The relationship between melanocytes and peripheral nerve sheath cells (Part I): melanocytic nevus (excluding so-called "blue nevus") with peripheral nerve sheath differentiation

Perineural differentiation in neurotized nevi

BACKGROUND

Perineuriomatous melanocytic nevi are rare and this may indicate the similar embryological source of melanocytes and peripheral nerves in the neural crest. Neurotized melanocytic nevi may resemble nerve sheath tumors histologically, and show schwannian differentiation. However, literature on whether neurotized nevi differentiate into perineural cells is controversial. We examined our cases of neurotized nevi for evidence of perineural differentiation.

MATERIALS AND METHODS

A total of 100 benign nevi with large neurotized component (microscopically involved a low power field 4.2 mm in diameter) were prospectively evaluated in excisional biopsy samples. Immunohistochemical stainings for EMA, Claudin1, Glut1 and neurofilament were performed.

RESULTS

Perineural differentiation was immunohistochemically detected in the neurotized component of the nevi in 61% of the cases with EMA and in all the cases with Glut1 and Claudin1. Axonal differentiation was not detected with neurofilament. The expression pattern, especially with Glut1, was usually in form of partial or complete staining surrounding the Meissner's corpuscle-like structure (MCLS). Also, a linear/curvilinear staining pattern was observed particularly with Claudin1. A diffuse staining pattern with EMA, Glut1 and Claudin1 was detected in a case with a microscopically distinct whorl structure, and in which spindle cells are separated from the superficial epithelioid melanocytes with an abrupt transition histologically. These findings of the case are compatible with previous reports of perineuromatous nevus.

CONCLUSION

Perineural differentiation is not uncommon and immunohistochemically observed in all nevi with a relatively large component of neurotization. To prevent misdiagnosing desmoplastic melanoma and overtreating patients, it is crucial to be aware of perineuromatous nevi.

Wagner-Meissner neurilemmoma of the lip occurring in a patient with neurofibromatosis type 1: A case report

Wagner-Meissner corpuscles are specialized mechanoreceptors located in the dermal papillae. Wagner-Meissner corpuscle-like structures are occasionally a component of certain types of tumors, such as melanocytic nevus and neurofibroma. Benign tumorous lesion entirely composed of Wagner-Meissner corpuscles are described as Wagner-Meissner neurilemmoma, and only four such cases have been reported. Here, we report the first case of Wagner-Meissner neurilemmoma in a patient with neurofibromatosis type 1. A 16-year-old Japanese male with neurofibromatosis type 1 presented with a tumorous lesion on the upper lip. Resection of the tumor was performed under a clinical diagnosis of neurofibroma. Histopathological examination revealed an unencapsulated, poorly-circumscribed tumor, comprised of abundant Wagner-Meissner corpuscle-like structures, which were composed of 5–15 lamellated Schwann cells containing eosinophilic cytoplasm and peripherally located nuclei. No spindle-shaped neoplastic cell proliferation, as seen in conventional neurofibroma, was observed. Accordingly, a diagnosis of Wagner-Meissner neurilemmoma was made. The pathogenesis of Wagner-Meissner neurilemmoma remains unclear. The hamartomatous or reactive proliferative nature has been proposed. In addition, this lesion may represent an extreme form of diffuse neurofibroma with abundant Wagner-Meissner corpuscles associated with neurofibromatosis type 1, even though the previously reported four patients did not have neurofibromatosis. Therefore, further studies are needed to clarify the pathogenesis of this extremely rare tumor, including its association with neurofibromatosis.

Melanocytic naevi with perineurial differentiation: a distinctive variant of neurotised naevi and a diagnostic pitfall with desmoplastic melanoma

AIMS

Spindle cell differentiation is not an uncommon finding in common acquired naevi, and may represent a form of neurotisation with Schwannian differentiation of melanocytes. Perineurial differentiation in this context appears to be very rare, and is only poorly documented in the literature. We therefore aimed to study this rare form of neurotisation in melanocytic naevi more comprehensively.

METHODS AND RESULTS

We have identified six melanocytic tumours showing spindle cell morphology and perineurial differentiation from routine and referral material. Clinical data and follow-up were obtained, and the histological and immunohistochemical features were analysed. The tumours affected middle-aged adults (median, 48 years; range, 26-74 years), with a wide anatomical distribution and benign follow-up (median, 13 months; range, 6-48 months). All tumours were nodular and circumscribed but asymmetrical, with extension into the deep dermis and superficial subcutis. A characteristic finding was a biphasic growth pattern with a lentiginous compound naevus in the superficial aspect and abrupt transition to a prominent nodular spindle cell proliferation in the deeper reaches. Spindle cells were bland and uniform, and arranged singly and in short fascicles in a loose fibromyxoid stroma. In areas, a whorled arrangement of slender spindle cells with wavy nuclei was seen. Distinctive intratumoral hypocellular nodules and peripheral lymphoid aggregates were additional features. By immunohistochemistry, the spindle cells were mainly S100-positive melanocytes. In areas, S100-negative/epithelial membrane antigen-positive spindle cells showing coexpression of Glut-1 and claudin-1 were closely admixed.

CONCLUSION

This perineurial differentiation probably represents a rare and unusual form of neurotisation. The tumours are benign but may be mistaken for desmoplastic melanoma. Awareness of and careful attention to the clinicopathological and immunohistochemical features allow reliable separation.

Unusual Histopathological Patterns in Melanocytic Nevi With Some Previously Undescribed Patterns

Melanocytic nevi are one of the most common diagnoses in the daily practice of any dermatopathologist. Although in the vast majority of cases the final diagnosis is not difficult, there are certain rare and unusual morphologic variations that can elicit some diagnostic problems. Although some of these variations can be considered as mere morphologic oddities, others might lead to a differential diagnosis with melanoma, or with other tumors, including epithelial or neural tumors. In the current report, we review many of these morphologic variations and discuss the main differential diagnosis, when appropriate.

Immunohistochemical and ultrastructural features of congenital melanocytic naevus cells support a stem-cell phenotype

Background Multiple congenital melanocytic naevi (CMN) in one individual are caused by somatic mosaicism for NRAS mutations; however, the lineage of the mutated cells remains uncertain.

Objectives To test the hypothesis that CMN may be derived from cutaneous stem cells.

Methods Sixty-six CMN samples from 44 patients were stained for immunohistochemical (IHC) markers of melanocytic differentiation (TYR, TRP1, TRP2, LEF1, MITF, cKit), pluripotency (nestin, fascin, CD133, CD20, CD34), monocyte/macrophage lineage (CD68, CD163, CD14), proliferation (Ki67) and MTOR/Wnt-signalling pathway activation (pS6, β-catenin). Semiquantitative scoring compared samples with naevus cell nesting (group 1) with those with only diffuse dermal infiltration (group 2). Transmission electron microscopy (TEM) was performed on 10 samples.

Results A normal melanocyte population was seen overlying many dermal CMN. Group 1 samples were significantly more likely to express melanocytic differentiation markers than group 2, and expression decreased significantly with depth. Expression of these markers was correlated with each other, and with nestin and fascin. CD20 staining was positive in a substantial proportion and was stronger superficially. Expression of β-catenin and pS6 was almost universal. Some samples expressed monocyte/macrophage markers. TEM revealed variable naevus cell morphology, striking macromelanosomes, double cilia and microvilli.

Conclusions Congenital melanocytic naevi development frequently coexists with normal overlying melanocyte development, leading us to hypothesize that in these cases CMN are likely to develop from a cell present in the skin independent of, or remaining after, normal melanocytic migration. IHC and TEM findings are compatible with CMN cells being of cutaneous stem-cell origin, capable of some degree of melanocytic differentiation superficially.

Differentiating Neurotized Melanocytic Nevi From Neurofibromas Using Melan-A (MART-1) Immunohistochemical Stain

Context.—Neurotized melanocytic nevi and neurofibromas are common, benign cutaneous neoplasms. Usually they are histologically distinct from each other; however, neurotized melanocytic nevi and neurofibromas can be clinically and histologically similar.

Objective.—To determine whether Melan-A (MART-1) immunohistochemical stain is sufficient to differentiate neurotized melanocytic nevi from neurofibromas.

Design.—Forty-nine consecutive specimens of melanocytic nevi with neurotization and 49 specimens of neurofibromas were selected. We used antibodies against Melan-A, S100, and neurofilament protein.

Results.—All of the melanocytic nevi showed Melan-A staining within the neurotized areas, with most of the areas staining strongly positive, whereas all the neurofibromas were completely absent of Melan-A stain. All of the nevi, including the neurotized areas, stained strongly and diffusely for S100, whereas all the neurofibromas showed a distinctive, sharp, wavy pattern of S100 staining. Neurofilament protein showed scattered staining of both melanocytic nevi and neurofibromas.

Conclusions.—Our data indicate that Melan-A immunohistochemical staining is helpful in differentiating neurotized melanocytic nevi from neurofibromas when distinction on histomorphology alone is difficult.

Cutaneous neoplasms with prominent Verocay body-like structures: the so-called "rippled pattern"

A striking appearance resulting from alternating areas of epithelial cell cords and stroma seen in some cutaneous adnexal neoplasms has been referred to as the "rippled pattern." Histologically, this pattern may be indistinguishable from Verocay bodies described in schwannomas. A number of common and clinically diverse cutaneous neoplasms can be linked by the presence of this unusual growth pattern. The heterogeneous group of tumors that have been known to demonstrate this feature includes those with epithelial, adnexal, fibrohistiocytic, mesenchymal, and melanocytic lineage. The objective of this review is to alert the dermatopathologist to the range of neoplasms, which can potentially show this attribute, so that a misdiagnosis can be avoided.

Primary intracranial malignant peripheral nerve sheath tumour responding to chemotherapy

Malignant peripheral nerve sheath tumours (MPNST) are a rare variety of soft tissue sarcomas (STS) arising from major peripheral nerve branches and typically located in the lower extremity, chest wall or the retroperitoneum. It is a biologically aggressive neoplasm for which the treatment of choice is surgery, but usually requires a multimodality approach, having been generally labelled as chemoresistant. We present a case of MPNST located intracranially with a good response to chemotherapy.

WT 1 expression in nevi and melanomas: a marker of melanocytic invasion into the dermis

BACKGROUND

WT1, first recognized as a tumor suppressor gene involved in the development of Wilms' tumor, may have apparently contradictory findings and functions. As WT1 has been identified as a molecular target for cancer immunotherapy, immunodetection of WT1 in tumor cells has become an essential step in cancer studies.

METHODS

We compare the expression of this protein among different types of melanocytic nevi and among stages in primary melanoma progression. Tissue microarrays containing normal tissues and 271 primary melanocytic lesion samples (163 primary melanomas and 108 nevi) were studied by immunohistochemistry using monoclonal antibody against WT1.

RESULTS AND DISCUSSION

The present study shows these: 1. WT1 protein is predominantly expressed in the cytoplasm of the neoplastic cells. 2. A higher rate of WT1 staining in melanocytic nevi against melanomas has been observed. 3. WT1 expression is increased in advanced stages of melanoma progression: a significant (p < 0.05) increase of expression of WT1 was detected in vertical cases 46.5% vs. radial cases 16.0%, in high levels of Clark (IV, V) 57.4% vs. low levels (I, II, III) 33.0% and when comparing depth of invasion within thickness subgroups. 4. Finally, this study establishes an association of WT1 protein expression with shorter overall survival in melanoma.

Neurotized nevi of the oral mucosa: an immunohistochemical and ultrastructural analysis of nevic corpuscles

BACKGROUND

Nevic corpuscle (NC), a stacked lamellar structure reminiscent of Meissner corpuscle, is frequently observed in dermal melanocytic nevi. Although the heading 'neurotized' is classically used for these nevi, the exact neural nature of NC has been a topic of considerable debate. Neurotized nevi have received little attention in the dental literature, and there was no information on NC in oral melanocytic nevi.

METHODS

Six cases of oral intramucosal nevi with a significant number of NC (two completely and four partially neurotized nevi) were examined immunohistochemically and ultrastructurally.

RESULTS

NC was composed of closely piled laminar cells devoid of visible melanin. NC and associated spindle nevus cells were immunopositive for S-100 protein but negative for HMB-45, myelin basic protein and epithelial membrane antigen. Within NC, no reactivity for neurofilament protein, protein gene product 9.5 or peripherin was evident. Numerous CD34-positive dendritic cells were located between nevus cells and often encircled NC. Ultrastructurally, NC consisted of concentrically layered elongated cells with a slender lamellated cytoplasm rich in thin filaments and pinocytotic vesicles. Their cytoplasmic processes were focally covered by external basal lamina and continuous to spindle nevus cells. Occasional NC cells contained a few melanosomes. There was no interposed axon in NC.

CONCLUSIONS

Despite the close resemblance to Meissner corpuscle, NC showed no axonal supply. NC cells lacked terminal Schwannian differentiation and appeared to be modified melanocytes with some perineurial ultrastructural characteristics. The presence of CD34-positive cells, presumably corresponding to endoneurial fibroblasts, further supports an organizational relationship of NC and peripheral nerve sheath elements.

Melanocytic “ball-in-mitts” and “microalveolar structures” and their role in the development of cellular blue nevi

To test the hypothesis of whether cellular blue nevi (CBN) may originate from "ordinary" compound and dermal nevi, a total of 275 melanocytic nevi including 59 CBN, 34 ordinary blue nevi, 87 combined nevi (including 43 so-called clonal nevi), 35 deep penetrating nevi, and 60 ordinary compound and dermal nevi (30 of each) were studied for the presence of so-called ball-in-mitts and microalveolar structures. A ball-in-mitts structure was defined as a single centrally placed melanocyte with a round to oval nucleus (the "ball" cell) and a clear, dusty, or pigmented cytoplasm encircled by a single dendritic cell (the "mitt" cell) with an oval to spindle-shaped nucleus and slender bipolar processes containing melanin and surrounding at least one fourth of the ball's diameter. A microalveolar structure was defined as a group of 2 to 10 centrally placed melanocytes with round to oval nuclei and clear, dusty, or pigmented cytoplasm (balls) surrounded by one or more cells (mitts) with spindle-shaped nuclei and slender bipolar processes containing melanin. Microscopically, ball-in-mitt and microalveolar structures were detected in all types of nevi studied, with the highest incidence in combined nevi (82%), CBN (76%), and ordinary "nonblue" nevi (73%). In CBN, ball-in-mitts and microalveolar structures tended to be located in the deeper portion of the lesions, whereas in ordinary nonblue nevi, they were most often found superficially, just below the epidermis; in clonal nevi, these structures were often confined to the "clonal" parts. Immunohistochemically, ball-in-mitts and microalveolar structures were positive for HMB45. Ultrastructurally, the balls tended to have round to oval nuclei, whereas the mitts possessed oval, elongated to spindled nuclei. Melanosomes were found in various stages in the cells of both structures. The cytoplasm of the mitts typically formed elongated polar processes, sometimes with club-like widenings at the ends, completely or partially encircling the balls. In the microalveolar structures, the adjacent cells forming the mitts surrounded the ball cells like a chain. Our study suggests that some or even most cases of CBN may evolve from ordinary nonblue nevi. This process may involve several steps and is probably reflected by the appearances of combined nevi, deep penetrating nevi, and CBN. These nevi often show a morphological overlap, and ball-in-mitts and microalveolar structures found in various stages of their development seem to greatly account for this overlap.

Melanocytic nevi are associated with neurofibromas in neurofibromatosis, type I, but not sporadic neurofibromas: a study of 226 cases

BACKGROUND

Neurofibromatosis, type 1, is associated with cutaneous melanin pigmentation, but an association with ordinary melanocytic nevi has not been described.

METHODS

This retrospective case-control study was designed to see if neurofibromas in patients with neurofibromatosis, type 1 (NF-1) differ from sporadic neurofibromas (SN) in their incidence of associated melanocytic nevi and other histologic features. Slides from 114 NF-1 were compared with 112 SN and 300 intradermal melanocytic nevi (IDN).

RESULTS

Small lentiginous melanocytic nevi were identified over 13 NF-1 (11%) but no SN (P=0.0002). Compared with other NF-1, NF-1 with nevi were more frequently associated with melanocytic hyperplasia, giant melanosomes and diffuse neurofibroma (P<0.03). Compared with SN, NF-1 were also more frequently associated with melanocytic hyperplasia, lentigo simplex-like changes, diffuse neurofibroma and plexiform neurofibroma (P<0.001). Sebaceous hyperplasia (14%), dermal elastosis (9%), lipomatous change (8%), epithelial cysts (4%) and keratin granulomas or folliculitis (3%) were not significantly different in prevalence between NF-1, SN and the control group of IDN.

CONCLUSIONS

This study suggests that there is a difference in the potential for melanocytic proliferation in NF-1 compared with SN. NF-1, SN and IDN are associated with a similar range of incidental histologic changes. Ball NJ, Kho GT. Melanocytic nevi are associated with neurofibromas in neurofibromatosis, type 1, but not sporadic neurofibromas. A study of 226 cases.

Nevogenesis-New Thoughts Regarding a Classical Problem

The development of melanocytic nevi is a multifactorial and heterogeneous biologic process that involves prenatal and postnatal steps. As a consequence, there are two main perspectives to nevi: that of a hamartoma and that of a benign tumor. In this review, dermatopathological studies on congenital and acquired nevi, including studies on age-related and location-dependent changes, are analyzed. These studies have lead to different hypothetical concepts on the evolution of individual lesions. In the light of findings from experimental embryology and stem cell biology, we discuss the histogenesis of nevi with special reference to the temporospatial sequence of melanocyte-basement membrane interactions and hair follicle genesis. Regarding the mechanisms of postnatal nevus development, epidemiological studies demonstrate the importance of constitutional and environmental influences, especially ultraviolet light. Possible molecular pathways of solar nevogenesis involve ultraviolet-induced alterations of the cellular microenvironment (eg, changes in the expression of cytokines and melanocyte adhesion molecules). Recent results and future directions of clinical and experimental research are presented.

Balloon cell nevus of the soft palate: an immunohistochemical and ultrastructural study

An ultrastructural analysis of oral balloon cell nevus of intramucosal type complemented with an immunohistochemical study was performed for the first time. The lesion was composed of large balloon cells with an admixture of small nevus cells and melanophages at the periphery. Balloon cells showed cytoplasmic accumulation of vacuoles of varying sizes and the presence of microgranular and vacuolated melanosomes were found. Residual cytoplasm contained no identifiable organelles. A spectrum of transitional forms between balloon cells and conventional nevus cells with microvacuoles was readily observed. Both cells exhibited intense immunoreactivity to multiple melanocytic markers. Ballooning phenomenon was not evident in melanophages containing a large amount of melanosome complex. It can be inferred, from the present and previous observations, that progressive vacuolization of melanosomes in nevomelanocytes may be responsible for the formation of peculiar ballooning appearance, suggesting an aberrant melanogenesis.

Bednár tumor associated with dermal melanocytosis: melanocytic colonization or neuroectodermal multidirectional differentiation?

BACKGROUND

Neuroectodermal differentiation or melanocytic colonization are the opposing theories of histogenesis for the Bednár tumor or pigmented dermatofibrosarcoma protuberans (DFSP).

OBSERVATION

A 31-year-old African-American woman presented with a 2-cm blue-black shoulder nodule of 1-year duration. Punch biopsy revealed a CD34+, Factor XIIIa-DFSP, harboring numerous, pigmented spindle S100+, Mart-1+ and HMB-45+ cells. Subsequent wide excision demonstrated pigmented dendritic and spindled cells widely scattered throughout the dermis of the 3-cm excisional margins and punch biopsy specimens of normal skin from both shoulders. This latter process was interpreted as dermal melanocytosis (nevus of Ito). The dermal pigmented spindle cells were Mart-1+ and CD34-, and were associated with non-pigmented CD34+, cytologically banal spindle cells, which were more numerous in the excisional margins than the contralateral shoulder.

CONCLUSION

Reported herein is a singular case of Bednár tumor associated with dermal melanocytosis. Although the coexistence of these processes implicates colonization of the DFSP by constituent dermal melanocytes, the mixed immunophenotype (CD34+ or Mart-1+ cells) of dispersed dermal spindle cells hints at the possibility of a common cell of origin: the putative neuromesenchymal cell. In effect, the Bednár tumor could represent one part of a spectrum of neural crest-derived dermal tumors that includes dermal melanocytosis, cellular blue nevus and conventional DFSP.

Intradermal melanocytic nevus with prominent schwannian differentiation

Features of peripheral nerve sheath differentiation such as neuroid cords, nerve corpuscles, fascicle-like structures, and, exceptionally, palisading have been reported in melanocytic nevi. We report an intradermal melanocytic nevus with prominent Verocay-like bodies. The upper portion of the neoplasm was composed of typical round intradermal nevus cells, many of which were pigmented. Within the deeper portion, there was a nonpigmented spindle cell proliferation with prominent Verocay bodies, simulating a neurilemmoma. Typical nevus nests merged with neurilemmoma-like areas. The entire lesion stained positively for S-100 and Mart-1 proteins and negatively for HMB-45 stain. Diffuse Mart-1 positivity excluded a collision of a melanocytic lesion with a neurilemmoma. The histopathologic features of this nevus further support a close relation between nevus cells and Schwann cells.