An examination of the cutoff value of the depth of invasion for prophylactic neck dissection in stage I/II tongue cancer.

In stage-I/stage-II oral tongue cancer, the cutoff value of depth of invasion (DOI) for prophylactic neck dissection is controversial. To examine the relationship between the DOI and the rate of occult lymph node metastasis. In addition, to examine the relationship between the DOI evaluated by magnetic resonance imaging (MRI) and pathological DOI. In this retrospective study, 95 patients with clinical T1-2/N0M0 oral tongue cancer were enrolled. The rate of occult lymph node metastasis per DOI between 2 and 11 mm was calculated from the total pathological lymph node metastasis and delayed neck metastasis cases. We measured DOI using MRI and compared DOI obtained from pathology. The total rate of occult lymph node metastasis was 23.9%. In the rate of occult lymph node metastasis per DOI, there were two peaks at point of 5 to 6 mm and 9 to 10 mm. And there was a significant correlation between the DOI evaluated by MRI and the pathological DOI (Pearson's correlation coefficient was 0.87). There was no consistent increase in the rate of occult lymph node metastasis per DOI. MRI was a useful modality to measure the DOI.