Learning reflectance confocal microscopy of melanocytic skin lesions through histopathologic transversal sections

Abstract

Histopathologic interpretation of dermoscopic and reflectance confocal microscopy (RCM) features of cutaneous melanoma was timidly carried out using perpendicular histologic sections, which does not mimic the same plane of the image achieved at both techniques (horizontal plane). The aim of this study was to describe the transverse histologic sections research technique and correlate main dermoscopic features characteristic of cutaneous melanoma (atypical network, irregular globules and pseudopods) with RCM and histopathology in perpendicular and transverse sections in order to offer a more precise interpretation of in vivo detectable features. Four melanomas and 2 nevi with different dermoscopic clues have been studied. Lesion areas that showed characteristic dermoscopic features were imaged by dermoscopy and confocal microscopy and directly correlated with histopathology in perpendicular and transverse sections. We presented the possibility to perform transverse sections as a new approach to understand RCM features. Atypical network showed different aspects in the 2 melanomas: in one case it was characterized by pleomorphic malignant melanocytes with tendency to form aggregates, whereas in the other elongated dendritic cells crowded around dermal papillae, some of them forming bridges that resembled the mitochondrial aspect at confocal and histopathology transversal sections. Pigment globules in melanomas and nevi differed for the presence of large atypical cells in the former, and pseudopods showed up as elongated nests protruded toward the periphery of the lesion. Transverse histologic research sections have a consistent dermoscopic and confocal correlate, and it may represent an help in confocal feature interpretation and an advance in improving melanoma diagnosis and knowledge of the biology of melanocytic lesions.

Figure 1. Superficial spreading melanoma in situ.

This lesion shows on dermoscopy (A) a slightly pigmented network (white circle corresponds to the punch area). RCM mosaic image (B, 1×1 mm) at the level of the DEJ shows irregular and dishomogeneous dermal papillae with dendritic cells (white arrows). RCM individual image (C, 0,5×0,5 mm) at the level of the DEJ shows dendritic cells forming “bridges” called mitochondria-like structures (white arrow). Perpendicular section (D) shows disarrangement of the rete ridge and the increased number of atypical melanocytes. Transverse section (E, HE staining) shows atypical melanocytes protruding into the dermal papillae forming bridges (black arrows). Transverse section (F, Melan-A staining) shows cells positive for Melan-A protruding into the dermal papillae (white arrows).

Figure 2. Superficial spreading melanoma in situ.

This lesion shows on dermoscopy (A) a broadened pigmented network (white circle corresponds to the punch area). RCM mosaic images (B and D, 1×1 mm) at the level of the DEJ show demarcated and non-demarcated rings separated by loosely thick interpappilary spaces (white arrows) and some plump bright cells and bright dots are visible within dermal papillae (arrowheads). Perpendicular section (C) shows disarrangement of the rete ridge and the increased number of atypical melanocytes in the epidermis. Transverse section (E) shows predominance of atypical melanocytes, isolated or in nests, enlarging the interpapillary spaces (black arrow).

Figure 3. Melanocytic Nevi.

These lesions show typical network (A) and regular globules (D), on dermoscopy. RCM mosaic image (B, 1×1 mm) at the level of the DEJ shows rings of bright polygonal cells surrounding roundish to oval dark areas corresponding to dermal papillae at DEJ. Transverse section (C) shows isolated melanocytes arranged around the dermal papillae and there are nevus cells nests within the epidermis. RCM mosaic image (E, 1,5×1,5 mm) at the level of the DEJ and dermis shows compact aggregates of large polygonal cells similar in morphologic features and reflectivity, forming polyhedral structures. Transverse section (F) shows dense nests composed of nevus cells within the dermis surrounded by a narrow band of epidermis.

Figure 4. Superficial spreading melanoma, Breslow thickness 0,8 mm.

This lesion shows on dermoscopy (A) irregular globules (white circle). RCM mosaic image (B, 1,5×1,5 mm) at the level of the DEJ shows irregularly shaped clusters (white arrow). Perpendicular section (C) shows compact aggregates of atypical melanocytes with a slight intercellular discohesion. RCM individual image (D, 0,5×0,5 mm) at the level of the DEJ shows a cluster with cells that are nonhomogeneous in morphologic features and reflectivity (white arrows). Transverse section (E) shows large amount of atypical melanocytes predominantly in nests with variable size and shape within the epidermis and the dermis. The black arrow points to the nest that makes the exact correlation with confocal image.

Figure 5. Superficial spreading melanoma, Breslow thickness 0,79 mm.

This lesion shows on dermoscopy (A) pseudopods (white circle corresponds to the punch area). RCM mosaic image (B, 3×3 mm) at the level of the DEJ shows compact aggregates of atypical cells distributed in a linear arrangement toward the periphery with a dense nest at the extremity (the area inside the dashed square is represented in figure C). RCM individual image (C, 0,5×0,5 mm) at the level of the DEJ shows a pseudopod in detail, characterized by elongated, dense and bright peripheral aggregate. Perpendicular section (D) shows nests of atypical melanocytes distributed contiguously toward the periphery along the DEJ. Transverse section (E) shows nests of atypical cells arranged in a linear manner throughout the periphery of the lesion (black arrows).