Ch.21 - Recognizing Abnormalities of Bone Density Flashcards
Role of conventional radiograph, CT, MRI:
Conventional radiograph –> Cortex is best seen in tangent.
CT –> Entire cortex is visualized.
MRI –> Particularly sensitive to assessment of the marrow.
Osteoblastic metastases, esp. from carcinoma of the prostate and breast, can produce:
FOCAL or GENERALIZED increase in bone density.
Other diseases that can increase bone density:
- Osteopetrosis.
- Avascular necrosis of the bone.
- Paget disease.
Hallmarks of Paget disease:
- Thickening of the cortex.
- Accentuation of the trabecular pattern.
- Enlargement and increased density of the affected bone.
Osteolytic metastases, esp. from lung, renal, thyroid, and breast cancer, can produce:
Focal areas of decreased bone density as can solitary plasmacytomas, considered to be a precursor to MM, the MC primary tumor of the bone.
Examples of diseases that can cause a generalized decrease in bone density include:
- Osteoporosis.
- Hyperparathyroidism.
- Rickets /osteomalacia.
Osteoporosis:
- Low bone mineral density and is most often either postmenopausal or age-related.
- Predisposes to pathologic fractures.
Pathologic fractures are those that occur:
With minimal or no trauma in bones that had a pre-existing abnormality.
Examples of diseases that can cause focal decrease in bone density include:
- Metastases.
- MM.
- Osteomyelitis.
Modality of choice in screening for skeletal metastases:
Radionuclide scan.
MRI –> To solve specific questions related to a lesion’s composition and extent.
There must be almost a …% reduction in the mass of bone in order for a difference in density to be perceived on conventional radiographs.
50%.
–> MRI is much more sensitive to the presence of medullary metastatic disease.
Causes of osteoblastic metastases:
- Prostate (MC in men).
- Breast - usually osteoLYTIC, but can be osteoBLASTIC, especially if treated.
- Lymphoma.
- Carcinoid tumors.
Causes of osteolytic metastases:
- Lung cancer –> MC in men.
- Breast cancer –> MC in females.
- RCC.
- Thyroid carcinoma.
Insufficiency fractures:
TYPE of a PATHOLOGIC fracture in which mechanically weakened bone fractures from a normal or physiologic stress.
Insufficiency fractures - MC in post menopausal women 2o to:
Osteoporosis.
Insufficiency fractures - Common sites:
- Pelvis.
- Thoracic spine.
- Sacrum.
- Tibia.
- Calcaneus.
Unlike other fractures that manifest themselves by a lucency in the bone, most insufficiency fractures display:
A sclerotic band (representing healing) on conventional radiographs.
Focal decrease in bone density:
- Metastatic disease to bone (osteolytic).
- Multiple myeloma.
- Osteomyelitis.
Metastatic disease to bone:
- Metastases to bone are far more common than primary bone tumors.
- Osteoblastic + Osteoclastic.
- UNCOMMON distal to the elbow/knee - when present, think widespread metastatic disease from lung/breast.
Study of choice for detecting skeletal metastases:
Radionuclide bone scan.
Diffuse decrease in bone density:
- Osteoporosis.
- Hyperparathyroidism.
- Rickets.
- Osteomalacia.
Some causes of vascular necrosis of the bone:
Intravascular –> SCA, polycythemia vera.
Vascular –> Vasculitis (lupus and radiation-induced).
Extravascular –> Trauma (fractures).
Idiopathic –> Exogenous steroids + Cushing/Legg-Calve-Perthes disease.
Focal increase in bone density:
- Carcinoma of the prostate (which can also cause a diffuse increase in bone density).
- Avascular necrosis of bone.
- Paget.
Diffuse increase in bone density:
- Carcinoma of the prostate (which can also cause a focal increase in bone density).
- Osteopetrosis.
Bone consists of:
A cortex of compact bone surrounding a medullary cavity containing cancellous bone arranged as trabeculae, separated by blood vessels, hematopoietic cells, and fat.
Almost all examinations of bone start with …?
Conventional radiographs obtained with at least 2 views exposed at 90 degrees angle to each other –> Orthogonal views.
Problems with conventional radiographs?
- Cannot visualize the entire circumference of a tubular bone.
- They are not particularly sensitive for demonstrating musculoskeletal soft tissue abnormalities, other than soft tissue swelling.
What is excellent to study bone marrow pathology?
MRI.
Cortical bone in MRI?
Has a very LOW signal intensity on conventional MRI.
MRI - Bone marrow disorders could be divided into 4 categories:
- Reconversion.
- Marrow replacement.
- Myeloid depletion.
- Myelofibrosis.
Reconversion refers to …?
Reversal of the normal conversion of the marrow cells so that red marrow repopulates bone from which it had been replaced by yellow marrow.
–> Chronic anemias (SCA) is an example.
Recognizing a generalized INCREASE in bone density:
- On conventional radiographs/CT –> Overall whiteness (sclerosis).
- Diffuse loss of visualization of the normal network of bony trabeculae in the medullary cavity –> Replacement by bone-producing elements.
- Loss of visualization of the normal corticomedullary junction.
Increase in bone density - Why is there loss of visualization of the normal corticomedullary junction?
Because of the abnormally increased density of the medullary cavity relative to the cortex.
Prototype for generalized increased in bone density?
Diffuse, blood-borne, metastatic disease from carcinoma of the prostate.
Metastatic disease to bone occurs in over …% of autopsied patients with carcinoma of the prostate.
80%.
Osteopetrosis is also called …?
Marble bone disease.
Focal sclerotic lesions can affect?
The cortex + Medullary cavity.
Focal sclerotic lesions - Those affecting the cortex …?
Usually produce periosteal new-bone formation (periosteal reaction), which leads to an appearance of thickening of the cortex.
Focal sclerotic lesions - Those affecting the medullary cavity …?
Will result in punctuate, amorphous sclerotic lesions surrounded by the normal medullary cavity.
Sclerotic lesions from metastatic carcinoma of the prostate are most often seen in …?
- Vertebrae.
- Ribs.
- Pelvis.
- Humeri.
- Femora.
What is currently the study of choice for detecting skeletal metastases from a carcinoma of the prostate?
Radionuclide bone scan.
Bone scans use IV administration of a minute amount of …?
Tc99m MDP –> Radioactively tagged tracer that affixes to bone.
Tc99m is the radionuclide used to tag …?
Methylene diphosphonate (MDP) –> The portion that directs the tracer to bone.
Activity in bone depends, in part, on its …?
Blood supply + Rate of bone turnover.
–> Processes with extremely high or extremely low bone turnover may produce FALSE (-) scans.
Osteoblastic lesions on bone scan?
Almost always show increased activity (greater uptake of the radiotracer).
Osteolytic lesions on bone scan?
ALSO usually show increased uptake of the radiotracer because of the repair that occurs in most, but NOT ALL, osteolytic processes.
MM and bone scan?
Bone scan is much LESS SENSITIVE in detecting MM because of its purely lytic nature –> Start with conventional radiograph of the skeleton.
Bone scans are sensitive or specific?
HIGHLY SENSITIVE, but not specific –> Require another procedure to rule out benign causes of positive bone scan.
2 causes of ivory vertebrae?
Metastases from breast/prostate.
What is the most sensitive modality for detecting avascular necrosis (AVN)?
MRI.
Why is it the MRI the most sensitive modality for detecting AVN?
Because AVN tends to affect the hematopoietic elements of the marrow earliest.
On conventional radiographs, the region of avascular necrosis appears …?
DENSER than the surrounding bone.
AVN on MRI?
There is usually a decrease from the normal high signal produced by fatty marrow.
On conventional radiographs, old medullary bone infarcts are recognized as …?
DENSE, amorphous deposits of bone within the medullary cavities of long bones, frequently marginated by a thin, sclerotic membrane.
Paget disease - Which sites are involves more commonly?
- Pelvis - MC.
- Lumbar spine.
- Thoracic spine.
- Proximal femur.
- Calvarium.
Paget disease is usually diagnosed using …?
Conventional radiography.
3 Imaging hallmarks of Paget disease:
- Thickening of the cortex.
- Accentuation of the trabecular pattern.
- Increase in the SIZE of the bone involved.
Recognizing a GENERALIZED DECREASE in bone density?
- Overall increase in lucency.
- Accentuation of the normal corticomedullary junction may be present in which the cortex stands out more strikingly.
- Compression of the vertebral bodies.
- Pathologic fractures may occur in the hip, pelivs, or vertebral bodies.
5 risk factors for osteoporosis:
- Exogenous steroids.
- Cushing.
- Estrogen deficiency.
- Inadequate physical activity.
- Alcoholism.
Osteoporosis predisposes to pathologic fractures in the …?
- Femoral neck.
- Compression fractures of the vertebral bodies.
- Fractures of the distal radius (Colles fracture).
Are conventional radiographs sensitive for detecting osteoporosis?
No, they are relatively insensitive.
How much bone must be lost before it is recognizable on conventional radiographs?
Almost 50%.
Findings of osteoporosis on conventional radiographs?
- Overall lucency of bone.
- Thinning of the cortex.
- Decrease in the visible number of trabeculae in the medullary cavity.
What is currently the most widely recommended method for bone mineral density measurements?
DEXA scan (Dual Energy X-ray Absorptiometry).
Some of the findings of hyperparathyroidism on conventional radiographs (4):
- Overall decrease in bone density.
- Subperiosteal bone resorption –> Radial side of the middle phalanges of the index + middle finger.
- Erosion of the distal clavicles.
- Well-circumscribed lytic lesions in the long bones called brown tumors and a salt-and-pepper appearance of the skull.
Brown tumors are also called …?
Osteoclastomas.
Time of growth plate closure in males and females?
Females –> 17.
Males –> 19.
The 3 imaging hallmarks of rickets:
- Fraying and cupping at the metaphyses of long bones including the ANTERIOR ends of the ribs –> rachitic rosary.
- Widening and irregularity of the epiphyseal plates.
- The bones are soft and pliable so there can be bowing of the femur and tibia.
Where is the rachitic rosary especially pronounced?
At the ends of bones where the max growth occurs such as the knees, wrists, and ankles.
Osteomalacia is MC due to?
Chronic renal failure.
Findings of osteomalacia on conventional radiographs:
- Overall decrease in bone density.
- Thinning of the cortex.
- Coarsening of the trabecular pattern due to resorption of secondary trabeculae.
- Pseudofracture (Looser line) –> HALLMARK.
What is the pseudofracture seen in osteomalacia?
A fracture that frequently occurs at multiple sites at the SAME TIME and is associated with NON UNION due to inadequate calcification of the healing fracture.
Common locations for pseudofractures in osteomalacia:
- Medial femoral neck + shaft.
- Pubic + ischial rami.
- Metatarsals.
- Calcaneus.
Pseudofractures typically appear as?
Short, lucent bands, at right angles to the cortex with sclerotic margins in later stages –> Frequently bilateral + symmetrical.
Focal decrease in bone density is produced by …?
Focal infiltration of bone by CELLS other than osteocytes.
On conventional radiographs, the classical findings of osteolytic metastases include:
Irregularly shaped, lucent bone lesions.
The osteolytic lesions are frequently characterized as belonging to one (or sometimes more) of 3 patterns:
- Permeative.
- Mottled.
- Geographic
in order of increasing size of the smallest and most discrete lesion visible.
Osteolytic metastases typically incite … or … reactive bone formation around them.
LITTLE or NO.
Osteolytic metastases in the spine preferentially destroy the …?
PEDICLES –> Pedicle sign.
Solitary form of MM:
Often seen as a soap-bubbly, expansile lesion in the spine or pelvis = Solitary plasmacytoma.
The MC early manifestation of MM is …?
DIFFUSE + SEVERE osteoporosis.
Plasmacytomas appear as …?
Expansile, separated lesions, frequently with associated soft tissue masses.
Later, in the disseminated form of MM …?
Multiple, small, sharply circumscribed (described as punched-out) lytic lesions of approx. the same size are present –> Usually without any accompanying sclerotic reaction around them.
Conventional radiographs or radionuclide bone scans more sensitive for MM?
Conventional radiographs.
Bone scans tend to underestimate the number + extent of lesions due to the absence of reactive bone formation.
Why osteomyelitis in children tends to occur in the metaphysis?
Because of its rich blood supply.
Findings of acute osteomyelitis on conventional radiographs:
- Focal cortical bone formation.
- Periosteal new bone formation.
- Soft tissue swelling + focal osteoporosis from hyperemia.
In adult osteomyelitis, the infections tends to …?
Involve the joint space more often than in children producing not only osteomyelitis but also septic arthritis!
Conventional radiographs may take up to … to display the first findings of osteomyelitis.
10 days –> MRI first.
Radionuclide scan for demonstration of osteomyelitis:
INDIUM-tagged white-cell scan.
