Thursday, November 11, 2010

Aortic Arch Anomalies

Embryology:


Primitive and dorsal aortas:


The first arteries to appear in the embryo are the right & left primitive aortas, each one developing as a continuation of the corresponding heart tube. They lie ventral to the foregut, and curve dorsally to continue as the right & left dorsal aortas.


As the two heart tubes fuse to form a single endocardial heart tube, the two primitive aortas fuse to from the aortic sac.



Normal schematic diagram of the primitive ventral and dorsal aorta, 6 aortic arches, dorsal aortic root segments (DARS), and 7th dorsal intersegmental artery (DISA).
http://www.ajnr.org/content/vol28/issue5/images/medium/zj40050704480011.gif





Embryonic aortic arch with dorsal and ventral arches and 6 branchial arches on right and left.
http://img.medscape.com/pi/emed/ckb/thoracic_surgery/424545-426233-723tn.jpg




Fate of the aortic arches:

  • First pair: A small part forms the maxillary artery, the rest disappears.
  • Second pair: A small part forms the stapedial & hyoid arteries, the rest disappears.
  • Third pair: forms the common, internal & external carotid arteries on each side.
  • Fourth pair: forms the aortic arch (AA) on the left side, and the right subclavian (RSC) artery on the right side.
  • Fifth pair: totally disappears.
  • Sixth pair: forms the right & left pulmonary arteries (PA) and the ductus arteriosus (DA).


Thus the arch of the aorta is derived from the left fourth primitive aortic arch. 




Normal schematic diagram of the aortic arch and the great vessels demonstrates the embryologic origins of the arch and its major branches. RIC indicates right internal carotid artery; REC, right external carotid artery, LIC, left internal carotid; LEC, left external carotid artery.
http://www.ajnr.org/content/vol28/issue5/images/medium/zj40050704480012.gif




Anatomy:


The ascending aorta continues with the aortic arch at the level of the sternal angle.

The arch passes backwards over the left bronchus, to reach the body of the 4th dorsal vertebra just to the left of the midline.
The aortic arch is convex upwards reaching the level of the mid point of the manubrium sterni, and concave downwards; in its concavity the pulmonary trunk divides into two branches.






Note that the normal aortic arch crosses over the left main stem bronchus. This is the normal left sided aortic arch.
http://www.hawaii.edu/medicine/pediatrics/pemxray/v6c19g.jpg




Branches of the aortic arch:


The arch gives the following branches in order:
  • Innominate (Brachiocephalic) artery; which divides into;
    • Right common carotid artery.
    • Right subclavian artery.
  • Left common carotid artery.
  • Left subclavian artery.



http://www.ucumberlands.edu/academics/biology/faculty/kuss/courses/CirculatorySystem/SuperiorArteries.jpg




Aortic arch anomalies


Aortic arch anomalies are classified as follows:
  • Aortic arch obstruction:
    • Coarctation of the aorta.
    • Interruption of the aortic arch.
  • Other aortic arch anomalies:
    • Right aortic arch.
    • Double aortic arch.
    • Cervical aortic arch.
    • Aberrant subclavian artery.
    • Isolated subclavian artery.
    • Tracheal compression by the innominate or the left common carotid artery.




Coarctation of the aorta


Definition:


Coarctation of the aorta (CA) refers to narrowing of the distal segment of the aortic arch.






Pathology:


Pathological types:


Two pathological types of CA are known:
  • Infantile type: CA occurs proximal to or immediately opposite the ductus arteriosus. The pressure in the AO distal to CA is lower than that in PA and blood flows from PA to AO (right-to-left shunt). Thus; the lower half of the body is supplied by RV output.
  • Adult type: The ductus is closed & CA occurs distal to the ligamentum arteriosusm. The lower half of the body is supplied by LV output.



A, Postductal coarctation of the aorta. B, Diagrammatic representation of the common routes of collateral circulation that develop in association with postductal coarctation of the aorta. C and D, Preductal coarctation. E, Sketch of the aortic arch pattern in a 7-week embryo, showing the areas that normally involute. Note that the distal segment of the right dorsal aorta normally involutes as the right subclavian artery develops. F, Abnormal involution of a small distal segment of the left dorsal aorta. G, Later stage, showing the abnormally involuted segment appearing as a coarctation of the aorta. This moves to the region of the ductus arteriosus with the left subclavian artery. These drawings (E to G) illustrate one hypothesis about the embryological basis of coarctation of the aort
http://img.medscape.com/article/703/899/703899-fig1.jpg




Secondary cardiac pathological changes:


The following cardiac pathological changes may occur in patients with coarctation of the aorta:
  • Proximal to coarctation: Cystic medial necrosis of the aorta.
  • Distal to coarctation: Post-stenotic dilatation & jet lesions.
  • Concentric LVH.
  • Collaterals development: especially in adults.



The aorta is opened longitudinally here to reveal a coarctation. In the region of the narrowing, there was increased turbulence that led to increased atherosclerosis.
http://library.med.utah.edu/WebPath/jpeg5/CV082.jpg




Collaterals in patients with aortic coarctation:


Since the lower half of the body has reduced blood supply, collaterals develop between arteries proximal to and those distal to the site of coarctation, trying to compensate for lower body ischemia:
  • Anterior system: Internal mammary artery with epigastric artery, to the iliac & femoral arteries, supplying the lower limbs.
  • Posterior system: Parascapular with posterior intercostal arteries, supplying the abdominal viscera.
Associated conditions:
  • Ventricular Septal Defect (VSD).
  • Patent Ductus Arteriosus (PDA).
  • Subvalvular Aortic Stenosis (AS).
  • Transposition of the Great Arteries (TGA).
  • Bicuspid aortic valve.
  • Aberrant right Subclavian Artery (SCA).
  • Parachute mitral valve.
Complications:
  • Congestive heart failure (CHF).
  • Dissecting aneurysm, usually proximal.
  • Infective endocarditis:
    • on an associated bicuspid aortic valve.
    • on jet lesions (Rare).
  • Valvular aortic regurgitation (AR).
  • Rupture of an aneurysm of the circle of Willis, with intracranial hemorrhage, due to upper body hypertension. 
  • Rare complications: 
    • Aortic rupture without dissection. 
    • Rupture of an intercostal artery aneurysm. 
    • Anterior spinal artery thrombosis. 
    • Development of calcific aortic stenosis.



Pathogenesis of aortic coarctation:


Development of coarctation is favored by factors resulting in intrauterine decrease of aortic flow & increase of ductal flow: e.g. mitral or aortic valve anomalies.
A contra-ductal shelf develops and bifurcates the ductal flow into: Retrograde flow to the left subclavian artery & anterograde flow to the descending aorta.
Ascending aortic flow supplies the innominate, left common carotid and vertebral arteries.
Very little flow reaches the aortic isthmus which becomes hypo-plastic.
If anterograde aortic flow does not improve after birth, the aortic isthmus will be patent but narrow: Infantile type of CA develops.
If anterograde aortic flow becomes normal after birth, isthmus narrowing will not be prominent, the ductus is closed and the shelf is exaggerated: Adult type of CA develops.


Effect of ductal flow:


Increasing ductal flow after birth, e.g. with Prostaglandin E2 infusion, augments the left-to-right shunt, and augments aortic flow, thus reducing the obstruction caused by coarctation.
In utero, factors that reduce ductal flow & augment aortic flow prevent the development of coarctation, e.g. pulmonary stenosis or atresia, and tetralogy of Fallot. These anomalies therefore, are never associated with coarctation of the aorta.



Pathophysiology:


The following pathophysiological changes may occur in CA:
  • LV pressure overload: due to obstruction to aortic flow.
  • Upper body hypertension: aortic obstruction creates a pressure gradient across the site of CA, with high pressure proximally. Reactive vascular hypertrophy occurs with further blood pressure elevation, further vascular hypertrophy, and a vicious circle is created.
  • Long standing CA causes chronic renal ischemia which can result in systemic hypertension.


Clinical picture:


Female/ male: 1/3


Symptoms:

  • In infancy:
    • 50 % of patients are asymptomatic.
    • and 50 % have CHF.
  • Beyond infancy:
    • Mostly asymptomatic.
    • A few have: mild dyspnea, fatigue, & lower limb claudication pains.
    • CHF re-appears: beyond the age of 20 years.


Signs:

  • In symptomatic infants:
    • CHF manifestations.
    • Murmur of coarctation: in inter scapular area.
    • Murmurs of associated lesions: e.g. VSD, PDA, MR.
  • In children and adults:
    • Disproportionate growth: of the chest, shoulders & upper limbs, compared to the lower half of the body.
    • Prominent arterial pulsations in the neck and suprasternal area.
    • Femoral pulse is weaker & delayed than the radial pulse, or even absent.
    • Blood pressure is lower in the lower limbs than in upper limbs: If the difference is minimal at rest, measurement should be repeated after exercise.
      • Differences in pulse & blood pressure may not be detected in presence of CHF.
      • Weak or absent pulsations in all sites suggests Critical aortic stenosis or aortic atresia.
      • Blood pressure difference between the 2 arms suggests origin of one subclavian artery distal to the coarctation site.
    • Local cardiac examination in children and adults:
      • Forceful apical impulse.
      • Accentuated S1 & A2.
      • Ejection click suggests bicuspid aortic valve.
      • Murmur of coarctation:
        • Best heard in the inter scapular region.
        • Radiates to the left axilla & the precordium.
        • Medium pitched, Blowing.
        • usually systolic but may be continuous.
      • Murmur of collaterals:
        • Heard over the chest wall & back.
        • Continuous.
        • Low pitched.
        • Seldom present before adolescence.


Chest x-ray:

  • In infants with CHF:
    • Cardiomegaly.
    • Pulmonary venous congestion.
  • In children:
    • Rib notching is characteristic, and indicates significant CA.
    • Heart size at upper limit of normal with LV configuration.
    • Figure 3 configuration of the left side of the aorta in over-penetrating film.
    • E - sign in the shadow of barium-filled esophagus.
  • In older non operated patients:
    • Prominent LV enlargement.
    • LA enlargement.



Note the post-stenotic dilatation in the coarctation aorta giving the appearance of a ski mogul (or figure 3 appearance).
http://www.meddean.luc.edu/lumen/meded/medicine/pulmonar/cxr/atlas/images/255a.jpg





Chest X-ray shows rib notching on the undersurface of the posterior ribs (white arrows).
http://www.cardiothoracicsurgery.org/content/figures/1749-8090-4-10-1-l.jpg





A penetrated view of the posterior ribs on the right side of chest. The notching is on the lower edges due to dilatation of the intercostal arteries. It affects ribs 4, 5, and 6 where it is maximal. This comes from a 30 year old male with coarctation of the aorta and was present bilaterally.Unilateral rib notching at this site can occur following thoracotomy and failed shunt in cyanotic heart disase.In this patient, the coarctation is at classic site at T4. When it is lower, rib notching will affect lower ribs. It will not be present in abdominal coarctation.
http://www.impaedcard.com/issue/issue38/somervillej/fig02.jpg




Rib notching (arrows).
http://biomedcentral.inist.fr/images/1749-8090-4-10-1.jpg




Electrocardiography:

  • In infants:
    • Right axis deviation.
    • RA enlargement (RAE).
    • RV ± LV hypertrophy (RVH ± LVH).
    • Rarely isolated LVH.
  • In children:
    • ECG is usually normal.
    • LA enlargement (LAE) & LVH may be present.
  • In adults:
    • High incidence of conduction defects & ventricular arrhythmia.



This ECG, shows rsR' pattern in the right chest leads indicating RVH. In addition there are deep S waves in the left chest leads.
http://pediatriccardiology.uchicago.edu/MP/CHD/Coarctation/ECG-RVH.jpg



Later in infancy, the expected LVH pattern (tall R waves in left chest leads & deep S waves in right chest leads) become evident:
http://pediatriccardiology.uchicago.edu/MP/CHD/Coarctation/ECG-LVH.jpg




Echocardiography:
  • Direct visualization of the site of coarctation in:
    • Supra sternal views.
    • Upper parasternal views.
    • Trans-Esophageal Echocardiography (TEE) views.
  • Location of constriction and its diameter.
  • Aortic root, ascending aorta, transverse aorta and descending aortic dimensions.
  • Left ventricular dimensions particularly wall thickness.
  • Presence of bicuspid aortic valve.
  • Presence/degree of aortic regurgitation.
  • Repaired coarctations may be associated with aneurysm formation, this is difficult to exclude on echocardiography, therefore, further imaging investigations may be indicated (e.g. MRI).
  • Turbulence / acceleration on colour Doppler echocardiography.
  • Doppler Measurements:
    • Peak velocity across bicuspid aortic valve / ascending aorta.
    • Peak velocity across the coarctation, noting the step-up at the site of the narrowing.
      • The Doppler severity of the coarctation may be underestimated in patients with significant collateral vessels supplying the descending aorta.



http://www.yale.edu/imaging/chd/e_coarct/e_coarct_ssn_1796892.jpg





Color flow mapping echocardiogram on the longitudinal suprasternal section, showing the aortic arch with turbulence in the descending portion at the aortic coarctation site
http://www.rbccv.org.br/imagensRBCCV/22-03-17-fig2.jpg





http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/CoA%20Slide1.JPG





http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/CoASlide4.JPG





http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/CoA%20Slide2.JPG





http://www.yorksandhumberhearts.nhs.uk/upload/ACHD%20files/CoA%20Slide3.JPG




Cardiac catheterization:


Cardiac catheterization is not usually needed for diagnosis, but may show:
  • High LA & LV pressures, with Low femoral artery pressure. Pressure difference is usually significant, unless there is hyper-dynamic circulation, e.g. large VSD or PDA.
  • Aortography is diagnostic.



Preoperative angiographic image of a severe coarctation of the aorta in a 23 years old patient.
http://www.ispub.com/ispub/ijtcvs/volume_11_number_2_2/the_effect_on_systolic_hypertension_after_repair_of_coarctation_of_the_aorta_in_adults/aorta-fig1.jpg




Postoperative angiogram of the same patient in previous figure that shows subclavian artery to descending aorta bypass graft.
http://www.ispub.com/ispub/ijtcvs/volume_11_number_2_2/the_effect_on_systolic_hypertension_after_repair_of_coarctation_of_the_aorta_in_adults/aorta-fig2.jpg





Still picture from an aortagram in coarctation of aorta in lateral view. The catheter is seen along the anterior border of the aorta. Prestenotic (above) and post stenotic dilatation of aorta are visible. Post stenotic dilatation is much more prominent. In this case, though the gradient across the defect was low the post stenotic dilatation was considerable. This illustrates the fact that there is no direct correlation between severity of the obstruction and the post stenotic dilatation. The coarct segment is seen as a shelf like negative shadow extending anteriorly from the posterior border of the aorta (arrow marked Co A). The region marked as Desc Ao is the post stenotic dilatation. Left subclavian artery is seen originating just above the coarctation and coursing upwards. So this is a classical post subclavian juxta ductal coarctation of aorta.
http://cardiophile.org/wp-content/uploads/2008/11/coarctation-of-aorta.jpg





This is a still picture from aortogram of coarctation of aorta in LAO view. LSA: left subclavian artery. Coarct segment is seen as a constriction just below the origin of the left subclavian artery. The prominent post stenotic dilatation of descending aorta is also visible. Prestenotic dilatation is not very prominent.
http://cardiophile.org/wp-content/uploads/2008/11/coarctation-of-aorta-lao-view.jpg




Video: Aortography.
http://www.youtube.com/watch?v=50eye_bpRAE






Other imaging modalities:


 Three-dimensional spiral CT showing the coarctation of the aorta (arrow) located distally to the left subclavian artery origin. AA: ascending aorta; DA: descending aorta; LS: left subclavian artery; LV: left ventricle.
http://eurheartj.oxfordjournals.org/content/24/16/F1.medium.gif





Thoracic CT scanning (reconstruction) showing the coarctation site (white arrow). The asterisk depicts the aneurysmal dilatation of the ascending aorta which is of greater diameter compared to the descending thoracic aorta (double asterisk).
http://biomedcentral.inist.fr/images/1749-8090-4-10-2.jpg





Thoracic CT scanning 3 weeks after balloon angioplasty showing patency of descending thoracic aorta with no post-dilatational aneurysm formation (white arrow).
http://biomedcentral.inist.fr/images/1749-8090-4-10-3.jpg





Volume rendered 3-D MRI images of pediatric coarctation of the aorta. Note demonstration of extensive collaterals.
http://www.madisonradiologists.com/Images/ContentPics/SvcAortaGreatVessels_PediatricCoarctationAorta_normal.gif





21-year-old woman with history of three previous aortic coarctation repairs, most recent of which was 8 years earlier and consisted of interposition Dacron (DuPont) graft. She presented emergently with massive hemoptysis. Oblique sagittal volume-rendered CT angiography reveals large pseudoaneurysm at proximal descending thoracic aorta.
http://www.ajronline.org/content/vol187/issue3/images/medium/05_0424_13a.gif




Natural history:


The long-term outcome is poor without intervention:
Mortality within the first year is 60% in patients with symptomatic coarctation and 90% in presence of other lesions.
Presentation in adulthood suggests mild to moderate post-ductal coarctation.
CHF in children responds well to medical treatment in the majority of cases. Collaterals also help to improve it.
CHF may appear only in the 4th decade.
Upper body HTN tends to progress in 1st year, then tends to improve with development of collaterals.
HTN complications appear in 2nd & 3rd decades, e.g. dissecting aortic aneurysm.
Infective endocarditis is always a risk.
The mean age of death in un-operated cases is 35 years.




Medical management:


Prostaglandin E1 may be needed in infants with acute pulmonary edema, to open the ductus & decrease the obstruction caused by coarctation.
Control of CHF, and HTN.
Pregnancy should be avoided, until correction of coarctation: Without correction, pregnancy carries a mortality rate of 10 % and a complication rate of 90 %.


Angioplasty:


Acute and long-term results of catheter-based aortoplasty for native aortic coarctation are similar to those of surgery.
Aortoplasty is associated with higher rates of aneurysm formation and restenosis.
Balloon aortoplasty appears to be better than surgery for recurrent coarctation.


Complications of catheter procedures:
  • Femoral artery injury and thrombosis.
  • Aortic aneurysm formation and rarely rupture.
  • Thromboembolic events.
  • Persistent hypertension is common (as many as 75%) especially with older age at correction, probably related to vascular structural changes, endothelial dysfunction, and abnormalities in the Rennin-Angiotensin-Aldosteron system.


Biodegradable stents:


Biodegradable stents may offer a solution for recurrence; the stents will keep the coarcted aortic segment open for a 3-6 month period, when the stents would dissolve.




Surgical management:


Surgery is indicated in symptomatic infants, otherwise operation is done at age 4-6 years. No need to wait to 10 years.
if surgery is done in the 1st year of life, the recurrence rate is as high as 33 %.


Indications for intervention beyond the neonatal period:
  • Congestive heart failure.
  • Upper extremity hypertension.
  • A gradient > 20 mm Hg across the obstruction:
  • Exercise testing may be used to provoke a gradient across the area of obstruction.


Surgical procedures:
  • Dacron patch aortoplasty.
  • Subclavian flap aortoplasty.
  • Excision & end-to-end anastomosis may result in recurrence, especially when done in the first year.



Video: Surgical techniques for coarctation of the aorta.
http://www.youtube.com/watch?v=cgR_XmRJcIg




Indefinite follow up:


Indefinite follow up is required for the following reasons:
  • Those followed up to be operated upon at 4-6 years may require earlier surgery if they get:
    • Progressive HTN.
    • Progressive cardiomegaly.
    • LVH in ECG.
    • Progressive fatigue or dyspnea.
    • Encephalopathy or stroke.
  • At 2-10 days post operatively: A serious syndrome may develop: Severe HTN, Abdominal pain & distension and Leukocytosis. This syndrome is thought to be due to mesenteric arteritis. It usually resolves, within 8-12 days, with control of HTN.
  • Re-coarctation may occur.



Re-coarctation:


Definition:


Re-coarctation is defined as: the re-development of a pressure gradient between upper limbs and lower limbs of 30 mmHg or more, at rest, after correction of coarctation of the aorta.


Management:


Angiography should be done, to prepare for re-operation.
Indications for re-correction:
A pressure gradient between upper limbs and lower limbs of 30 mmHg or more, at rest.
Those with significant gradient only after exercise should probably also undergo surgery.

Indications for conservative medical management (Control of HTN. and restriction of activity):
  • Patients with no significant gradient at rest or exercise.
  • Patients in whom operative risk is very high.



Lateral aortogram of a 7-year-old girl who underwent repair of a maximal coarctation (no communication between the transverse aorta and descending aorta) and hypoplastic aortic arch at 1 month of age. The initial repair involved pericardial patch enlargement of the hypoplastic transverse aorta and resection of the coarctation with end-to-end anastomosis augmented with a left subclavian flap aortoplasty. Recoarctation developed and responded to balloon dilatation when she was 2 years of age. A recurrent long-segment recoarctation developed distal to the left carotid artery, as shown on this aortogram. Note that the left subclavian artery has been used to augment the transverse aorta.
http://jtcs.ctsnetjournals.org/content/vol120/issue5/images/small/110462001.gif




Interruption of the aortic arch




Definition:


Interruption of the aortic arch is defined as: Lack of channel between the aortic arch and the descending aorta.
The descending aortic flow comes from the pulmonary arterial system via the ductus arteriosus.




Pathology:


The descending aorta is supplied by the ductus arteriosus; usually on the left side, rarely on the right side.
The arch & descending aorta may be connected by an atretic segment; a condition known as atresia of the aortic arch.


Origin of the great arteries:


The origin of the three big branches of the aortic arch; (1) the innominate artery, which divides into the right subclavian (RSC), & the right common carotid (RCC), arteries), (2) the left common carotid (LCC) artery, and (3) the left subclavian (LSC) artery, differs in patients with interruption of the aortic arch as follows:


  • In 50 % of cases, the innominate (IA) and left common carotid (LCC) arteries arise from the proximal segment, while the left subclavian (LSC) artery arises from the distal segment.





  • In 40 % of cases, all the three branches of the aortic arch arise from the proximal segment.






Other possibilities (10%) are shown in the following figure:







Associated conditions:
  • In most cases, congenital heart disease is associated:
  • VSD: the commonest.
  • Transposition of the great arteries (TGA).
  • Persistent truncus arteriosus (PTA).


Clinical picture:


Interruption of the aortic arch is a very rare congenital anomaly.
It presents similar to coarctation but: Pulse may be weak in one or both upper limbs (According to the origin of subclavian arteries), besides the lower limbs.
Right common carotid pulse is normal, which differentiates this anomaly from critical aortic stenosis or atresia.


Investigations:


Echocardiography mainly helps to differentiate the case from critical AS & aortic atresia.
Angiography is diagnostic.


Natural history:


Survival beyond infancy is uncommon and is possible only in the following cases:
PDA with very high pulmonary vascular resistance.
PDA for enough time to develop collaterals between the two aortic segments.


Medical management:


Control of CHF.
Prostaglandin E1 infusion to open the ductus, may permit cardiac catheterization & surgery under more favorable conditions.


Surgery:


Only patients who developed collaterals are candidates for surgery.
Vascular graft is established between the two segments of the aortic arch.
Operative risk is very high: Survival depends on LV function.




Right aortic arch




Pathology:


The aortic arch passes over the right bronchus instead of the left bronchus.
It may or may not have a retro-esophageal segment.
The ductus arteriosus may be left-sided, right-sided, or absent.


Tracheal and esophageal compression:


Tracheal & esophageal compression may occur by the following structures:
  • Anterior: pulmonary arteries.
  • Posterior: aortic arch.
  • Right: aortic arch.
  • Left: Ductus arteriosus.


Aortic arch branching in cases of right aortic arch:
  • Mirror-image branching: is the most common: left-sided innominate artery arises first, followed by right common carotid, and finally right subclavian artery. 98 % of these cases have associated Congenital heart disease.



Normal aortic branching.
http://www.tabers.com/tabersonline/ub?cmd=repview&type=tabers_21&name=a300p0





Right aortic arch with mirror-image branching and retroesophageal ligamentum arteriosum.
http://img.medscape.com/pi/emed/ckb/thoracic_surgery/424545-426233-884tn.jpg


  • Aberrant left subclavian: less common. Left common carotid arises first, followed by right common carotid, right subclavian, and finally left subclavian. The last passes behind the esophagus from right to left. If it connects with PDA or ligamentum arteriosum it creates a vascular ring. 10 % of these cases have Congenital heart disease.



Right Arch with Aberrant left subclavian artery.
http://www.radiologyassistant.nl/images/thmb_4723299d20e80right-arch-abberant-lft-sca.jpg





Right aortic arch with aberrant left subclavian artery and left ligamentum arteriosum.
http://img.medscape.com/pi/emed/ckb/thoracic_surgery/424545-426233-841tn.jpg


  • Isolated left subclavian: (i.e. its origin from PA): least common.





Clinical picture:


The importance of right aortic arch lies in: Tracheal & esophageal compression & associated anomalies.

Right aortic arch is found in:
  • 0.1 % of population.
  • 50 % of pulmonary atresia with VSD.
  • 30 % of persistent truncus arteriosus.
  • 30 % of tetralogy of Fallot.
  • 20 % of Double-outlet RV.
  • 10 % of transposition of the great arteries.
  • 5 % of Tricuspid atresia.
In the absence of vascular ring and congenital heart disease: patients are asymptomatic.




Chest x-ray:
  • Postero-anterior view:
    • The aortic knuckle & descending aortic margin appear on the right side. These may, however, be obscured by the thymus.
    • Barium-filled esophagus may show an indentation on the right.
  • Lateral view:
    • A retro esophageal structure may be seen: i.e. aortic segment, Ductus or ligamentum arteriosum, or Aberrant subclavian artery.



Surgery:


Tracheal or esophageal compression is relieved, e.g. by division of the ligamentum arteriosum.
Associated anomalies are dealt with.
Otherwise, no need for surgery.




Double aortic arch




Pathology:


Double aortic arch occurs due to persistence of the right and left dorsal aortas: normally, the aortic arch is formed by the left 4th primitive aortic arch, while the right 4th primitive aortic arch forms the right subclavian artery. The remaining part of the right dorsal aorta distal to the right 4th primitive arch is obliterated. If the right dorsal aorta persists fusing with the left dorsal aorta, a double aortic arch occurs.
The 2 arches pass posteriorly over the bronchi, to join behind the esophagus and form the descending thoracic aorta.
Each common carotid & subclavian artery arises from its corresponding arch.
The ductus or ligamentum arteriosum connect the left aortic arch with the left pulmonary artery.



Double aortic arch.
http://img.medscape.com/pi/emed/ckb/thoracic_surgery/424545-426233-789tn.jpg




Clinical picture:


Double aortic arch is the most common form of symptomatic vascular rings:
  • 75 % are symptomatic.
  • 20 % have associated anomalies: e.g. VSD, tetralogy of Fallot.

Symptoms:
  • Respiratory distress, ranging from mild tachypnea to life threatening stridor & apnea.
  • Symptoms are aggravated by: Feeding, Crying, Respiratory infections.

Signs:
  • Supra sternal & intercostal retractions.
  • Cyanosis.
  • Rhonchi.
  • Hyper-extension of the neck is noted; if flexion is tried it may precipitate respiratory obstruction.




Chest x-ray:


One or more of the following may be seen:
  • Right Para-tracheal shadow.
  • Esophageal compression.
  • Emphysema, collapse, consolidation…etc.




Cardiac catheterization:


Aortography is diagnostic and evaluates the relative size, patency, and branches of each arch.




Natural history:


The majority become symptomatic at 2 months, usually with rapid progression.
Postoperatively, mild symptoms may persist for several months.




Medical management:


Management of respiratory problems, particularly respiratory infections.




Surgery:


Division of the smaller arch.
Suspension of the larger arch is rarely needed.
Adhesions are released.




Cervical aortic arch




Pathology:


The aortic arch, right or left, lies high-up in the supra-clavicular region, usually on the right side.
It may be due to arrest of the normal downward migration.




Clinical picture:


Most patients are asymptomatic. A few may have stridor or dysphagia.
A mass is felt in the supra-clavicular region, with a thrill & murmur over it.
A delay in femoral pulse may be appreciated & digital compression of the mass may reduce the femoral pulse volume.




Chest x-ray:


Widening of superior mediastinum.
Trachea may be displaced to the other side.
Esophageal compression may occur, if the descending aorta crosses the mid line.




Cardiac catheterization:


Aortography is diagnostic and differentiates the case from carotid artery aneurysm or carotid Arterio-venous fistula.




Surgery:


Surgery is not usually needed.
If pressure symptoms are present, compression is released accordingly.




Aberrant subclavian artery




Pathology:


Aberrant right subclavian artery (RSCA) arises as the 4th branch of aortic arch: i.e. right common carotid (RCC), followed by left common carotid (LCC), left subclavian (LSCA), and finally RSCA.
Aberrant left subclavian artery (LSCA) arises as the 1st branch of aortic arch: i.e. LSCA, followed by Innominate (RSC + RCC), finally LCC. Aberrant LSCA may be associated with right aortic arch.
Thus each aberrant SCA arises in the wrong side, and needs to cross the midline to the other side; thus it passes behind the esophagus to reach its corresponding arm.



Aberrant right subclavian artery.
http://www.radiologyassistant.nl/images/thmb_474858f5af7584-tek.jpg





MR argiography showing an aberrant right subclavian artery arising from the aortic arch distal to the left subclavian artery.
http://www.ispub.com/ispub/ijorl/volume_3_number_1_39/dysphagia_due_to_rare_cause/dysphagia-fig2.jpg





Barium swallow showing posterior indentation of thoracic part of esophagus.
http://www.ispub.com/ispub/ijorl/volume_3_number_1_39/dysphagia_due_to_rare_cause/dysphagia-fig1.jpg





1. Aberrant Right subclavian artery, 2. Innominate artery compression syndrome, 3. Right Arch Mirror Image, 4. Right Arch with Aberrant left subclavian, 5. Double Aortic Arch, 6. Double Arch with Atretic Segment
http://www.radiologyassistant.nl/images/thmb_4bfa41e83d246Overview-arch-anomalies.jpg





Double Arch: In the embryo a double arch with two brachiocephalic vessels on each side is present. If double aortic arch persists, it forms a vascular ring around trachea and esophagus. Double Arch with Atretic Segment: Posterior part of the left arch becomes atretic. This nonpatent remnant persists as a fibrous cord tethering the anterior left arch to the descending aorta. Normal Left Arch: The posterior part of the right arch involutes. The two brachiocephalic vessels on the right form the right innominate artery. Right Arch with mirror branching: Mirror image of normal left arch. Posterior part of the left arch involutes. The two brachiocephalic vessels on the left form the left innominate artery. Left Arch with aberrant right subclavian artery: Right arch between the right subclavian and right common carotid artery involutes. First branch is the right common carotid, followed by the left carotid and the left subclavian artery. The last branch is the right aberrant subclavian artery. Right Arch with aberrant left subclavian artery: Mirror image of the left arch with aberrant right subclavian artery. Left arch between the left subclavian and left common carotid artery involutes. First branch is left common carotid, followed by right carotid and right subclavian artery. The last branch is the left aberrant subclavian artery. When you look at these illustrations, you have to realize, that these are views from above, while CT-images have a 'view from feet'. On a CT-image the ascending aorta will be on the upper part of the image and the descending aorta will be on the lower part.
http://www.radiologyassistant.nl/images/thmb_4bfa2b907fc95overview-embryology.jpg





A: The common vascular pattern encountered in 399 of the 400 bodies studied. On the right side, the common carotid [RCC] and subclavian [RS] arteries arise as branches of the innominate artery, while on the left [LCC, LS] they arise directly from the descending aortic arch. B: An anomalous right subclavian artery arises from the descending thoracic aorta distal to the left subclavian artery. C: In addition to the anomalous right subclavian artery, a bicarotid axis [occurs] from which both the right and the left common carotid arteries take origin. D: An example of this same anomalous right subclavian artery arising from the descending aorta, but here associated with a left innominate artery. E: A right aortic arch with the left subc1avian artery arising as the last branch from the arch, and crossing behind the esophagus en route to the left upper extremity. In their series, Daseler and Anson found no examples of the variations depicted in the lower three illustrations.
http://www.anatomyatlases.org/AnatomicVariants/Cardiovascular/Images0300/0311.gif




Clinical picture:


Aberrant right or left SCA rarely produces symptoms: only if associated with vascular rings.
With coarctation of the aorta; if both SCA arise distal to obstruction the pulse will be small in all limbs. This condition may be confused with critical AS in the young. In the adult, radial pulse & blood pressure may be deceivingly normal.




Surgery:


In presence of pressure manifestations, the vessel is divided & ligated.
Subclavian steal syndrome may then develop: where the blood flows from the vertebral artery to the arm with ligated subclavian supply, resulting in cerebral ischemia.




Isolated subclavian artery




Pathology:


The isolated SCA arises from the homo-lateral PA, or arises normally but with atresia.
Collaterals develop from the other SCA to the isolated one.
It is always opposite to the side of AO arch.
Isolation of left SCA is 4 times more common than the right.


Associated conditions:
  • Interruption of the aortic arch.
  • Tetralogy of Fallot.




Clinical picture:


It does not produce symptoms: only those of associated conditions.
Signs:
Delayed pulsations and decreased BP in the affected arm.




Chest x-ray:


The aortic arch is opposite to the side of delayed pulsations & decreased blood pressure.




Aortography:


Late opacification of the isolated SCA from collaterals.
Rarely the catheter may pass via PDA to PA to isolated SCA.




Natural history:


With the passage of time, subclavian steal syndrome may develop.




Surgery:


Surgery is not usually needed unless sharing in a vascular ring & causing compression symptoms.
It may be ligated, and if long enough, anastomosed to the aorta in the appropriate site.




Tracheal compression by the great arteries




Pathology: 

The trachea may be Compressed by the innominate artery: if it arises more posterior than usual. 
Tracheal compression by the left common carotid artery occurs if it arises more to the right than usual, or arises as a third branch of the innominate artery.




Clinical picture:


Stridor, wheezing, and apnea may occur.




Investigations:


Aortography is diagnostic.
Bronchoscopy reveals pulsatile anterior compression of the trachea.




Management:


Conservative management is adequate in the majority: improvement of symptoms occurs with increasing tracheal rigidity.
Surgery is needed in severe cases: right thoracotomy is used for innominate but left thoracotomy for left common carotid: The artery is pulled anteriorly by sutures passed in the periosteum of the sternum.
Symptomatic relief is dramatic after surgery.

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