Circumferential hyperechogenecity as an ultrasound sign of infected abdominal aortic aneurysm.

A 72-year-old man was admitted to the local hospital with a 2-day history of abdominal pain and mild back pain with low-grade fever. Computed tomography (CT) without contrast enhancement demonstrated a fusiform abdominal aortic aneurysm (AAA) of 45×48 mm in the infrarenal aorta and a nephrolith with ectatic renal pelvis. Therefore, antibiotics were given intravenously for 6 days for a diagnosis of pyelonephritis. The patient was then referred to our hospital because of worsening symptoms. His white blood cell count was 12 400/μL. Contrast-enhanced CT revealed a 53×55-mm AAA, which was larger than that of 6 days before, with periaortic fat stranding (Figure 1, left and center, arrows). Importantly, delayed-phase images further identified peri-aortic fat stranding (Figure 1, right, arrows). Interestingly, under these conditions, ultrasound examination demonstrated homogeneous, hyperechogenic, and thickened tissue adjacent to the surrounding AAA (Figure 2, arrows, and Movie I in the online-only Data Supplement). Thus, an infected aneurysm was suspected because of the rapid development and size dila-tation of the aneurysm, although the blood culture was negative. The patient immediately underwent open surgical repair with omental coverage for infected AAA. A surgical specimen showed histopathologically intensive neutrophilic infiltrate destroying the aortic wall with thickened adventitia (Figure 3). A few gram-positive cocci were seen by Gram staining. The postoperative course was satisfactory and uncomplicated. Infected AAA is a life-threatening disease with a high mortality rate. Thus, rapid diagnosis of infected AAA before rupture is important. Clinical diagnosis of infected AAA is made on the basis of the presence of nonspecific symptoms and signs such as fever, abdominal or back pain, and leuko-cytosis combined with a pulsatile abdominal mass. Therefore, diagnosis of infected AAA depends mainly on radiological modality; specifically, contrast-enhanced CT provides valuable information to demonstrate saccular shape with lobulated contour and characteristic findings such as periaortic soft-tissue mass, fat stranding, gas bubbles, and fluid collections. In particular, the presence of subtle periaortic fat stranding in contrast-enhanced CT scan may be an early-stage finding in infected AAA. Interestingly, as shown in Figure 2, ultra-sound can clearly demonstrate the periaortic fat stranding as circumferential periaortic hyperechogenic tissue in infected AAA. Ultrasound examination produces superior CT-like images and appears to be useful for the noninvasive diagnosis of infected AAA, although further prospective examination should be done to demonstrate its sensitivity and specificity. Disclosures None.