Agenesis

Agenesis is the congenital absence of an organ or tissue due to failure of development during embryogenesis. It differs from aplasia, where an organ forms but fails to develop further, and from hypoplasia, where an organ is present but underdeveloped. In medical literature, agenesis is used to describe complete non-formation of the structure rather than later loss or incomplete growth.

Agenesis can affect many organ systems. Commonly discussed examples include renal agenesis (absence of one or both kidneys), pulmonary agenesis (absence of one or both lungs), and limb agenesis (partial or complete absence of limbs). A related set of conditions involves reproductive and reproductive tract structures, such as Müllerian agenesis, in which congenital absence of a uterus or parts of the vagina occurs. Agenesis can also refer to brain structures, such as agenesis of the corpus callosum, and to ocular development, as in anophthalmia or severe ocular agenesis. The clinical impact varies widely with the affected organ and whether the agenesis is unilateral or bilateral.

Causes are diverse and can be genetic, chromosomal, or environmental. Genetic mutations in developmental pathways, chromosomal abnormalities, and teratogenic exposures during pregnancy are among the risk factors. Bilateral agenesis of essential organs (such as kidneys or lungs) is frequently associated with severe morbidity or mortality, whereas unilateral agenesis may allow normal function of the remaining organ.

Diagnosis is often possible before birth with ultrasound or MRI and is confirmed by postnatal imaging and genetic testing when indicated. Management depends on the specific organ involved and may include surveillance, supportive therapies, surgical correction, or transplantation in select cases.