Dermatology: Practical and Conceptual Image Letter | Dermatol Pract Concept. 2025;15(4):5743 1 Line-field Confocal Optical Coherence Tomography Features of Merkel Cell Carcinoma Gerardo Palmisano1,2,3, Jacques Lasudry4, Lucas Boussingault1,5, Véronique del Marmol1,5, Ketty Peris2,3, Mariano Suppa1,5,6 1 Department of Dermatology, Hôpital Erasme, HUB, Université Libre de Bruxelles, Brussels, Belgium 2 Departement of Dermatology, Catholic University of the Sacred Heart, Rome, Italy 3 UOC di Dermatologia, Dipartimento di Scienze Mediche e Chirurgiche, Fondazione Policlinico Universitario A. Gemelli – IRCCS, Rome, Italy 4 Department of Ophthalmology, Hôpital Erasme, HUB, Université Libre de Bruxelles, Brussels, Belgium 5 Department of Dermatology, Institut Jules Bordet, HUB, Université Libre de Bruxelles, Brussels, Belgium 6 Groupe d'Imagerie Cutanée Non Invasive (GICNI) of the Société Française de Dermatologie (SFD), Paris, France Key words: Merkel Cell Carcinoma, LC-OCT, Skin Imaging Citation: Palmisano G, Lasudry J, Boussingault L, del Marmol V, Peris K, Suppa M. Line-field Confocal Optical Coherence Tomography Features of Merkel Cell Carcinoma. Dermatol Pract Concept. 2025;15(4):5743. DOI: https://doi.org/10.5826/dpc.1504a5743 Accepted: April 27, 2025; Published: October 2025 Copyright: ©2025 Palmisano et al. This is an open-access article distributed under the terms of the Creative Commons Attribution- NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original authors and source are credited. Funding: None. Competing Interests: None. Authorship: All authors have contributed significantly to this publication. Corresponding Author: Gerardo Palmisano, Departement of Dermatology, Catholic University of the Sacred Heart, Rome, Italy. ORCID ID: 0009-0000-9681-1681. Email: palmisanogerardo@gmail.com Case Presentation A 74-year-old male presented with a 1 cm rapidly grow- ing red ulcerated nodule located on the right upper eyelid (Figure 1A). Dermoscopy showed arboriform and linear ves- sels and structureless pinkish-white areas (Figure 1B). Based on clinical and dermoscopic criteria, the differential diagnoses included basal cell carcinoma (BCC), amelanotic melanoma, and Merkel cell carcinoma (MCC). Line-field confocal opti- cal coherence tomography (LC-OCT) examination displayed a flattened dermal-epidermal junction due to the nodular der- mal proliferation of hyporeflective nests separated by hyper- reflective collagen septa with some bright round cells, better highlighted in the horizontal image (Figures 1C and D). In addition, basaloid lobules with millefeuille pattern, indicating BCC, or nests of atypical melanocytes were absent. Hence, the dermal proliferation of hyporeflective nests and bright round cells at LC-OCT, as previously described by Soglia et al. [1], raised the suspicion of MCC, which was later confirmed by the histopathological examination (Figure 1E). Teaching Point MCC is an aggressive neuroendocrine tumor with often unspecific clinical and dermoscopic features [2] that is histopathologically characterized by dermal nodules with cells clustered in sheets or nests (Figure 1E). LC-OCT, through its high resolution and penetration, may be a valid additional tool in the diagnosis of MCC [1]. LC-OCT’s non-invasive, real-time, near-histologic resolution allows visualization of dermal proliferation of hyporeflective nests and bright cells as well as peri-nodular black silhouettes 2 Image Letter | Dermatol Pract Concept. 2025;15(4):5743 corresponding to extensive neoangiogenesis due to rapid tumor growth displayed by dermoscopy as arboriform and linear vessels. References 1. Soglia S, Pérez-Anker J, Fraghì A, et al. Line-field confocal optical coherence tomography and reflectance confocal mi- croscopy of Merkel cell carcinoma.  J Eur Acad Dermatol Venereol. 2023;37(10):e1223-e1225. DOI:10.1111/jdv.19211. PMID: 37191203. 2. Gauci ML, Aristei C, Becker JC, et al. Diagnosis and treatment of Merkel cell carcinoma: European consensus-based interdisciplin- ary guideline - Update 2022. Eur J Cancer. 2022;171:203-231. DOI:10.1016/j.ejca.2022.03.043. PMID: 35732101. A B C D E Figure 1. Clinical, dermoscopic, vertical, and horizontal LC-OCT and histopathological appearance of Merkel cell carcinoma of the right upper eyelid in a 74-year-old male. Clinical appearance of a nodular lesion localized on the right upper eyelid (A). Dermoscopy revealed the presence of arboriform and linear vessels and structureless pinkish-white areas (B). Vertical LC-OCT showed a flattened dermal-epidermal junction due to dermal nodular proliferation with perinodular vessels (red arrows). The dermis presented hyporeflective nests (red circle) separated by collagenous septa (green arrow) and bright round cells (C), prominent in the horizontal image (red star) (D). His- topathological examination showed dermal proliferation of layers and nests of small homogeneous cells, somewhat discrete, interspaced by connective septa (H&E staining, 100x) (E).