Detection of basal cell carcinomas in Mohs excisions with fluorescence confocal mosaicing microscopy British Journal of Dermatology

Background High-resolution real-time imaging of human skin is possible with a

confocal microscope either in vivo or in freshly excised tissue ex vivo. Nuclear and

cellular morphology is observed in thin optical sections, similar to that in conventional

histology. Contrast agents such as acridine orange in fluorescence and

acetic acid in reflectance have been used in ex vivo imaging to enhance nuclear

contrast.

Objectives To evaluate the sensitivity and specificity of ex vivo real-time imaging

with fluorescence confocal mosaicing microscopy, using acridine orange, for the

detection of residual basal cell carcinoma (BCC) in Mohs fresh tissue excisions.

Methods Forty-eight discarded skin excisions were collected following completion

of Mohs surgery, consisting of excisions with and without residual BCC of all

major subtypes. The tissue was stained with acridine orange and imaged with a

fluorescent confocal mosaicing microscope. Confocal mosaics were matched to

the corresponding haematoxylin and eosin-stained Mohs frozen sections. Each

mosaic was divided into subsections, resulting in 149 submosaics for study. Two

Mohs surgeons, who were blinded to the cases, independently assessed confocal

submosaics and recorded the presence or absence of BCC, location, and histological

subtype(s). Assessment of confocal mosaics was by comparison with corresponding

Mohs surgery maps.

Results The overall sensitivity and specificity of detecting residual BCC was 96Æ6%

and 89Æ2%, respectively. The positive predictive value was 92Æ3% and the negative

predictive value 94Æ7%. Very good correlation was observed between confocal

mosaics and matched Mohs frozen sections for benign and malignant skin

structures, overall tumour burden and location, and identification of all major

histological subtypes of BCC.

Conclusions Fluorescent confocal mosaicing microscopy using acridine orange

enables detection of residual BCC of all subtypes in Mohs fresh tissue excisions

with high accuracy. This observation is an important step towards the long-term

clinical goal of using a noninvasive imaging modality for potential real-time surgical

pathology-at-the-bedside for skin and other tissues.