Introduction

Polyester grafts have been successfully used in the treatment of abdominal aortic aneurysms since the 1950s. Graft dilatation is an infrequent complication following such procedures. The mechanism underlying graft dilatation remains unclear and so far the procedures to be followed in such cases have not been definitely established.

Case report

A 68-year old man was brought to the hospital by Emergency Transport Services in a very serious general condition, conscious but confused, with signs of hypovolemia and without detectable blood pressure. An ultrasound examination performed in the accident and emergency department revealed a large abdominal aortic aneurysm, with signs indicating its rupture (presence of fluid area in the retroperitoneal space). The diagnosis was confirmed by an emergency computed tomography of the abdomen and pelvis minor. It detected a ruptured aneurysm measuring 7.5 cm in diameter at the widest point and an extensive hematoma in the retroperitoneal and pelvic space (fig. 1). The aneurysm originated below the renal arteries. The patient was qualified for emergent surgery. On the opening of the abdomen a large retroperitoneal hematoma and a ruptured abdominal aortic aneurysm were found. The aneurysm extended from below the renal arteries up to the aortic bifurcation. Iliac arteries were found to be normal and patent. The diameter of the aneurysm reached 8 cm at the widest point. The abdominal aorta was repaired, using a straight graft, 2.2 cm in diameter and about 8.0 cm in length (InterGard Knitted, manufacturer: InterVascular), and with end-to-end anastomosis. The operation lasted about 2.5 hours. After surgery the patient was transferred to the Intensive Care Unit (ICU) for further treatment. Having spent two weeks in the ICU and an additional week in the General Surgery Ward, he was discharged. He left hospital in a good general condition, without neurological deficits, the dorsalis pedis and the posterior tibial arterial pulses being palpable in both feet.

During the period prior to his hospitalisation the patient had been treated for hypertension and chronic obstructive pulmonary disease (COPD). The abdominal aorta aneurysm had not been detected since the patient produced no symptoms.

Since leaving hospital in July 2008 the patient has been systematically followed up by the Surgical Outpatient Department.

An ultrasound scan performed during the second month following the operation showed the blood flow through the graft to be normal, the anastomosis to be water-tight and the graft diameter to be circa 3.0 cm. Another scan conducted 6 months later detected a further dilatation of the graft (3.6 cm). Iliac arteries were found not to be dilated. A computed tomography angiography (CTA) scan of the abdominal aorta performed 14 months after the operation showed a dilatation all the way up the graft whose diameter was now reaching 4.2 cm (fig. 2). Subsequent CTA scans conducted one and two years later showed a still further dilatation of the aortic graft: 3.7 cm (2.5 years after the surgery) and 4.0 cm (3.5 years after the surgery) (fig. 3). The latest ultrasound scan, done about 5 years after the surgery, showed that the graft diameter reached 4.7 cm. The patient was referred for a CTA scan that confirmed the graft dilatation reaching 4.7 cm at the widest point. The vascular anastomoses, both proximal and distal, were patent and normal (fig. 4–6).

Since the surgery the patient has been consistently treated for hypertension and COPD. His blood pressure has been within the normal range, with systolic pressure around 140 mm Hg. The patient is a non-smoker. He remains in a good general condition and is self-sufficient, showing no neurological deficits, the dorsalis pedis and the posterior tibial arterial pulses being palpable in both feet and the ankle brachial pressure index being 1.0 on both sides. He has not been complaining of any abdominal pain and has been producing no symptoms of chronic intestinal ischemia. The only complication of the surgery is the creation of an abdominal wall hernia in the laparotomy scar.

Discussion

Polyester grafts have been used in various surgical procedures for over half a century. They are a recognised form of vascular reconstruction and arterial bypass surgery. However, the use of these prostheses has been unavoidably accompanied by complications related to their grafting and their very structure. Amongst the most common complications are: intra– and post-operatic haemorrhaging, infections, graft thrombosis and occlusions, anastomotic leaking, anastomotic and other pseudoaneurysms, dilatation of grafts to various degrees, including true aneurysms and graft rupture.

Minor graft dilatations are frequently mentioned by medical literature around the world. It is often claimed that practically every graft dilates by circa 8–20% in relation to the original diameter [1–3]. This is 18% on average, increasing by 5–6% for smokers [1]. These dilatations can be observed already shortly after grafting, even during the first few days following surgery [4]. Several months after the operation the graft usually ceases to widen or the dilatation is minimal. One study even points to a discrepancy between the actual dilatation and that specified by the manufacturer. It has been additionally noted that the graft diameter further increases immediately after it was implanted, the vascular clamps released and blood flow through the graft re-established. According to the same study, no further considerable dilatation has been registered [5]. Numerous studies have shown that polyester grafts are more prone to dilatation than the polytetrafluoroethylene ones [6]. Further, polyester woven grafts compare less favourably with knitted ones [1, 7], the loose structure of their fibres making them more susceptible to stretching. A minor increase in the graft diameter is clinically asymptomatic and inconsequential.

As opposed to a dilatation in the range of 10–20%, which is probably a common phenomenon, a ten– or a hundredfold diameter increase (as in the above-discussed case where a 100% increase occurred) is much less frequent and may be of considerable clinical significance. The infrequency of this phenomenon may be due to its undervaluation, to other correlated complications obscuring the problem such as, for example, graft thrombosis [2], or to the lack of long-term post-operative care for patients. Graft aneurysms often form many years after surgery. There are known diagnosed cases of aneurysms forming 10, 13 or even 19 years after grafting [8–10]. These patients often produced alarming clinical symptoms such as dyspnoea or stridor (in the case of thoracic aortic graft dilatation) [8], or palpable pulsating tumours within the abdominal area or in lower limbs. A significant percentage of these patients required repeat surgery and a new graft.

The phenomenon of graft dilatation is not easy to elucidate and has not been thoroughly investigated. There are numerous hypotheses, none of which, however, offers an equivocal explanation. It is likely that several factors contribute to graft dilatation and, in some cases, to the formation of aneurysm-like dilatation. Amongst the most frequently listed factors are: faulty manufacturing procedures, inappropriate graft storage and/or sterilisation, intra-operative handling of grafts and microdamage to their fibres, progressive partial degradation of the material of which the graft is made, adaptation of the graft tissue to the environment of the patient’s body, sustained impact of hydrostatic forces and of pulsatile blood flow, external pressure on and irritation of the graft. A hematoma or an abdominal infection may also lead to the degradation of the graft. Finally, the very structure of the graft wall, that is the particularly loose disposition of fibres in woven polyester grafts, may render the graft susceptible to dilatation [1, 2, 6, 8, 9, 11].

Conclusions

The formation of dilatation in vascular grafts is an intriguing yet underrated phenomenon that has not yet been definitely elucidated. Such cases are often reported casuistically.

Given the impossibility of predicting how the graft will perform and to what degree it will dilate, patients bearing grafts require regular and long-term ambulatory monitoring and periodical scans.

The factors potentially responsible for such complications of vascular procedures should be, where possible, eliminated. Patients ought to be encouraged to have a healthy lifestyle, to deal with infections and chronic conditions including hypertension, to quit smoking and to respond early to any worrying symptoms. During surgery the graft should be handled with care, all blood and hematomas within the operating field should be immediately removed and post-operative infections should be prevented.

The question remains how to treat patients in whom a considerable graft dilatation has occurred. What should be the standard procedure in such cases? It seems obvious that symptomatic patients who suffer from various complications ought to be surgically treated. However, what should be done with those in a good general condition and reporting no symptoms? A regular follow up care is an obvious solution. After the graft has reached dimensions that qualify an aneurysm for surgical treatment, an elective operation should be considered, choosing – depending on the conditions and possibilities – endovascular or open surgery.

References

1. Nunn DB, Carter MM, Donohue MT, Hudgins PC (1990) Postoperative dilation of knitted Dacron aortic bifurcation graft. J Vasc Surg; 12: 291–297.

2. Van Damme H, Deprez M, Creemers E, Limet R (2005) Intrinsic structural failure of polyester (Dacron) vascular grafts. A general review. Acta Chir Belg; 105: 249–255.

3. Wilson SE, Krug R, Mueller G, Wilson L (1997) Late disruption of Dacron aortic grafts. Ann Vasc Surg; 11: 383–386.

4. Goëau-Brissonnière OA, Qanadli SD, Ippoliti A, Pistolese GR, Coggia M, Pollock JG (2000) Can knitting structure affect dilation of polyester bifurcated prostheses? A randomized study with the use of helical computed tomography scanning. J Vasc Surg; 31: 157–163.

5. Alonso-Pérez M, Segura RJ, Luján S et al (2001) Knitted Dacron grafts used for abdominal aortic reconstruction: sizing references. Vasc Surg; 35: 457–461.

6. Schroeder TV, Eldrup N, Just S, Hansen M, Nyhuus B, Sillesen H (2009) Dilatation of aortic grafts over time: what to expect and when to be concerned. Semin Vasc Surg; 22: 119–124.

7. Robinson DA, Lennox A, Englund R, Hanel KC (1999) Graft dilatation following abdominal aortic aneurysm resection and grafting. Aust N Z J Surg; 69: 849–851.

8. Attaran S, Field M, Kuduvalli M, Desmond M, Oo A, Rashid A (2010) True aneurysm of a Dacron tube graft 19 years after repair of coarctation of the aorta. Ann Thorac Surg; 90: 1000–1001.

9. Han I, Shigematsu H, Nunokawa M et al (1994) Nonanastomotic aneurysm formation in a Dacron arterial graft: report of a case. Surg Today; 24: 1007–1010.

10. Khaira HS, Vohra H (2002) True aneurysm in a femoro-popliteal dacron graft – a case report and literature review. Cardiovasc Surg; 10: 644–646.

11. Boss A, Stierli P (1993) Dacron prosthesis dilatation. Case report and review of the literature. Helv Chir Acta; 60: 153–156.

Adres do korespondencji:

lek. Jarosław Piotr Miszczuk

Wojewódzki Szpital Specjalistyczny, Oddział Chirurgii Ogólnej i Naczyniowej

ul. Bialska 104/118, 42–200 Częstochowa

tel.: 500 049 861

e-mail: miszczuk25@poczta.onet.pl

Acta Angiol Vol. 20, No. 1 pp. 32–38

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ISSN 1234–950X

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