Mohs Surgery vs Primary Excision for Eyelid BCCs

Abstract

Introduction: The aims of management of basal cell carcinoma are for complete excision, and minimise damage to the surrounding tissues. Our aim is to compare the proposed defect of a primary excision biopsy with the actual defect following Mohs micrographic surgery on the same lesions.

Materials and Methods: A cohort of 23 patients about to undergo Mohs micrographic surgery for eyelid basal cell carcinomas was recruited. The lesions were assessed regarding size and location. A digital photograph of the lesions pre Mohs excision and the defects post Mohs excision for analysis on the Photoshop Adobe package using the caliper function to measure the eyelid lesion, and defects and to calculate the area.

Results: All 18 patients had solitary basal cell carcinomas; 9 (50%); 10 of the 18 cases having a larger proposed primary excision defect and the remaining 8 cases a larger post-Mohs micrographic surgery defect area.

Discussion: Basal cell carcinoma is the most common non-melanoma malignant eyelid tumour. The results supported basal cell carcinomas, particularly morphoeic types, are difficult to examine, and location is a poor predictor of recurrence. We did not find that Mohs micrographic surgery universally reduces the size of the defects area. However, if the primary aim of the surgery is to cure the patient and prevent recurrence, Mohs is still the best choice.

KEYWORDS::

• Ophthalmology
• Oculoplastics
• Basal cell carcinomas
• Mohs micrographic surgery

Declaration of interest: For this study there has been no support/funding recieved by the authors to carry out the study, or any other commercial relationships relevant to the article’s subject matter. We confirm no conflict of interest.

VARIABLES INVOLVED IN MEASUREMENTS OF DEFECTS FROM THE DIGITAL PICTURES

• 1. The surface field of the defect is not parallel to the camera, but the measuring strip is.

  This would make the apparent measurements of the defect smaller than the true value.

The variation calculation is

Y = x/cosØ

Where Y is the true value of the defect, x is the apparent measurement on the measuring strip, and Ø is the angle of the surface of the defect from the parallel to the camera/measuring strip.

• For 5°. Y = 1.004x

• For 10°. Y = 1.02x

• For 15°. Y = 1.04x

• For 20°. Y = 1.06x

• For 30°. Y = 1.15x

• For 45°. Y = 1.41x

• 2. The surface defect is parallel to the camera but the measuring strip is not.

  This would make the apparent measurement of the defect larger than the true value.

The variation calculation is

Y = xcosØ

• For 5°. Y = 0.996x

• For 10°. Y = 0.985x

• For 15°. Y = 0.966x

• For 20°. Y = 0.940x

• For 30°. Y = 0.866x

• For 45°. Y = 0.707x

• 3. Both defect and measuring strip are not parallel with camera.

  This can make the apparent measurement bigger or smaller than the true measurement of the defect. This variation is a combination of 1. and 2.

• 4. The variation caused by perspective caused by the measuring strip being a distance in front of the defect.

This is difficult to calculate. But due to the relatively small distances involved should be negligible.