Chapter30 Aorta

790

Section V: Cardiac Radiology

A

B

C

Figure 30.55.  Takayasu Arteritis. Axial nonenhanced ( A ) and contrast-enhanced ( B ) CT images at the level of the right pulmonary artery in a 54-year-old man demonstrate hyperattenuating circumferential wall thickening along the ascending aorta ( arrows ). Attenuation-corrected PET image ( C ) at the same level demonstrates corresponding increased uptake that has been shown to correlate with active disease.

agents. With the advent and widespread availability of peni- cillin and effective tuberculosis treatment, however, infectious aortitis is now most commonly caused by Staphylococcus aureus and Salmonella but can also be seen in Listeria, Clos- tridium septicum, and Campylobacter infections. Involvement of the aorta most commonly occurs due to hematogenous seeding in the setting of high-grade bacteremia, but infection may also arise directly from adjacent structures—for exam- ple, the aortic root/aortic valve or para-aortic mediastinal lymph nodes—and may be caused by traumatic or iatrogenic inoculation. Early diagnosis of aortitis (and vasculitis in general) may be difficult owing to the vague signs and symptoms, par- ticularly in the acute phase. Given the common diagnostic uncertainty, imaging plays a vital role, both to confirm the presence of inflammatory sequela and to narrow the differen- tial diagnosis, given patterns of findings. However, it is crucial to interpret these findings in the presenting clinical context, as different entities show considerable overlap at imaging and certain etiologies can demonstrate more suggestive signs or symptoms. For instance, GCA and Takayasu arteritis pre- dominantly affect the ascending aorta, aortic arch, and branch vessels and may be indistinguishable on imaging alone. How- ever, the populations most typically affected (patients over 50 for GCA and under 30 for Takayasu) are distinct and presen- tation may differ (e.g., temporal headache and symptoms of polymyalgia rheumatica in GCA). Acute complications associated with aortitis include intra- luminal thrombus and aneurysm formation. Infected aortic aneurysms are rare, encompassing 0.06% to 2.6% of all aneu- rysms, and may lead to severe hemorrhage/sepsis and death if untreated. Aortitis may also be complicated by dissection and rupture, which are more likely in the acute phase of inflamma- tion. Luminal stenosis may occur in the acute inflammatory or the chronic fibrotic phase. Complete vascular occlusion may also occur, more often in branch vessels but even pos- sibly in the aorta (most commonly in the distal abdominal aorta) and/or iliac vessels in severe cases. Aortoenteric fistula may develop between the aorta and adjacent structures—for example, esophagus, stomach, small or large bowel—a rare complication seen most often in the setting of infectious or inflammatory aneurysm. CTA is one of the primary modalities used to assess for vasculitis. The inflammatory wall thickening (defined as

greater than 3 mm) in aortitis may be circumferential or cres- centic and may involve arch and other smaller branch ves- sels, depending on the etiology. Crescentic thickening may be difficult to distinguish from IMH, particularly on non–con- trast-enhanced (NECT) imaging (Fig. 30.55). Classically, the wall thickening in IMH is confluent over the site of involve- ment and is often hyperattenuating. In aortitis, the thicken- ing may be discontinuous or more variable along diseased segments. Intramural enhancement is a more specific sign of mural inflammation and may be reduced or absent after initiation of treatment—for example, corticosteroids in rheu- matic disease. Patients with Takayasu arteritis often demon- strate multifocal areas of wall thickening/luminal narrowing along the aorta and arch vessels, as well as other vascular structures such as the coronary arteries and/or pulmonary arteries. MR imaging has slightly worse spatial resolution than CTA but provides additional information owing to its superior soft tissue characterization (Fig. 30.56). Wall thickening is well seen and intramural T1 hypointensity and T2 hyperintensity due to mural edema suggests active disease. Periaortitis in idiopathic disease will demonstrate T1 hypointensity and T2 hyperintensity, while chronic periaortic fibrosis will typically be both T1 and T2 hypointense. Contrast-enhanced imag- ing with gadolinium-based agents can demonstrate similar intramural enhancement characteristics to contrast enhanced CT, which again may be less or not evident after appropriate treatment. Chronic periaortic fibrosis will demonstrate avid enhancement. Nuclear medicine imaging, specifically PET-CT with 18 F- FDG, is a valuable tool for the assessment of aortitis. Mural thickening can be seen on the CT portion of the exam and FDG uptake in the aortic wall can be used to assess disease activity and treatment response (Figs. 30.55 and 30.56). Aortic Tumors Primary aortic tumors are exceedingly rare, with only about 150 cases reported, and typically carry a dismal prognosis due to advanced local and/or metastatic disease at the time of diagnosis as well as complications typically secondary to tumor embolization with distal vascular occlusion and end-organ ischemia/infarction. By histopathologic classification,