Line field confocal optical coherence tomography for the non-invasive diagnosis of basal cell carcinoma

Introduction Basal cell carcinoma (BCC) is the most common skin cancer in the general population. Treatments vary from surgical excision with Mohs or standard technique to photodynamic therapy, cryotherapy, ablative laser, topical Imiquimod or 5-Fluorouracil, depending on the subtype. Non-invasive methods such as reflectance confocal microscopy (RCM) and optical coherence tomography (OCT) have gained a foothold in the daily practice to optimize diagnosis and subtype-oriented treatment, with high sensitivity and specificity. The new device Line-field confocal OCT (LC-OCT) allows imaging at higher resolution compared to conventional OCT, whilst reaching a higher detection depth than RCM. In this ongoing study, a new LC-OCT device was used to pre-operatively image lesions suspicious for BCCs, in order to determine structured criteria for the bedside diagnosis of BCCs based on the known OCT and RCM patterns, compared to histology. Material and Methods Fifty clinically suspicious BCC were enrolled in the study. Each lesion was imaged using dermoscopy, OCT, LC-OCT and confocal microscopy (Vivascope®). The LC-OCT device (DAMAE Medical, Paris) is based on a two-beam interference microscope with line illumination allowing three imaging modalities: vertical, en-face and 3D. Results In vertical mode, nodular BCCs are clearly visible as sharply demarcated tumour nests, hyporefrective compared to the surrounding layers, with palisading of the peripheral cells and surrounded by a dark rim corresponding to clefting. Cystic subtypes show dark, cystic structures in the center, while pigmented subtypes display bright cells in the nests. Nodular tumours are often surrounded by a hyperrefrective stroma. In superficial BCCs, smaller, interconnected basaloid nests are attached to the lower part of the epidermis, reproducing a “string of pearls” structure as in OCT. Infiltrating BCCs are identified by strands and cords of atypical basaloid cells, similar to the “shoal of fishes” structures described in OCT. The higher resolution compared to OCT allows a quicker and easier diagnosis with less confounding. However, as in RCM, deeper BCC nests might not be easily identified. In en-face mode, slightly altered epidermal architecture with enlarged spaces between keratinocytes shows an atypical honeycombed pattern as in RCM, sometimes with radial streaming, with disrupted DEJ; at the depth of the upper dermis, BCCs appear as in RCM as roundish or cord-like hyperrefrective nests with peripheral palisading, surrounded by dark clefting and bright stromal reaction. In infiltrating BCCs, tumour islands are just hinted at through dark shadows. Dilated and canalicular blood vessels are also visible. Discussion Thanks to its nearly cellular resolution and high penetration depth, LC-OCT combines the advantages of RCM and OCT and allows the non-invasive, real time diagnosis of BCCs and their subtypes. Main architectural patterns described in OCT and RCM are also recognizable in vertical and en-face mode, respectively. Tumour nests surrounded by a dark rim and bright stromal reaction characterize nodular BCCs, while smaller nests arranged in a string of pearls structure correspond to superficial tumours. Infiltrating tumours create a shoal of fishes pattern. In our experience, the vertical mode provides a more intuitive diagnosis compared to the en-face. However, the combination of the two-visualisation modes increases the diagnostic accuracy. The 3D function allows a 3D reconstruction.