Quality of the Surgical Piece in Mohs Micrographic Surgery for Periocular Basal Cell Carcinomas Using a Slit Knife is Better Than Using a Conventional Scalp.

Sir,

Performance of Mohs micrographic surgery (MMS) for basal cell carcinomas (BCC) requires a 45°-angled incision. This condition is difficult to achieve in irregularly shaped areas such as the periocular region (mainly in the internal canthus). Furthermore, no clinical trials have been conducted to address the recurrence of BCCs depending on whether they were treated with MMS versus conventional surgery.[1] Some authors have suggested a similar recurrence rate among both procedures, which has been linked to a deficient surgery procedure due to the difficulty in achieving the 45° angle.[2] To solve this problem, a surgical tool usually used in ophthalmological surgery has been suggested: slit knives (SK).[3] The SK has a long grip for easy handling; its head provides a 45° angle and a pointed tip with a bilateral bevel. These characteristics allow a complete excision with a single circular movement in the most comfortable direction for the surgeon.

The objective of this study was to compare the quality of the surgical piece after performing MMS for BCC in the periocular area by using either a conventional n° 15 scalpel (CS) or SK.

A quasi-experimental study with a non-equivalent control group was performed. Consecutive patients who underwent MMS for periocular BCC were included from May 2017 to September 2019. The dermatologist surgeon decided at his own discretion which tool to use: CS or SK (Alcon, ClearCut, slit knife, double bevel, angled, 2.75 mm [Alcon, Fort Worth, TX]) [Figure 1]. Epidemiological variables were compiled as well as BCCs and surgical procedure data. The pathological slides processing was carried out by the same two technicians. The quality of the piece was blinded-evaluated (only the surgeon knew which tool was used) by a pathologist by using a 1–10 scale referring to two aspects: quality of borders (10 points being the ideal MMS specimen with completely smooth borders and 1 being the worst score referring to a piece with such serrated borders that it avoided the usual processing) and global quality for histopathological processing (10 points being the specimen with the ideal shape that showed no problems when processing the piece and 1 being the worst score referring to an specimen that is impossible to process for MMS). The study was approved by the local ethics committee.

Figure 1

Cutting process with SK

Altogether, 49 periocular BCC were included. Of them, 24 BCC underwent MMS using CS and 25 with SK. No differences were found regarding baseline characteristics or BCC variables of both groups except age (CS group with a median of 67 years and SK group with a median of 53 years, P = 0.02) and location (SK was used mainly in inner canthus and CS in the lower eyelid, P < 0.01). No recurrent BCCs were included.

Referring to the quality of the obtained pieces during MMS, the median score for the quality of borders was 8 when using CS and 9 when using SK (P = 0.03). The median global quality for histopathological processing was 7.5 when making use of CS and 8 when employing SK (P = 0.04). All results are presented in Table 1.

Table 1

Complete epidemiological, BCCs and surgical procedure data. CS: Conventional scalp. SK: Slit knife

	CS group	SK group	P
Number of patients	24	25	-
Mean age (years)	67	53	0.02
Male %	41.7	48	0.87
Locations
Inner canthus	8	20	<0.01
Lateral canthus	2	1
Upper eyelid	1	0
Lower eyelid	13	4
Histopathological subtypes
Infiltrative	18	17	0.39
Micronodular	0	3
Superficial	1	0
Expansive	1	1
Nodular	0	1
Non-refered	4	3
Median BCC size (mm)	7	8	0.64
Number of MMS stages
1	16	19	0.71
2	8	5
3	0	1
Borders quality (median)	8	9	0.03
Global quality (median)	7.5	8	0.04

These results suggest that SK is at least as good as the CS to perform MMS for periocular BCC. In fact, a higher percentage of BCC were located in the inner canthus when SK was used, which is the most difficult place to perform the 45°-angle incision. Given this, if both groups had included BCC in similar locations, the differences could have been even wider. The main limitation is the absence of randomisation, which led to groups differences, and the strength in the pathologist blinded evaluation of the pieces.

In conclusion, this sample encourages us to use SK for MMS in irregularly shaped areas such as the periocular location and also in other types of surgery as in the outer ear canal. More studies are needed to assess if the use of SK for MMS in periocular BSS can improve the recurrence rate compared with CS.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.