The document discusses pulmonary vessels and abnormalities that can be seen on chest x-rays. It notes that enlarged main pulmonary arteries and hilar pulmonary arteries can indicate increased pulmonary blood flow from conditions like ASD, VSD, and PDA. Decreased pulmonary blood flow from things like TOF can result in smaller pulmonary vessels, called pulmonary oligemia. Pulmonary arterial hypertension can also enlarge these vessels and be seen in lung diseases, embolism, or left-to-right shunts. Pulmonary venous hypertension commonly arises from mitral valve disease or left heart failure and enlarges upper zone vessels. The aorta can dilate from aneurysms, hypertension, or valvular diseases and dissecting aneurysms need

1. Pulmonary Vessels * It is not possible to measure the diameter of the MPA from the plain film (usually subjective); but if there are variable degrees of bulging, means enlarged MPA. * Assessment of the hilar pulmonary arteries is more objective & the diameter of the Rt. lower lobe artery at its mid-point (normally 9 – 16 mm). * The size of pulmonary vessels with the lung reflects the pulmonary blood flow. * Increase pulmonary blood flow is seen in ASD, VSD, & PDA, & all of these will lead to Systemic to Pulmonary (Lt. to Rt. shunt) & these will to increase pulmonary blood flow.

2. Pulmonary Vessels * Hemodynamically significant Lt. to Rt. shunt is (2/1 ratio or more) & this will produce CXR findings; if less ratio there will be no CXR findings & all the pulmonary vessels will (from the MPA to the periphery of the lung) will be enlarged, & this is called " Pulmonary Plethora ". * There is good correlation between the size of the vessel on CXR & degree of the shunt. * Decrease pulmonary blood flow, all the vessels are small " Pulmonary Oligemia ". * The commonest cause of decrease pulmonary blood flow is TOF & pulmonary stenosis.

3. * Obstruction of the Rt. ventricle outflow + VSD will lead to Rt. to Lt. shunt. * Pulmonary stenosis will cause oligemia only is severe cases & babies or very young children. Pulmonary Vessels

4. Pulmonary Arterial Hypertension * The pressure in the pulmonary artery depends on : 1- Cardiac output. 2- Pulmonary vascular resistance.

5. Pulmonary Arterial Hypertension * Conditions that cause significant pulmonary arterial hypertension all increase the resistance of blood flow through the lungs, examples : 1- Various lung diseases (cor pulmonale). 2- Pulmonary embolism. 3- Pulmonary arterial narrowing in response to mitral valve diseases or Lt. to Rt. shunt . 4- Idiopathic pulmonary hypertension.

6. Pulmonary Arterial Hypertension * By CXR : There will be enlargement of the mean pulmonary artery + the hilar pulmonary artery, vessels within the lung tissue are normal or small. * Eisenmenger's syndrome : Greatly raised pulmonary artery resistance in association with ASD , VSD , & PDA leading to reverse shunt (i.e. : Rt. to Lt. shunt ).

7. Pulmonary Arterial Hypertension * The cause of pulmonary arterial hypertension may be visible on the CXR as cor pulmonale & mitral valve diseases. Pulmonary Arterial Hypertension due to ASD & Eisenmenger's syndrome

8. Pulmonary Venous Hypertension * The commonest causes of pulmonary venous hypertension are : 1- Mitral valve diseases. 2- Lt. ventricular failure. * In normal upright person ( by CXR ) the lower zone vessels are larger than the upper zone. * In pulmonary venous hypertension the upper zone vessels are enlarged . * In severe cases , the upper zone vessels become larger than that of the lower zone, & eventually Pulmonary Edema will supervene & may obscure the blood vessels.

9. Pulmonary Venous Hypertension Pulmonary Venous Hypertension in a patient with Mitral Valve Disease

10. Aorta * With aging the aorta becomes elongated, elongation necessarily involve unfolding , where the ascending aorta will deviate to the Rt. & the descending aorta to the Lt. , because the aorta is fixed at the aortic valve & the diaphragm . * Unfolding aorta is easily confused with aortic dilatation . * Aortic dilatation of the ascending aorta is due to : 1- Aneurysm. 2- Aortic regurgitation or aortic stenosis. 3- Systemic hypertension. * The two common causes of descending aortic aneurysm are : 1- Atheroma. 2- Aortic dissection. (Also, there is a rare cause as previous trauma following decelerating injury).

11. Aorta * By CXR : 1- The diagnosis of aortic aneurysm may be obvious, but substantial dilatation may be needed before the bulge of Rt. mediastinal border can be recognized. 2- Atheromatous aneurysm invariably shows calcification of their walls. * CT scan with IVCM or CT angiography or MRA are very useful to assess the aneurysm. Note : IVCM = I.V. C ontrast M edia. MRA = M agnatic R esonance A ngiography.

12. Dissecting Aortic Aneurysm It is important to know the extent of the dissecting aneurysm as those involving the ascending aorta are treated surgically & those confined to the descending aorta are treated with hypotensive drugs. * By CXR : Two congenital aortic anomalies can be seen, & they are : 1- Coarctation of Aorta. 2- Rt. sided aortic arch, in association with TOF, Pulmonary Atresia, & Truncus Arteriosus, or it also can be isolated with no clinical significance.

13. Dissecting Aortic Aneurysm Trans-Esophageal Echocardiogram showing the True (T) & False (F) lumina in the descending aorta

14. Dissecting Aortic Aneurysm CT-scan showing the displaced intima (arrows) separating the true & false luminae in the ascending & descending aorta