Note: Uptake often involves an entire extremity.
Bone scan delayed phase in a pt with recent shingles
Think reflex sympathetic dystrophy (complex regional pain syndrome)
Note: Asymmetric periarticular uptake on delayed bone scan.
What is the purpose of combining a Tc-99m sulfur colloid scan with an In-111 WBC scan?
To identify infected bone marrow
Note: Sulfur colloid and WBC scans should both accumulate in bone marrow in a spatially congruent manner (i.e. they should overlap). Combining these studies can help you identify infected bone marrow (which would be photopenic on sulfur colloid and hot on WBC).
In-111 WBC uptake in a bone that appears photopenic on Tc-99m sulfur colloid scan…
Bone marrow infection in that bone
How old must a bone marrow infection be to show up on a Tc-99m sulfur colloid/In-111 WBC dual scan?
Approximately 1 week old infection
Note: Before this infection might not show up on these scans.
How can you differentiate an In-111 WBC scan from a gallium scan?
Spleen is much hotter than liver on In-111 WBC
Liver is hotter than spleen on gallium (and there may be GI activity, which you shouldn’t see on In-111 WBC)
Bone marrow infection in right proximal femur
Possible bone marrow infection (WBCs frequently fail to migrate to the spinal bone marrow, resulting in photopenia rather than the hot WBC uptake you would expect in infection)
Note: This is why gallium scans are preferred when looking for spinal osteomyelitis.
What is the most common reason to perform a nuclear imaging study on an orthopedic prosthesis?
To differentiate prosthesis infection from aseptic loosening
What is the best nuclear imaging study to differentiate prosthetic infection from aseptic loosening?
Combined Tc-99m sulfur colloid and In-111 WBC scans
Tc-99m MDP scan showing focal uptake along the stem and lesser trochanter of a hip arthroplasty…
Think aseptic loosening
Note: This could also be seen in infection (though uptake is usually more diffuse in the setting of infection). You need a combined sulfur colloid/WBC study to differentiate.
What is the main benefit of a bone scan when evaluating an orthopedic prosthesis?
A negative bone scan excludes BOTH prosthetic infection and aseptic loosening (focal periprosthetic uptake is nonspecific and you need to do a combined sulfur colloid/WBC study)
Where is Tc-99m MDP radiotracer uptake expected in a neuropathic foot?
Tarsal and metatarsal joints
Note: In diabetics it is difficult to differentiate these arthritic changes from infection and you should get a combined sulfur colloid/WBC study.
In a diabetic pt 3 phase bone scan, how can you differentiate between reduced soft tissue clearance (due to decreased peripheral blood flow) and true bone infection?
Add a 4th (extended delay) phase to see if soft tissue uptake is cleared
When would you consider using Tc-99m HMPAO instead of In-111 WBC to look for infection?
- Pediatric pts (Tc-99m has a lower absorbed dose and shorter imaging time)
- Hand/foot imaging (Tc-99m makes better images of smaller bones)
What are the downsides to using Tc-99m HMPAO rather than In-111 WBC to look for infection?
Tc-99m HMPAO has:
- Shorter half-life of 6 hours (limiting delayed imaging)
- Normal GI and gallbladder uptake (which can obscure lesions in those areas)
What is the critical organ for In-111 WBC?
Spleen
How does labeling WBCs with In-111 affect the WBCs?
- Neutrophils continue to function normally (no significant effect)
- Lymphocytes tend to be killed by the radiation (but don’t turn into cancer)
How can you tell if there has been WBC fragmentation on an In-11 WBC scan?
There would be unusually increased uptake in the liver and bone marrow
