Nevus with fat: clinical characteristics of 100 nevi containing mature adipose cells

Prevalence and clinicopathological characteristics of lipomatous neurofibromas in neurofibromatosis 1: An investigation of 229 cutaneous neurofibromas and a systematic review of the literature

BACKGROUND

Lipomatous neurofibroma (Lnf) is a histopathological variant with adipocytes noted among cells of cutaneous neurofibromas. We aimed to investigate the prevalence and clinicopathological features of Lnfs of neurofibromatosis 1 (NF1)-associated cutaneous neurofibromas and to review the literature systematically. We also evaluated the expression of leptin (a hormone involved in lipid metabolism) in neurofibromas to better understand the pathogenesis of Lnfs.

METHODS

A prospective histologic study was conducted on 229 cutaneous neurofibromas from 85 NF1 individuals. Leptin expression was immunohistochemically evaluated in 111 cutaneous neurofibromas. To systematically review the literature, two authors independently performed literature searches without year restriction.

RESULTS

Forty (17.5%) neurofibromas were lipomatous. Lnfs were significantly larger lesions and associated with females. Eighteen (7.9%) of all neurofibromas had multinucleated floret-like giant cells, and these were associated with Lnfs. All neurofibromas expressed leptin. We systematically reviewed 13 articles. Three large studies investigated Lnfs mainly in sporadic neurofibromas and suggested that 0.3% to 8.0% of tumors (NF1 and sporadic) are Lnfs.

CONCLUSION

In NF1, Lnfs are common, mainly in larger tumors and women. All cutaneous NF1-neurofibromas express leptin. It is unknown if the expression of leptin accounts for the lipomatous variant, but it may have a role in the pathogenesis of cutaneous neurofibroma.

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.

Lipomatous Change in Uveal Melanoma: Histopathological, Immunohistochemical and Cytogenetic Analysis

PURPOSE

The aim of this study was to describe a case of lipomatous change in uveal melanoma.

PROCEDURES

The patient presented with a 2-year history of blurry vision. A full examination of the right eye revealed a dome-shaped pigmented subretinal mass in the choroid with a thickness of 9 mm and a diameter of 15 mm. The eye was enucleated and prepared for histopathologic, genetic and molecular investigation.

RESULTS

Histopathology revealed a small circumscribed area consisting of mature adipocytic appearing cells with abundant clear cytoplasm and small peripheral flattened nuclei within a spindle-cell melanoma of the uvea. The cytoplasm of the adipocytic cells stained negative for periodic acid-Schiff and Alcian blue and positive for Melan-A, HMB-45 and tyrosinase, confirming melanocytic lineage. Fluorescence in situ hybridization analysis confirmed trisomy of chromosome 6p22 and disomy of chromosome 3p13 in the nuclei of both the tumor spindle type B cells and in the nuclei of lipomatous tumor cells.

CONCLUSIONS

Lipomatous change can be added to the many histopathologic faces of uveal melanoma. To our knowledge, this is the first report of lipomatous change in uveal melanoma performed with cytogenetic investigations.

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.

Cutaneous lipomatous neurofibroma: characterization and frequency

BACKGROUND

There are numerous variants of cutaneous neurofibroma reflecting its manner of growth and histologic composition. Lipomatous neurofibroma is the latest described variant with only eight cases reported.

METHODS

A systematic study based on 320 consecutive specimens diagnosed of cutaneous neurofibroma was carried out. Conventional microscopy, immunohistochemistry, and statistical methods were used to determine the presence of fat cells, their amount, distribution, and frequency.

RESULTS

Intratumoral fat was observed in 22 (6.9%) neurofibromas. All these were dermal neurofibromas. Intraneoplastic fat was divided into two groups: focal and diffuse (regularly interspersed). Eighteen tumors (5.6%) presented adipocytes focally intermingled with the spindle cells. There were four (1.3%) neurofibromas showing spindle cell proliferation with regularly scattered adipocytes. Lipomatous neurofibroma was more frequent located on head and neck than non-lipomatous neurofibroma ( p = 0.04). Neurofibromas without mature adipocytes were more frequently immunoreactive for CD34 compared with tumors showing intratumoral fat ( p = 0.02).

CONCLUSIONS

We suggest that both metaplasia and aberrant adipose differentiation from multipotential cells may result in lipomatous neurofibroma. Focal presence of adipose cells may be attributable to metaplasia as the pathogenic mechanism. The fatty tissue being intrinsic to the tumor structure in its diffuse form, the lesion represents a distinctive tumor of the peripheral nerve sheath.

Intratumoral fat in neurofibroma

Three cases of a solitary neurofibroma showing focal fatty changes are reported. Fatty changes in a neurofibroma are rarely observed and have not been reported, and also, the pathogenesis of neurofibroma has not been clarified. We postulate that the fatty changes in a neurofibroma may be the result of so-called senescent change or chronic injury. The origin of adipose cells may be attributable to fatty infiltration from abutting tissues or to a metaplasia of tumor cells or resident fibroblasts.