High-frequency 30-MHz sonography in preoperative assessment of tumor thickness of primary melanoma: usefulness in determination of surgical margin and indication for sentinel lymph node biopsy

Abstract

Background: High-frequency sonographic imaging has been used for the preoperative evaluation of primary malignant melanoma. In the present study, to identify the usefulness of 30-MHz sonography for determination of the surgical margin and indication for sentinel lymph node biopsy, the correlation between sonometric and histometric tumor thickness was investigated.

Methods: A total of 74 primary melanomas, in patients seen at the dermatology clinic, Shinshu University Hospital, from 1998 to 2006, were evaluated using high-frequency sonographic equipment with two probes (15 MHz and 30 MHz), and tumor thickness was measured using electronic calipers before surgical treatment. All the primary lesions were surgically excised and Breslow's tumor thickness was measured histologically.

Results: In 68 melanomas, excluding 2 lesions of melanoma in situ and 4 lesions with poor sonographic images, sonographic and histologic thickness showed good correlation (r = 0.887). Particularly, in 26 melanomas affecting the soles of the feet, sonographic and histologic thickness showed excellent correlation (r = 0.945). Regarding the T categorization, in which T1-T4 are divided at 1, 2, and 4 mm in thickness, the categories determined with sonometry corresponded very well to those determined with histometry. The correspondence was particularly excellent in thinner primary lesions with thickness around 1 mm. We excised almost all these primary melanomas with surgical margins based on the sonometric thickness. In 22 patients with sonometric thickness more than 1 mm, sentinel lymph node biopsy and/or radical lymphadenectomy was performed.

Conclusion: High-frequency sonography (30-MHz) is very useful in the preoperative prediction of tumor thickness, particularly in thinner primary lesions, which allows us to determine surgical margins and indication for sentinel lymph node biopsy.