Dermatology - Nodule

Dermatology - Nodule 
​The term "nodule" is derived from the Latin word "nodulus," which means a little knot. A nodule is a firm, circular, or oval-shaped abnormality that is bigger than a papule. Palpable nodules may be present, affecting the epidermis, dermis, or subcutaneous tissue.

Nodules can have either a clear boundary (superficial) or an unclear boundary (deep). When they are located in the layer of tissue just below the skin, they are generally more easily detected by touch than by sight. Nodules may exhibit either firm or pliable characteristics when examined by touch.

They can have a domed and smooth morphology or possess a surface characterized by warts or a central depression resembling a crater.
The distinction between a nodule and a papule lies on their respective levels of involvement and size. Nodules arise due to the presence of inflammatory infiltrates, neoplasms, or metabolic deposits in the dermis or subcutaneous tissue.