Which cyanotic congenital heart lesion is characterized by a single arterial trunk arising from the heart, supplying the systemic, pulmonary, and coronary circulations?

Explanation

## Truncus Arteriosus — Embryology and Anatomy **Key Point:** Truncus arteriosus is a rare cyanotic lesion in which a single arterial trunk arises from the heart, supplying systemic, pulmonary, and coronary circulations. It results from failure of the truncus arteriosus to divide into the aorta, pulmonary artery, and aortic arch during embryonic development. ### Embryologic Basis **High-Yield:** The truncus arteriosus normally divides during weeks 4–6 of gestation via neural crest cell migration and formation of truncal ridges. Failure of this division results in a single trunk overriding a ventricular septal defect (VSD), with a single semilunar valve (often dysplastic). ### Classification of Truncus Arteriosus | Type | Anatomy | Frequency | | --- | --- | --- | | **Type I** | Pulmonary artery arises from the common trunk | 50% | | **Type II** | Pulmonary arteries arise from the posterior aspect of the trunk | 35% | | **Type III** | Pulmonary arteries arise from the descending aorta | 10% | | **Type IV** | Pulmonary arteries arise from the aorta (now classified as pulmonary atresia with systemic-to-pulmonary collaterals) | Rare | ### Clinical Features **Clinical Pearl:** Infants with truncus arteriosus present with mild cyanosis (because pulmonary blood flow is not restricted) and signs of congestive heart failure (high pulmonary blood flow). This contrasts with TOF, where severe cyanosis dominates. **Mnemonic:** **TRUNCUS** — Truncal ridge failure, Rare lesion, Unites three circulations, Needs VSD, Common valve dysplasia, Univentricular origin, Single trunk. ### Association with DiGeorge Syndrome (22q11 Deletion) **High-Yield:** Truncus arteriosus is strongly associated with DiGeorge syndrome (22q11 microdeletion) in 30–40% of cases. Look for additional features: cleft palate, thymic hypoplasia, hypocalcemia, cardiac defects.