Which of the following describes an abnormal growth of blood vessels?

Spider naevi is characterized by an abnormal growth of blood vessels that appear as small, spider-like veins under the skin. These lesions often have a central red spot with extended red lines resembling a spider’s legs radiating outward. They are typically associated with increased blood flow and can be seen in various conditions, such as liver disease or hormonal changes.

The other options do not pertain to abnormal blood vessel growth. Alopecia involves hair loss and does not relate to vascular changes. Psoriasis is a skin condition characterized by rapid skin cell production leading to scaling, not directly involving blood vessel formation. Onychomycosis refers to a fungal infection of the nails, which is unrelated to blood vessel abnormalities. Thus, the definition of spider naevi aligns directly with the question regarding abnormal growth of blood vessels.