Q Regarding bone marrow imaging, which of the following are true?
A. Only 10% of an injected 99mTc sulphur colloid dose is taken up by bone marrow
B. A bony metastasis classically shows as a hot spot on a marrow scan
C. In normal adults, activity should not be seen in femora
D. Appendicular extension of bone marrow activity is not seen in myelofibrosis
Explanation
Correct Answer: A.
More than 90% of the injected dose is removed by the reticuloendothelial system (mainly the liver and spleen, obscuring images of the lower thoracic spine and ribs) and the remaining 10% localises in bone marrow. Bone marrow scans have a limited clinical role, but can show extramedullary haemopoiesis, guide red marrow biopsies and help identify bony infarcts in sickle cell anaemia (cold spots).
As these scans demonstrate active red marrow, any process that replaces normal marrow will show as a photopenic defect. Focal defects are also seen in infarction, osteomyelitis, radiotherapy and Pagets disease.
In normal adults, it is usual to see activity extending as far as the proximal third of the femur and humerus. Extension beyond this is abnormal. In neonates, red marrow extends to the peripheries, but with age the marrow retracts and adopts the adult pattern. Therefore, the scan appearance is age dependent.
There is decreased central activity (due to marrow fibrosis), but peripheral marrow hyperplasia is seen in 50% of patients. Peripheral marrow extension is also seen in all forms of haemolytic anaemia, Hodgkins disease and polycythaemia rubra vera. However, with recovery, normal central activity may be seen with peripheral extension. Other causes of reduced central marrow activity include: chronic myeloid leukaemia, myelofibrosis, chronic renal failure, lymphoma, multiple myeloma, metastases and radiotherapy.
A. Only 10% of an injected 99mTc sulphur colloid dose is taken up by bone marrow B. A bony metastasis classically shows as a hot spot on a marrow scan C. In normal adults, activity should not be seen in femora D. Appendicular extension of bone marrow activity is not seen in myelofibrosis Explanation
Correct Answer: A.
More than 90% of the injected dose is removed by the reticuloendothelial system (mainly the liver and spleen, obscuring images of the lower thoracic spine and ribs) and the remaining 10% localises in bone marrow. Bone marrow scans have a limited clinical role, but can show extramedullary haemopoiesis, guide red marrow biopsies and help identify bony infarcts in sickle cell anaemia (cold spots).
As these scans demonstrate active red marrow, any process that replaces normal marrow will show as a photopenic defect. Focal defects are also seen in infarction, osteomyelitis, radiotherapy and Pagets disease.
In normal adults, it is usual to see activity extending as far as the proximal third of the femur and humerus. Extension beyond this is abnormal. In neonates, red marrow extends to the peripheries, but with age the marrow retracts and adopts the adult pattern. Therefore, the scan appearance is age dependent.
There is decreased central activity (due to marrow fibrosis), but peripheral marrow hyperplasia is seen in 50% of patients. Peripheral marrow extension is also seen in all forms of haemolytic anaemia, Hodgkins disease and polycythaemia rubra vera. However, with recovery, normal central activity may be seen with peripheral extension. Other causes of reduced central marrow activity include: chronic myeloid leukaemia, myelofibrosis, chronic renal failure, lymphoma, multiple myeloma, metastases and radiotherapy.