Type II endoleak in Thoraflex hybrid stent-graft for frozen
elephant trunk operation
Introduction
Type II endoleaks after hybrid stent grafts for frozen elephant trunk
operation have been rarely described.
Case Report
A 55 year old hypertensive woman presented 6 years ago with an
uncomplicated Stanford type B acute aortic dissection (SVS/STS acute
type B3,10) managed conservatively. Follow up CT scans
showed progressive aneurysmal dilatation of zone 3 (63mm) and zone 4-10
(47mm) with retrograde extension into arch (non A-non B extension in
Stanford type B, SVS/STS chronic type B2,10)(Fig 1A).
She was asymptomatic but had strong family history of sudden death (no
connective tissue disorders).
She underwent a frozen elephant trunk (FET) operation with 26/28F, 150mm
hybrid stent graft (Thoraflex THP2628X150B, Vascutek, Inchinnan,
Scotland) with uneventful recovery. Postoperative scan (day 7) confirmed
false lumen obliteration around stent-graft, good placement and distal
seal of endostent (Fig 1B). She represented 1 month later with
breathlessness and anemia (haemoglobin 88 gm%). CT scan showed large
zone 2/3 collection (Fig 1C, 1D) with contrast extravasation between the
aortic wall and stent endograft with type IIa endoleak (retroleak from a
large 3rd intercostal artery)(Fig 2,3).
She was managed conservatively and remained stable. Subsequent serial
scans showed no extravasation, stable size and thrombosis of the sac.
Comment
There is emerging expert consensus for concurrent single stage
stabilization of arch and ‘downstream’ dissected aorta with hybrid stent
grafts (1). Endoleaks with stent grafts after FET have not been
extensively reported or characterized. Type 1b endoleaks (distal stent
leaks) are the most commonly described. Leuhr reported 11% incidence of
endoleaks (not classified) in a European multicentre study (2). Kandola
et al reported 10/36(28%) endoleaks in their experience of single stage
FET with Thoraflex device over a 10 year period. Only one (2.7%) was a
type 2 endoleak that did not cause sac expansion and was managed
conservatively (3). Similarly, stent graft induced new entry (SINE)
endoleaks have not been extensively reported or characterized after FET.
The reported incidence of distal SINE after thoracic endovascular
aneurysm repair (TEVAR) is up to 25%. They are due to excessive
oversizing (>10%) of the distal stent graft relative to
the true lumen of the chronic dissection. These are usually asymptomatic
and discovered on routine surveillance imaging.
Classification and reporting of endoleaks after stent grafts in aortic
dissection are distinct from those after endovascular interventions in
non-dissected aortas due to the presence of the stent graft in the true
lumen and the additional false lumen (4). A type II endoleak is a
retroleak into the space between the stent graft and the aortic wall
(IIa – single vessel, IIb – two or more vessels). This extravasation
can further extend into the false lumen from a fenestration between
false and true lumens of the dissected aorta with resultant
pressurization, sac expansion and rupture. In hybrid stent grafts (i.e.
Thoraflex), the retroleak can potentially occur from a bronchial or
intercostal artery that branch off from the proximal descending thoracic
aorta.
Sizing for hybrid stent grafts in chronic dissections remains
contentious but is largely guided by experience from TEVAR. Generally a
10% oversize for the distal luminal diameter and a 3cm distal landing
zone for a good seal is considered optimum. The proximal seal in FET is
provided by the cuff anastomosis and is of little concern for type 1a
endoleaks. For a small true lumen in dissected aorta however, even
slight oversizing may rupture the dissection membrane at the distal end
and an undersized middle of the stent graft may not completely
obliterate the dilated aortic sac. Unlike open repair where large feeder
aortic branches are closed directly, these vessels continue to feed the
low pressure sac with retrograde flow (with potential gradual
pressurization and expansion of the sac). The natural history in FET
usually is a gradual thrombosis and obliteration of the false lumen in
over 90%. An intraoperative open aortoscopy before stent graft
deployment can potentially identify large aortic branches in the
descending thoracic aorta (5).
Indications for operation are persistent extravasation with sac
enlargement after failure of conservative management. The enlarging sac
may compress/stretch surrounding structures pulmonary arteries, airways,
recurrent laryngeal nerve and cause erosion or perforation.
Identification of feeding inflow vessels and characterizing endoleak
type is possible with digital subtraction and dynamic computed
tomography angiography. Access to these vessels is difficult as they
open between the stent graft and the aortic wall. TEVAR and direct
ostial embolization are not possible due to problems with access.
Percutaneous transthoracic sac embolization and open surgery or
conservative follow up may be the only options.
There is very limited experience of managing endoleaks after FET (6).
Treatment remains challenging and most experience is from endovascular
aortic aneurysm repair (EVAR) and TEVAR. In EVAR, they are common but
mostly benign. Akmal et al in a review of 6 EVAR studies reported
overall technical success rates of 17-100% with translumbar,
transarterial, and transcaval embolization approaches with various
agents (7).
Prophylactic feeder vessel embolization prior to EVAR is a promising
treatment with limited experience. Rokosh et al reported significantly
greater mean reduction in the maximum aortic diameter (0.69 vs 0.54 cm;
P = .006), with a greater proportion experiencing sac regression of ≥5
mm (53.5% vs 48.7%) at mid-term follow-up (14.6 ± 6.2 months) (8). The
reintervention rates were similar without prophylactic embolization even
though it was a significant independent predictor of sac regression
(odds ratio, 1.34; 95% confidence interval, 1.04-1.74; P = .024). This
approach is fraught with risks of perforation, rupture and spinal cord
ischemia in the setting of an acute aortic dissection. There are also
logistical problems of operating in hybrid theatres and need for
emergency interventional radiology services.
Type 2 endoleaks after FET may be seen more often as worldwide
experience with hybrid stent grafts continues to increase.
References
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during acute type A aortic dissection repair. J Thorac Cardiovasc
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repair of aortic aneurysms: How to reduce the incidence of endoleak
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Figure Legends -
Figure 1 – Progression of the initially stable Stanford type B to non
A-non B with retrograde extension into arch and increasing dilatation of
zone 2/3 in contrast CT scans of the chest (A – preoperative sagittal
scan, B – immediate postoperative sagittal scan at 1 week showing false
lumen obliteration around the stent. C – coronal scan and D – axial
scan at 1 month showing increase in size). ThF – Thoraflex hybrid stent
graft, TL – true lumen, FL – false lumen.
Figure 2 – Sagittal CT scan of the chest showing the large intercostal
feeder vessel (white arrow).
Figure 3 – 3D reconstruction of the thoracic aorta showing the large
intercostal
feeder vessel for type IIa endoleak (red arrow).