Case Author(s): John R. Leahy, M.D. and Tom R. Miller, M.D., Ph.D. , 09/13/98 . Rating: #D3, #Q3

Diagnosis: Aortic root graft infection

Brief history:

48 year-old man with Marfan's syndrome and fever.

Images:

24-hour delayed dual-intensity whole body images are shown.

View main image(iw) in a separate image viewer

View second image(iw). Axial SPECT images through the chest.

View third image(ct). CT of the chest obtained one week prior to the WBC scan.

View fourth image(xr). Chest x-ray obtained the day of the the WBC scan.

Full history/Diagnosis is available below

Diagnosis: Aortic root graft infection

Full history:

This is a 48 year-old man with Marfan's Syndrome who had aortic valve replacement in 1990, and an aortic root graft placement in 1996. He presented with a three-day history of fever, elevated WBC count, and S. aureus bacteremia.

Radiopharmaceutical:

511 uCi In-111 labeled autologous leukocytes i.v.

Findings:

Whole Body Images and SPECT: Two foci of increased In-111 leukocyte accumulation are seen in the left chest on the planar images. The use of SPECT allows more accurate localization of these lesions. The first is adjacent and just posterior to the lower sternum. The second lesion is in the left lower lobe parenchyma.

Chest CT: Soft tissue density is seen around the aortic root graft. There is no abscess/fluid collection noted. No lesions are seen in the left lower lobe.

Chest radiograph: Opacity is seen in the retrocardiac left lower lobe, consistent with infiltrate.

Discussion:

Approximately 2% of vascular grafts become infected at some point. CT has limited sensitivity (as low as 37% in one study) in diagnosis of graft infections. Gas around the graft is considered diagnostic of infection, but is present in only 50% of infected grafts. The soft tissue around the graft on this CT was felt to be consistent with either post-operative changes or infection. The sensitivity of labeled leukocyte scans is higher than CT, with studies showing between 90% and 100% sensitivity. Perigraft hematoma, graft thrombosis, and pseudoaneurysms can result in a false positive scan, accounting for a specificity of between 53% and 100%. In the immediate post-operative period (7 days), wound healing may also cause nonspecific uptake, but this does not usually lower specificity for graft infection.

The activity in the left lower lobe parenchyma was felt to be secondary to interval development of pneumonia between the CT and leukocyte scan. Its presence was confirmed on the chest radiograph.

Of note, the application of SPECT for imaging indium studies is not always useful because of the low activity administered in these studies often resulting in a poor signal-to-noise ratio. In this case however, the relatively intense activity in the lesions, and the lack of significant adjacent activity as well as optimization of digital image reconstruction resulted in diagnostically relevant images.

References:

Wagner HN, Szabo Z, Buchanan JW : Principles of Nuclear Medicine, 2nd ed. Philadelphia, W. B. Saunders Company 1995; 741.

King MW, Schwinger RB, et al: Digital restoration of indium-111 and iodine-123 SPECT images with optimized Metz Filters. JNM 27: 1327-1335, 1986.

Followup:

The man underwent removal and replacement of the prosthetic aortic valve and aortic root graft. Acute and chronic inflammation was found on pathology. Gram positive cocci were also noted. No organisms grew out of the graft culture; however he had been on two weeks of antibiotics prior to graft removal.

ACR Codes and Keywords:

References and General Discussion of Indium -111 WBC Scintigraphy (Anatomic field:Heart and Great Vessels, Category:Inflammation,Infection)

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Case number: iw008

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