Development of aortic arch

Dr Vinayak M Nadiger

• First arch arteries to appear in the embryo are Rt & Lt primitive aorta

• Each primitive aorta consists of1.a portion lying ventral to the foregut ( ventral

aorta)2.an arched portion lying in the first pharyngeal

arch3. and a dorsal portion lying dorsal to the gut

(dorsal aorta)

ventral aorta develops ventral to foregut .• dorsal aorta is formed dorsal to the foregut• After fusion of two endocardial heart tubes ,two ventral aorta partially fuse to formaortic sac• unfused part remain as right & left horns ofthe sac ( some define aortic sac as the mostdistal part of the truncus arteriosus)

diagram showing 6 paired branchial arches and an intersegmental artery .The branchial arches connectpaired ventral aortae and dorsal. IA indicates

intersegmental artery

Fate of arch arteries

• The majority part of the first &second arch artery disappear

• In adult life – the first arch artery is represented by maxillary artery

• The second arch artery – persist for some part of fetal life as the stapedial artery

• The fifth arch artery also disappears• Only 3rd ,4th & 6th arch artery remains

FATE OF AORTIC ARCHES1. First aortic arch – disappears (except a small portion which

formspart of maxillary artery).2. Second arch artery – disappears (except the stapedial artery

which also disappears after birth).3. Third aortic arch forms :a. Common carotid artery from

itsproximal part.b. Internal carotid artery from its distal part.

4. Fourth aortic arch :• a. On the right side forms proximal part of right subclavian artery.• b. On the left side forms part of arch of aorta

5. Firth aortic arch disappears.‐6. Sixth aortic arch: a. Proximal part forms pulmonary artery b. Distal part –i) Disappears on right side. ii) Forms ductus

arteriosus

• Ascending aorta is formed by aortic sac.• The Rt horn of the aortic sac forms the brachiocephalic

arteryA)Part of arch of aorta between brachiocephalicand left common carotid arteries is formed by left horn of

aortic sac.B). Part of arch of aorta between left commoncarotid and left subclavian arteries is formed by left 4th aortic

arch.c). Remaining part is formed by left dorsal aorta up to the level of the future lower border of4th thoracic

vertebra.• Descending aorta-by The left dorsal aorta below the

attachment of 4th arch artery and by fused median vessels

Formation of normal left AA

Left AA with Abarrent right SCA

Left AA with aberrant rt sub clavian

Right AA

Rt AA with Abarrent left SCAKommerell diverticulum

Right sided AA with aberrant lt sub clavian a

Rt AA WITH ISOLATION OF THE LEFTSCA

Double aortic arch

Pulmonary HTN

Plain X-Ray

By the time the diagnosis of pulmonary arterial hypertension is made, 90% of patients have an abnormal chest radiograph .

-low sensitivity and specificity.

Plain film

-elevated cardiac apex due to right ventricular hypertrophy.-enlarged right atrium.-prominent pulmonary outflow tract.-enlarged pulmonary arteries.-pruning of peripheral pulmonary vessels.

(+ve) Findings :

The X-ray shows gross enlargement of the cardiac shadow. The right border extends far to the right indicating gross right atrial enlargement

Lateral chest radiograph shows filling of the retrosternal airspace (arrow), a result of right ventricular dilatation.

Chest radiograph reveals enlargement of the pulmonary vasculature and the central pulmonary arteries (arrows).

Secondry hypertension By atrial septal defect

Lateral CXR of the same patient, showing enlarged pulmonary artery.

Cardiomegaly and prominent bilateral pulmonary arteries in the hilar areas can be seen in the posteroanterior chest radiograph

Computed Tomography

1- CT is good , noninvasive , used to confirm presence of pulmonary hypertension.2- It is useful in delineating the anatomic detail of the pulmonary vasculature.3-CTPA is the best method for demonstrating emboli.4- Contrast-enhanced images may show intraluminal abnormalities in the arteries and veins and can detect emboli if it’s large.

Advantages of CT

Enlarged pulmonary trunk >29 mm diameter is often used as a general predictive cut-off Enlarged pulmonary arteriesMural calcification in central pulmonary arteriesEvidence of previous pulmonary emboli

Extra-cardiac vascular signs:

T angiogram shows dilatation (29 mm or more) of the main pulmonary artery.

Axial contrast-enhanced CT scan ,shows central pulmonary artery dilatation with aneurysmal enlargement of the left lower lobe pulmonary artery .

-Right ventricular hypertrophy: defined as wall thickness of more than 4 mm.

-Straightening or bowing (towards the left ventricle) of the interventricular septum- Right ventricular dilatation - Decreased right ventricular ejection fraction- Dilatation of the inferior vena cava and hepatic veins- Pericardial effusion

Cardiac signs :

right ventricular myocardium (white arrow) is more than 4 mm thick. Straightening of the interventricular septum (black arrow) also is seen.

right ventricular dilatation, which is defined as a diameter ratio (the ratio of the right ventricular diameter [black arrow] to the left ventricular diameter [white arrow]) greater than 1:1 at the midventricular level.

reflux of contrast material into the inferior vena cava, which is dilated, and hepatic veins

Centrilobular ground-glass nodules (Cholesterol granuloma).Neovascularity: tiny serpiginous intrapulmonary vessels that often emerge from centrilobular arterioles.

Parenchymal signs:

Axial contrast-enhanced CT scan shows corkscrewlike peripheral pulmonary arteries (arrows), findings indicative of plexogenic arteriopathy.

Axial contrast-enhanced CT scan shows an eccentric wall-adherent thrombus (arrow) in the right interlobar pulmonary artery .

Axial contrast-enhanced CT scan shows:-right atrial and ventricular enlargement with inverted interventricular septum- right ventricular hypertrophy,- -eccentric chronic thrombus causing a crescent-shaped intraluminal filling

defect (arrow) in the left lower lobe pulmonary artery.

Axial contrast-enhanced CT scan shows a thrombotic mass (straight arrows) in the right main pulmonary artery.

Echocardiography

- It’s performed to estimate the pulmonary artery systolic pressure and to assess right ventricular size, thickness, and function.

- evaluate right atrial size, left ventricular systolic and diastolic function, and valve function.

- detecting pericardial effusions and intracardiac shunts.

- uses Doppler ultrasound to estimate the pulmonary artery systolic pressure.

Advantages

1. Right ventricular enlargement (RVE).

2. Right ventricular hypertrophy (RVH).

3. Right atrial enlargement (RAE).

4. Functional tricuspid regurgitation (TR) with a high velocity regurgitant jet by Doppler (TR jet).

5. The interventricular septum is shifted toward the left ventricular cavity.

Main findings

The short axis view from a 2-D echocardiogram shows significant right ventricular pressure and volume overload as a result of pulmonary hypertension.

The short axis view from a 2-D echocardiogram shows significant right ventricular pressure and volume overload as a result of pulmonary hypertension.

Angiography

Right heart catheterization may be required. -Pulmonary angiography is the most accurate modality for evaluating the anatomy and pathophysiology of pulmonary hypertension

-The disadvantage :it is an invasive procedure as one cannulates the right side of the heart and thea pulmonary artery.

Selective right pulmonary arteriogram demonstrates large central pulmonary arteries and attenuation of the peripheral vessels.

Pulmonary hypertension. Selective left pulmonary arteriogram reveals large central pulmonary arteries and attenuation of the peripheral vessels

Angiograms showing a healthy pulmonary artery (left) and a pulmonary artery with numerous blockages (right).

Magnetic resonance Imaging

Cardiac MRI showing dilated right ventricle (Axial View )

Cardiac MRI showing dilated right ventricle (Sagittal view).

Magnetic Resonance Angiography from a patient with PH

Magnetic Resonance Angiography in patient with Chronic Thromboembolic Pulmonary Hypertension.