A 28-year-old woman presented to her local rural hospital with acute-onset severe chest pain which came on at rest. There was no inciting physical or emotional stressor. She had a known diagnosis of Turner syndrome (XO) with prior documentation of a normal functioning bicuspid aortic valve. Her diagnosis of bicuspid aortic valve was based on a cardiac catheterization performed in early childhood and subsequent clinical examinations. She had no murmur to suggest aortic insufficiency or stenosis and had no prior cardiac imaging evaluations. She was seen routinely by a pediatric cardiologist every 2 years until the age of 18 years. She was subsequently lost to follow up.

At the time of her last routine pediatric cardiology visit 10 years ago she had been provided with instructions regarding the need for routine care and the possible need for cardiovascular surgery in the future but had not been instructed on where to seek care now that she had reached adult age. She assumed she could no longer be seen at a pediatric institution and did not successfully transition to an adult facility.

At the time of her presentation to the emergency room, she had a blood pressure (BP) in both arms of 160/80 mm Hg. A chest x-ray was performed which showed a widened mediastinum thus prompting a computed tomography (CT) angiogram which demonstrated a dilated ascending aorta measuring 3.6 cm yielding an indexed score of 2.4 cm/m² (with a normal value for this patient population defined as <2.2 cm/m²).¹ There was no dissection of the ascending aorta. She had a bovine arch wherein the first head and neck vessel gave rise to both carotid arteries.² There was focal aneurysmal dilation of the distal aortic arch extending to the proximal portion of the left subclavian artery and proximal descending thoracic aorta. There was a focal dissection beginning in the distal aortic arch with propagation into the proximal left subclavian artery and into the descending thoracic aorta. The right subclavian artery was aberrant in origin arising from the descending thoracic aorta just distal to the left subclavian artery.

The patient was started on a labetalol infusion with an achieved goal systolic BP of 100 mm Hg. Attempts were made to transfer the patient to an appropriate medical facility for further management. In light of the limited nature of the dissection, the lack of ascending aortic involvement, and a maximal aortic diameter less than established surgical criteria, an attempt at conservative management was attempted.³ Despite optimal blood pressure control, serial scans over a period of 4 days demonstrated progressive dilation of the involved aortic segment and thus the decision was made to proceed with intervention. A hybrid procedure approach was undertaken. Bilateral carotid artery to subclavian artery bypass grafts were first placed to establish flow to both subclavian vessels. This was then followed by placement of a covered stent in the distal arch at the site of the dissection. The patient was discharged on pravastatin, aspirin, and lisinopril.

CASE EXPLANATION

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  Aortic dilation, aneurysms, and dissections can be seen in a wide variety of connective tissue diseases, patients with known syndromes (like Turner). It is now being increasingly reported in adult patients with congenital heart disease. Aortic dilatation has been described in adult women with Turners syndrome, where aortic valve morphology, age, and blood pressure can be major determinants of the aortic diameter.

  
  
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  Such patients may face a significant risk of premature cardiovascular death due to aortic dissection, ischemic heart disease, and stroke. Careful and continuous monitoring of the aorta in this patient group is therefore of vital importance.

  
  
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  This case also highlights the importance of timely transition of care for adults with congenital heart disease, so patients are not lost to follow up and continue to receive appropriate lifelong care.

EPIDEMIOLOGY

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  Frequency of aortic dilation varies according to the underlying syndrome, mutation, or congenital cardiac defect.

  
  
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  Aortic dilation was historically underdiagnosed in patients with all of these entities for the following reasons:

  
  
  
  
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    Failure to image affected portion of the aorta which is often in the mid-to-high ascending aorta

    
    
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    Lack of consideration of body size and age in determining whether an aortic diameter was normal

    
    
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    Lack of appreciation of aortic dilation as pathologic in contrast to a normal part of the underlying structural disease entity (ie post stenotic dilation)⁴

    
    
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    Lack of routine screening of high-risk patients, namely family members of patients with a bicuspid aortic valve,⁵ and family members of older patients with aortic dissection

  
  
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  Patients with bicuspid aortic valve may have an isolated cardiac defect which is often familial, or the valvular abnormality may be indicative of an underlying syndrome or well characterized familial aortopathy (Figure 12-1 and Tables 12-1 and 12-2).

  
  
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  Within a population of children and young adults, moderate or severe ascending aortic dilation was present in 5% and 16%, respectively.⁶ Aortic dissection or rupture has been documented to occur in 8% of those with dilation.⁷

  
  
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  In patients with tetralogy of Fallot the aorta is typically larger than normal since birth.⁸ A subset of these patients will have ongoing pathologic aortic dilation placing them at risk for aortic insufficiency⁹ and aortic dissection.¹⁰ Within this population, male gender, pulmonary atresia type tetralogy of Fallot, and persistent ventricular septal defects (Figures 12-2, 12-3A, and 12-3B) have been identified as risk factors for aortic complications.⁹

  
  
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  The incidence of progressive aortic dilation in patients with conotruncal abnormalities like those with d-transposition of the great arteries (D-TGA) (Figure 12-4) and patients with single ventricles s/p Fontan palliation (Figure 12-5) are not yet fully appreciated given that this adult patient population remains in its infancy. Rare cases of patients with D-TGA with aortic dilation causing coronary compression and dissection have been reported.¹¹

ETIOLOGY

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  Progressive aortic dilation and aortic dissection are seen in the following categories:

  
  

  A. The following are the names of certain genetic syndromes:

  
  
  
  
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    Turner syndrome¹

    
    
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    Marfan syndrome¹²

    
    
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    Loeys-Dietz syndrome¹³

    
    
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    Type IV Ehlers-Danlos syndrome (EDS)¹⁴

    
    
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    Others (neurofibromatosis,¹⁵ Shprintzen-Goldberg syndrome,¹⁶ autosomal dominant polycystic kidney disease, etc)⁴ with the incidence of the syndrome and aortic dilation noted in Table 12-1.

  
  
  
  

  B. Patients with the following congenital cardiac conditions:

  
  
  
  
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    Bicuspid aortic valve⁷

    
    
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    Coarctation or interruption of the aorta⁷ (Figure 12-6)

    
    
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    Conotruncal defects including D-TGA (Figure 12-4),¹⁷ tetralogy of Fallot,¹⁸ pulmonary atresia/ventricular septal defect (VSD) (s/p Fontan palliation)⁹

    
    
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    Others including aberrant subclavian artery¹⁹ and bovine aortic arch²

    
    
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    Postoperative patients following the Ross procedure²⁰

  
  
  
  

  A. Familiar thoracic aortic aneurysms²¹ due to the genetic mutations identified in Table 12-2:

  
  
  
  
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    There continues to be some controversy as to whether the aortic dilation seen in association with congenital cardiac defects represents an intrinsic aortopathy or whether the dilation occurs secondary to abnormal flow dynamics.

  
  
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  Evidence that it stems from an intrinsic aortopathy includes the following:

  
  
  
  
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    The degree of aortic stenosis does not relate to the degree of aortic dilation.²²

    
    
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    Patients with a normal functioning bicuspid aortic valve (BAV) often have significant dilation.²²

    
    
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    Dilation is present from early childhood and the rate of aortic growth is abnormal.^{6, 22}

    
    
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    First-degree family members of probands with BAV have increased incidence of aortic aneurysm and dissection even in the presence of a tri-leaflet valve.⁵

    
    
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    Decreased fibrillin content has been documented in the aorta of patients with BAV.²³

  
  
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  Evidence that aortic dilation occurs secondary to abnormal flow dynamics includes data documented as follows:

  
  
  
  
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    The angle between the systolic ejection jet and the ascending aorta correlates aortic diameter in both patients with BAV as well as normal controls.²⁴

    
    
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    Ascending aortic curvature has been shown to be more important than aortic size in predicting aortic dissection in a mathematical model.²⁵

  
  
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  It is most probable that a combination of a genetic predisposition yielding to abnormal aortic wall architecture exists which then results in abnormal aortic stiffness and distensibility^{7, 26} thereby predisposing to progressive aortic dilation which may be accentuated by abnormal flow jets.

  
  
  
  
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    Aortic dissection, irrespective of the underlying cause of aortic dilation, is often preceded by an inciting factor²⁷ namely a physical or emotional stressor,²⁸ and occurs more commonly in those with the following comorbidities: hypertension,²⁹ smoking,³⁰ obesity,³¹ and hyperlipidemia.³¹