You searched for: “aplasia
aplasia (s) (noun), aplasias (pl)
The complete or partial failure of tissue to grow or to develop; arrested or abnormal development: Aplasia is the defective development, or congenital (present at birth) absence, of an organ or tissue.

Dr. Lawson was discussing the aplasia of a localized area of the skin on Tina's scalp which was covered by a thin, almost transparent membrane.