NUCLEAR MEDICINE Flashcards
1
Q
DIFFUSE INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
(‘SUPERSCAN’) 4
A
- Widespread bone metastases—most common sources include
prostate and breast. Uptake is diffuse but often patchy/
asymmetrical. Long bones less commonly involved. - Metabolic bone disorders—osteomalacia, hyperparathyroidism
and renal osteodystrophy. Uptake is diffuse and symmetrical.
Proximal long bones usually involved, with prominent uptake in
the skull and mandible. May have focal areas of very high uptake
due to brown tumours in hyperparathyroidism. - Myeloproliferative disorders—e.g. myelofibrosis, mastocytosis,
leukaemia, lymphoma and Waldenstrom’s macroglobulinaemia. - Widespread polyostotic Paget’s disease or fibrous dysplasia—
usually multifocal rather than diffuse
2
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Neoplastic 5
A
- Metastatic—multiple randomly scattered lesions especially in the
axial skeleton. Solitary lesions in typical locations, e.g. sternum in
breast cancer, pelvis/sacrum/lower lumbar spine in prostate cancer. - Hypertrophic pulmonary osteoarthropathy—tramline sign:
linear, symmetrical uptake along the periphery of the long bones
(distal > proximal). Corresponds to the periosteal reaction seen on
plain film. See Section 1.24 for a list of causes. - Primary bone tumours—e.g. Ewing sarcoma, osteosarcoma.
Solitary, but may also have distant bone metastases - Erdheim-Chester disease*—skeletal involvement in 96%, typically
femur, tibia and fibula. Less commonly ulna, radius and humerus.
Bilateral symmetrical increased metadiaphyseal uptake
corresponding to osteosclerosis on plain film. - Eosinophilic granuloma/Langerhans cell histiocytosis*—variable
uptake (increased or decreased). Most common sites include skull,
pelvis and femur. Less common sites include ribs, humerus,
mandible and spine
3
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Joint disease 2
A
- Degenerative—most common sites include:
(a) Cervical and lumbar spine—facet joint arthropathy is often
best seen on posterior views, in the lumbar spine appearing to
lie between two adjacent vertebrae. Arthropathy at the
intervertebral disc is often best seen on anterior views due to
cervical and lumbar lordosis.
(b) Hips and knees—most commonly seen in the superior aspect
of the hip joints and medial compartment of the knees at the
site of maximal load.
(c) Shoulders—three potential sites of focal arthropathic uptake:
glenohumeral joint, acromioclavicular joint and greater
tuberosity (due to rotator cuff impingement).
(d) Other common sites—sternoclavicular joints, hands, ankles
and feet. - Inflammatory arthropathies—uptake is related to increased blood
flow to the affected joint, resulting in diffuse tracer accumulation
surrounding the joint rather than the focal uptake associated with
degenerative change. Distribution depends on the underlying
arthropathy.
4
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Fractures 4
A
- Traumatic—80% of fractures demonstrate tracer uptake on
bone scan 24 hours after injury (may be delayed in elderly/
osteoporotic patients). By 1 week, 100% of fractures are visible
on bone scan. Aligned fractures in ribs are always traumatic (i.e.
not pathological). With single lesions elsewhere, always ask if
history of trauma ± correlate with plain film. As the fracture
evolves, the bone scan appearances change with three distinct
phases:
(a) Phase 1—0 to 4 weeks: diffuse increased uptake at the fracture
site ± fracture line.
(b) Phase 2—4 to 12 weeks: intense linear uptake at the fracture
site.
(c) Phase 3—12 weeks to 2 years: gradual reduction in uptake. - Stress—caused by abnormal stress on a normal bone. Bone scans
are commonly used in their detection and can be combined with
SPECT-CT when evaluating smaller bones, e.g. hallux, sesamoids and pars defects. Bone scans can differentiate between tibial stress
fractures (focal uptake usually at the junction of the mid-distal
thirds of the tibia) and shin splints (periostitis at the insertion of
tibialis and soleus muscles causing longitudinal linear increased
uptake involving ≥ one-third of the posterior tibial cortex).
Enthesopathy and periosteal reactions related to stress will all show
increased uptake, e.g. plantar fasciitis shows focal uptake at the
inferior aspect of the calcaneum. - Insufficiency—caused by normal stress on an abnormal bone, e.g.
osteoporosis, metabolic bone disorders. Common sites include
tibial plateau, calcaneum, sacrum (H-shaped ‘Honda’ sign), lesser
trochanter of femur (especially in metabolic bone disorders) and
vertebral bodies (compression fractures). - Nonaccidental injury*—bone scans can detect radiologically
occult fractures and may be considered if the clinical suspicion
is high.
5
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Paget’s disease
A
Can affect any bone, but most commonly seen in the spine
(especially lower lumbar spine), femora, skull and pelvis.
Characterized by diffuse increased uptake within the affected
bone, often starting from one end and progressing until the entire
bone is involved. The associated bony expansion and
flame-shaped advancing edge may also be visible on bone scan.
The exception to this rule is in the skull, where the increased
uptake starts in the skull base and progresses to the vertex during
the lytic/active phase of the disease, corresponding to the classic
‘osteoporosis circumscripta’ on plain film.
70% of patients have polyostotic disease. On a bone scan the
intensity of tracer uptake can vary depending on the phase and
treatment of the disease. Complications—bone deformity, fracture
and malignant degeneration (e.g. osteosarcoma)—are often well
seen on bone scan due to the increased uptake in the underlying
Pagetic bone
6
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Infection 4
A
- Periprosthetic infection—see Section 15.3.
- Dental infection/sinusitis—including Garre’s sclerosing
osteomyelitis of the mandible. Focal uptake in the mandible or
maxilla. - CRMO/SAPHO—multifocal areas of uptake; CRMO usually occurs
in children or adolescents and favours metaphyses of long bones (especially femur and tibia, also clavicle); SAPHO usually occurs in
adults and favours sternoclavicular joints (commonest site of
involvement, bull’s head sign), manubriosternal joint,
costochondral joints, spine (paravertebral hyperostosis) and
sacroiliac joints (often unilateral). - Paediatric polyostotic osteomyelitis—6.8% of osteomyelitis in
infants is polyostotic (up to 22% in neonates) due to
haematogenous spread of infection. Bone scan is largely replaced
by MRI (whole-body STIR) but can still be useful in patients unable
to tolerate MRI
7
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Benign lesions
A
- Osteomas—skull and mandible; also ivory osteomas in paranasal
sinuses. - Fibrous cortical defect/nonossifying fibroma—variable uptake,
increased in healing or fracture. - Bone island—usually no uptake; low-grade uptake has been
reported in larger lesions. - Osteoid osteoma—increased uptake on blood pool images and
late (bone phase) images, ± a central intense focus of uptake
corresponding to the nidus on anatomical imaging, surrounded by
less intense uptake corresponding to the surrounding sclerosis. - Fibrous dysplasia—persistent increased uptake on bone scan;
20%–30% polyostotic, commonly unilateral and monomelic (one
limb). - Melorheostosis—monostotic or polyostotic, monomelic,
commonly involves long bones. - Osteochondroma—increased uptake in an adult suggests growth
or malignant degeneration. - Enchondroma.
- Heterotopic bone formation.
8
Q
FOCAL INCREASED UPTAKE ON
WHOLE-BODY BONE SCANS
Avascular necrosis (AVN
A
- <1 month—photopenia at the site of AVN.
- 1–4 months—increased uptake around the area of AVN due to
peripheral revascularization (e.g. ‘donut’ sign in the hip). - 4–10 months—diffuse increase at the site of AVN as healing
occurs. - > 10 months—either the scan returns to normal (uncomplicated
healing) or there is increased uptake due to sclerosis and
secondary degenerative changes
9
Q
INCREASED UPTAKE ON LOCAL VIEW
BONE SCANS 2
A
- Joint replacement—two-phase bone scans (blood pool and late)
are used to look for evidence of loosening or infection. Normal
scans have a high negative predictive value, but a significant
number of normal prosthetic joints continue to accumulate tracer
years after surgery.
(a) Loosening—typically shows increased uptake only on the late
phase images with normal uptake on the blood pool phase.
(i) Hips—focal increased uptake in the greater and lesser
trochanters and at the tip of the femoral prosthesis
suggests loosening.
(ii) Knees—normal uptake can persist for up to 4 years.
Uptake at the femoral prosthesis normalizes first, followed
by the lateral tibial prosthesis, with the medial tibial
prosthesis normalizing last. Any focal uptake not
conforming to this pattern is suspicious for loosening.
(b) Infection—increased uptake surrounding the prosthesis on
both the blood pool and late phase images.
(c) Synovitis/capsulitis—following knee replacement. Increased
uptake in the synovium/capsule on the blood pool phase
only. - Complex regional pain syndrome—two- or three-phase (dynamic
flow, blood pool and late) bone scan. Increased uptake in the
affected limb on all three phases in a periarticular distribution.
Over time this increased uptake normalizes; in chronic cases
decreased uptake may be seen on all phases
10
Q
INCREASED UPTAKE ON BONE SCANS
NOT DUE TO SKELETAL ABNORMALITY
Artefacts 6
A
- Urine contamination—can be anywhere.
- Extravasated injection in the arm/leg—± uptake in the draining
sentinel node. - Post surgery—increased uptake due to hyperaemia.
- Arterial injection—increased uptake in the injected arm distal to
the injection site. - Tracer preparation problems.
(a) Free pertechnetate—uptake in stomach, thyroid, GI tract and
salivary glands.
(b) Colloid formation due to aluminium—liver uptake, reduced
bone uptake.
(c) High pH—uptake in liver, gallbladder and GI tract. - Equipment.
(a) Edge effect—apparent increased uptake at the edges of the
field.
(b) Distance from camera/rotation of patient—bones closer to
the camera will appear to show increased uptake.
(c) Summation artefact—contamination of the collimator/
camera
11
Q
INCREASED UPTAKE ON BONE SCANS
NOT DUE TO SKELETAL ABNORMALITY
Physiological variants 6
A
- Epiphyses.
- Calcification of costal cartilages.
- Bladder diverticulum.
- Nipples.
- Renal anomalies.
- Hyperostosis frontalis.
12
Q
INCREASED UPTAKE ON BONE SCANS
NOT DUE TO SKELETAL ABNORMALITY
Soft-tissue uptake 2
A
- Calcification—e.g. myositis ossificans, dermatomyositis,
hyperparathyroidism, calcified tumours/metastases, vascular
calcification, calcific tendonitis, tumoural calcinosis, calcified
abscess and alveolar microlithiasis. - Others (noncalcified):
(a) Infarcts—cardiac, cerebral.
(b) Renal uptake—long term antibiotics, chemotherapy,
hypercalcaemia and hypercalciuria.
(c) Malignant pleural effusions and ascites.
(d) Metastases—commonly liver metastases from colon, breast or
small cell carcinoma.
(e) Amyloidosis—cardiac uptake.
(f) Tumour—e.g. inflammatory breast cancer.
(g) Hypercalcaemia with metastatic calcification—uptake in lungs
and stomach.
(h) Amiodarone lung
13
Q
PHOTOPENIC AREAS ON BONE SCANS
6
A
- Artefacts—the most common cause.
(a) External—metal objects, e.g. coins, belts, lockets and buckles.
(b) Internal—joint prostheses, pacemakers. - Lytic metastases—e.g. renal, thyroid and lung.
- Avascular lesions—e.g. bone cysts.
- Spinal haemangiomas—occasionally slightly increased uptake.
- Radiotherapy fields—nonanatomical, usually oblong in shape.
- Multiple myeloma*—bone scan often normal due to the lack of
osteoblastic activity; larger lesions may be photopenic or show
increased uptake.
14
Q
VENTILATION-PERFUSION MISMATCH ON V/Q SCANS Mismatched perfusion defects Perfusion defect > ventilation defect 8
A
- Pulmonary embolus—especially if multiple and segmental.
- Bronchial carcinoma—but more commonly matched.
- Tuberculosis*—typically affects an apical segment.
- Vasculitis—polyarteritis nodosa, SLE, etc.
- Tumour/fat embolus.
- Post radiotherapy.
- Pulmonary hypertension.
- Pulmonary artery narrowing.
15
Q
VENTILATION-PERFUSION MISMATCH ON
V/Q SCANS
Mismatched ventilation defects 5
A
- Chronic obstructive pulmonary disease (COPD).
- Pneumonia.
- Lung collapse—of any cause.
- Pleural effusion.
- Bronchial carcinoma—the rarest appearance
16
Q
MATCHED VENTILATION-PERFUSION
DEFECTS ON V/Q SCANS
Multiple 9
A
- Chronic bronchitis.
- Pulmonary infarct/chronic pulmonary embolus (PE)—do not confuse with the mismatched perfusion defect of acute PE.
- Asthma or acute bronchitis—may also show mismatched ventilation or perfusion defects.
- Bullae—long-standing bullae have scarce vessels and hypoventilation results in vascular constriction.
- Collagen vascular disease.
- Lymphangitis carcinomatosa.
- Pulmonary hypertension.
- Sarcoidosis*.
- Intravenous drug abuse.
17
Q
MATCHED VENTILATION-PERFUSION
DEFECTS ON V/Q SCANS
Solitary 3
A
- Pneumonia—results in hypoventilation and compensatory
hypoperfusion with a corresponding area of opacification on CXR
(triple match). This cannot be distinguished from a pulmonary
infarct on V/Q scan or CXR alone. - Bulla.
- Pulmonary infarct
