Non-melanocytic lesions
Inflammatory
Post-inflammatory hyperpigmentation (523, 649)

  • Melanophages in number variable scattered in the papillary dermis, rarely in the upper part of the reticular dermis too.
  • Melanin increased in amount in the epidermis.
Dermatofibroma (183, 520)

  • Proliferation of fibrocytes and histiocytes (lipophages and siderophages early in the course) in a mass in the reticular dermis, those cells appearing to be splayed between thickened bundles of collagen at the lateral margins.
  • Melanin increased in amount in the epidermis.
Hamartomas
Collagenous nevus, papillary dermal type (111, 441, 442)

  • Thin papillations above the surface of the skin, each seemingly consisting of a dermal papilla in caricature covered by an epidermis normal.
  • Slight increase of melanin in the epidermis.
Nevoid hyperkeratosis of the nipple (443)

  • Broad mammillations, each formed by a subtly elevated dermal papilla, interrupted by thin epidermal rete ridges pigmented markedly.
Hemorrhage
Ungual and subungual (668)

  • Erythrocytes extravasated in the nail plate and in the dermis beneath it.

 

Benign Neoplasms
Solar lentigo, including lichen planus-like keratosis (466, 467, 468, 469, 470, 647, 648, 771)

  • Nubbins of pigmented keratocytes, some of them typified at times by a small protrusion at the base of it and at a right angle to surface epidermis, alternating with dermal papillae in somewhat periodic fashion beneath which is solar elastosis in abundance.
  • In time, the protrusions at the base may become sufficiently elongate to be connected to the nubbins, thereby creating a pattern reticulate.
  • A lichenoid infiltrate of lymphocytes joined eventually by melanophages may obscure the base of the lesion, which then is referred to as a “lichen planus-like keratosis,” it being nothing other than a solar lentigo in the process of regression as manifested by necrotic keratocytes, some of them in clusters at times, and by changes in the cornified layer, one often being parakeratosis.
Seborrheic keratosis (26, 49, 506, 507, 508, 509)

  • An epidermis thickened by two populations of cells, namely, pigmented “basaloid” ones with scant cytoplasm that make up the bulk of the lesion and nearly non-pigmented “squamoid” cells with copious cytoplasm situated immediately beneath the stratum corneum and around tunnels formed by infundibula.
  • Nuclei of both types of cells are small, roundish, monomorphic, and relatively equidistant from one another.
  • Infundibular tunnels that house corneocytes disposed in pattern laminated and basket-woven are known conventionally as “horn psuedocysts.”
Malignant neoplasms
Basal-cell carcinoma, pigmented (574)

  • Aggregations of abnormal trichoblasts, those at the periphery being columnar and aligned in a palisade.
  • Clefts often separate the aggregations from adjacent altered stroma.
  • Melanin in the cytoplasm of neoplastic trichoblasts, the latter being accompanied by melanocytes scattered among them.
Solar keratosis, pigmented (95)

  • Nubbins of abnormal keratocytes in the lower third at least of an unusually thickened epidermis.
  • Altered cornification in the form consistently of parakeratosis (it alternating with orthokeratosis above acrosyringia and acrothrichia) and often of dyskeratotic cells.
  • Episodically, suprabasal clefts that house acantholytic, dyskeratotic cells.
  • Melanin increased in the abnormal keratocytes.
Melanocytic lesions
Benign
Melanosis (4, 431, 432, 433, 436, 437, 438, 650)

  • Uniform hyperpigmentation of the epidermis, most apparent in the basal layer, but accentuated at the base of rete ridges.
  • Melanocytes displaying dendrites and having small monomorphic nuclei and scant cytoplasm increased in number, but stationed at the dermoepidermal junction.
  • A few melanophages may be present in the uppermost part of the dermis.
Simple lentigo (336)

  • Increase in number of melanocytes with small, oval, monomorphic nuclei disposed as solitary units at the dermoepidermal junction and equidistant from one another there.
  • Epidermis hyperpigmented markedly by thin elongate rete ridges of equal length.
  • Melanophages present in the papillary dermis.
Nevus of Ota, nevus of Ito (521, 522)

  • Markedly bipolar slender melanocytes pigmented strikingly with a nucleus unobtrusive and affiliated with a few melanophages scattered as few solitary units through the reticular dermis and, at times, in septa of the subcutaneous fat.
Nevi

  • Congenital
    • Classic acral (439, 440, 581)
      • Melanocytes disposed as solitary units, but also in discrete nests at the dermoepidermal junction.
      • Scatter of solitary melanocytes and nests of them above the dermoepidermal junction often.
      • Nests of melanocytes present commonly, too, in the uppermost part of the dermis.
    • Superficial [Ackerman's nevus] (339, 340, 741)
      • Melanocytes in the epidermis arranged mostly in largish nests at the dermoepidermal junction and in the papillary dermis in such numbers that part of the dermis is widened by them.
      • A few melanocytes may be present in the uppermost part of the reticular dermis.
      • Nuclei of melanocytes are small and monomorphic.
      • The large nests of melanocytes sometimes are confined entirely to the epidermis.
    • Superficial and “deep” [Zitelli's nevus] (86, 341, 342, 343, 344, 345, 454, 669, 742, 744, 745, 772)
      • Monomorphic melanocytes disposed in nests and as solitary units in the upper half of the reticular dermis arranged there often in adnexocentric and angiocentric fashion; others appear as solitary units “splayed” between bundles of collagen.
      • Some nests may be present at the dermoepidermal junction.
    • Deep [Mark's nevus] (743)
      • Dense diffuse infiltrate of melanocytes of a nevus throughout the dermis, within widened septa of the subcutaneous fat, and sometimes in fascia and skeletal muscle
      • Nests, cords, and strands of the melanocytes may be present, as may be signs of neural differentiation
      • At times, the melanocytes are lodged in number variable in the wall of veins
      • Nests and/or fascicles may be encountered at the dermoepidermal junction
    • Masson’s blue neuronevus (359)
      • Involvement extensive of the reticular dermis and often the upper part of the subcutaneous fat by two populations distinct: (1) aggregations composed of fascicles of melanocytes with monomorphic oval nuclei and pale cytoplasm that house little melanin and (2) strikingly dendritic, markedly pigmented melanocytes around and in between aggregations fascicular, they, too, having monomorphic oval nuclei.
    • Common blue (Jadassohn-Tieche) (360, 525)
      • Tangles of bipolar, dendritic, markedly pigmented melanocytes with small monomorophic nuclei, some of those cells organized in ill-formed fascicles, distributed throughout much or all of the reticular dermis.
    • Combined (80, 364, 369, 370, 524)
      • A “superficial” or “superficial and ‘deep’” congenital nevus in which there is more than one population of melanocytes, sometimes several of them, e.g., “Spitz’s” cells, “balloon” cells, and “deep penetrating” cells, in addition to cells conventional in a congenital nevus.
    • Miescher’s (526, 570)
      • Dome-shaped with nests, cords and strands of monomorphic melanocytes arranged in the shape of a wedge throughout the dermis, the apex of the wedge pointing in the direction of the subcutaneous fat positioned just beneath it.
    • Unna’s (17, 773)
      • A polypoid lesion oriented vertically made up of nests, cords, and strands of monomorphic melanocytes in a papillary dermis widened extraordinarily by them.
      • Some melanoncytes also in the reticular dermis in fashion adnexocentric, and, in loci, as solitary unites “splayed” between collagen bundles.
    • Congenital speckled lentiginous nevus (nevus spilus) (35, 455, 666)
      • One component resembles simple lentigo with thin pigmented rete ridges along which melanocytes disposed as solitary units equidistant from one another are increased in number. A second component consists of small nests of melanocytes positioned at the dermoepidermal junction and in the upper part of the dermis, some of them there disposed as solitary units in fashion adnexocentric mostly and/or “splayed” between bundles of collagen.
    • Persistent (“recurrent”) (5, 87)
      • Melanocytes disposed as solitary units in the epidermis often predominate over nests of melanocytes in some high-power fields, some being scattered in the upper reaches of it, including the granular and cornified layers, and nests of melanocytes not being equidistant from one another.
      • Nuclei of melanocytes are monomorphic.
      • Some discrete nests may be present in the upper part of the dermis.
      • A scar is apparent immediately below the epidermis.
      • Beneath the scar may be found a typical “superficial and ‘deep’” congenital nevus.
      • Rarely does the intraepidermal component of the nevus extend beyond the scar.
    • Special site (33, 88, 434)
      • In the dermis a congenital nevus, one either “superficial” or “superficial and ‘deep.’”
      • Nests of melanocytes in the epidermis largish, not equidistant from one another, confluent in loci often and positioned mostly at the dermoepidermal junction.
      • Some nests may be present well above the junction.
      • Intraepidermal component sometimes asymmetrical.
    • Yet to be classified
      • Superficial congenital nevus, probable
  • Acquired
    • Clark’s (34, 337, 338, 451, 452, 453)
      • Silhouette of a benign neoplasm, flat or very slightly raised, with small nests of melanocytes at the dermoepidermal junction and, at times, in small numbers in the papillary dermis in the very center of the lesion.
      • Nuclei of melanocytes small, oval, and monomorphic.
    • Spitz’s (351, 354, 355, 361, 363, 365, 366, 367)
      • Silhouette of a benign neoplasm.
      • Nests of melanocytes may be present in the epidermis alone or in the epidermis and the dermis together; the uppermost part of the subcutaneous fat may be affected uncommonly.
      • A majority of melanocytes in nests and/or fascicles display nuclei larger considerably than those of a Clark’s nevus, copious cytoplasm which often is amphophilic, and shapes variable, among them being round, oval, fusiform, plasmacytoid, and polygonal.
      • Pseudoacantholysis of melanocytes is common.
      • Often there are compact orthokeratosis, focal hypergranulosis, adnexal hyperplasia, dull pink globules in the epidermis, and clefts between nests/fascicles of melanocytes and keratocytes adjacent to them.
    • Reed’s (356, 357, 358, 362, 368)
      • Silhouette of a benign neoplasm.
      • Fascicles and nests of melanocytes pigmented markedly, positioned entirely at the dermoepidermal junction and, at times, in a papillary dermis that may be widened by them.
      • A patchy lichenoid infiltrate of melanophages is an accompaniment usual.
      • Nuclei of melanocytes are oval/spindle and monomorphic, and the cytoplasm sports striking dendrites responsible for the melanin abundant in melanocytes, keratocytes, and macrophages.
    • Yet to be classified
Malignant
Melanoma
In situ (50, 77, 78, 90, 306, 307, 308, 309, 310, 326, 371, 372, 373, 435, 586, 587, 588, 589, 646,693, 694, 695, 774, 775)

  • Silhouette of a malignant neoplasm.
  • A proliferation of melanocytes confined to surface and infundibular epidermis, and sometimes also to eccrine ducts; rarely are sebaceous units affected.
  • Melanocytes disposed at least as solitary units, but often in aggregation too, are increased considerably in number at the dermoepidermal junction; solitary melanocytes are not equidistant from one another and neither are nests equidistant from one another.
  • Melanocytes often positioned well above the dermoepidermal junction, sometimes in the upper reaches of the epidermis, including the granular zone and cornified layer.
  • Aggregations often vary greatly in size and shape, sometimes assuming bizarre outlines geometric, as a consequence sometimes of confluence of them.
No longer in situ (“invasive”) (6, 89, 327, 328, 329, 330, 374, 375, 484, 485, 539, 566, 567, 568, 569, 667, 670, 681, 682, 683, 684, 685, 692, 695, 718, 719, 720)

  • Silhouette of a malignant neoplasm.
  • Findings in the epidermis of “melanoma in situ.”
  • In the dermis, failure of maturation of melanocytes both in terms of size of aggregations and size of nuclei, as well as variation considerable in size and shape of aggregations, they often having peculiar outlines geometric and displaying uneven distribution of melanin in melanocytes and macrophages.
Persistent (538)

  • Silhouette of a malignant neoplasm.
  • Findings histopathologic of melanoma in situ often in which, as a rule, the proliferation of melanocytes in the epidermis extends well beyond the scar in the upper part of the dermis.
  • Sometimes the neoplastic cells are confined to the dermis and/or the subcutaneous fat in the context of a scar from a previous surgical procedure.
In association with a nevus (76, 291, 293, 294, 295, 590, 691, 716, 717)

  • Two silhouettes, one of a malignant neoplasm and the other a benign one.
  • Two populations of melanocytes, at least, are discernable, one with the characteristics of melanoma and another with attributes of a melanocytic nevus, the later usually being one superficial or superficial and “deep.”
Metastatic (112, 482, 536, 537, 685)

  • Silhouette of a malignant neoplasm.
  • No sign of melanoma in situ as a rule, the exception being epidermotropically metastatic melanoma.
  • In the presentation uncommon of epidermotropically metastatic melanoma, the intraepidermal component neither favors the dermoepidermal junction nor extends beyond the intradermal component of the neoplasm.
With regression (484, 485, 681, 682)

  • Fibrosis and/or melanosis in a widened papillary dermis.
  • Total, focal, or partial depending on whether no neoplastic melanocytes are residual (“total), whether neoplastic melanocytes are residual in the dermis and epidermis but in which no melanoma in situ is present above a discrete locus of regression in the papillary dermis (“focal”), or whether in the context of a focus of regression in the papillary dermis, melanoma in situ remains above it (“partial”).