Quiz 45: What is your diagnosis?

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Diagnosis: Quiz 45

Quiz 45

Answer: Combined congenital nevus

Criteria for diagnosis clinically: A well-circumscribed, smooth-surfaced, tan plaque within which resides a discrete blue-black papule is a combined congenital nevus.

Differential diagnosis clinically: The blue-black papule could, conceivably, be a melanoma, but it is less than 3.0 mm in diameter, which militates strongly against that possibility. Nevertheless, biopsy must be performed in order to resolve the issue.

Criteria for diagnosis histopathologically: This asymmetrical lesion is characterized on the left side by an epidermis papillate in which melanocytes disposed as solitary units and arranged in small nests are positioned at the dermoepidermal junction, in the papillary dermis, and in the upper part of reticular dermis, where patchy aggregations predominate above and solitary units mostly "splayed" between bundles of collagen preponderate below, those being attributes of a superficial and "deep" congenital nevus. On the right side the melanocytes in the epidermis are organized mostly in largish nests that are not equidistant from one another and have become confluent in loci, as well as being disposed as solitary units, some of which seem to be present above the dermoepidermal junction. Just below those changes in the upper part of the reticular dermis are melanocytes strikingly dendritic and abundantly pigmented with large, plump oval, monomorphic nuclei, joined by many melanophages, both types of cells also "splayed" between bundles of collagen, those findings being ones of a type of "blue nevus," the lesion, in totoqualifying as a combined congenital nevus.

Differential diagnosis histopathologically: The changes on the right side of this lesion, i.e., the melanocytes dendritic dramatically and pigmented conspicuously in the reticular dermis, and immediately above them the large nests of melanocytes, as well as the solitary melanocytes, in the epidermis could be misinterpreted as those of melanoma, but that locus is much too small to be a primary cutaneous melanoma (in a primary melanoma tiny neoplastic melanocytes arrayed as solitary units predominate over ones arrayed in nests, at least in one or two high power fields, and those melanocytes would not have descended to such an extent into the reticular dermis). In short, this lesion, in its entirety, is a congenital nevus in which there are several different populations of melanocytes.

Clinicopathologic correlation: The plaque is made up of melanocytes of the congenital nevus, those in the dermis especially. It is tan because melanin is present in the cytoplasm of melanocytes and keratocytes in the epidermis and in melanocytes in the upper part of the dermis, and it is smooth because the cornified layer is normal, whereas the darkly pigmented papule placed eccentrically is made up mostly of deeply pigmented melanocytes in the reticular dermis, the color being blue-black because so much melanin is present in melanocytes and macrophages in the reticular dermis, it being contributed to also by melanin in melanocytes and keratocytes in the epidermis.

Options for therapy predicated on knowledge of histopathologic findings: The biopsy removed the lesion completely, that being the best method for assessing it histopathologically.

1) It is easy to misinterpret the "heavily" pigmented proliferation of melanocytes in the reticular dermis and the changes in the epidermis just above them as those of melanoma that began in association with a preexisting congenital nevus. In fact, the nuclei of those greatly pigmented melanocytes are large, but they are monomorphic, and none is in mitosis. In the epidermis immediately overlying the eye-catching changes in the upper part of the dermis, nests of melanocytes predominate over melanocytes disposed as solitary units and those nests are stationed at the dermoepidermal junction. Just beneath those nests, bundles of collagen in the papillary dermis are arrayed in concentric/lamellar fashion, yet another indication usually of benignancy. At the periphery of the lesion a little beyond the dermal component in question is an obvious junctional nevus, another clue to the lesion  in toto being a nevus. What seems at first blush to be scatter of solitary melanocytes above the dermoepidermal junction in the discrete focus that absorbs us here is an illusion, it being a consequence of the specimen having been oriented slightly obliquely prior to sectioning of it.

2) Not uncommonly, congenital nevi are "combined," that is, they consist of more than one pattern of arrangement of melanocytes and/or of more than one population of melanocytes. In that latter association may be "Spitz's cells," "deep penetrating cells," or "pagetoid cells," in addition to those conventional of a superficial and "deep" congenital nevus. In this particular instance, the changes on the left of the lesion as viewed at scanning power magnification are those of a superficial and "deep" congenital nevus, whereas those on the right are those of one type of so-called blue nevus, it also being congenital.

3) In the interest of consistency, we name nevi eponymically, such as Unna's, Miescher's, Spitz's, Reed's, Masson's, etc. Because it was John Zitelli who first characterized the congenital nevus that we designate "superficial and 'deep'"1, we, in Interactive Quizzes succeeding, will refer to that kind of congenital nevus as "Zitelli's nevus." Because it was Tièche, then a student more than 100 years ago of Josef Jadossohn, who brought attention to a particular type of a nevus made up of extraordinarily pigmented dendritic melanocytes interspersed between bundles of collagen in the reticular dermis2, he calling it "blue nevus," we, in future Quizzes, will refer to that nevus (present here on the right side of the lesion) as "Tièche's nevus."

 

1. Zitelli JA, Grant MG, Abell E, et al. Histologic patterns of congenital nevocytic nevi and implications for treatment. J Am Acad Dermatol 1984;11:402-409.

2. Tieche M. Uber benign Melanome ("Chromatophorome") der Haut-"blaue Naevi." Virchows Arch Pathol Anat 1906;186:212-229.

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