hypoplasia

Hypoplasia is a developmental condition characterized by underdevelopment or incomplete development of an organ or tissue, resulting in a smaller size or reduced cellularity. It denotes inadequate growth during organogenesis, typically due to impaired cell proliferation. It is distinct from aplasia (complete absence of an organ or tissue) and from atrophy (a decrease in size after normal development).

Causes of hypoplasia include genetic mutations that affect organ formation, exposure to environmental teratogens, maternal malnutrition, infections during pregnancy, irradiation, and ischemia. Hypoplasia can be focal, affecting part of an organ, or diffuse, involving the entire organ. The underlying mechanisms often involve disrupted signaling pathways that regulate cell proliferation and differentiation.

Common examples include dental enamel hypoplasia (defective enamel thickness due to disrupted ameloblast activity), renal hypoplasia (incomplete development of renal parenchyma), pulmonary hypoplasia (incomplete lung development), and optic nerve hypoplasia. In cardiology, hypoplasia is seen in conditions such as hypoplastic left heart syndrome, where components of the left side of the heart are underdeveloped.

Diagnosis relies on clinical assessment, imaging studies such as ultrasound, radiographs, MRI or CT, and, when appropriate, histology or genetic testing. The clinical impact depends on the affected organ and the extent of underdevelopment; some cases are mild with few symptoms, while others require lifelong management.

Management is organ-specific and may include observation, supportive care, surgical intervention, or transplantation in severe cases. Prognosis varies from excellent for minor hypoplasia to significant morbidity for hypoplasia of critical organ systems. See also aplasia, dysplasia, and atrophy.