: The majority of cutaneous hypersensitivity reactions to exogenous tattoo pigments can be histologically classified as lichenoid or granulomatous. The etiology is still uncertain but is generally accepted to be a delayed-type hypersensitivity reaction to either the pigment itself or its carrier solution. In this report, we review the literature concerning adverse reactions to tattoos. In addition, we describe the second case of a localized granulomatous dermatitis to the red dye within a tattoo that histologically resembled granuloma annulare. This is the first reported example of a perforating granuloma annulare-like reaction.
Clinicopathologic correlation is crucial to the correct diagnosis of disorders of the nail unit. This chapter will explore four common clinical scenarios and how pathology can help differentiate between their various etiologies. These include: dark spot on the nail plate (melanin versus heme), subungual hyperkeratosis (onychomycosis versus psoriasis), longitudinal melanonychia (benign versus malignant), and verrucous papule (verruca versus squamous cell carcinoma). Consideration must be given to both when to perform a biopsy and the location of the biopsy site, which must be based on an understanding of the origin of the changes. An overarching principle is that lesions within the same differential diagnosis may be present concomitantly, such as malignant melanoma of the nail unit associated with hemorrhage. Therefore, even with a biopsy-proven diagnosis, the clinician must always monitor lesions of the nail unit for appropriate response to treatment and consider an additional biopsy for recalcitrant lesions.
Solitary fibrous tumor is an uncommon mesenchymal neoplasm that can arise in both pleural and extrapleural locations. Composed of spindled cells intimately admixed with collagen bundles arranged in a "patternless pattern," this heterogeneous tumor can mimic a variety of benign and malignant mesenchymal neoplasms. We present the histological and immunohistochemical findings of two primary cutaneous solitary fibrous tumors, discuss the differential diagnosis, and review the literature. Although solitary fibrous tumors in cutaneous and subcutaneous regions are extremely rare, it should be considered in the differential diagnosis of primary spindle cell neoplasms of the skin.
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