The Excision Comparison Tool

Compare the relative area and length of standard rhombic surgical excisions with variable margins.

Lesion Size (in cm):
Excision A Margin Size (in mm):
Excision B Margin Size (in mm):
Compare Excisions

Excision	Area (cm²)	Length (cm)
Excision A
Excision B

About This Tool

Skin cancer is typically excised in a "rhombic" or "rhomboid" shape (see below). Traditionally, the length to width ratio is 3:1.¹

To achieve a certain cure rate, a specific margin size is selected—generally 1 to 2 centimeters for melanoma, or 4 mm for basal cell carcinoma, among others. However, the margins needed can vary based on the surgical technique used, with Mohs surgery requiring smaller margins than wide local excision to achieve a similar cure rate.

For instance, in the study "Clinical Characteristics of Basal Cell Carcinomas of the Vulva: An Institutional Retrospective Review" by Munoz et al., vulvar basal cell carcinomas were treated with either Mohs surgery using 3 mm margins or vulvectomy with 6 mm margins.²

This tool shows that for a 1 cm basal cell carcinoma, vulvectomy results in a scar that is 38% longer and requires the removal of 89% more skin.

Calculating The Area of The Rhombic Excision

The area of the rhombic excision was previously described by Tilleman et al as:

Where a is the length to width ratio and d is the width/diameter of the surgical defect. Note that for a standard 3:1 rhombic excision, the above equation simplifies to A = 1.5841*d² .

This formula can be derived from the below image. To do so, add the area of the circle to the area of four triangles (only one is pictured in the image), and then subtract the area of the sector of the circle occupied by the triangles.

1. Raveh Tilleman T, Tilleman MM, Krekels GA, Neumann MH. Skin waste, vertex angle, and scar length in excisional biopsies: comparing five excision patterns–fusiform ellipse, fusiform circle, rhomboid, mosque, and S-shaped. Plast Reconstr Surg. 2004 Mar;113(3):857-61. doi: 10.1097/01.prs.0000105338.66597.a0. PMID: 15108876. ↩︎
2. Muñoz G, Singla P, Hurst E, Council ML. Clinical Characteristics of Basal Cell Carcinomas of the Vulva: An Institutional Retrospective Review. Dermatol Surg. 2023 Jan 1;49(1):13-16. doi: 10.1097/DSS.0000000000003648. PMID: 36533789 ↩︎