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Growth of abdominal aortic aneurysm after endoluminal repair
(Portuguese PDF version)

Ricardo Aun,1 Glauco Fernandes Saes,2 Adriano Tachibana,2 Alex Lederman,2 Hilton Waksman,2 Fernando Tavares Saliture Neto,2 Otávio Ninomiya2

1.Director of the Centro Paulista de Cirurgia Vascular, São Paulo, SP, Brazil.
2.Physician, Centro Paulista de Cirurgia Vascular, São Paulo, SP, Brazil.

Correspondence:
Centro Paulista de Cirurgia Vascular
Av. Albert Einstein, 627, 11° andar, Sala 1109
CEP: CEP 05651-901 - São Paulo, SP, Brazil
Phone: +55 (11) 3742.1365/3742.5117/3747.3109
Fax: +55 (11) 3747.3507
E-mail: aun@einstein.br or aun@uol.com.br

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ABSTRACT

The authors report a post-operative aneurysmal sac growth with no endoleaks presence. Low pressure inside the aneurismal sac was observed. Possible causes for dilation and treatment are discussed. The original endoprosthesis was maintained with surgical sac reduction.

Key-words: abdominal aortic aneurysm, bleeding, surgery.

J Vasc Br 2004;3(4):387-91

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While endoluminal stent-graft repair of abdominal or thoracic aortic aneurysms appears effective in the short-term, it is a relatively new procedure and the long-term success of the grafts is still uncertain; only very few cases have reached a survival rate of more than four or five years. Endoleaks and growth of the aneurysm diameter are two of the most serious and frequent complications of endoluminal grafts. It must be noticed that the aneurysm growth may occur even when no leak is detected by usual imaging, especially computed tomography scans, ultrasound, magnetic resonance and arteriography.

The expansion of the aneurysmal sac after an endovascular repair may be delayed, even if it presented initial regression in the short-term. Two methods can be used to monitor pressure inside the aneurysmal sac, one is the direct intraoperative approach by translumbar puncture, the other is the selective cannulation of the branches of the inferior mesenteric artery. Other methods under development consist of sensors implanted with the stent graft. All these methods and theories are still not enough to explain the cases developed with aneurysmal growth. In the case we report here, there was no association between increased aneurismal volume and increased aneurysm sac pressure, for example.

CASE REPORT

An 80-year-old patient with a 7,6 cm diameter aneurysm in the infrarenal abdominal aorta underwent endoluminal repair with a bifurcated Excluder® endoprosthesis. During computed tomography scan monitoring performed at every 6 months, an aneurysm growth was detected with no evidence of endoleaks. After 3 years, the aneurysm diameter reached 11 cm but remained asymptomatic up to three months ago, when the patient reported continuous and moderate pain in the gastric mesentery and left flank. Another tomography scan was required and revealed that the diameter had na increase to 12.5 cm. On physical examination, the patient presented with a visible abdominal distension (Figure 1); there was a palpable non-pulsatile mass without murmur or thrill in the vascular paths, and strong pulses were felt in all segments. Arterial pressure was 130 x 190 mmHg, heart rate 78 bpm and respiratory frequency 14 ipm.

Figure 1 - Evident abdominal expansion due to a non-pulsatile and non-painful mass on palpation

Computed tomography scans requested are shown in Figures 2 and 3.

Figure 2 - Computed tomography scan of the abdomen showing an enlarged aortic aneurysm after treatment with the Excluder® endoprosthesis, which remained patent, and the interior of the aneurysmal sac with thrombosis. October 11th, 2001. Anteroposterior diameter 8 cm.

Figure 3 -Computed tomography scan of the abdomen with evident volume increase and no evident endoleak. Note the density difference between image A and the rest of the aneurysmal sac B. May 6th, 2004.

The patient was submitted to an open surgery for endoluminal stent-graft withdrawal and aneurysm repair. The aneurysmal sac was approached retroperitoneally with an oblique incision on the left. When opened, it revealed no pulsatile wall motion and was deformable on palpation. There was no need for aortic clamping because the aortic neck had already been dissected.

The aneurysmal sac pressure, measured with a Jelco® 16 puncutre needle, revealed to be 15 mmHg below the patient's mean blood pressure (97 mmHg at the moment of puncture).

Figure 4 - Exposure of the aneurysm by left extraperitoneal approach and aneurysmal sac puncture.

We proceeded with the aneurysmal sac opening and emptying, no bleeding and a large amount of serosanguinous fluid were detected (Figure 4), but there was no sign of infection. The stent-graft was fully covered by thrombi and jelly-like material (Figure 5).

Figure 5 - Intraoperative aspect of the aneurysmal sac showing the graft completely covered by thrombi and jelly-like material.

The edges of the aneurysm were overlapped and closed with an interrupted mattress suture, as shown in Figure 6.

Figure 6 - Final aspect and closure of the aortic native wall with intermittent mattress suture.

The biochemical, cytological and bacterioscopic test results revealed a transudate fluid whose components are presented in Table 1.

Table 1 - Biochemical and cytologic elements of the aneurysmal sac internal fluid

Test	Dosage
Amylase	39 mg/dl
Glucose	119 mg/dl
Creatinine	1.1 mg/dl
Urea	46 mg/dl
Protein	8.4 mg/dl
Cholesterol	585 mg/dl
Triglycerides	332 mg/dl
Erythrocytes	1,030,000 cel/mm³
Leukocytes	5,400 cel/mm³
Neutrophils	cel/mm³
Eosinophils	cel/mm³
Lymphocytes	cel/mm³

No bacterial increase was detected after 72 incubation hours. In the third postoperative period the patient was discharged from hospital asymptomatic. Currently, he is on the 60^th postoperative day with no complaints and totally recovered from the aneurysm. Imaging monitoring shows the prosthesis attached to the wall

DISCUSSION

The case we report here brings into light some important concepts of the endovascular abdominal aortic aneurysm repair, which start to appear as the technique becomes more widely known.

The first one is that the abdominal aortic aneurysm may have a continued growth after repair, even if no endoleak is detected.

Second, the aneurysmal sac may have a delayed growth after endovascular repair, even if it had an initial regression after surgery, and third, the repressurization of the aneurysmal sac may contribute to its growth, however this can happen with low internal pressures as well.

Because of these potential problems, it is mandatory that all patients who have undergone abdominal aortic aneurysm repair be monitored with an ultrasound, angiotomography and arteriography scans to detect endoleaks in the postoperative period. After leaks are excluded, the aneurysmal sac pressure measurement can be measured with direct approach by translumbar puncture or selective cannulation of the branches of the inferior mesenteric artery, besides the intraoperative direct puncture of the aneurysmal sac.

White et al.¹ reported three cases of successful endovascular aortic aneurysm repair that developed aneurysmal sac growth in the 18^th postoperative month. An increase in the internal pressure of the aneurysmal sac was detected. Another report, by Lin et al.,² described an increase in the aneurysmal sac size found in the late follow-up of three patients who had presented initial regression in the aneurysm diameter after endovascular repair.

The mechanism responsible for increasing the aneurysmal sac pressure after endovascular repair is still unclear. Some theoretical studies discuss possible causes, like:

a) direct transmission of the stent-graft lumen pressure to the sac;^1,3,4
b) low flow leak paths;²
c) proteolytic degradation of the clot, which makes the aneurysmal sac wall thinner;
d) pressure transmitted through the graft wall associated with the porous graft coverage would lead to the production of fluid and serous transudate fluid.⁵

The aneurysmal sac enlargement can be divided into five categories^1,6,7 based on causative factors (see Table 2).

Table 2 - An overview of the main theories that try to explain the aneurysmal sac expansion in the absence of endoleaks

Factors	Causes
I - Pressure transmitted to the aneurysmal sac by the external limits of the graft	thrombus-proximally placed thrombus layer between the prosthesis and the wall low flow leak path, intermittent or sealed by thrombu
II - Pressure transmitted through the graft wall	graft porous material transudate fluids the graft wall is pulsatile
III - Pressure transmitted by collaterals	thrombi in the inferior or lumbar mesentery artery
IV - Pressure resultant from an accumulation of aneurysmal sac fluid	fibrinolysis of thrombus/hygroma graft infection enzymathic activity
V - Aneurysmal sac enlargement without increased pressure	weakening of the aneurysmal wall by enzymathic activity genetic modulation growth factors infection

Based on Dubenec et al.⁶.

There is little information about which would be the best therapeutic approach to the aneurysmal sac enlargement. Some alternatives are:

a) conservative treatment monitored with imaging examinations; b) conservative treatment with measurement of the internal pressure of the aneurysmal sac; c) conventional surgical approach; and d) secondary endovascular treatment.

In the case reported, after the internal pressure of the aneurysm and the site of the stent-graft were detected, we opted for reducing the aneurysmal sac volume by remodeling it, with no graft replacement. We believe that increased enzymathic proteolytic activities inside the aneurysmal sac may damage its wall and thereby promote the aneurysmal growth. This hypothesis, however, needs further confirmation studies, as we did not performed specific examinations yet.

REFERENCES

1. White GH, May J, Petrasek P, Waugh R, Stephen M, Harris J. Endotension: an explanation for continued AAA growth after successful endoluminal repair. J Endovasc Surg 1999;6:308-15.

2. Lin PH, Bush RT, Katzman JB, et al. Delayed aortic aneurysm enlargement due to endotension after endovascular abdominal aortic aneurysm repair. J Vasc Surg 2003:38:840-2.

3. Meier GH, Parker FM, Godziachvili V, Demasi RI, Parem FN, Gayle RG. Endotension after endovascular aneurysm repair: the Ancure experience. J Vasc Surg 2001;34:421-7.

4. Parodi JC, Berguer R, Ferreira LM, La Mura R, Schermerhorn ML. Intra-aneurysmal pressure after incomplete endovascular exclusion. J Vasc Surg 2001;34:909-14.

5. Williams GM. The management of massive ultrafiltration distending the aneurysm sac after abdominal aortic aneurysm repair with a polytetrafluoroethylene aortobiiliac graft. J Vasc Surg 1998;28:551-5.

6. Dubenec SR, White GH, Pasenau J, Tzilalis V, Choy E, Erdelez L. Endotension: a review of current views on pathophysiology and treatment. J Cardiovasc Surg 2003;44:553-7.

7. White GH. What are the causes of endotension? J Endovasc Ther 2001;8:454-6.