Metabolic Bone Disease - Radiology (13.01.2020) Flashcards
Main imaging methods
X-rays
CT
Bone densitometry
=> density
MRI
Radionuclide bone scans
=> biochemical composition (MRI), bone turnover (RBS)
Radiological sign vs. pathology
Pathology
- A disease process that gives rise to symptoms, signs,
biochemical disturbances and changes in imaging
appearance.
Radiological sign
- A change in imaging appearance, whether structural or functional, that may point towards a pathology
-> not the same thing
Osteoporosis
Decreased quantity of bone mass
Microstructure normal
- gives rise to:
Fragility fractures
Deformity
Pain
Radiological diagnosis of osteoporosis
- Diagnosis is with bone densitometry (aka dual-energy absortiometry, DEXA)
- A measure of bone mineral density (BMD)
- Compares BMD to normal reference databases
and gives
▪ T-score (ref database white adult premenopausal females)
▪ Z-score (ref database age and sex matched) - T-score -1.5 to -2.5 = osteopenia; less than -2.5 = osteoporosis
FRAX
fracture risk assessment tool
=> likelihood of major fracture in 10 years time
-> as a practitioner it will also give you guidelines re management
What do you see radiologically in osteoporosis?
- Loss of cortical bone/thinning of cortex
- Loss of trabeculae
- Insufficiency fractures (due to normal stress on abnormal bones)
=> not easy to differentiate between osteoporosis and osteomalacia
Insufficiency fractures
- due to normal stress on abnormal bones
- e.g. in sacrum, underside of femur neck, pubic rami, vertebral bodies
- XR/CT: density
- MRI: chemical composition
- Bone scan: bone turnover. Areas of increased uptake, Honda sign
Osteomalacia
- Decreased bone mineral
- Osteopenic bone
- Soft bones
- Too much un-mineralised osteoid:
Looser’s zone
- Compensatory: secondary hyperparathyroidism may be superimposed if calcium stays low
Osteomalacia vs. Rickets (radiology)
- Radiology depends on age and closure of growth plate.
Osteomalacia
- Mature skeleton
- Osteopenia
- Looser’s zones
- Codfish vertebrae
- Bending deformities
Rickets
- Before growth plate closure
- Radiological signs centred mainly to growth plates
- Changes of osteomalacia
- Indistinct/frayed metaphyseal margin
- Widened growth plate without calcification
- Cupping/splaying metaphyses due to weight bearing (not clean margin, normally it is a very nice clean cut margin; also widened metaphysis)
- Enlargement of anterior ribs
- Osteopenia (bending of the bones, soft bones)
Looser’s zones
Pseudo/insufficicnecy fractures at high tensile stress areas
- Medial proximal femur
- Lateral scapula
- Pubic rami
- Posterior proximal ulna
- Ribs
=> typically short Lucent lines, whiter around the fracture (sclerosis, attempt to lay down new bone)
Codfish vertebrae
- Biconcave deformity of vertebrae (should be a bit concave normally, but these are exaggerated)
- also, they are larger radiologically
- Seen in
- Osteoporosis
- Osteomalacia
Rickets - radiological features
- Indistinct/frayed metaphyseal margin
- Widened growth plate without calcification
- Cupping/splaying metaphyses due to weight bearing (not clean margin, normally it is a very nice clean cut margin; also widened metaphysis)
- Enlargement of anterior ribs
- Osteopenia (bending of the bones, soft bones)
Hyperparathyroidism
- Primary (due to parathyroid adenoma)
- PTH up, calc down, phosphate down
- Bone resorption
- Secondary(duetoothersystemicbiochemical imbalance, chronic kidney disease, rickets/osteomalacia)
- PTH up, calc down, phophate normal or down
- Bone resorption AND increased density
- Tertiary (autonomous)
- PTH up, calc up, phosphate down
Common theme:
- bone resorption
- increased density
Bone resorption in HPT
- Subperiosteal
- Subchondral (e.g. dark gleonoid fossa)
- Intracrotical (salt and pepper skull)
- Brown tumours (not a real malignancy, caused by collection of large cells
Renal osteodystrophy
-> collection of bone changes in renal disease
Osteomalacia and osteoporosis
Secondary hyperparathyroidism
- Subperiosteal erosions, brown tumours
- Sclerosis – vertebral endplates giving a rugger jersey spine (sclerosis of end plate, resorption of middle part of vertebrae)
- Soft tissue calcification (vessels, cartilages) -> gap between knee and tibia should be dark but: meniscus calcified)
Paget’s disease
- Disease of bone remodelling
- Lytic phase
- Mixed lytic/sclerotic phase
- Sclerotic phase
- Bone pain, deformity, spontaneous fractures
- usually one bone, unlikely to jump over joints
- May get nerve entrapment (because bones expand in the sclerotic phase), spinal stenosis and
deafness - Osteogenic sarcoma
- Raised serum alk phos, urinary hydroxyproline,
pyridinoline cross-links
Radiological aspects of Paget’s disease
- Cortical thickening
- Bone expansion
- Coarsening of trabeculae
- Osteolytic, osteoclerotic and mixed lesions
- Osteoporosis circumscripta (in scalp)
=> most patients found in the mixed or in the sclerotic phase.
What can radiology show in terms of bones?
- Imaging can reveal structural failures such as fractures and ligamentous injuries
- Also serves as proxy to metabolic dysfunction
What does DEXA stand for?
dual energy x-ray absorptiometry
Insufficiency fractures - how do they appear on scans?
XR/CT: looks at density
- initially normal
- later you may get some callus, periosteal reaction
- more commonly increased sclerosis around fracture lines (you see loosened line and white (sclerosis as an attempt to heal) surrounding it.
MRI: looks at chemical composition
- acute: bone oedema i.e. low signal on T1, high signal in T2 and STIR
Bone scan: looks at bone turnover.
- increased bone turnover as the bone attempts to heal
- Areas of increased uptake, Honda sign in stress fractures
What does the imaging in osteomalacia depend on?
- on the age and if the growth plates have closed.
In which conditions are codfish vertebrae seen?
- osteomalacia
- osteoporosis
Conclusion
- Use the right tools for the right pathology
- Remember bone has a structural as well as a
metabolic role. - Some radiological signs are characteristics
but many will be common to different pathologies. Thus always start from first principles.
When is a salt and pepper skull seen?
- in hyperparathyroidism, brown tumours in the skull
rugger jersey spine
- sclerosis of end plate, resorption of middle part of vertebrae
- center of vertebrae dark, edges are white on XR or CT
- seen in renal osteodystrophy (here secondary hyperparathyroidism)
Mickey Mouse sign
- seen in Paget’s disease on bone scan
- increased uptake by a single vertebrae
- when 1 vertebrae is affected
- thick cortex, coarse trabeculae, bigger
