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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Atresia | 2/2 | https://en.wikipedia.org/wiki/Atresia | reference | science, encyclopedia | 2026-05-05T07:26:18.542702+00:00 | kb-cron |
Renal agenesis occurs when the ureteric bud doesn't fuse with the metanephric blastema during embryogenesis, leading to the nephron and, in some cases, the ureter being absent. Unilateral renal agenesis occurs in 1 in 1000 live births, in contrast bilateral renal agenesis occurs in 1 in 3000 to 4000 pregnancies. Unilateral renal agenesis has a very good prognosis, whereas bilateral renal agenesis has a high rate of perinatal mortality and morbidity due to the lack of amniotic fluid, resulting in lethal pulmonary hypoplasia. The diagnosis of renal agenesis is usually made during a midgestation anatomy ultrasound examination. A genetic syndrome or other anomalies are linked to approximately 30% of cases of renal agenesis.
=== Tricuspid atresia ===
Tricuspid atresia is a form of congenital heart disease whereby there is a complete absence of the tricuspid valve. Therefore, there is an absence of right atrioventricular connection. This leads to a hypoplastic (undersized) or absent right ventricle. This defect is contracted during prenatal development, when the heart does not finish developing. It causes the systemic circulation to be filled with relatively deoxygenated blood. The causes of tricuspid atresia are unknown.
=== Vaginal atresia ===
Vaginal atresia is a birth defect that causes uterovaginal outflow tract obstruction. It happens when the urogenital sinus fails to form the caudal portion of the vagina. Fibrous tissue replaces the caudal portion of the vagina. Vaginal atresia is thought to affect one in every 5000-10,000 live female births. The anomaly is frequently undetected until adolescence, when primary amenorrhea or abdominal pain caused by an obstructed uterovaginal tract leads to a diagnostic evaluation.
== References ==