Pathology of the blue nevus

Introduction

blue naevi They are benign lesions that often appear in childhood or adolescence. Blue nevi and dermal Melanocytoses are believed to be the result of dermal arrest of precursor cells migrating from the neural crest in a manner similar to congenital naevi. GNAQ / GNA11 mutations They have recently been found in various forms of blue nevi. The causal cells are dendritic. melanocytes, which are bipolar or stellate and have long dendritic processes. These cells typically produce abundant melanin.

Mongolian spots, nevus from Ota and nevus from Ito

Also known as dermal melanocytosis, Mongolian spots, nevi of Ota, and nevi of Ito are histopathologically similar to blue nevi and are characterized by a sparse population of scattered dendritic melanocytes in the lattice dermis without stromal alteration (figure 1).

Common blue nevus

Histopathologically, blue nevi have a collection of dendritic melanocytes in the dermis (Figure 2). Pure blue common nevi should not involve epidermis. the connective tissue around the melanocytes is generally sclerotic, sometimes deeply, when described as a scleral blue nevus. Aggregation of melanocytes on appendices and neurovascular bundles are common. Melanophages They are also usually present in large numbers, partially explaining the blue clinical presentation.

Uncommon, dendritic melanocytes do not produce melanin (amelanotic blue nevus). These cases can cause diagnostic confusion due to their morphological similarity to dermatofibroma or extremely difficult. desmoplastic melanoma (figure 3). Notably, cutaneous metastasis of conventional evil one melanoma may appear morphologically identical to blue nevi.

Epithelioid blue nevus

Epithelioid blue nevus is also called pigmented epithelioid melanocytoma. Instead of thin dendritic melanocytes, cells in an epithelioid blue nevus are large, round, and pale in color. cytoplasm (Figure 4). the cellular morphology may be difficult to appreciate without bleaching the section to remove the copious melanin pigment. the nuclei are generally uniform without mitotic exercise. Actually yes mitosis are easy to find, the injury It is more likely to be an unusual melanoma.

Patients with Carney complex can develop multiple blue epithelioid nevi. Some of these lesions are called animal melanoma, because they resemble the melanoma seen in animals. Figure 5 was, in fact, a gray horse melanoma.

Cellular blue nevus

The cellular blue nevus is generally much larger than a common blue nevus and generally affects the entire dermis. The superficial subcutis It is also often involved. The architecture is a fairly distinctive mass composed of a lobular tongue or tongues in the deep dermis (Figure 6). Cell density is noticeably higher compared to regular blue nevi. Cells can be round, oval, or spindle-shaped. Multinucleate giant cells they are occasionally seen in cell areas and can be numerous in some cases.

Necrosis and / or numerous mitoses suggest that the tumor it is an unusual melanoma rather than a blue cell nevus.

License plateblue nevus type

These blue nevi are really great common blue nevi. They are sometimes confused clinically with Mongolian spots. They can measure up to 10 cm and are usually congenital.

Interestingly proliferative nodules sometimes they occur in plaque-like blue nevi. The nodules resemble epithelioids or, less commonly, cellular blue nevi. The only times we have seen biopsies of plaque-like blue nevus were cases in which these nodules arose and there was clinical concern of evolving melanoma.

Combined nevus

The term combined nevus is used to describe two or more distinct nevi cell elements, or neural crest lines differentiation, in a single melanocytic nevus. For example, some nevi may have components of a dysplastic nevus, blue nevus, Spitz nevi and congenital nevi within the same lesion. Combined nevi can be problematic, especially when there is a Spitz component or clone epithelioid cells, as they can mimic melanoma that develops in a nevus (Figure 7). They are also clinically problematic, e.g. a small component of blue nevus can easily be mistaken for melanoma that develops into a bland nevus.

Differential diagnosis blue nevus

Blue nevus pathology needs to be differentiated since primary and metastatic melanoma, especially animal melanoma, pigmented Spitz naevus and pigmented spindle cell cane.