Ultrasound-only guidance is technically feasible for a substantial proportion of cryoablation procedures, Alex Barnacle (Great Ormond Street Hospital, London, UK) reported at the 2019 annual meeting of the British Society of Interventional Radiology (BSIR; 13–15 November, Manchester, UK). Using ultrasound instead of computed tomography (CT) for intraprocedural imaging eliminates the radiation burden, which Barnacle said “is of primary importance”, especially when treating children.
“Wherever possible, ultrasound is the preferred imaging modality in paediatric interventional radiology, to avoid or minimise radiation dose in childhood,” she stated. Therefore, Barnacle and colleagues set out to investigate if ultrasound-only guidance was viable for intraprocedural navigation, and an assessment of their initial experience proves that it is.
The team reviewed all cryoablation procedures performed at their institution, and selected those for which only ultrasound was used. They collected their data prospectively, and had institutional review board approval for the study.
Over 29 months, interventionalists at Great Ormond Street Hospital performed 25 cryoablation procedures using only ultrasound as image guidance. Twenty-one lesions were treated in 20 children; most of these were soft tissue lesions in the extremities. “The age range and therefore the weight range was really diverse in this paediatric group”, Barnacle said. The median age was 11.4 years (ranging from five months to 16.5 years), and the median weight was 37.9kg (ranging from 7.5kg to 94.2kg). Whilst cone beam CT was available as back up for all cases, no procedure required the investigators to convert to CT guidance.
Since starting a new ablation service, interventional radiologists at the London-based paediatric hospital have been referred increasingly complex cases. “As often happens when you start a new service, you get sent quite a hodgepodge of cases,” Barnacle explained. “We were often sent patients as a last resort, where people had tried every other therapy first, so our initial experience was with a whole bunch of different conditions, from venous malformations to fibro-adipose vascular anomaly (FAVA), which is one of the primary diseases that we use cryoablation for in our centre.” Incidentally, this latter pathology was the first condition in children for which treatment with cryoablation was fully described. “Increasingly,” Barnacle continued, “we are being referred more aggressive diseases, and some oncological diseases as well.”
Detailing some examples of these more complex cases, Barnacle went on to describe a patient with a fast flow vascular anomaly in their forearm. Surgical debulking had been attempted twice previously, but had been followed by rapid regrowth. There was a large vessel in the centre of the lesion, and the arm was “very hot”, Barnacle recounted. “We wanted to cryoablate this,” she said, “but we were not sure what to do about the temperature.” The interventionalists performed an angiogram and embolized the central vessels, before going on to cryoablation. This had “really good results”, according to Barnacle, who enthused: “We are trying to push the boundaries with what we are doing in these patients.”
This involves being more aggressive in their treatment. Whilst Barnacle and colleagues used a range of one to five probes per procedure for the 20 patients in this study, they now sometimes use significantly more than five in some circumstances. The team use a standard freeze-thaw cycle twice, and lots of hydrodissection. Commenting on this, Barnacle opined: “I think this just reflects the fact that many of these lesions are very superficial, especially in children, who by their very nature do not have much subcutaneous fat.”
Speaking from the floor, Society of Interventional Oncology (SIO) president-elect Matthew Callstrom (Mayo Clinic, Rochester, USA) asked about the natural history of these vascular malformations in children, and how aggressive Barnacle felt the interventionalists need to be to have an impact on tumour growth over time. “Do you treat the entire mass, or do you try and treat 80%—what is your goal?”, he asked.
“We are getting more aggressive now,” Barnacle replied. “The nice thing is you are not having to get margins, so you have some leeway. […] Increasingly, we are trying to get the whole thing in one go.” However, she cautioned against using very aggressive cryoablation with large ice balls in very small children, describing a one-and-a-half-year-old patient who did not respond well to this type of intervention. “She was pretty unwell for a few days [after cryoablation]”, Barnacle reported. “She clearly had some kind of immune response and a cytokine storm afterwards. She tolerated the second procedure much better, when we used a decreasing dose of steroids over a week and gave her antibiotics and other support, but that initial experience made us wary.”