Differential Diagnosis for a New Mole 4.5 cm in Diameter in a Child

Single Most Likely Diagnosis

• Congenital Melanocytic Nevus: This is a common benign skin lesion that can be present at birth or appear during early childhood. The size of the mole (4.5 cm) is consistent with a congenital melanocytic nevus, which can vary greatly in size.

Other Likely Diagnoses

• Acquired Melanocytic Nevus: Although less likely than congenital nevi given the size, acquired nevi can appear in childhood and grow to significant sizes.
• Dermatofibroma: A benign skin growth that can appear as a firm, round, brownish to purple growth, which might be considered in the differential for a new mole, especially if the child has a history of trauma to the area.

Do Not Miss Diagnoses

• Malignant Melanoma: Although rare in children, melanoma is a potentially deadly diagnosis that must be considered, especially with a new or changing mole. The ABCDE criteria (Asymmetry, Border, Color, Diameter, Evolving) can help identify suspicious lesions.
• Atypical Spitz Tumor: A rare tumor that can mimic melanoma and is more common in children. It often presents as a firm, pigmented nodule.

Rare Diagnoses

• Blue Nevus: A rare, benign melanocytic lesion that can appear as a blue-gray mole. It is less common and might be considered if the mole has a distinctive blue color.
• Nevus of Ota: A congenital condition characterized by blue-gray pigmentation, usually affecting one side of the face. It's rare and might be considered if the mole is part of a larger pigmentation pattern.