Radiology 5th year, 14th lecture/part one (Dr. Abeer)
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.
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.
* 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
Pulmonary Arterial Hypertension * The pressure in the pulmonary artery depends on : 1- Cardiac output. 2- Pulmonary vascular resistance.
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.
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 ).
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
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.
Pulmonary Venous Hypertension Pulmonary Venous Hypertension in a patient with Mitral Valve Disease
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).
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.
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.
Dissecting Aortic Aneurysm Trans-Esophageal Echocardiogram showing the True (T) & False (F) lumina in the descending aorta
Dissecting Aortic Aneurysm CT-scan showing the displaced intima (arrows) separating the true & false luminae in the ascending & descending aorta