Archived case 184 · September 10-September 17, 2015
57-year-old male status post aortic repair. Chest radiographs at the discharge and follow up radiographs and CTA 3 months later are shown.
What is the differential for this finding?
Additional Clinical History Recent history of ascending aorta resection and replacement with a 30 mm synthetic interposition graft for a 51 mm heavily calcified ascending aortic aneurysm. The patient presented for a routine pre-operative chest radiograph in preparation for renal transplant. Radiologic Findings Baseline post-operative frontal chest radiograph for comparison (Figure 1). Follow-up frontal chest radiograph at presentation demonstrates interval development of a right "hilum overlay sign" manifest as an eccentric focal convex mediastinal contour abnormality (Figure 2). Select chest CTA images (Figure 3-7) including reformatted arterial phase coronal (Figure 3) and parasagittal (Figure 4) multi-planar reconstructions (mediastinal windows); unenhanced (Figure 5), arterial (Figure 6) and delayed phase (Figure 7) cinematic axial images (mediastinal windows) reveal the new mediastinal based contour abnormality stems from a large, low-attenuation, circumferential perigraft fluid collection around the entire length of the synthetic graft. Note the absence of active contrast extravasation, surrounding inflammatory changes, associated bubbles or air collection and or wall enhancement. Subsequent CT-guided aspiration was performed (not illustrated) and 280 mL of serosanguinous fluid was aspirated. Both bacterial and fungal cultures were negative. The patient was discharged home. About a month later follow-up CT imaging (not illustrated) showed recurrent perigraft fluid accumulation. Lymphoscintigraphy (not illustrated) was performed to exclude a chyle leak and was negative. A second CT guided aspiration (not illustrated) was performed yielding 165 cloudy brown serous fluid and a pigtail catheter was placed. The laboratory evaluation was again unrevealing. The drain output gradually decreased and it was removed 5 days later. The patient was discharged home and remains under ongoing surveillance. Answer Diagnosis: PERIAORTIC GRAFT SEROMA
PERIAORTIC GRAFT SEROMA
Answer
Diagnosis: PERIAORTIC GRAFT SEROMA
Differential Diagnosis
· Endoleak
· Peri-graft infection
· Postoperative liquefied hematoma
· Infected hematoma
Discussion
This case nicely highlights the utility of the “hilum overlay” sign on conventional chest radiography and the application of such in steering the differential diagnosis appropriately. The proximal segment of the left and right pulmonary arteries lie lateral to the cardiac silhouette or just within its outer edge in the vast majority of normal individuals. Felson described this normal apposition of the main pulmonary arteries to the lateral edge of the cardiopericardial silhouette as the rationale behind the “hilum overlay” sign. Specifically, the configuration of an anterior mediastinal mass can mimic an enlarged heart or pericardial sac. However, an anterior mediastinal mass cannot reside directly medial to the pulmonary artery because of the heart and pericardium. Therefore, a true hilar mass will often overlap the main pulmonary arteries which can then be seen projecting within the margins of the mass (also see Case of the Week May 6-13, 2010). Thus, on the basis of the chest radiograph alone, this process is localized to the anterior mediastinum and a post-operative complication related to the interposition aorta graft would be the leading differential diagnostic consideration.
Accumulation of low-attenuation perigraft fluid is most often due to infection, which needs to be excluded. Bleeding due to anastomotic dehiscence without infection is a less frequent cause and also needs to be excluded and is more frequently encountered in the early post-operative course. In approximately 50% of cases, the cause of the low attenuation perigraft fluid collection is not identified (Sundaram et al). It is hypothesized that the latter perigraft low attenuation fluid collections are the result of a post-operative seroma and or inflammatory edema that evolves as a result of an allergic reaction to the synthetic graft material or the surrounding bovine pericardium.
Perigraft seromas in particular have been reported in association with a variety of vascular procedures, including peripheral by-pass grafting as well as conventional and endovascular aortic aneurysm repair. Seromas are relatively common in superficially placed grafts (e.g., axillofemoral and femorofemoral bypasses), whereas deep graft seromas occur much less frequently and have been described mainly with abdominal aorta grafts.
Treatment
Treatment options include drainage, however due to recurrence, endovascular repair or surgery may be necessary in select cases.
Selected Readings:
1. Ahn S.S, Machleder HI, Gupta R, Moore WS. Perigraft seroma (clinical, histological, and serologic correlates). Am J Surg. 1987; 154:173–178.
2. Blumenberg RM, Gelford ML, Dale WA. Perigraft seromas complicating arterial grafts. Surgery. 1985; 97:194–203.2.
3. Chua SK, Azarisman SM, Glenie T, Baillie T, Teo KS, Worthley SG. Magnetic resonance imaging in the diagnosis and surveillance of HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" thoracic HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" aortic HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" perigraft HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" seroma HYPERLINK "http://www.ncbi.nlm.nih.gov/pubmed/22983879" and its complications. Vasc Endovascular Surg. 2012 Nov; 46(8):691-2.
4. Chu LC, Johnson PT, Cameron DE, and Fishman EK. MDCT Evaluation of Aortic Root Surgical Complications . American Journal of Roentgenology 2013; 201:4, 736-744
5. Cuff RF, Thomas JH. Recurrent symptomatic aortic sac seroma after open abdominal aortic aneurysm repair. Journal of Vascular Surgery. 2005; Volume 41, Issue 6, 1058 – 1060
6. Felson BF. Localization of Intrathoracic Lesions In: Chest Roentgenology 1973; W.B. Saunders, Philadelphia: 39. 5.
7. Kondo Y, Muto A, Dardik A, Nishibe M, Nishibe T. Perigraft Seroma After Surgical Aortoiliac Aneurysm Repair with Knitted Polyester Grafts: Report of Two Cases. Annals of Vascular Diseases. 2009; 2(1):44-46.
8. Parker MS, Chasen MH, Narinder P. Radiologic Signs in Thoracic Imaging: Case-Based Review and Self-Assessment Module. American Journal of Roentgenology. 2009; 192: S34-S48.
9. Sundaram B, Quint LE, Patel S, et al. CT Appearance of Thoracic Aortic Graft Complications. American Journal of Roentgenology. 2007; 188: 1273-1277.
Original case written by its authors at Virginia Commonwealth University and published at this address as part of a weekly teaching collection. Reproduced here as an archive.