Extravasation During a Bone Scan Injection
Mr. R is a 68-year-old man with metastatic prostate cancer and new bone pain, booked for a whole-body bone scan. The prescribed activity is 740 MBq of Tc-99m MDP. You establish a 22 G IV in the right antecubital fossa. During the injection Mr. R flinches and pulls his arm back; a 3 cm soft-tissue swelling appears at the site and you feel resistance on the plunger. After removing the needle you measure the syringe plus tubing in the dose calibrator: 410 MBq remains. The department is fully booked, the next camera slot is tomorrow at 09:00, and the referring physician has already told the patient the scan will "show whether the cancer has spread."
1. Set out your immediate actions and show how you decide whether to give more activity.
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Immediate actions: stop injecting, remove the needle, apply gentle pressure then a warm compress and elevate the arm, and mark the site so it is not later read as pathology.
Dosimetry reasoning, not guesswork:
- Delivered = 740 − 410 = ~330 MBq systemically, with an unknown but substantial fraction of the 410 MBq retained in the arm/tubing.
- Counting syringe and tubing gives an upper bound on residual, so my estimate of the infiltrated activity is uncertain - I state that uncertainty rather than inventing a number.
- I do not simply re-inject the missing 410 MBq. That would add to total patient dose for a study that may still be interpretable, and the residual in the arm will partly clear into the circulation over hours anyway.
- Options: (a) proceed with ~330 MBq and accept longer imaging times; (b) give a modest supplement (e.g. ~150–200 MBq at a fresh, proximal site) to reach a workable count rate; (c) reschedule.
The choice belongs to the authorized user/radiologist; my job is to give them the numbers and the image quality implication. Everything is documented on the requisition, including the site of infiltration.
2. Three hours later the images show intense focal soft-tissue activity in the right antecubital fossa and axilla, and skeletal uptake that looks faint. There is a questionable focus in the right 7th rib. Do you report the study as is, repeat tomorrow, or do something else?
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I would not let the study leave the department without a diagnostic-quality decision by the radiologist.
What the artefacts mean:
- The arm and axillary activity is retained dose in the extravasated limb - it is not metastatic disease, but it also degrades the adjacent shoulder/rib cage and any axillary node assessment.
- Faint skeletal uptake means poor count statistics, and a single equivocal rib focus on a low-count image is exactly the situation where noise is read as disease.
The judgement:
- If the clinical question is "are there widespread bone metastases," a low-count scan of the axial skeleton may still answer it, and repeating for cosmetics adds dose without changing management.
- If the question turns on that rib focus, the study is non-diagnostic for that question. Options are a delayed repeat limited to the thorax tomorrow (lower activity, longer acquisition, better statistics), or a different modality.
- My action: escalate to the radiologist with the time-activity history, the estimated administered activity, and my opinion on which questions the study can and cannot answer. Document the same. Tell the patient honestly that the injection partly went into the tissue, that this is common and settles, and that we may need part of the test again - the referring physician has already raised the stakes by promising a definitive answer.