CHICAGOIn a surprising discovery, reported at RSNA 2007, researchers from Germany have found that whole-body staging of patients with recently diagnosed malignant melanoma using either MRI or PET/CT could miss a substantial number of metastatic lesions (see cover art).
More than 50,000 US patients will be diagnosed each year with melanoma, according to the National Cancer Institute. The disease is usually confined within a skin lesion but can spread through the body during advanced stages. Good prognosis depends on accurate tumor staging, which is done with CT, MRI, ultrasound, or scintigraphy.
The whole-body exam has recently been recognized as the most accurate for staging. Radiologists must be aware, however, that regional or lymph node metastases could appear within a few months of the resection of a melanoma, and they cannot trust blindly in the primary imaging performed immediately after surgery, said Florian Vogt, MD, of the Department of Diagnostic and Interventional Radiology at the University Hospital of Essen.
"You should always scan these patients at least a couple of times within 1 year of the primary staging. There might be future metastases, so these patients need long-term follow-up," Dr. Vogt said in an interview.
Dr. Vogt and colleagues enrolled 60 consecutive patients who underwent whole-body 1.5T MRI and whole-body FDG-PET/CT for staging of regional lymph nodes (N) and distant metastases (M) after primary tumor resection. The investigators followed the American Joint Committee on Cancer Staging guidelines for tumor classification and used biopsy and clinical follow-up as gold standards.
Two radiologists interpreted MR images, while PET/CT scans were read by one radiologist and one nuclear physician; 56 patients completed the mean follow-up of 748 days.