Sonography outperforms nuclear medicine for lymph node detection

Contrast-enhanced lymphosonography finds more sentinel lymph nodes than can established nuclear medicine techniques, according to preliminary animal studies focusing on melanoma.

Dr. Barry Goldberg, director of diagnostic ultrasound at Thomas Jefferson University Hospital, and colleagues studied how the location of melanoma tumors in swine affected the number of sentinel lymph nodes associated with each tumor. They used contrast-enhanced sonography, established nuclear medicine methods, and blue dye-guided surgery to find and evaluate lymph nodes.

When results of the two minimally invasive techniques were compared with the surgical method, the researchers found that lymphosonography performed significantly better than nuclear medicine. They reported their findings at the 2006 RSNA meeting.

Twenty-four swine had 39 melanoma tumors, 10 of them in the head and neck. Blue dye-guided surgery, the gold standard for sentinel lymph node location, found a total of 47 sentinel lymph nodes for those 10 head and neck tumors. Surgery located a total of 94 sentinel lymph nodes for the 29 tumors located in other parts of the body. More sentinel lymph nodes per tumor for melanoma were located in the head and neck, an average of 4.7 nodes per tumor versus 3.24 per tumor elsewhere in the body.

Both of the minimally invasive methods were more accurate when detecting sentinel nodes in the body than in the head and neck, but contrast-enhanced lymphosonography outperformed nuclear medicine in both groups. Lymphosonography using Sonazoid (GE Healthcare, Oslo) detected 77% of the sentinel lymph nodes for tumors in the head and neck, while nuclear medicine using technetium-99m found only 58%. For melanoma tumors located in other parts of the body, lymphosonography detected 94% of the sentinel lymph nodes, while nuclear imaging found 73%.

No human trials have been conducted, but improvements in the detection of sentinel lymph nodes could improve staging. Goldberg has conducted previous studies using other animal models to investigate how accurately lymphosonography can detect specific levels of metastases in sentinel lymph nodes.

Dr. Emma Starritt and colleagues published a study in 2005 in the Annals of Surgical Oncology examining the threshold at which high-resolution ultrasound could detect metastases in sentinel lymph nodes of human melanoma patients. They located the sentinel lymph nodes using nuclear imaging, then used high-resolution ultrasound without contrast to try to detect metastases. They could detect only metastases 4.1 mm in diameter or larger.