CT-Guided Thermal Ablation of a Femoral Neck Osteoid Osteoma in a Ten-Year-Old

Options.

• NSAIDs alone. Symptoms often resolve spontaneously over 2–3 years as the lesion matures. This avoids procedural risk but means years of medication with gastrointestinal and renal effects, missed school, and continued night pain. It is a reasonable choice for a mildly symptomatic child or one with a nidus dangerously close to critical structures.
• Open curettage or excision. Highly effective but more invasive, requires a larger exposure, and in the femoral neck carries risks of fracture, growth disturbance, and avascular necrosis.
• Percutaneous thermal ablation (radiofrequency or cryoablation). Success is above 90%, with immediate pain relief in most children, minimal recovery, and small access tracts. It is first-line at most pediatric centers.

Choosing here. The proximity to the physis and articular cartilage is the deciding factor. Thermal injury can cause growth arrest or chondrolysis, so a 4-mm margin demands active protection: hydrodissection or gas dissection to displace the physis and capsule, an internally cooled or cryoablation probe, and careful multiplanar planning of the approach. Cryoablation offers better visualization of the ice ball and possibly a lower risk of chondral injury, at the cost of longer procedure time. Multidisciplinary discussion with orthopedics and shared decision-making with the family should replace the pre-booked curettage.

Dose-reduction strategies.

• Use the CT scanner's fluoroscopy mode with last-image-hold, pulsed low-dose fluoroscopy, and collimation to the region of interest; avoid continuous fluoroscopy.
• Limit diagnostic-quality acquisitions to a single pre-procedure planning scan and a short post-procedure check; use 80–100 kVp and tube-current modulation, and consider iterative reconstruction.
• Use an anterolateral or lateral approach that avoids the gonads and minimizes beam-on time; mark the skin entry point with a radiopaque marker on the planning scan rather than repeated fluoroscopic probing.
• Consider ultrasound or MRI guidance where the lesion is visible, and consider MR-guided high-intensity focused ultrasound, which avoids ionizing radiation entirely.
• Keep the anesthesiologist and the family informed of cumulative dose during long cases.

Metrics to record.

• CT dose index volume (CTDIvol) and dose-length product (DLP) for each acquisition, plus cumulative DLP.
• Fluoroscopy time and air kerma at the reference point; peak skin dose if the case is prolonged.
• Compare against pediatric diagnostic reference levels for the procedure and use the data for quality improvement.
• The teaching point for the family: diagnostic CT and CT-guided intervention are not the same dose, and a focused pediatric protocol is a fraction of an adult abdomen/pelvis study.

Clinical confirmation is primary.

• Night pain typically resolves within days to a few weeks. Ask specifically about night pain and analgesic use at 2–6 weeks and at 3 months; resolution is the best evidence of success.
• If pain persists beyond 6–8 weeks, consider incomplete ablation, a second nidus, or an alternative diagnosis, and re-image.

Imaging follow-up.

• No routine CT. The ablation zone and surrounding edema can look worrisome for months and do not correlate with outcome.
• If imaging is needed, MRI without contrast is preferred: it shows the ablation defect and marrow edema without ionizing radiation. Expect edema to persist for 3–6 months and to resolve over a year.
• Reserve CT for procedural planning of a repeat ablation, using a limited low-dose protocol.

Counseling points.

• Warn about the small risk of fracture in the femoral neck and give activity guidance for the first 6 weeks.
• Mention the small risk of skin burn and of growth disturbance given the proximity to the physis, and document the thermal-protection measures used.
• Arrange orthopedic follow-up with radiographs at 6 weeks and 3 months to monitor the physis and hip joint rather than repeated cross-sectional imaging.