Precursors To Melanoma And The Problematic Nevomelanocytic Proliferation
Section 7 -
Recurrent Melanocytic Nevus
Neil Crowson, MD
Cynthia M. Magro, MD
Martin C. Mihm, Jr., MD
Case # 7. Recurrent Melanocytic Nevus
Recurrence of a nevus manifests as repigmentation in the scar at the site of a previous incomplete
elliptical, punch or shave excision, electrodessication, or dermabrasion of a melanocytic lesion. The
pigmentation within or adjacent to the scar is irregular, stippled or scalloped with a variegated color
ranging from tan to dark brown or black (Kornberg and Ackerman, 1975; Sexton and Sexton, 1991). Similar
changes appear in nevi partly ablated through trauma of which the patient may be unaware. Recurrent nevi
are often flat, reflecting the mainly intraepidermal proliferation; repigmentation occurs within weeks to
months of the original excision, unlike recurrent melanoma, where repigmentation occurs years later.
Where a skin graft has been applied, showers of tan or black dots may appear in its center. The source
of the cells that repopulate the epidermis are those nevus cells that remain in reticular dermal-based
adnexal structures, in the deep-seated dermal component, or the adjacent epidermis after incomplete
removal (Arrese Estrada et al., 1990; Sexton and Sexton, 1991; Crowson et al., 2001).
The original lesion is usually a compound nevus, an intradermal nevus being seen in 32% of cases and
a junctional nevus in 5%. Less than 10% of recurrent nevi arise from prior dysplastic nevi, probably as
the latter are more aggressively treated ab initio. The recurrent nevus can
be easily recognized at scanning magnification by a trizonal arrangement with a high-density
intraepidermal melanocytic growth over a dermal scar with a subjacent remnant of benign nevus. Other
features help to differentiate it from two other common scenarios associated with dermal fibrosis and an
atypical intraepidermal melanocytic growth, namely regressed and/or recurrent melanoma (Blessing, 1999).
The intraepidermal growth in recurrent nevi manifests sharp lateral circumscription, whereby the lateral
boundaries are defined by the scar from the prior procedure; in some instances the junctional
proliferation may be more broad, extending laterally past the confines of the scar, and is often more
pronounced than that observed in the original excision (Sexton and Sexton, 1991). The intraepidermal
component is cytologically that of a nevus, be it of common acquired, dysplastic, or congenital subtypes.
Over the scar, however, the melanocytes are enlarged with epithelioid cytology, round to oval nuclei,
abundant cytoplasmic pigment, variable sizes and shapes and conspicuous nucleolation. The chromatin is
evenly dispersed and the N/C ratios are not increased. The atypia is mild or moderate in degree;
features of high-grade dysplasia such as increased N/C ratios, increased and irregularly distributed
chromatin, and angulated nuclear contours are not seen. The melanocytes are in a single-cell and nested
array, with confluence of growth, nest variability of shape, location, and orientation, and nest
dyshesion (Sexton and Sexton, 1991). The single-cell growth is mainly lentiginous, but there may be
some upward pagetoid growth to the suprabasilar epidermis and spinous layer, sparing the granular cell
layer. The epidermis may manifest loss of the retiform architecture. There is often intense
melanization of keratinocytes. Mitotic activity is seen in less than 10% of cases. Melanocytes may grow
along the basal layer of adnexal structures. The dermis demonstrates parallel arrangement of collagen
with neovascularization. There may be patchy perivascular lymphocytic infiltrates but lichenoid
inflammation is absent. Nucleolated nevomelanocytes similar to those in the epidermis may be seen within
the scar, being confined to the superficial dermis and not prominent relative to the intraepidermal
component. The cells are usually nested.
The recurrent Spitz nevus is typically intradermal in location and may permeate the subcutis.
Recurrent Spitz nevi resemble the desmoplastic Spitz nevus by virtue of dermal fibrosis (Stern, 1985).
There is a low incidence of recurrence in classical Spitz nevi; one study failed to show any recurrences
in 49 such patients during a follow-up period of 5.0 years (Kaye and Dehner, 1990). Recurrent dysplastic
nevi manifest cytoplasmic retraction artifact as clear spaces and clefts around nests or individual nevus
cells showing variable cytologic atypia indistinguishable from the recurrent common acquired nevus. We
emphasize the importance of reviewing the originally excised melanocytic proliferation, as the
distinction of recurrent dysplastic nevus from recurrent common acquired nevi is difficult. The
exception is those recurrent nevi in which the residual lesion is available for analysis peripheral to
Differentiation from Malignant Melanoma with Regression and Recurrent Melanoma
Regressive fibrosis in melanoma is different from a scar, with a delicate pattern of thin collagen
fibers in an edematous matrix containing scattered mononuclear cells with prominent ectatic venules
oriented perpendicularly to the epidermis. In contrast, a scar is often hypovascular with laminated
thick bundles of collagen in a parallel disposition to the epidermis. When vessels are present they are
small and may be closely aggregated. In regressed melanoma, there is usually prominent inflammation that
may be lichenoid with conspicuous melanophage accumulation. The infiltrate in recurrent nevi is sparse
and when present is often localized around blood vessels.
In regressed melanoma the epidermis is attenuated and is devoid of melanocytes. In recurrent nevi,
the epidermis shows melanocytic hyperplasia and hypermelanosis. In regressed melanoma a severely
atypical intraepidermal or dermoepidermal melanocytic proliferation is found outside the areas of
regressive stromal fibrosis, in contrast to recurrent nevi where the pattern and cytology of melanocytic
growth is often banal. A residual lesion is identified in only 25% of regressed melanomas, versus a much
higher frequency in recurrent nevus. The residual lesion identified in melanoma is usually severely
atypical, while the residual lesion in a recurrent nevus is not.
With respect to differentiating recurrent melanoma from recurrent nevus, if indeed the recurrent
melanoma is on the basis of residual primary melanoma rather than representing metastatic disease, we
adhere to the following rules:
1) The cytology in recurrent melanoma is that of melanoma. Other supportive features are atypical
mitoses and necrosis, neither of which are present in the recurrent nevus.
2) Most recurrences in scar sites of previously excised melanoma are metastases with a constellation
of light microscopic findings that, apart from a recurrent Spitz nevus, should not be confused with a
recurrent nevus. The hallmarks are nodules of spindle and/or epithelioid cells amidst a scar,
coagulative necrosis within the tumor nodules, vascular invasion, and brisk mitotic activity (Yu and
Grading Atypia in Recurrent Nevi
We do not grade atypia in recurrent nevi; it always looks worse than in the original biopsy and,
especially in young children and adolescents, it may be severe with upward migration of melanocytes n the
epidermis. Most important is an assessment of the original specimen and the atypia of melanocytes in
residual nevus peripheral to the scar. If it is a recurrence of a dysplastic nevus we so indicate
following tissue review.
- Blessing K. Benign atypical naevi: diagnostic difficulties and continued controversy Histopathology
- Crowson AN, Magro CM, Mihm MC, Jr. Recurrent melanocytic nevus. In: Crowson AN, Magro CM, Mihm MC,
Jr. The melanocytic proliferations : a comprehensive textbook of pigmented lesions. New York : John
Wiley and sons, 2001:195-207.
- Kaye VN, Dehner LP. Spindle and epithelioid cell nevus (Spitz nevus). Natural history following
biopsy. Arch Dermatol 1990;126:1581–1583.
- Kornberg R, Ackerman AB. Pseudomelanoma. Arch Dermatol 1975;111:1588–1590
- Sexton M, Sexton CW. Recurrent pigmented melanocytic nevus. A benign lesion, not to be mistaken for
malignant melanoma. Arch Pathol Lab Med 1971;115:122–126.
- Stern JB Recurrent Spitz's nevi. A clinicopathologic investigation. Am J Dermatopathol 1985;7
- Yu LL, Heenan PJ. The morphological features of locally recurrent melanoma and cutaneous metastases
of melanoma. Hum Pathol 1999;30:551–555.