Acquired Diseases of the Thoracic Great Vessels

Frandics P. Chan

This chapter reviews acquired pediatric diseases of the thoracic aorta, venae cavae, pulmonary arteries, and pulmonary veins. Acquired pediatric aortic disease is uncommon, but radiologists and imagers play an important role in the care of patients who have sustained traumatic aortic injury. Pulmonary embolism is the most common acquired disease of the pulmonary artery. The most common acquired abnormalities of the pulmonary veins and venae cavae are obstruction or stenosis caused by luminal occlusion or extrinsic compression from mediastinal pathologies. Hemodynamically significant obstruction of the superior vena cava (SVC) leads to SVC syndrome, whereas obstruction of the pulmonary veins leads to pulmonary venous hypertension.

Acquired Diseases of the Thoracic Aorta

Pathology of the aorta can be categorized into aortic aneurysm, aortic dissection, and aortic stenosis.¹ Although each aortic disease may present one or more of these manifestations, it is the clinical consequences of aneurysm, dissection, or stenosis that determine mortality and morbidity (Table 83-1).

Table 83-1

Principal Etiologies of Acquired Aortic Diseases

Manifestation	Causes
Aortic aneurysm	Infectious aortitis
	Inflammatory aortitis
	Takayasu syndrome (acute, chronic)
	Systemic lupus erythematosus
	Sarcoid
	Connective tissue disease
	Marfan syndrome
	Ehlers-Danlos syndrome (vascular type)
	Loeys-Dietz syndrome
	Arterial tortuosity syndrome
	Neurocutaneous disease
	Tuberous sclerosis
	Trauma or postsurgical (pseudoaneurysm)
Aortic dissection	Connective tissue disease
	Marfan syndrome
	Ehlers-Danlos syndrome (vascular type)
	Trauma
Aortic stenosis	Inflammatory aortitis
	Takayasu syndrome (chronic)
	Congenital rubella syndrome
	Radiation
	Neurocutaneous disease
	Neurofibromatosis (type I)
	PHACES syndrome
	Postsurgical
	Coarctation repair
	Aortopulmonary shunts

PHACES, Posterior fossa malformations, hemangiomas, arterial anomalies, cardiac defects, eye abnormalities, sternal cleft and supraumbilical raphe.

Normally, the caliber of the aorta gradually decreases in size from the sinotubular junction to the aortic hiatus. An aortic aneurysm is defined as an abnormal dilation of the aorta, which may undergo progressive expansion. An aortic aneurysm may form if wall stress increases, as in the case of systemic hypertension, or if the aortic wall weakens, as in the case of Marfan syndrome (see Chapter 79). The expansion rate of an aneurysm is determined by the wall stress, which increases with diameter. Thus a large aneurysm is more likely to expand than a small aneurysm, and the expansion is an accelerating process until rupture occurs.

Aortic dissection can occur in children as a complication of trauma or connective tissue diseases. A dissection is created when blood forces through a tear in the aortic intima and progressively separates the intimal layer from the aortic media, creating a true lumen that originally was connected to the aortic root and a false lumen that was not connected to the aortic root. Dissection can cause end-organ ischemia if the branch arteries supplying the organ are obstructed by the dissection flap. Dissection can weaken the aortic wall sufficiently to cause catastrophic rupture.

Aortic stenosis is defined as a narrowing that limits perfusion to organs supplied by the aorta distal to the stenosis. It may cause systemic hypertension, left ventricular pressure overload, and end-organ ischemia.

Trauma

Overview: Trauma is a major cause of death in children and results primarily from motor vehicle accidents, although firearm injury (Fig. 83-1) and child abuse are other important causes of traumatic death. Survival of a child with a traumatic aortic injury until arrival at the emergency department is rare, accounting for one to two cases per year at large metropolitan level I pediatric trauma centers. Operative treatment involves fewer than 0.14% of all trauma patients, and only 6% of all traumatic ruptures of the aorta occur in patients younger than 16 years.^2,3 The outcome of traumatic aortic injury in the pediatric population is directly related to timely diagnosis, proper treatment, and hemodynamic status at the time of presentation.

Figure 83-1 An aortic false aneurysm from a gunshot wound in an 18-year-old man.
Volume rendering of a computed tomography angiogram shows a false aneurysm (arrowheads) that follows the track of a bullet. The bullet first entered the chest horizontally, parallel to the aortic arch, rupturing the aorta. Then it was deflected downward and came to rest (arrow) adjacent to the descending aorta (DAo).

Imaging: Chest radiographic findings such as pleural capping at the left lung apex, obscuration of the aortic arch, mediastinal widening, pleural effusion, pneumothorax, pulmonary contusion, tracheal and nasogastric tube deviation, and upper rib and clavicle fracture in the setting of blunt trauma should raise clinical suspicion for an aortic injury (Fig. 83-2). Historically, the definitive diagnosis of traumatic aortic injury was made by conventional catheter angiography. Today, computed tomographic angiography (CTA) has supplanted catheter angiography as the diagnostic method of choice.^4,5 CTA allows speedy and precise visualization of the traumatic aortic injury. Care should be taken to identify the location of aortic rupture, active extravasation of arterial contrast, a dissection flap extending to major aortic branches, hemothorax and hemopericardium, and other organ and musculoskeletal injuries.

Figure 83-2 Aortic rupture in a 16-year-old boy as a result of a motor vehicle accident.
A, An axial image from a computed tomography (CT) angiogram shows a ruptured descending aorta at the level of the ligamentum arteriosum (arrow) and two pseudoaneurysms (arrowheads) extending beyond the aortic wall. B, A volume-rendered image of the CT angiogram shows the relationship between one of the pseudoaneurysms (arrowheads) and the ligamentum arteriosum (arrow) between the aorta (Ao) and the pulmonary trunk (PA).

Treatment and Imaging Follow-up: The goals of treatment of pediatric traumatic aortic rupture are identical to those in adults. The mainstay of treatment is operative repair of the aorta.⁶ Patients for whom surgery poses a high risk have been treated successfully with endovascular stent grafts, with deployment during adenosine-induced cardiac arrest. CTA should be performed immediately after stent placement, with a follow-up study in 48 hours to document the stability of the repair. Rarely, observational management for an intimal tear has been utilized in patients with comorbidities too severe to allow intervention.

Acquired Diseases of the Pulmonary Artery

Pulmonary Embolism

Overview: Pulmonary embolism (PE) is an uncommon but potentially fatal disease in children.⁷ In pediatric patients with deep venous thrombosis and PE, the mortality rate from all causes has been reported to be as high as 16%, whereas the mortality rate directly attributable to deep venous thrombosis or PE was 2.2%.⁸ The most common risk factor for PE in children is catheter thrombosis, which develops in as many as 50% of patients with central venous catheters.⁹ Other risk factors are peripartum asphyxia, dehydration, septicemia, trauma and burns, surgery, hemolysis, malignancy, and renal disease such as nephrotic syndrome. Rarely, PE can be seen in the setting of intracranial venous sinus thrombosis and Klippel-Trénaunay syndrome. Abnormal coagulation factors associated with adult PE that also have been reported in children are antiphospholipid antibodies, factor V Leiden mutation, and deficiencies in protein S, protein C, and antithrombin III.¹⁰

Clinical diagnosis of PE often is difficult because most cases of venous thrombosis in children are silent. Symptoms of PE may be masked by intrinsic lung disease or other underlying illness. In one series, 40% of proven cases of PE were negative in the d-dimer assay. Therefore a negative d-dimer assay in pediatric patients cannot exclude PE. A high level of clinical suspicion in the presence of risk factors is imperative.

Imaging: Traditionally, catheter pulmonary angiography was considered the diagnostic gold standard.¹¹ In current clinical practice, catheter pulmonary angiography has been replaced by noninvasive CT pulmonary angiography (CTPA) performed with high-speed multidetector CT. The accuracy of the detection of PE by CTPA in an adult population has been studied in the Prospective Investigation of Pulmonary Embolism Diagnosis II trial.¹²

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