What is a characteristic feature of a Mongolian spot in newborns?

A characteristic feature of a Mongolian spot in newborns is that it presents as large gray or blue-green patches of skin. These dermal melanocytoses are common congenital skin markings that may appear at birth or shortly thereafter. Typically located on the lower back or buttocks, these spots result from the proliferation of melanocytes in the dermal layer of the skin—essentially clusters of pigment-producing cells that failed to migrate completely to the epidermis during fetal development. They can vary in size and can often be mistaken for bruising, which is why it’s important for healthcare providers to recognize them.

The other options describe different types of conditions or abnormalities that are not related to Mongolian spots. For example, a benign bright red, raised tumor refers to a nevus simplex (angel’s kiss or stork bite), while a subperiosteal collection of blood relates to a cephalohematoma, an accumulation of blood between the skull and the periosteum. Membranous or bony nasal obstruction would indicate issues such as choanal atresia, which is unrelated to the presentation of Mongolian spots. Recognizing the distinct features of Mongolian spots is crucial in differentiating them from other conditions during neonatal assessments.