hypoplastic

Hypoplastic is an adjective used in medicine and biology to describe tissue or organ underdevelopment, where the organ or structure is smaller or less developed than normal due to incomplete cellular proliferation or differentiation during embryogenesis. It contrasts with aplasia (no development) and atrophy (degeneration after normal development). The term derives from Greek hypo- "under" and plastos "formed."

In humans, hypoplasia can affect various organs and tissues. The most widely known is hypoplastic left heart syndrome, a congenital condition in which the left-sided heart structures are underdeveloped, affecting systemic blood flow. Dental contexts describe enamel hypoplasia, where enamel is thin or pitted due to disturbances during tooth formation. Hypoplasia may also affect bones (osseous hypoplasia), hair, nails, or the brain's structures, often named for the involved tissue (e.g., cerebellar hypoplasia).

Causes include genetic mutations, teratogenic exposures, nutritional deficiencies, infection, or mechanical disturbances during fetal development. The severity ranges from mild underdevelopment with few symptoms to life-threatening malformations depending on the organ involved.

Diagnosis typically relies on clinical evaluation augmented by imaging (ultrasound, X-ray, CT, MRI) or histology. Treatment is organ-specific and may involve surgical correction, medical management, or supportive care; in some cases hypoplasia is incompatible with long-term survival.

See also: hypoplasia; aplasia; dysplasia; hyperplasia; atrophy.