“The first thing we look at is the general architecture of the node. Resting and reactive nodes have a hypoechoic hilus and a hyperechoic cortex. As they become infiltrated with tumor, the hilus becomes more hyperechoic, and areas of metastasis stand out as much more hyperechoic than the surrounding node.”
Another tip-off is overall shape. If the ratio of the long axis to short axis diameter is less than 2, the lymph node is more likely to be malignant, she said.
“One more important factor that can’t be seen on CT is the node’s vascular pattern. Both resting and reactive nodes tend to have a centralized vascular pattern in the hilus. With tumor infiltration you start to see an asymmetrical vascularization as the nodes are replaced by tumor. The perfusion becomes much more peripheral.”
Cost is another consideration, Dr. Ruiz said. Five CT scans conducted over the recommended 2 years of follow-up will run about $5,000. Five scans with magnetic resonance imaging come in at about $6,500. PET CT is, of course, the most expensive, racking up a national average cost of $28,500 for five scans.
Ultrasound is amazingly inexpensive, Dr. Ruiz said. The national average cost of one scan is around $180, bringing the 2-year cost of five surveillance scans to $900.
Finally, clinicians and patients should consider the potential impact of repeated radiation exposure. “This can really add up over the follow-up period. Because there’s a 10-year latency period for these cancers, this might not be an issue for our older patients, but it really is something to consider in younger ones. “
However, she acknowledged that it’s not a completely rosy picture.
“Ultrasound is very user dependent, but we do think that by putting this in the hands of dermatologists with special training, we can solve this issue. In Europe, ultrasound’s very high sensitivity and specificity, combined with clinical exams, really improves disease detection.”
Unfortunately, at this point, anyone who wants to learn the technique has to go to Europe. “I trained in Germany, where I took a standard 3-day course, did 250 supervised scans, and completed an exam. I realize that’s unrealistic for most people,” she said. But a training protocol is being developed at Brigham and Women’s, under the auspices of the institution’s imaging experts, who felt that 3 days and 250 supervised scans was excessive. The Brigham and Women’s program comprises 8 hours of didactic training and at least 30 supervised scans with at least three abnormalities correctly identified, and will be put into place soon, Dr. Ruiz said.
The biggest obstacle to large-scale adoption of this protocol is data – there are not a lot, at least now.
“We are working on that, too. In conjunction with the Skin Cancer Foundation, we’re launching a prospective study. We want to recruit 80 patients with T2B/T3 cutaneous SCCs. They get both and ultrasound and a CT scan at diagnosis and every 6 months for 2 years,” she said.