Education, Research & Development
Bone Case 5 Answers
1) Are there any abnormal areas of uptake?
There are multiple areas of increased activity through the axial skeleton and proximal long bones.There is absent renal activity but tracer is seen within a enlarged, irregular bladder.
2) What term is often ascribed to these appearances?
When there is absent renal activity, it tends to be called a "superscan".However, there are superscans and superscans.
Some grossly abnormal scans may be (bizarrely) difficult to call abnormal and it is always worth checking for all the other scintigraphic features.
Other features include:
Soft tissue uptake. Generally speaking, the more tracer that is taken up by the bone, the less soft tissue uptake will occur.The ratio of uptake in bone: soft tissue is often most markedly raised in metabolic disease Bladder activity. Again, the more tracer that is taken up by bone, the less renal tract excretion will occur.
Activity in skull and long bones. This tends to be seen more in metabolic bone disease and actually decreased in metastatic disease. The "headless" appearance in metastatic superscans is a recognized phenomenon.
Unusual bone activity patterns such as prominent costochondral junctions and 'tie' sign in sternum
3) Give a differential diagnosis
4) But given the clinical information, what is the likely diagnosis?
Differential diagnosis includes:
Metastatic disease - tracer uptake tends to be patchy and irregular. This can
be minimal in advanced disease and it can be difficult to distinguish from metabolic
causes on scintigraphy alone. Prostate cancer is the most likely primary but the literature cites breast, lymphoma, stomach, nasopharyngeal as known to cause superscans
Osteomalacia - shares features of metabolic bone disease but may be associated with pseudofractures
Hyperparathyroidism - most commonly seen as a secondary or tertiary phenomenon in chronic renal failure with renal osteodystrophy.
Delayed imaging - simply imaging at longer period of time than usual (3-4hrs) will simply allow more bone uptake and may mimic a bone scan.
Other metabolic bone disorders such as fluorosis, renal tubular acidosis, hypervitaminosis D, and rickets.
Congenital bone disorders such as osteopetrosis can cause such appearances
Myeloproliferative disorders (such as systemic mastocytosis, Waldenstrom macroglobulinemia, Leukemia, aplastic anemia, myelofibrosis,)
Hyperthyroidism is often cited but I cannot find a reference to it and I suspect this of being a medical urban myth promoted by too many post-graduate medical MCQs.
Actual diagnosis - metastatic prostate cancer. Click here or here to see other examples of superscans due to disseminated prostate cancer. Click here to see an example of a superscan due to secondary hyperparathyroidism in chronic renal failure
The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.