Deep penetrating nevus
Ronald J. Barr, M.D.
Dermatology Online Journal: 3(1): 7

Clinical History

A 30-year-old man had a raised, bluish lesion on his upper back for an unknown period of time. The clinical impression was a blue nevus.



FIGURE 1

Figure 1: One centimeter uniform dark brown-black nodule on the upper back.


Important microscopic Features

  1. The lesions are usually symmetrical and wedge shaped with the apex in the deep reticular dermis or even subcutaneous fat.
  2. There is usually little junctional component.
  3. The upper dermal portion of the tumor is well-circumscribed and demonstrates cellular fascicles and nests of spindle-shaped cells containing variable amounts of cytoplasmic melanin.
  4. Superficially these clusters are compact and become separated deeper into the lesion.
  5. In the deeper portion of the lesion the cellular aggregates are often associated with blood vessels, nerves and adnexal structures.
  6. The cells are usually spindle-shaped with abundant cytoplasm, often finely distributed. There is usually some variation in nuclear size, shape and staining characteristics, but mitotic figures are extraordinarily rare.


FIGURE 2 FIGURE 3 FIGURE 4


Figure 2: Low power. The lesion extends into the deep dermis and consists of clusters of nevomelanocytic cells with uniformly distributed, heavily pigmented melanophages.
Figures 3 and 4: Mid and high power. The nevomelanocytic cells are present in nests and fascicles. They are elongated and contain finely distributed melanin pigment. They are slightly pleomorphic and no mitotic figures are identified.


Differential Diagnosis

  • Combined nevus
  • Cellular blue nevus
  • Spitz's nevus
  • Malignant melanoma, either primary or metastatic

Comment

This is an unusual, recently described nevomelanocytic lesion that must be distinguished from malignant melanoma since it is benign and often occurs about the head and neck in young adults. It can be validly argued that these are peculiar variants of combined nevi or blue nevi. They can often be distinguished from malignant melanoma by their symmetry, lack of pagetoid epidermal involvement, lack of mitotic figures, and lack of a typical melanoma host response which includes fibroplasia and lymphoplasmacytic infiltrate which often accompanies deeper melanomas.

References

1. Seab JA Jr., Graham JH, Helwig EB: Deep penetrating nevus. Am J Surg Pathol 13:39, 1989.

2. Mehregan DA, Mehregan AH: Deep penetrating nevus. Arch Dermatol 129:328, 1993. 

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