ABSTRACT
Onychocytic matricoma is a rare, benign tumor of the nail matrix. It is considered an acanthoma of the nail matrix that produces onychocytes and, clinically, appears mostly as a longitudinal melanonychia with a corresponding thickened nail plate. It has overlapping histopathologic features with ungual seborrheic keratosis. Because of the clinical presentation, it could mimic a foreign body, but malignancies such as squamous cell carcinoma and melanoma should be ruled out. Due to the possibility of malignant evolution (onychocytic carcinoma), removal should be considered ( Figures 21.1 and 21.2 ).
