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Other Layers (Basal Cell Layer, Dermal-Epidermal Junction and Upper Dermis)

By means of RCM, basal cells appear at a depth of approximately 50 to 100 μm below the stratum corneum. Going in depth, dermal papillae correspond to dark round to oval areas circumscribed by refractive cells, corresponding to melanocytes and melanin-rich keratinocytes.

Architecture

Predominant overall pattern

Examining skin lesions, the overall architecture is evaluated on «Mosaics» acquired at the DEJ, corresponding to a montage of full resolution individual images at a given depth «stitched» together to create a collage image with an area ranging between 4x4 to 8x8 mm, showing a portion or the whole lesion.

One or more of the following patterns can be present in a lesion:

Ringed Pattern

Predominance of edged papillae at DEJ corresponding to dermal papillae surrounded by a rim of small bright cells appearing as bright rings sharply contrasting with the dark background (Fig. 23,24).

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Figure 23. Overall ringed architecture in a 4x4 mm mosaic

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Figure 24. At full resolution the architecture shows up to be constituted by rings of bright cells surrounding dermal papillae

Meshwork Pattern

Predominance of junctional thickenings corresponding to enlargements of the inter-papillary space formed by aggregated cells and/or clusters bulging within the dermal papilla in contiguity with the basal layer (Fig. 25,26).

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Figure 25. Overall meshwork architecture in a 4x4 mm mosaic. Meshes are enlarged, sometimes showing nests bulging within dermal papillae

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Figure 26. At full resolution the architecture appears to be constituted by junctional nests enlarging interpapillary spaces

Clod Pattern

Predominance of dense compact or dense&sparse clusters of melanocytes within dermal papillae. Also presence of «white papillae» (see definition in the «Aggregate» section) may defined a clod pattern (Fig.27,28).

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Figure 27. Overall clod architecture in a 4x4 mm mosaic, constituted by round to ovoid globular structures corresponding to junctional and/or dermal discrete melanocytic nests

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Figure 28. At full resolution the architecture appears to be constituted by roundish dermal dense melanocytic nests, fulfilling the papillary space

Aspecific Pattern

Lack of one of the previous patterns, resulting in a non specific architecture, constituted by sheets of cells or uneven undefined structures.

A non uniform architecture constituted by unevenly distributed dermal papillae, irregular in size and shape, usually without a demarcated rim of bright cells (non edged papillae), and separated by series of large reflecting cells (Fig. 29,30), is typically observed in Melanomas.

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Figure 29. Aspecifc pattern. In this example dermal papillae are still detectable, but they are unevenly distributed throughout the lesion and are irregular in size and shape. Dermal papillae usually show a not clearly outlined contour (non edged papillae), appearing separated by series of bright cells, sometimes clustered into non discrete junctional aggregates

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Figure 30. At full resolution, non edged and irregular papillae show up, usually along with some atypical cells

Sometimes in Melanomas, a complete disarrangement of the dermal-epidermal architecture, and the marked cell proliferation, forming sheets or non discrete aggregates of atypical cells at the DEJ and in the upper dermis, result in the complete disruption of the rete-ridge. Dermal papillae are not visible anymore, and the diagnosis is suggested by the cytology (Fig. 31,32).

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Figure 31. In this exaple, proliferation of bright atypical cells in shhet-like structure obscures dermal papillae and DEJ architecture. Remnants of DEJ architecture and papillae are still present at the periphery of the lesion (invasive Melanoma)

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Figure 32. At full resolution, the sheet-like structure appears to be constituted by pleomorphic cells, with bright cytoplasm and dark nucleus, corresponding to malignant melanocytes

In non melanocytic skin malignancy, such as Basal Cell Carcinomas and Squamous Cell Carcinomas, dermal-epidermal architecture is disarranged, with complete loss of dermal papillae pattern. Tumour mass proliferation causes the disruption of the rete ridge. Predominantly in Basal Cell Carcinomas, tumour mass silhouettes are visible on mosaics, usually dark in non-pigmented tumours, but showing irregular bright reflective structures in the middle of the parenchyma in pigmented ones (Fig. 33,34).

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Figure 33. Aspecific architecture in Basal Cell Carcinoma, presenting large tumour islands appearing as dark silhouettes in the mosaic

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Figure 34. At full resolution, dark silhouettes correspond to aggregates of tightly packed cells, forming cords and nodules

Papillary contour features

After defining the overall pattern/s, characteristic descriptors of dermal-epidermal junction are taken into account, particularly focusing on the definition of the outlines of dermal papillae contours.

1. Edged papillae

Edged papillae correspond to dermal papillae with clearly outlined contours. An «Edged papilla» may results circumscribed by a rim of refractive cells, appearing as bright rings sharply contrasting with the dark background (Fig. 35,36), or by «Junctional nests» constituted by compact melanocytic aggregates with sharp borders (Fig. 37).

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Figure 35. Edged papillae, with typical cells, surrounded by rings of bright cells

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Figure 36. Edged papillae, with typical cells, surrounded by rings of bright cells

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Figure 37. Edged papillae, surrounded by dense, compact junctional nests

2. Non edged papillae

Non edged papillae are reported for the observation of dermal papillae without a demarcated rim of bright cells, but separated by a series of large reflecting cells (Fig. 38, 39) or by non discrete aggregates of melanocytes at the DEJ (Fig. 40).

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Figure 38. Non edged papillae, separated by series of reflecting cells, also showing few atypical bright cells at the DEJ

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Figure 39. Non edged papillae, with atypical cells at the DEJ

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Figure 40. Non edged papillae, separated by non discrete aggregates of melanocytes at the DEJ

3. Edged & Non edged papillae

Edged & Non edged papillae corresponds to the presence of both the above descriptors within the same lesion.

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Figure 41. Edged&Non edged papillae. On the left side papilla contours are clearly outlined, whereas on the right side non-edged papillae are present

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Figure 42. Edged&Nonedged Papillae. On the right side, papillae outlined by rings of reflecting cells are visible, whereas on the left side there are papillae without a demarcated rim of cells

4. Non visible papillae

Papapillary architecture appears to be substituted by spreads of cells (Fig. 43). Cell proliferation at DEJ and in upper dermis results in the complete disruption of the rete-ridge. This pattern is predominantly observable in Melanomas.

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Figure 43. Proliferation of atypical cells at DEJ leads to the disappearance of the papillary architecture, completely covered by the spread of cells

5. Totally disarranged

Complete loss of papillary architecture, substituted by non homogeneously bright areas (Fig.44). This aspect is frequently observable in non melanocytic skin cancers, such as Basal Cell Carcinomas and Squamous Cell Carcinomas, owing to the growth of tumour masses disrupting the DEJ architecture.

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Figure 44. Totally disarranged papillary contours, owing to the tumor islands growth ina Basal Cell Carcinoma. Dark shadows intermingled with bright collagen filaments are visible

Polycyclic papillary contours and/or enlarged interpapillary spaces with edged papillae

Polycyclic papillary contours

Gray anastomosing elongated structures, separated by dark areas, showing a brain-like appearance (Fig. 45). This structure is frequently observable in Solar Lentigos and Seborrheic Keratoses.

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Figure 45. Polycyclic papillary contours

Enlarged interpapillary spaces with edged papillae

Very large interpapillary spaces forming a retiform pattern with meshes constituted by a honeycombed or cobblestone aspect, frequently interrupted by round dark structures containing bright amorphous material, corresponding to milia-like cysts (Fig. 46).

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Figure 46. Edged papillae separated by enlarged interpapillary spaces

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Figure 47. Enlarged interpapillary spaces and milia-like cysts, corresponding to the amorphous roundish structure with a brighter central plug

Aggregates

Junctional nest

The presence of clusters of reflecting cells corresponding to junctional melanocytic nests, is described in melanocytic lesions. Usually, discrete compact aggregates with no atypical cells characterize melanocytic nevi, whereas melanomas show irregular, non homogeneous and non discrete aggregates constituted by atypical cells.

Dysplastic nevi frequently show irregular nests with short interconnection and with elongated shape, corresponding to the bridging or to the confluence of junctional nets, sometimes with few large bright nucleated cells (atypical cells).

Junctional nests are oval compact cellular aggregates, bulging within the dermal papillae (Fig. 51-53) or enlarging the inter-papillary spaces (Fig. 54-56), formed by clustered cells, directly in connection with the basal cell layer.

1. Aspect

Aspect is evaluated, according to the predominant appearance, as «homogeneous», when constituted by dense compact aggregates (Fig. 51-54), or «irregular», when formed by non discrete clusters witj irregular shapes and distribution (Fig. 55-57).

2. Extent

Extent is evaluated into 3 different level, considering the percentage of the lesion area showing the feature, «<10%», «10-50%», or «>50%».

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Figure 51. Junctional nest. Dense compact aggregate (homogeneous)

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Figure 52. Junctional nest. Homogeneous compact aggregates

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Figure 53. Junctional nest bulging into the dermal papilla

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Figure 54. Junctional nests enlarging interpapillary spaces (homogeneous)

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Figure 55. Irregular junctional nests, in a atypical/dysplastic nevus. Irregular in size and shape non discrete aggregates, sometimes showing short interconnections

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Figure 56. Irregular junctional nests in an atypical/dysplastic nevus. Elongated discrete and non discrete aggregates, sometimes showing atypical cells

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Figure 57. Irregular, non homogeneous, junctional nest in a Melanoma

Dermal nests

The presence of clusters of refractive cells forming oval to roundish structures immediately below the basal cell layer, corresponding to melanocytic nests, is reported.

1. Extent

Extent is evaluated into 3 different grades, considering the percentage of the lesion area showing the feature, «<10%», «10-50%», or «>50%».

According to their aspect, dermal nests are divided into 3 different types:

2. Dense Nests

Dense Nests correspond to compact aggregates with sharp margin and similar cells in morphology and refractivity (Fig. 58-60).

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Figure 58. Dense nests: compact aggregates of polygonal cells

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Figure 59. Dense nest: a compact aggregate of polygonal cells surrounded by a dark rim on the right side is suggestive of the dermal location. On the left, the dense aggregate is in connection with the basal layer, so it should be classified as a junctional nest

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Figure 60. Dense clusters: compact aggregates of polygonal cells

3. Dense & Sparse Nests

Dense and sparse nests (dishomogeneous clusters) correspond to non discrete aggregates with sharp and regular margins and non homogeneity in cell morphology and refractivity, with the presence of evident cells not tightly aggregated within the nest (Fig. 61-66).

Large dense and sparse nests, with large round non pleomorphic cells with bright cytoplasm and dark nuclei, scattered on the superface of the nest, are characteristic of the dermal component in congenital nevi and of dermal nevi, Meischer and Unna type.

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Figure 61. Large Dense and sparse nest, constituted by an aggregate of large round non pleomorphic cells, in a dermal nevus. Dense and sparse nests constituted by aggregates of pleomorphic cells, non homogeneous in size, shape and reflectivity, are observable in Melanomas

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Figure 62. Dense and sparse clusters in a Melanoma: dishomogeneously aggregated cells. It shows the contemporary presence of cells aggregated in clusters and evident bright cells apparently not aggregated

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Figure 63. Dense and sparse clusters in a Spitz nevus

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Figure 64. Dense and sparse clusters in a Melanoma: irregularly aggregated and isolated cells within a sharply demarcated dark area

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Figure 65. Dense and sparse clusters

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Figure 66. Dense and sparse clusters in a Melanoma

4. White Papillae

White Papillae correspond to dense nests with low reflective melanocytes. Dermal papillae appear filled with a grainy whitish hue, sometimes centered by small dark hole or canalicular structures corresponding to the loops of the capillaries. At full resolution sometimes it is possible to see the blurred contours of the polygonal cells forming the cluster (Fig. 67).

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Figure 67. White papillae. Dermal papilla is filled by a grainy whitish hue. Blurred cell contours are observable

Cerebriform clusters

Cerebriform clusters correspond to cellular clusters consisting of confluent amorphous aggregates of low reflecting cells exhibiting granular cytoplasm without evident nuclei and ill defined borders, being the aggregates brain-like in appearance, showing a fine hyporeflective «fissure» like appearance (Fig. 68,69). Although their observation is unfrequent, cerebriform nests are specific for invasive Melanomas, and they are usually located within the nodular component of the tumour.

Extent

Extent is evaluated into 3 different grades, considering the percentage of the lesion area showing the feature, «<10%», «10-50%», or «>50%».

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Figure 68. Cerebriform clusters: confluent aggregates of small low reflecting cells separated by hyporeflective fissure-like appearance

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Figure 69. Cerebriform clusters

Cord like/nodular structures with palisading cells

Distinct aggregates of tightly packed cells, forming trabeculae or cordlike structures and nodules, and surrounded by cleftlike nonrefractile dark spaces. The nuclei of the cells at the periphery of the tumor are arranged parallel to each other («palisading»). Irregular bright reflective structures in the middle of the parenchyma are usually observable (Fig. 70-72). These structure are highly sensitive and specific for Basal Cell Carcinoma diagnosis.

Extent

Extent is evaluated into 3 different grades, considering the percentage of the lesion area showing the feature, «<10%», «10-50%», or «>50%».

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Figure 70. Cordlike structures with palisading cells

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Figure 71. Cord-like structure with palisading cells and bright reflective structures in the middle of the parenchyma

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Figure 72. Nodular structure with palisading cells and bright reflective structures in the middle of the parenchyma

Cells in sheet-like structures

It corresponds to cells in the transition of the epidermis and dermis not aggregated in clusters but closely distributed in the same plane. Dermal papillae are not distinguishable due to the loss of normal rete ridge pattern. These cells are usually exhibiting a hyperrefractive cytoplasm (Fig. 73-75).

Extent

Extent is evaluated into 3 different grades, considering the percentage of the lesion area showing the feature, «<10%», «10-50%», or «>50%».

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Figure 73. Cells in sheet like structures (non visible papillae), with non pleomorphic cells

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Figure 74. Cells distributed in sheet like structures (non visible papillae), with pleomorphic cells

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Figure 75. Cells distributed in sheet like structures (non visible papillae), with spindled cells (and marked atypia)

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