blue nevus blue nevus a blue nevus is a type of coloured mole, typically a single well-defined blue-black bump. blue nevusother namesblue neuronevus, dermal melanocytoma, nevus coeruleus, nevus bleublue nevusspecialtydermatologysymptomssingle well-defined blue-black bumpcomplicationsrarely malignant transformationtypesdendritic, cellularcausesuncleardiagnostic methodvisualisation, dermoscopydifferential diagnosisdermatofibroma, melanomatreatmentmonitoring, excisionprognosisgoodfrequencyfemale>male the blue colour is caused by the pigment being deep in the skin. diagnosis is by visualisation and dermoscopy. a biopsy is sometimes performed, or the whole lesion surgically removed. the outcome is generally good but there is a small chance of cancerous transformation. differential diagnosis includes dermatofibroma and melanoma. blue nevi are more common in females than males. it was first studied in 1906 by tièche, a student of josef jadassohn. classification blue nevi may be divided into the following types:: 701 a patch blue nevus (also known as an "acquired dermal melanocytosis", and "dermal melanocyte hamartoma") is a cutaneous condition characterized by a diffusely gray-blue area that may have superimposed darker macules. a blue nevus of jadassohn–tièche (also known as a "common blue nevus", and "nevus ceruleus") is a cutaneous condition characterized by a steel-blue papule or nodule.: 701 a cellular blue nevus is a cutaneous condition characterized by large, firm, blue or blue-black nodules.: 701 an epithelioid blue nevus is a cutaneous condition most commonly seen in patients with the carney complex.: 701 a deep penetrating nevus is a type of benign melanocytic skin tumor characterized, as its name suggests, by penetration into the deep dermis and/or subcutis. smudged chromatic is a typical finding. in some cases mitotic figures or atypical melanocytic cytology are seen, potentially mimicking a malignant melanoma. evaluation by an expert skin pathologist is advisable in some cases to help differentiate from invasive melanoma.: 701 an amelanotic blue nevus (also known as a "hypomelanotic blue nevus") is a cutaneous condition characterized by mild atypia and pleomorphism.: 701 a malignant blue nevus is a cutaneous condition characterized by a sheet-like growth pattern, mitoses, necrosis, and cellular atypia.: 701 micrograph of a blue nevus showing the characteristic pigmented melanocytes between bundles of collagen. h&e stain blue nevus cellular blue nevus epithelioid blue nevus malignant blue nevus