FDG Extravasation During Breast Cancer Staging
A 68-year-old woman with right-sided invasive ductal carcinoma comes for FDG PET/CT staging. A 12.6 mCi (466 MBq) dose is injected through a 24-gauge catheter in the right hand. Ten minutes into the 60-minute uptake she reports burning; there is a 4-cm area of swelling and erythema at the site. The syringe and tubing are assayed afterward at 5.2 mCi. Images show intense focal uptake at the right wrist and a linear streak of activity up the forearm. SUV analysis is requested, and the surgeon wants to know whether the right axilla is involved before operating in two days. The rest of the study is otherwise of good quality, and the patient lives 90 minutes away.
1. Can you calculate the infiltrated activity from these numbers? What does the extravasation do to the SUV data?
Read the worked answer
No - the numbers do not give the infiltrated activity.
- 12.6 mCi was in the syringe before injection; 5.2 mCi remained in the syringe and tubing.
- That means 7.4 mCi left the syringe, but the split between systemic circulation and peri-venous tissue is unknown. Some of the "missing" activity is in the vein, some in the soft tissues, and some is retained in the dead space of the catheter.
- Quantifying the tissue fraction requires imaging the site against a known standard or a well-count comparison - and even then it remains an estimate.
Effect on SUV: SUV is activity concentration divided by (administered activity ÷ body weight). If only ~8–9 mCi reached the blood pool but SUV is normalized to 12.6 mCi, all SUV values are underestimated, including the liver reference. Because the error is roughly proportional, tumour-to-liver ratios are partially preserved, but absolute thresholds and Deauville-style grading lose validity. State this explicitly in the report rather than quoting numbers the referring team will compare against published cut-offs.
2. Can the right axilla be reported as negative? What do you recommend to the surgeon?
Read the worked answer
No. Report the right axilla as indeterminate, not negative.
- The extravasation is at the wrist, and the forearm streak indicates lymphatic drainage from the injection site toward the epitrochlear and axillary chains. Activity in transit can mimic or mask axillary nodes.
- Scatter and reconstruction artefacts from the intense wrist focus further degrade the ipsilateral axilla.
- The clinical cost of a wrong answer here is high: it changes the axillary surgical approach in two days.
Options to offer the surgeon:
- Axillary ultrasound with fine-needle aspiration - fast, low-dose, and decisive if positive; do this first if the axilla is the pivotal question.
- Repeat PET on another day with a left-arm injection - justified only if the result would change management and the axilla cannot be resolved by ultrasound; this means another ~10 mSv and another 90-minute journey.
- Proceed to sentinel node biopsy as planned and treat the PET axillary finding as non-contributory.
What you must not do is let a study compromised by extravasation quietly become a "negative axilla" in the chart.
3. Describe your immediate management of the extravasation and the reporting and documentation that follows.
Read the worked answer
Immediately
- Stop the injection; disconnect and gently aspirate any residual at the cannula tip; remove the catheter.
- Apply a warm compress and elevate the arm; mark the borders of the swelling and measure it.
- Check distal perfusion, sensation and capillary refill; ask about pain, numbness or blistering.
- Reassure the patient, and give her written advice to return or call if pain, blistering, induration or numbness develops. She lives 90 minutes away - make sure she has a direct contact number and understands she should not wait until the next appointment.
Documentation and reporting
- Record the time, site, gauge, activity before injection, residual assay, appearance, patient symptoms and instructions given.
- Notify the authorized user and the RSO and file an incident report.
- This is typically not a 10 CFR 35.3045 medical event - the intended radiopharmaceutical reached the intended patient by the intended route - but the RSO confirms the institutional/state position, and the event is logged and reviewed.
- If a repeat study is later justified, document the clinical rationale and the additional dose estimate before scheduling it.