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Congenital melanocytic nevus (CMN) is a neural crest-derived hamartoma, which appear at or soon after birth. CMN has a dynamic course and may show variable changes over time, including spontaneous involution. Spontaneous involution of CMN is a rare phenomenon and is often reported in association with halo phenomenon or vitiligo. The mechanism of halo phenomenon is yet to be investigated but is suggested to be a destruction of melanocytes by immune responses of cytotoxic T cells or IgM autoantibodies. Here, the authors report an interesting case of spontaneously regressed medium-sized CMN with halo phenomenon and without vitiligo, which provides evidence that cytotoxic T cells account for the halo formation and pigmentary regression of CMN.

We report a case of sporadic cutaneous neurofibroma showing diffuse eosinophil infiltration in a 72-year-old woman. The neurofibroma had been on the skin of the left anterior shoulder for approximately 10 years. The presence of mast cells is well known in neurofibroma. However, infiltration of neurofibromas by eosinophils has not yet been documented. We propose that eosinophil infiltration is mediated by the effects of mast cells. We suggest that this is indirect evidence that mast cells in some neurofibromas are not quiescent but active. We also reintroduce the notion that acid-fast stains are a useful method to discriminate between mast cell granules and eosinophil granules.

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.

Poromas have been classified as eccrine neoplasms, but several recent reports of poroid tumors with sebaceous, follicular, and apocrine differentiation have challenged this concept. We report a case of apocrine poroma with sebaceous differentiation. A 69-year-old man presented with an asymptomatic elevated erythematous plaque. Histopathology revealed cellular nests composed of cuboidal poroid cells and sebocytes. The nests varied in size and were entirely intraepidermally arranged in a growth pattern similar to that of hidroacanthoma simplex. Given the common embryologic origin of folliculosebaceous and apocrine units, we believe that this lesion represents an apocrine poroma with sebaceous differentiation.

We report a case of nevus spilus with neurotized nevus studied by immunohistochemical methods using S-100, leu-6, glial fibrillary acid protein (GFAP), and myelin basic protein (MBP). Histologic findings of the speckled lesion showed irregular rete ridge elongation, increased epidermal melanocytes and melanin in the epidermis, and scattered nevus cell nests in the upper dermis, but showed neurotized nevus in the deep dermis, which has many features of neurofibroma. Diffuse expression of S-100 protein and MBP, focal staining with GFAP, and lack of staining with leu-7 were observed, Leu-7, positive only in neurofibromas and not in neurotized nevus, appears to be the more pertinent method for distinguishing neurotized nevus from neurofibroma.

Eruptive vellus hair cyst (EVHC), steatocystoma multiplex (SM), and epidermoid cyst are characterized by formation of multiple cutaneous cysts and have a resemblance in clinical features but have distinctive histologic features. We present herein two patients, who had EVHC, SM, and EVHC with sebaceous gland, and who also had EVHC, SM, and epidermoid cyst with sebaceous gland and vellus hairs. In addition, the interrelation among the three diseases is discussed. We think that EVHC, SM and epidermoid cyst are within the same spectrum of the disease process.

Lymphoepithelial cyst of the oral cavity is an uncommon cystic lesion lined with stratified squamous epithelium surrounded by lymphoid tissue. We report a case of lymphoepithelial cyst associated with two large epithelial inclusion cysts.

A case of focal acantholytic dyskeratosis (FAD) in a 55-year-old woman is reported. The lesion was located on the lip and manifested as a painful, oozing, crusted patch lasting for 20 years. Although FAD has been recently reported in the mucosa of the anal canal without cutaneous lesion, we report a case of FAD that appeared on the lip with clinical manifestation.