Excision Comparison Tool

Compare the relative area and length of standard rhomboid 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 the shape of a “rhomboid” (as it is traditionally called, although it is not entirely rhomboid in the mathematical sense). 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, for certain neoplasms, such as atypical nevi, recommended margins are less clearly defined. This tool may prove helpful when considering whether to take a 2 or 4 mm margin for an atypical nevus.

This tool may also assist in selecting an appropriate treatment. Certain treatment modalities can achieve similar cure rates with smaller margins.

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

Our 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 Rhomboid

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

$A=\frac{d^2}{2}\times \left(\sqrt{a^2-1}+\arcsin \left(\frac{1}{a}\right)\right)$

Where a is the length to width ratio and d is the width (or the diameter of the circle). This 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 ↩︎