The melanocytic differentiation pathway in congenital melanocytic nevi: theoretical considerations

Risk of Malignant Transformation Arising From Giant Congenital Melanocytic Nevi: A 20-year Single-center Study

BACKGROUND

Although giant congenital melanocytic nevus (GCMN) is regarded as premalignant, the incidence and risk factors of malignant transformation are controversial.

OBJECTIVE

This study aimed to share the authors' surgical experience with GCMNs and provide data on their demographics, malignant transformation, and prognosis.

METHODS

This single-center, consecutive study included 152 patients with GCMN who visited this center from March 2000 to February 2020. Their medical documentation was reviewed retrospectively, and the nevi were classified according to the size as follows: Group 1, 10 to 19.9 cm (n = 45); Group 2, 20 to 39.9 cm (n = 62); and Group 3, ≥40 cm (n = 45).

RESULTS

Seven malignancies were found (4.6%; 4 melanomas, 2 rhabdomyosarcomas [RMS], and 1 malignant peripheral nerve sheath tumor [MPNST]). The risk increased according to the nevus size (2.2% in Group 1, 3.2% in Group 2, and 8.9% in Group 3) but the difference was not statistically significant (p = .3305).

CONCLUSION

Malignant transformation from GCMN cannot be ignored. It can include transformation into melanoma, RMS, and MPNST. Early surgical resection and regular follow-up should be performed in patients with nevi ≥10 cm.

Imaging and clinical features of neurocutaneous melanosis in the pediatric population

BACKGROUND

Neurocutaneous melanosis (NCM) is a rare nonfamilial phakomatosis characterized by the presence of congenital melanocytic nevi and abnormal melanocytes infiltration of the leptomeninges.

OBJECTIVE & METHODS

This paper shows the importance of early diagnosis and the most important imaging features of the disease on CT and MR scans. PubMed database was searched from January 1972 to September 2020. Papers including imaging findings of NCM, clinical, follow-up, and treatment features were collected, selecting only 89 studies.

DISCUSSION

NCM is a term used for the first time by van Bogaert in 1948. It refers to a condition caused by an error during morphogenesis and migration leading to leptomeningeal melanocytic accumulation. Although histological findings are the gold standard for diagnosis confirmation, neuroimaging and clinical features strongly support the suspect of NCM. Localization and extension of the lesions are predictive of neurological manifestations related to increased intracranial pressure, mass lesions, or spinal cord compression. CT demonstrates sites of increased density in the anterior temporal lobe - mainly the amygdala - thalami, cerebellum, and frontal lobes base. However, MRI is the best imaging method to diagnose central nervous system lesions, often appearing as T1-short signal areas of the cerebral parenchyma, indicative of central nervous system melanosis. MRI can also reveal associated intracranial and intraspinal abnormalities.

CONCLUSION

Early imaging, when available, is helpful if NCM suspect is raised and may be of guidance in comparing later studies. NCM requires a multidisciplinary approach since it is a multisystem disease with a genetic component.

Carbon Dioxide Cryotherapy for Treatment of Nasal and Perinasal Congenital Melanocytic Nevi

Congenital melanocytic nevi, reported in 1% to 6% of newborns. There are many complications the most dangerous is the malignant transformation, but the most depressive is the cosmetic one specially for facial lesions. There is a wide range of treatment modalities none of them provide an acceptable solution for facial lesions. In this study we provide a simple, cheap and effective treatment modality for nasal and perinasal congenital melanocytic nevi. In our study, significant improvement was observed with no repigmentation throughout the follow-up period. We conclude that carbon dioxide cryotherapy is an effective treatment modality for nasal and perinasal congenital melanocytic nevi that should be used by others to stand on its long-term persistence and possible complications.

Giant congenital melanocytic nevus associated with lipoma in an Indian man

Congenital melanocytic nevus is a inborn melanocytic proliferation either present since birth or soon afterward and shows characteristic histopathological features comprising proliferation of benign melanocytes and extension of nevus cells into the deep reticular dermis and subcutis. We report the case of a 35-year-old male patient who presented with a progressively enlarging soft tissue mass in bilateral flank region. High-resolution ultrasound imaging showed multiple lipomatous masses within the soft tissues on the either flank region. Subsequent excision of the soft tissue mass showed a well-circumscribed lipomatous lesion with diffuse infiltration by benign appearing melanocytes within the fat lobules established by immunohistochemistry, which was positive for HMB45 and S100. This case serves to illustrate the initial diagnostic challenge in a male patient as well as the plasticity of the neural crest cells.

New insights into neurocutaneous melanosis

BACKGROUND

Neurocutaneous melanosis is a rare disorder in which children with large cutaneous melanotic nevi have associated melanosis in the brain. Although many affected children have structurally normal brains, some have associated developmental disorders or brain anomalies.

OBJECTIVES

To determine the range of extent of brain melanosis as assessed by magnetic resonance imaging (MRI) and to investigate the frequency and types of associated brain anomalies.

MATERIALS AND METHODS

We retrospectively reviewed brain and spine MRIs of 80 patients with congenital melanocytic nevi (range: 1 day to 22 years of age) affiliated with Nevus Outreach Inc. from 1998 to 2017. Central nervous system (CNS) melanosis was diagnosed when a mass with abnormal parenchymal T1 hyperintensity was seen. The locations of abnormal signal, associated malformations, the presence of contrast enhancement and, in patients with more than one MRI, changes over time were recorded. Associations among findings were analyzed using chi-square test or Fisher exact test.

RESULTS

Brain abnormalities were identified in 33 patients. The most common finding was melanosis in the amygdala, which was found in 31 patients (an isolated finding in 14 patients). Nineteen patients had melanosis in the brainstem, cerebellum, cerebral cortex or thalamus. Cerebral and/or spinal leptomeningeal enhancement was uncommon (five patients). Hindbrain melanosis was associated with cerebellar and pontine hypoplasia (P=0.012). Brain melanosis was most easily seen on T1 images prior to myelination; reduced/loss of visibility was noted as the CNS matured.

CONCLUSION

Brain melanosis is a common manifestation in children with large cutaneous melanotic nevi, most commonly found in the anterior temporal lobes (amygdala), brainstem, cerebellum and cerebral cortex. Hindbrain melanosis is associated with hypoplasia of the affected structures. Early imaging is optimal to provide the greatest sensitivity for diagnosis and to guide proper management.

The High Multiplicity of Prenatal (Congenital Type) Nevi in Adolescents and Adults

In the absence of work on prenatal nevogenesis, it has long been necessary to define congenital melanocytic nevi by clinical detection on neonatal skin examination. They are seen in approximately 1% of newborns, with multiplicity in approximately 3% of cases. Melan-A staining of grossly normal fetal skin recently demonstrated fetal nevi, whose features validated certain traditional histologic criteria for "congenital type" nevi that may not have been detectable at birth. This suggested that many clinically acquired nevi actually formed in utero, like congenital nevi. Prenatal nevi has been suggested as a preferred synonym for "congenital type" nevi. Prenatal nevi were detected in 6 of 25 fetuses (24%), a strikingly higher incidence than congenital nevi in newborns. In this series of 354 patients with prenatal (congenital type) nevi encountered in routine practice at a community hospital, over 30% of both adolescents and adults had multiple prenatal nevi; a strikingly higher rate of multiplicity than congenital nevi in newborns. This high multiplicity may reflect origin beneath the epidermis, with many prenatal nevi working their way up to the surface of the skin decades after birth.

Druggable targets in pediatric neurocutaneous melanocytosis: Molecular and drug sensitivity studies in xenograft and ex vivo tumor cell culture to identify agents for therapy

BACKGROUND

Neurocutaneous melanocytosis (NCM) is a rare congenital disorder that presents with pigmented cell lesions of the brain or leptomeninges in children with large or multiple congenital melanocytic nevi. Although the exact pathological processes involved are currently unclear, NCM appears to arise from an abnormal development of melanoblasts or melanocyte precursors. Currently, it has an extremely poor prognosis due to rapid disease progression and lack of effective treatment modalities.

METHODS

In this study, we report on an experimental approach to examining NCM cells by establishing subcutaneous tumors in nude mice, which can be further expanded for conducting molecular and drug sensitivity experiments.

RESULTS

Analysis of the NRAS gene-coding sequences of an established NCM cell line (YP-MEL) and NCM patient cells revealed heterogeneity in NRAS Q61K that activated mutation and possibly consequential differential sensitivity to MEK inhibition. Gene expression studies were performed to compare the molecular profiles of NCM cells with normal skin fibroblasts. In vitro cytotoxicity screens of libraries of targeted small-molecule inhibitors revealed prospective agents for further evaluation.

CONCLUSIONS

Our studies provide an experimental platform for the generation of NCM cells for preclinical studies and the production of molecular and in vitro data with which to identify druggable targets for the treatment.

Neurocutaneous Melanosis: An Atypical Presentation

An eleven-year-old male child presented with multiple small melanocytic nevi in a generalized distribution and a giant congenital melanocytic nevus (GCMN) over the lumbosacral area since birth. He had had difficulty in walking since the age of two and a half years. Histopathological examination revealed intradermal melanocytic nevi. Serial Magnetic Resonance Imaging (MRI) scans showed brainstem atrophy with central nervous system abnormality suggestive of neuromelanosis. Clinically and histologically, the diagnosis was suggestive of neurocutaneous melanosis (NCM). The present case is reported due to its clinical presentation of quadriparesis, which has been rarely reported as a manifestation of neurocutaneous melanosis.

Hydrosurgery, a new therapeutic perspective in early care of giant congenital nevi: a preliminary series of four cases

BACKGROUND

Congenital melanocytic nevi are present at birth or may appear in the first weeks of life. Small and medium-size lesions are relatively common, affecting approximately 1% of newborns; large or giant melanocytic nevi occur in 1/20,000-1/500,000 births. The main concern raised by these lesions is their potential risk of degeneration which is strongly size-dependent and estimated in the literature between 0% and 40% over a lifetime. Although multiple treatment modalities have been described, to date there is no consensus regarding their optimal management.

PATIENTS AND METHODS

Four neonates (three females and one male) presenting giant congenital nevi with a mean age 12 days (7-24 days) were referred to our Plastic Surgery department for treatment from 2012 to 2013. All patients underwent an alternative dermabrasion procedure with the innovative use of hydrosurgery. All procedures were performed under general anaesthesia by the same senior operator (Dr. B.Bayet).

RESULTS

The mean operating time was significantly reduced compared to conventional techniques. No complications were observed in the postoperative course. Good final results were obtained in three patients after a mean follow-up of respectively 11, 8 and 4 months. The first operated neonate showed a complete recurrence of pigmentation of the treated areas after 6 months.

CONCLUSIONS

The need for early treatment in giant congenital nevi is admitted by all. Hydrosurgery is easy to use and allows to achieve a selective and symmetric resection with an obvious cleavage plane and clean-cut borders. Furthermore, this procedure has convinced us with its speed of use, ensuring significant time saving, and therefore less morbidity for the neonate. Aesthetic results as well as recurrence rate may be comparable to conventional techniques. However, regular follow-up to detect any malignancy is necessary.

Encephalocraniocutaneous lipomatosis with neurocutaneous melanosis

Encephalocraniocutaneous lipomatosis is a rare neurocutaneous syndrome characterized by classical cutaneous and ocular lesions with central nervous system anomalies. We describe an infant with classical encephalocraniocutaneous lipomatosis characterized by probable naevus psiloliparus, frontal subcutaneous lipomas, ocular limbal dermoids and arachnoid cysts, and ventriculomegaly. He also had giant congenital nevus with leptomeningeal melanosis. This case represents a rare association between encephalocraniocutaneous lipomatosis and neurocutaneous melanosis.

Mechanical properties of growing melanocytic nevi and the progression to melanoma

Melanocytic nevi are benign proliferations that sometimes turn into malignant melanoma in a way that is still unclear from the biochemical and genetic point of view. Diagnostic and prognostic tools are then mostly based on dermoscopic examination and morphological analysis of histological tissues. To investigate the role of mechanics and geometry in the morpholgical dynamics of melanocytic nevi, we study a computation model for cell proliferation in a layered non-linear elastic tissue. Numerical simulations suggest that the morphology of the nevus is correlated to the initial location of the proliferating cell starting the growth process and to the mechanical properties of the tissue. Our results also support that melanocytes are subject to compressive stresses that fluctuate widely in the nevus and depend on the growth stage. Numerical simulations of cells in the epidermis releasing matrix metalloproteinases display an accelerated invasion of the dermis by destroying the basal membrane. Moreover, we suggest experimentally that osmotic stress and collagen inhibit growth in primary melanoma cells while the effect is much weaker in metastatic cells. Knowing that morphological features of nevi might also reflect geometry and mechanics rather than malignancy could be relevant for diagnostic purposes.

Neurocutaneous melanocytosis

Neurocutaneous melanosis or neurocutaneous melanocytosis is a rare sporadic congenital disorder characterized by the presence of giant and/or multiple satellite congenital melanocytic nevi in the skin and benign melanocytic pigmentation of the leptomeninges. These two defining features were recognized more than a century ago. A third characteristic feature is proliferative nodules arising from giant nevi. The etiology is unknown, but neurocutaneous melanosis is considered a developmental disorder of melanocyte precursors from neural crest. The distinctive unique distribution of the congenital giant nevi that gives a "garment" appearance is also an expression of the neural crest. The neurological manifestations often appear in infancy.The special association of neurocutaneous melanosis with Dandy-Walker malformation complex may be explained by a common pathogenesis. Mortality in infancy and childhood is high.

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.

High prevalence of angiotropism in congenital melanocytic nevi: an analysis of 53 cases

The mechanisms responsible for the development of congenital melanocytic nevi (CMN) have yet to be elucidated. A potential clue to their origin is the observation of angiotropism of nevus cells in CMN. Interestingly, neural crest stem cells (NCSCs), the precursors of melanocytes, demonstrate angiotropism in the embryo. There is accumulating evidence that NCSCs migrate along the external surfaces of vessels during a portion of their journey to the skin. Comparable angiotropism and migration of melanoma cells have been described as extravascular migratory metastasis in melanoma. In this report, we systematically examined for the first time, the frequency of angiotropism in 53 CMN. The lesions originated from 27 females and 26 males with an average age of 9.81 years (range 0.42-28 years). The mean nevus size was 7.43 cm (range 0.3-40 cm). Twenty-seven (50.9%) of the 53 lesions were less than 1.5 cm in diameter. Sixteen nevi (30.2%) were medium sized (1.5-19.9 cm), and 10 CMN (18.9%) were large/giant (>20 cm in diameter). The trunk was the most common location (23/53) followed by the head and neck (17/53). Thirty-eight (71.7%) of the 53 lesions were compound melanocytic nevi, and 15 (28.3%) of the 53 lesions were dermal nevi. In summary, angiotropism was observed in 50 (94.3%) of 53 cases. Consequently, such angiotropism may potentially explain the origin of the precursor cells giving rise to CMN. Further explanations concerning dysregulated growth are clearly needed for the actual appearance of CMN and their physical characteristics.

Amygdalar neuromelanosis intractable epilepsy without leptomeningeal involvement

Neurocutaneous melanosis (NCM) is a rare, congenital neuroectodermal dysplasia generally resulting in early death from neurological decline due to leptomeningeal involvement. Nonmeningeal CNS epileptogenic lesions presenting in later childhood in the absence of leptomeningeal disease are rare. This report summarizes a rare presentation and curative epilepsy surgery. The authors discuss the case of a 14-year-old girl with NCM who originally presented with intractable partial-onset seizures. The MRI, PET, and SPECT studies subsequently revealed a focal epileptogenic source in the right temporal lobe. Results of video-electroencephalography monitoring concurred with the imaging findings, and a right temporal lobectomy was performed including the medial structures. Following surgery, histopathological features of the lesion included multiple scattered mononuclear cells with brown pigmentation in the amygdala specimen. The patient remains seizure free 2 years postresection, and no longer needs medication for seizure management. This patient presented with an atypical CNS manifestation of NCM that is curable by epilepsy surgery. Her intractable epilepsy developed secondary to amygdalar neuromelanosis, which had no associated leptomeningeal melanosis, an uncommon occurrence. As evidenced by the lack of seizure activity following resection, the patient's quality of life greatly improved after neurological surgery.

Human giant congenital melanocytic nevus exhibits potential proteomic alterations leading to melanotumorigenesis

Background

A giant congenital melanocytic nevus (GCMN) is a malformation of the pigment cells. It is a distress to the patients for two reasons: one is disfigurement, and the other is the possibility of malignant changes. However, the underlying mechanisms of the development of GCMN and melanotumorigenesis in GCMN are unknown. Hence, the aim of this study was to identify the proteomic alterations and associated functional pathways in GCMN.

Results

Proteomic differences between GCMN (n = 3) and normal skin samples (n = 3) were analyzed by one-dimensional-liquid chromatography-tandem mass spectrometry Relative levels of the selected proteins were validated using western blot analysis. The biological processes associated with the abundance modified proteins were analyzed using bioinformatic tools. Among the 46 abundance modified proteins, expression of 4 proteins was significantly downregulated and expression of 42 proteins was significantly upregulated in GCMN compared to normal skin samples (p < 0.05). More importantly, 31% of the upregulated proteins were implicated in various cancers, with five proteins being specifically related with melanoma. The abundance modified proteins in GCMN were involved in the biological processes of neurotrophin signaling, melanosome, and downregulated of MTA-3 in ER-negative breast tumors. In particular, an increase in the expression of the 14-3-3 protein family members appeared to be associated with key cellular biological functions in GCMN. Western blot analysis confirmed the upregulation of 14-3-3epsilon, 14-3-3 tau, and prohibitin in GCMN.

Conclusion

These findings suggest that GCMN exhibits potential proteomic alterations, which may play a role in melanotumorigenesis, and the significant alteration of 14-3-3 family proteins could be a key regulator of the biological pathway remodeling in GCMN.

On the development of neurocutaneous units--implications for the histogenesis of congenital, acquired, and dysplastic nevi

This study of spontaneous abortions and fetal deaths in utero used immunostains to evaluate the structure of developing cutaneous nerves. Melan-A immunostains were also used to screen 25 cases of grossly normal fetal skin for occult fetal nevi. Discrete portions of epidermis were generally supplied by branches emanating from regularly spaced deep cutaneous nerves, producing a wedge shape, interpreted as neurocutaneous units (NCU). Deeper nerves embraced broader portions of epidermis. Some nerves ran parallel to epidermis, especially near the superficial vascular plexus at the junction of superficial and deep dermis. Nerve sheath stem cells in each NCU may supply the melanocytes needed by the corresponding portion of epidermis. Transformed nerve sheath stem cells may lead to formation of occult prenatal nevi, whose histology and histogenesis may best be understood in terms of NCUs. In particular, the size and shape of a nevus may be largely determined by its NCU of origin. Six fetal nevi were detected, and 3 occult lumbosacral Mongolian spots; all in deep dermis, no later than the middle of the second trimester, mainly with a pattern of singly dispersed deep dermal melanocytes. These findings suggest that congenital (prenatal) nevi begin as intradermal nevi. In addition to explaining congenital nevi, these findings have implications for the histogenesis of acquired (postnatal) nevi and dysplastic nevi.

Extrafollicular dermal melanocyte stem cells and melanoma

Recent studies suggest that extrafollicular dermal melanocyte stem cells (MSCs) persist after birth in the superficial nerve sheath of peripheral nerves and give rise to migratory melanocyte precursors when replacements for epidermal melanocytes are needed on the basal epidermal layer of the skin. If a damaged MSC or melanocyte precursor can be shown to be the primary origin of melanoma, targeted identification and eradication of it by antibody-based therapies will be the best method to treat melanoma and a very effective way to prevent its recurrence. Transcription factors and signaling pathways involved in MSC self-renewal, expansion and differentiation are reviewed. A model is presented to show how the detrimental effects of long-term UVA/UVB radiation on DNA and repair mechanisms in MSCs convert them to melanoma stem cells. Zebrafish have many advantages for investigating the role of MSCs in the development of melanoma. The signaling pathways regulating the development of MSCs in zebrafish are very similar to those found in humans and mice. The ability to easily manipulate the MSC population makes zebrafish an excellent model for studying how damage to MSCs may lead to melanoma.

The risk of melanoma and neurocutaneous melanosis associated with congenital melanocytic nevi

Congenital melanocytic nevi are commonly encountered in clinical practice. Although the development of malignant melanoma arising in small and intermediate congenital melanocytic nevi is rare, there is a significant risk of malignant degeneration associated with large congenital melanocytic nevi, in particular those that arise on the torso in the so-called "bathing trunk" distribution, where the risk is estimated to be about 2.5% to 5%. The risk of malignant melanoma arising within a large congenital melanocytic nevus is highest in the first 5 to 10 years of life and carries a significant mortality. Large congenital melanocytic nevi, in particular those overlying the posterior axis and occurring in the context of multiple satellite melanocytic nevi, are also associated with the development of neurocutaneous melanosis, which may result in neurologic and neurodevelopmental sequelae and is associated with a significant risk of primary central nervous system melanoma and death.

Large congenital melanocytic nevi: associated risks and management considerations

Large congenital melanocytic nevi (LCMN) in neonates can cause considerable concern for parents, family members, and physicians. A detailed understanding of the medical risks, including cutaneous melanoma (CM), extracutaneous melanoma (ECM), and neurocutaneous melanocytosis (NCM), as well as the psychological stress that these lesions can cause in patients, will guide informed management decisions as well as provide comfort to parents. Current data indicate that LCMN greater than 20 cm, and more likely greater than 40 to 60 cm, are the lesions at greatest risk for complications such as CM, ECM, and NCM. Additionally, lesions on the trunk are at greater risk for developing CM, and LCMN in association with numerous satellite nevi are at greatest risk for NCM. Individualized management plans, including clinical observation, magnetic resonance imaging (MRI), and possibly surgery should be based on the risk versus benefit ratio, taking into account the size of the LCMN, its location, the number of satellite nevi, symptoms, and numerous other factors which will be reviewed. This paper will provide a detailed analysis of the risks associated with LCMN, as well as a discussion regarding management and treatment options.

Angiotropic neonatal congenital melanocytic nevus: how extravascular migration of melanocytes may explain the development of congenital nevi

In the following report we describe a medium-sized congenital melanocytic nevus (CMN) on the upper back of a female patient biopsied at 9 days of age. This case is a unique variant of CMN occurring in the neonatal period that mimics malignant melanoma. This is not only because of histologic features such as a large round or ovoid cellular phenotype of melanocytes mimicking melanoma cells but also because of conspicuous angiotropism, a finding not previously reported in such CMN. Immunostaining for blood and lymphatic vessels demonstrated angiotropism of melanocytes about blood vessels but not lymphatics. We have already emphasized the significance of angiotropism as a marker of extravascular migratory metastasis (EVMM) of melanoma. EVMM, a process by which tumor cells migrate along vessels and other tracks, has striking parallels with the migration of embryonic stem cells from the neural crest. Thus we propose, because angiotropism is a common finding in CMN and metastatic melanoma, that (1) such pathways of cellular migration may result in the genesis of CMN and other melanocytic neoplasms; and (2) the dysregulation of such embryonic pathways may result in the retrograde migratory phenomena of melanoma as already described. In summary, extravascular cellular migration of melanocytes seems to be fundamental for melanoma (perhaps other cancer) metastasis but also hypothetically may be important for the development of other melanocytic lesions such as CMN and requires further investigation.

Neurocutaneous melanosis: surgical pathological features of an apparently hamartomatous lesion in the amygdala

Neurocutaneous melanosis (NCM) is a rare, congenital phakomatosis characterized by the presence of congenital melanocytic nevi and a benign or malignant pigmented cell tumor of the leptomeninges of the CNS. Here the authors report the surgical pathological features of a lesion in the left amygdala in a 10-year-old girl with giant congenital pigmented nevi and mesial temporal lobe epilepsy. The lesion exhibited high intensity on T1-weighted MR images and low intensity to isointensity on T2-weighted images. A left anterior temporal lobectomy and hippocampectomy were performed. Histologically, the lesion was composed of melanin-containing polygonal cells arranged in solid alveolar or multiple lobular patterns. Immunohistochemically, the cells were immunoreactive for HMB45, S100 protein, and vimentin, the profiles being consistent with those of melanocytes. Bundles of astrocytic processes surrounded the nests of melanocytes. Melanin-containing and dysmorphic neurons were also scattered near the nests. In the temporal neocortex adjacent to the amygdaloid melanocytic lesion, cortical dysplasia with cortical laminar disorganization was evident. Based on the histopathological features, the parenchymal lesion appeared to be hamartomatous in nature rather than a neoplasm, involving aberrant migration of melanocytes into the developing neuroepithelial tissue. This case appears to represent an unusual CNS manifestation of NCM.

Giant congenital melanocytic nevi

BACKGROUND

: Giant congenital melanocytic nevi are rare lesions with the potential to regress into malignant melanoma and/or neurocutaneous melanosis. Appropriate investigations include a screening magnetic resonance imaging scan, neurologic evaluation, and serial clinical observations looking for the development of these complications. Numerous excisional and nonexcisional options have been described for the management of giant congenital melanocytic nevi.

METHODS

: A MEDLINE search was performed to obtain all relevant citations.

CONCLUSIONS

: To successfully treat these complex lesions, the plastic surgeon must understand the disease process, the natural history and complications, and the options for treatment.

Congenital melanocytic naevi

Congenital melanocytic naevi, consisting of clusters of naevo-melanocytes, develop in utero. Although many congenital naevi are visible at birth, some may not become evident until later in life. The timing of naevo-melanocyte proliferation, senescence and melanogenesis may all contribute towards determining when a naevus will become clinically manifest on the skin. Besides the fact that congenital melanocytic naevi may be aesthetically displeasing, resulting in a multitude of psychosocial issues, they also increase the risk for developing cutaneous melanoma, leptomeningeal melanoma, neurocutaneous melanocytosis, malformations of the brain and, rarely, other tumours such as rhabdomyosarcoma and liposarcoma. Whereas the risk of developing malignancy in association with congenital naevi is dependent, to some extent, on the size of the naevus, the risk of developing neurocutaneous melanocytosis correlates best with the number of satellite naevi. Management of patients with congenital melanocytic naevi requires individualization, taking into account the naevus size and location, and the risk of developing cutaneous melanoma or neurocutaneous melanocytosis. When contemplating treatment options, it is important to set realistic expectations and to address the possible aesthetic and functional outcomes, while at the same time addressing the risk for developing cutaneous and/or extracutaneous melanoma.

State of the art, nomenclature, and points of consensus and controversy concerning benign melanocytic lesions: outcome of an international workshop

The following communication summarizes the proceedings of a one-day International Workshop focusing on the histology of benign melanocytic nevi. Areas of controversy identified in 6 focus sessions were the nomenclature and relationships among common nevi including nevi with halo reactions, traumatized nevi, "dysplastic" nevi, and nevi from particular anatomic sites; developmental biology and frequency of malignant transformation associated with congenital nevi; the characterization and biologic nature of atypical spitzoid neoplasms; the basic definition of particular melanocytic cellular phenotypes, and the nomenclature and biologic nature of many candidate blue nevi, combined nevi, and other controversial lesions such as deep penetrating nevus and pigmented epithelioid melanocytoma. Concentrated data collection and follow-up, molecular characterization, and future consensus Workshops may facilitate the resolution of some of these problems. The Group recommended the description of ambiguous or "borderline" lesions as tumors with indeterminate or uncertain biologic/malignant potential. The participants also advised that such lesions at a minimum should be managed by complete excision with clear surgical margins.

Stem cells for epidermal melanocytes--a challenge for students of dermatopathology

Many obstacles to belief in stem cells for melanocytes arise in the routine practice of cutaneous histopathology. However, the fundamental principle of stem cell theory says that normal stem cells arise during development, are present in adult organs as tissue-determined stem cells, and are little changed, if at all, from their embryonic counterparts. This paradox can be resolved by focusing on the process of epidermal melanocyte development in utero. Stem cells for melanocytes originate in the neural crest. Although much remains to be learned, this author proposes that these stem cells then take a small step to the paraspinal ganglia and then follow the axonal signposts to the skin provided in the course of normal cutaneous innervation. The epidermis may then induce these stem cells in the nerve sheath to give rise to immature dermal melanocytes, which migrate up into the epidermis. It is proposed that these melanocyte stem cells also persist after birth in the superficial nerve sheath and give rise to transient, immature, inconspicuous dermal migratory melanocytes when replacements for epidermal melanocytes are needed in postnatal skin.

Giant congenital melanocytic nevi

LEARNING OBJECTIVES

After studying this article, the participant should be able to: 1. Define what is meant by a giant congenital melanocytic nevus and understand its histologic properties. 2. Know the natural history and potential complications associated with a giant congenital melanocytic nevus. 3. Outline the nonsurgical and surgical options available to treat a giant congenital melanocytic nevus.

BACKGROUND

Giant congenital melanocytic nevi are rare lesions with a propensity to degenerate to malignant melanoma. Certain lesions also may be associated with neurocutaneous melanosis, which can on occasion be symptomatic. Appropriate investigations include a screening magnetic resonance imaging scan, neurologic evaluation, and serial clinical observations for the development of cutaneous melanoma. A variety of nonsurgical and surgical options are possible for the treatment of giant congenital melanocytic nevi.

METHODS

A MEDLINE search was performed to gather all pertinent articles from 1955 to 2005.

RESULTS

Giant congenital melanocytic nevi are a difficult diagnostic and reconstructive challenge, requiring careful preoperative evaluation, staged surgical excision, and lifelong patient monitoring and follow-up. With proper treatment, patients can expect a decreased risk of melanoma, with the possibility for early detection and cure of melanoma, amelioration of symptoms, improved aesthetics and psychosocial sequelae, and maintenance of function.

CONCLUSION

The plastic surgeon treating these challenging lesions must have a solid working knowledge of the disease's histology, its natural history and complications, and the options for treatment.

Neurocutaneous melanosis with associated Dandy-Walker complex

CASE REPORT

The authors report the case of a child with neurocutaneous melanosis associated with a Dandy-Walker complex. Magnetic resonance (MR) images showed shortened T1-weighted images in areas involving the amygdala, mesencephalon, rostral brain stem, and superior cerebellar surface compatible with melanin deposits. There was also partial agenesis of the cerebellar vermis with an enlarged fourth ventricle cyst along with a high-lying torcular and ventricular enlargement. Endoscopic fenestration and biopsy of the cyst wall was performed without evidence of abnormal melanin deposits in the meninges.

OUTCOME

The patient eventually required ventriculoperitoneal shunting and at 1-year follow-up did not develop evidence of primary CNS melanoma. ILLUSTRATION: Computed tomography and MR images consistent with neurocutaneous melanosis and the Dandy-Walker complex are presented along with photographs of the cutaneous nevi.

DISCUSSION

The major clinical and radiological features of this rare association, with only 11 previously reported cases, are discussed in detail.

Giant congenital melanocytic nevi of the trunk and an algorithm for treatment

Giant congenital melanocytic nevi (CMN) are rare, congenital, disfiguring lesions with a risk of degeneration to malignant melanoma. Giant CMN are associated with an increased risk of malignant degeneration. In a minority of cases, patients with giant CMN may have associated neurocutaneous melanosis with leptomeningeal involvement. Giant CMN of the trunk pose difficult diagnostic and reconstructive problems requiring complex multistage treatment. For high-risk cases, diagnostic evaluation in the form of neuro-imaging is an essential component of the planning phase. Although nonsurgical options for the treatment of giant CMN have been advocated, these modalities may decrease the burden of nevus cells but do not result in complete removal of these cells. The ability to monitor nevus cells that remain after nonsurgical management of giant CMN remains questionable. These nonsurgical options include dermabrasion, laser ablation, and chemical peel. In contrast, direct excision of the nevus is the mainstay of treatment of nonsurgical management of giant CMN. There are numerous surgical options to resurface the resultant cutaneous defect after excision of the nevus. The simplest of these options consists of serial excision and direct closure of the defect in stages. However, if the defect cannot be closed by direct cutaneous advancement, other options for wound resurfacing include split- or full-thickness skin graft, tissue expansion, and free tissue transfer. Tissue expansion should be viewed as a category of treatment options because expanders can be used to create an expanded full-thickness skin graft, local expanded flaps adjacent to the lesion, or expansion of a free tissue donor site. Given the diversity of reconstructive options that use tissue expansion, these techniques have evolved as the primary treatment method for giant CMN of the trunk. The authors outline an approach to the evaluation of giant CMN of the trunk, review the risks of melanoma and of neurocutaneous melanosis, describe their preferred treatment regimen, and offer a treatment algorithm for giant CMN of the trunk.

Embryology of the neural crest: its inductive role in the neurocutaneous syndromes

Neural crest cells are first recognized at the lateral margin of the neural placode shortly after gastrulation, although they are not committed to their diverse fates until later. After dorsal closure of the neural tube, neural crest cells separate and migrate throughout the embryo to form many structures of ectodermal origin (eg, dorsal root and autonomic ganglia, peripheral nerve sheaths) and mesodermal origin (eg, blood vessels, melanocytes, adipose tissue, membranous bone, connective tissue, most of the ocular globe). Terminal differentiation occurs after migration is complete. Three regions of the neural tube generate neural crest: rhombencephalon, mesencephalon, and prosencephalon, each with a different migratory pattern. The most important genes promoting neural crest differentiation and migration are those with a dorsalizing influence in the vertical axis of the neural tube (eg, PAX3, BMP4, ZIC2), some segmentation genes (eg, WNT1), genes that inhibit neural crest (eg, EGR2), and neural crest-specific differentiating genes (eg, SLUG, SOX10). In the neurocutaneous syndromes, diverse features result from abnormal neural crest differentiation, providing a more encompassing embryologic basis for these disorders than the traditional view that these syndromes are somehow related to skin and brain because both are ectodermal derivatives. Abnormal angiogenesis, areas of abnormal pigmentation that sometimes follow the lines of Blashko, nerve sheath proliferations, disorders of chromaffin tissue, lipomes and benign and malignant tumors are frequent features. Many defective genes in neurocutaneous syndromes have an additional function as tumor suppressors. Interactions between genes associated with these disorders and others essential to neural crest formation, migration, and differentiation, are a likely molecular genetic basis for these diseases. The craniofacial abnormalities associated with many cerebral malformations and cutaneous lesions in some neurocutaneous syndromes emphasize an important inductive role of the neural tube in the development of non-neural tissues, mediated through neural crest.

Childhood malignant blue nevus of the ear associated with two intracranial melanocytic tumors-metastases or neurocutaneous melanosis?

Blue nevus is an uncommon pigmented tumor of dermal melanocytes that has traditionally been classified into common and cellular variant. It is usually a skin tumor in adults but can become apparent in early childhood or even be present at birth. Malignant blue nevus is a rare melanocytic tumor of the skin arising from a preexisting cellular blue nevus. We report a multinodular blue nevus of the left ear in an 11-year-old girl who also had 2 intracranial melanocytic lesions. Differential diagnosis between metastases from malignant blue nevus and neurocutaneous melanosis is discussed.

Neurocutaneous melanosis

Neurocutaneous melanosis (NCM) is a rare congenital disorder characterized by the presence of large or multiple congenital melanocytic nevi in association with benign or malignant proliferation of melanocytes in the leptomeninges. NCM is believed to occur as a consequence of an error in morphogenesis in neural ectoderm in the developing embryo. Animal models suggest that aberrant expression of the hepatocyte growth factor/scatter factor (HGF/SF) may be involved in the pathogenesis in the NCM. While the majority of patients with NCM have large congenital melanocytic nevi in a posterior axial distribution, a significant proportion of patients present with multiple smaller nevi in the absence of a single larger lesion. Neurologic manifestations generally occur within the first two years of life, and are often related to increased intracranial pressure. Associated structural anomalies of the CNS have been reported in NCM, particularly the Dandy-Walker complex. The long-term clinical significance of characteristic magnetic resonance findings in neurologically asymptomatic patients is unclear. Approximately half of NCM patients develop CNS melanoma. The prognosis of symptomatic patients remains poor.

A distinctive type of widespread congenital melanocytic nevus with large nodules

We report an unusual case of congenital melanocytic nevus presenting in a 19-year-old African woman as widespread papules and variably sized nodules and tumors affecting the entire body, including the palms, soles, and oral mucous membrane. Histopathologic examination of 3 representative skin lesions showed mainly dermal aggregations of round to oval, focally pigmented, monomorphous melanocytes, arranged in nodular and plexiform patterns. Scattered areas with spindle-shaped dendritic melanocytes surrounded by fibrosis were also noted in the center of the lesions. The clinical and histopathologic findings were similar to those in 2 other previously reported cases, except that in 1 of the earlier cases the skin nodules were composed of spindle-shaped cells, suggesting a type of blue nevus. The findings in our case indicate a broader spectrum of morphologic features in this condition, with dermal aggregations of melanocytes showing congenital features, representing a common histopathologic denominator. Based on this observation, we suggest the term "widespread congenital dermal nevus with large nodules" to be the most appropriate for this rare, but distinctive, type of congenital nevus.

Congenital melanocytic nevi. Evaluation and management

This article discusses the care of patients with CMN, who often require a multidisciplinary approach involving pediatricians, family physicians, internists, dermatologists, psychologists, plastic surgeons, neurologists, and radiologists. The cosmetic and psychosocial issues, combined with the knowledge of the increased risk of developing melanoma or NCM, is a huge burden that many of these patients and their families have to carry. This article describes the importance for physicians to help these patients and families come to terms with these issues, as well as remind their patients and their family members that although melanoma, NCM, or other complications can develop, most affected individuals do not develop any complications. The article mentions that there are many healthy, happy, functional adults with large, small, and multiple CMN alive today.

Neurocutaneous melanosis in association with encephalocraniocutaneous lipomatosis

We describe a white female infant with neurocutaneous melanosis (NCM) and encephalocraniocutaneous lipomatosis (ECCL). Multiple, giant and small congenital melanocytic nevi (CMN) were observed on the head, neck and trunk and involved 70% of body surface area. Histologic examination of several CMN revealed atypical nodular proliferations of dermal nevomelanocytes. In a small (<1 cm) truncal CMN, single and dyscohesive intraepidermal nests of atypical nevomelanocytes simulating a superficial spreading melanoma, were observed. The placenta was grossly normal and histologically demonstrated multiple banal appearing nevomelanocytes within the stroma of its villi. At the 17-month follow-up no evidence of primary or metastatic melanoma was present. This previously undescribed association of NCM, ECCL and placental nevomelanocytes provides strong support for the hypothesized causal role of anomalous neural crest morphogenesis and migration in the development of all three disorders. The genetic mechanism underlying these complex birth defects has been hypothesized to result from the action of lethal autosomal dominant genes surviving by mosaicism.

Cerebral mass due to neurocutaneous melanosis: eight years later

Neurocutaneous melanosis (NCM) is associated most commonly with giant congenital melanocytic nevi (CMN), in particular those on the scalp or in a posterior axial location that are accompanied by satellite congenital nevi. It also can occur in patients with multiple medium-sized CMN. In general, the prognosis of those with symptomatic NCM is poor, even in the absence of malignancy, while the prognosis of those with asymptomatic NCM detected via screening varies and is more difficult to predict. Herein we report an asymptomatic patient with a giant CMN and multiple satellite nevi who had a screening magnetic resonance imaging (MRI) study at age 5 months that showed a rounded area of increased signal in the right temporal lobe on T1-weighted images, suggestive of parenchymal melanosis. This melanotic mass was resected at age 10 months, and histologic examination of the surgical specimen showed prominent perivascular collections of benign, pigment-containing melanocytes within cerebral tissue. The patient remains healthy 8 years later. His excellent long-term outcome and other reports of NCM with localized central nervous system (CNS) involvement apparent on MRI may have implications for management, including early imaging of patients with high-risk CMN and potential surgical intervention for NCM.

Make PEEC, not war: does evasive transdifferentiation protect from carcinogenesis?

DNA repair and immune surveillance are established mechanisms that secure a programmed escape from the evolution of cancer (PEEC) by healing and elimination, respectively. Evasive transdifferentiation, i.e. silencing of carcinogenic events, is an emerging concept with potentially broad applicability that paradigmatically includes the claim that common acquired melanocytic nevi represent a programmed rescue from malignity for initiated melanocytes. This hypothesis is difficult to test. Research into the molecular mechanisms that govern the development of acquired melanocytic nevi, however, should result in the identification of a molecular master switch and an associated set of genes that - beyond the processes involved in apoptosis - may help bypass carcinogenesis and may be of therapeutic benefit in the future.

Periorbital congenital melanocytic nevus associated with ankyloblepharon

We report periorbital congenital melanocytic nevus associated with ankyloblepharon in a 2-month-old boy. This unusual presentation may be explained by the assumption that the development of the congenital melanocytic nevus (CMN) in utero was related to the failure of normal eyelid separation, which occurs around the 20th week of gestation.

A clinicopathologic study of 45 pediatric soft tissue tumors with an admixture of adipose tissue and fibroblastic elements, and a proposal for classification as lipofibromatosis

The tumor described here as lipofibromatosis is a rare pediatric neoplasm that has been variously interpreted as a type of infantile or juvenile fibromatosis, a variant of fibrous hamartoma of infancy, and a fibrosing lipoblastoma. This report details the clinicopathologic features associated with 45 cases of this soft tissue entity. The study group consisted of 32 males, 12 females, and one person of unstated gender. The patients presented with a soft tissue mass (range, 1-7 cm) involving the hand (n = 18), arm (n = 8), leg (n = 7), foot (n = 6), trunk (n = 5), or head (n = 1). Eight tumors were evident at birth. The individuals ranged in age from 11 days to 12 years (median age, 1 yr) at the time of initial biopsy or resection. Microscopic examination revealed abundant adipose tissue with a spindled fibroblastic element that chiefly involved the septa of fat and skeletal muscle. The process generally did not cause extensive architectural effacement of fat as is common with conventional fibromatoses, and it did not have a primitive nodular fibromyxoid component as is characteristic of fibrous hamartoma of infancy. The fibroblastic element exhibited focal fascicular growth and typically had limited mitotic activity (< or = 1 mitosis/ 10 high-power fields) and cytologic atypia. Oftentimes, small collections of univacuolated cells were present at the interface between some of the fibroblastic fascicles and the mature adipocytes. The tumors entrapped vessels (n = 45), nerves (n = 44), skin adnexa (n = 16), and skeletal muscle (n = 18). Focal immunoreactivity was present in some tumors for CD99, CD34, alpha-smooth muscle actin, BCL-2, and less frequently, S-100 protein, muscle actin (HUC 1-1), and EMA. However, no reactivity was detected for desmin (D33 and D-ER- 1 clones), keratins, or CD57. Follow-up data were available for 25 individuals (median follow-up period, 6 yrs 7 mos) with regrowth of the tumor or persistent disease documented in 17 (72%). The following events were more common in the group with recurrent or persistent disease: congenital onset, male sex, hand and foot location, incomplete excision, and mitotic activity in the fibroblastic element. Although it is likely this tumor comprises part of the spectrum of what has been referred to in the literature as infantile/juvenile fibromatosis, its clinicopathologic features and, in particular, its distinctive tendency to contain fat as an integral component, warrant separate classification as a "lipofibromatosis."

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

Among thousands of specimens of melanocytic nevi, not including giant congenital melanocytic nevus or blue nevus, 42 melanocytic nevi that showed peripheral nerve sheath differentiation were collected. The patterns of melanocytic nevi with peripheral nerve sheath differentiation may be classified into three groups: 1) "neurotized and neural nevi" with nests of "neuroid cords" and "nevic corpuscles" (the most common pattern); 2) nerve fascicle-like structures with no relation to neurotized and neural nevi; and 3) palisading melanocytes of a nevus in nests of conventional melanocytic nevi (a rare pattern). Each pattern may represent a different expression of nerve sheath differentiation in melanocytic nevi. Some melanocytic nevi with nerve fascicle-like structures show discrete structures closely resembling authentic nerve fascicles, confirming a close relationship between melanocytes and peripheral nerve sheath cells (Schwann cells and probably perineurial cells in part) and suggesting derivation of the two types of cells from common precursor cells of the neural crest and their de novo development in the dermis rather than by Abtropfung of melanocytes from the epidermis. In addition, the high prevalence of Unna, Miescher, and superficial congenital nevi in melanocytic nevi with peripheral nerve sheath differentiation suggests a different character or process for these congenital melanocytic nevi than for Clark and Spitz nevi (junctional and compound types).

The relationship between melanocytes and peripheral nerve sheath cells (Part II): blue nevus with peripheral nerve sheath differentiation

Peripheral nerve sheath differentiation was studied in 120 specimens of blue nevi (112 specimens of "common" blue nevi and 8 specimens of "cellular" blue nevi). In 10 of 112 common blue nevi, fascicles of pigmented dendritic melanocytes or less pigmented spindle-shaped melanocytes with S-shaped nuclei were associated with wavy delicate collagen bundles. In 4 of these 10 specimens, the melanocytes showed a perifollicular arrangement. These nerve fascicle-like structures were seen in some cellular blue nevi (5 of 8 specimens). Structures closely resembling authentic nerve fascicles were not observed in common or cellular blue nevi. The fascicles with S-shaped nuclei and fibrillary collagenous tissue observed in blue nevi (which were well detected in the cellular type but rarely found in the common type) may be peripheral nerve sheath features and perhaps evidence that dermal dendritic melanocytes in the reticular dermis may have arisen within a peripheral nerve sheath milieu from primitive fibroblast-like precursors. Some of the examples presented here may be identical to those reported for "pilar neurocristic hamartoma" or "neurocristic hamartoma." I also speculate on the pathogenesis of blue nevi based on the observations made in this study.

Pigmented (melanotic) neurofibroma: a clinicopathologic and immunohistochemical analysis of 19 lesions from 17 patients

Neurofibromas with melanin-laden pigmented cells are rare, accounting for less than 1% of all neurofibromas accessioned to the Soft Tissue Registry of the Armed Forces Institute of Pathology between the years 1970 and 1996. This study analyzes the clinicopathologic features associated with 19 specimens removed from 17 patients. Eleven males and six females, ranging in age from 2 to 61 years (median, 28 years), participated in the study. Nine of 15 patients whose race was provided were black. Eight patients (47%) are known to have neurofibromatosis, and two others (12%) are strongly suspected of having this disorder; two patients have similarly affected family members. Eight patients were noted to have multiple skin tumors, and in each of two cases, two pigmented neurofibromas were available for review. Two patients had hypertrichosis and cutaneous hyperpigmentation resembling a hairy nevus, and one had a café au lait spot directly overlying a pigmented neurofibroma. Tumors ranged in size from 1.7 to 50 cm in greatest dimension and involved the buttock or leg (n = 6), head or neck (n = 8), trunk (n = 2), wrist or hand (n = 2), and an unspecified site (n = 1). The neurofibromas exhibited diffuse (n = 15), combined diffuse and plexiform (n = 2), combined diffuse and intraneural epithelioid (n = 1), and nonspecific (n = 1) growth patterns. The process involved the skin (n = 14), subcutis (n = 18), and/or skeletal muscle (n = 3). Wagner-Meissner-like bodies were identified in 11 tumors, and mitoses (average, less than one mitosis per 10 high-power fields) were present in three lesions. All examples contained scattered pigmented cells with dendritic, tadpole-shaped, spindled or epithelioid morphology. These cells were positive with Fontana-Masson (nine of nine) and Warthin-Starry (pH, 3.2; four of four) stains, and were depigmented with a melanin bleach method (two of two). An iron stain was negative. The tumors had immunoreactivity for S-100 protein (11 of 11), HMB-45 ( 10 of 11), Melan-A (four of four), tyrosinase (four of four), and CD34 (four of four). Although recurrences are documented, none of the tumors are known to have undergone malignant transformation. A pigmented neurofibroma can be confused with a pigmented dermatofibrosarcoma protuberans (Bednár tumor) because the melanin-laden cells of both processes are similar. However, the latter entity exhibits a more extensive storiform growth, has greater immunoreactivity for CD34, and lacks a diffuse proliferation of S-100 protein-positive Schwann cells.

The melanocyte differentiation pathway in spitz nevi

The nature of Spitz nevi is poorly understood, and their distinction from malignant melanoma can be difficult. Although there is general agreement on the diagnostic criteria, experts continue to have some differences, and controversial cases are not rare. A major obstacle to progress in this area is the lack of basic knowledge about melanocyte differentiation in Spitz nevi, as compared with ordinary nevi and malignant melanomas. Based on the hypothesis that normal melanocytes may have a differentiation pathway with discrete stages, it is suggested that the features of Spitz nevi may reflect homeostatic mechanisms governing maturation in the melanocyte differentiation pathway, whereas those of malignant melanomas may reflect carcinogen-induced aberrations. This perspective may be helpful in the continuing effort to develop optimal criteria for the differential diagnosis of Spitz nevi from malignant melanomas.

The spectrum of neurocristic cutaneous hamartoma: clinicopathologic and immunohistochemical study of three cases

Neurocristic cutaneous hamartomas result from aberrant development of the neuromesenchyme. Thus, the elements within these tumors reflect the spectrum of differentiation that results from migration of neural crest-derived cells. We present three cases, in addition to routine hematoxylin-eosin staining, a battery of immunohistochemical staining, including S-100 protein, HMB-45, EMA, CD34, and neurofilament-protein stains, was performed on each specimen. A dermal melanocytic component was the dominant feature of two of these lesions, while neurosusenticular and neuromesenchymal components dominated in one tumor. Both tumors that developed on the scalp showed effects on the overlying epidermis and/or on adnexal development. The melanocytic component was positive for S-100 protein and HMB-45. The surrounding stroma showed tactoid bodies and increased CD34 staining. Neurocristic cutaneous hamartomas represent dysplastic development of neural crest-derived cells. Although melanocytic cells have been previously reported to be the dominant cell population, neurosusentacular and neuromesenchymal cells also may be the principal component. In cephalic areas, the neuromesenchyme may not only be an important component of the tumor, but may also effect the development of the overlying epithelium and adnexal structures. Although none of these cases presents evidence of malignant transformation, identification of these tumors could be important if malignant transformation results in the development of tumors with a distinctive biologic behavior.