1) BRIEF INTRODUCTION:
The most frequent location is the femoral artery,
which is usually damaged due to an iatrogenic cause.
This complication is more frequent nowadays,
due in part to the use of large caliber introducers and the combined anticoagulation and antiplatelet therapy.
Ultrasound is a very useful technique,
not only as a diagnostic tool but also as a guide for percutaneous treatment.
Sometimes treatment is not necessary and we can wait and see if the pseudoaneurysm solves spontaneously.
Most visceral pseudoaneurysms (which are very rare) will need treatment because of their high mortality risk.
They appear in the following locations in frequency order: hepatic artery,
splenic artery and other arteries such as the superior mesenteric artery,
gastroduodenal artery,
pancreaticoduodenal artery and renal arteries.
The diagnosis is usually made by CT,
conventional angiography or MRI.
There are different percutaneous therapeutic possibilities depending on the location and characteristics of the lesion.
Coils,
gelatin sponges,
liquid polymer embolization,
and stent placement are often the first line therapy for visceral pseudoaneurysms.
2) IMAGING FINDINGS:
2.1.
General feature:
- Rounded structure with flow inside that depends on an artery and that may have internal thrombus,
surrounding hematoma or peripheral calcification.
2.2.
US:
- Grayscale:
- Anechoic cystic structure adjacent to the artery (this feature is also present in other entities such as cysts,
seromas or hematomas).
[ Fig. 9 ]
- We can also study:
- Its pulsatility.
- Size of the sac.
[ Fig. 10 ]
- Lobes.
[ Fig. 11 ]
- Communicating neck between the artery and the pseudoaneurysmal sac [ Fig. 15 ].
- Neck (length and width). [ Fig. 10 ]
- Presence of: septa; a thrombus inside the pseudoaneurysm (intermediate or hypoechoic echogenicity) [ Fig. 12 ]; surrounding hematoma.
- US Doppler:
- "Ying-yang" sign: it consists of the presence of a turbulent flow inside the pseudoaneurysm (this can also be seen in saccular aneurysms).
[ Fig. 13 ]
- The hallmark in the diagnosis of pseudoaneurysms is the demonstration of a neck between the sac and the artery with a blood flow that goes from one side to the other ("to and fro"). The component "to" represents the blood flow that enters the pseudoaneurysm in systole,
while the component "fro" represents the blood flow that leaves it during diastole.
[ Fig. 14 ]
Disadvantage: difficulty in assessing deep (visceral) arteries or vessels in trauma patients with fractures and bruises.
It is also limited in cases of obesity,
gas interposition and arteriosclerosis.
2.3.
Angio-CT [ Fig. 3, Fig. 4 ]:
- Unenhanced CT:
- Low-attenuation rounded structure arising from the donor artery.
- Intermediate or high attenuation (chronic or acute haemorrhage) adjacent to the pseudoaneurysm indicates pseudoaneurysmal rupture.
- Well-delineated wall (except in mycotic pseudoaneurysms: thickened,
irregular or ill-defined wall).
- Contrast-enhanced CT:
- Contrast material-filled sac (probably partially filled due to partial thrombosis).
- The donor artery is adjacent to the pseudoaneurysm.
Their communication may be seen.
Cuts of 1-3 mm can help detect small pseudoaneurysms or pseudoaneurysms inside vascular organs (e.g.
spleen).
They can show complications: interval growth,
rupture (extravasation persists while in uncomplicated PSA a wash-out in late phases occurs) and mass effect.
Advantages:
- It is not operator dependent.
- Short acquisition time.
- It can help detect associated injuries or diseases (such as pancreatitis) [ Fig. 3 ].
- Surgical planning can be obtained from the axial images.
- It can provide a global perspective on the entire vasculature (unlike conventional angiography).
[ Fig. 16 ]
- The 3D reconstructions improve the splenic artery’s evaluation,
being able to distinguish tortuous veins of aneurysms/pseudoaneurysms.
Disadvantages:
- Imaging artifacts (bullet fragments,
metal objects).
- Inferior spatial resolution than conventional angiography: limited detectability of subtle anomalies.
- Difficult to differentiate between pseudoaneurysms and true aneurysms in small visceral arteries.
- More contrast material needed than in angiography.
- Endovascular therapy cannot be performed at the time of diagnosis (unlike conventional angiography).
2.4.
3D gadolinium-enhanced MR angiography:
Advantages:
- Allows visualization of a lesion in any projection.
- Contrast material or ionizing radiation is not necessary.
- Axial spoiled gradient-echo or spin-echo T1-weighted axial sequence allows the visualization of intraluminal thrombus and the sac size evaluation.
Disadvantages:
- Long acquisition time.
- Not useful in trauma setting.
- Motion artifacts.
- Metallic artifacts (surgical,
orthopedic,
pacemakers).
- Claustrophobia.
- Vessel tortuosity.
- Turbulent flow.
- Pulsatility.
2.5.
Conventional angiography:
- Although conventional angiography remains the standard of reference for the diagnosis of PSA,
non-invasive diagnostic methods should be considered for initial diagnosis.
- It allows a real-time hemodynamic assessment of a particular vascular bed,
allowing the identification of collateral vessels to evaluate the expendability of the donor artery (important in treatment planning).
- It can detect pseudoaneurysms that have not been identified with other techniques.
- It can differentiate lesions that have a similar appearance at CT such as arteriovenous fistulas or vascular malformations.
Main disadvantage: it is an invasive technique that associates complications (pseudoaneurysms,
hematomas,
arteriovenous fistulas,
distal embolization,
arterial spasm,
ischemia,
intimal dissection and vessel thrombosis).
Other disadvantages: use of ionizing radiation and iodinated contrast material.
Differential diagnosis:
- Tortuous vessels.
- Hyperdense and small intrapancreatic tumors (pancreatic islets tumor).
- True aneurysms.
It is essential for the diagnosis of the pseudoaneurysm to take into account the clinical context:
Visceral pseudoaneurysms may resemble true aneurysms,
but there is a number of features that should make us think more about the first option: more irregular margin,
surrounding hematoma,
clinical context (true aneurysms are usually incidental findings while pseudoaneurysms are usually present in patients with acute trauma or a large volume of abdominal procedures).
3) TREATMENT:
3.1.
When should we treat them?
There is no consensus about this,
but:
- Some pseudoaneurysms may spontaneously thrombose,
but there is no way to predict it.
- High rupture risk groups: the pregnant woman or in pregnant age,
patients that have undergone a liver transplant,
patients with cirrhosis or portal hypertension.
- All complicated pseudoaneurysms should be treated.
In non-complicated pseudoaneurysms we have to evaluate: size,
symptomatology,
comorbidities, and the anatomical location:
- In the case of post-catheter iatrogenic pseudoaneurysms,
it should always be treated when:
- Diameter > 3 cm.
- Sac growth / Symptomatic / Not resolved in a prudential time.
In our Centre,
all of them are treated,
regardless of its size,
if an anticoagulation reversal is acceptable temporarily.
- In the case of visceral pseudoaneurysms,
the risk of spontaneous ruptures is very high regardless of its diameter,
associating a very high mortality.
That’s why treatment is always recommended,
regardless of its size.
Even so,
they would be indications of treatment:
- Diameter > 2 cm.
- Sac growth / Symptomatic / Not resolved in a prudential time.
- Splenic/renal pseudoaneurysms in pregnant women (due to the high risk of ruptures in the 3rd trimester).
- Mesenteric pseudoaneurysms (due to their high risk of complications in the case of rupture,
thrombosis or embolization).
3.2 When shouldn’t we treat them? TREATMENT CONTRAINDICATIONS:
- Relative contraindications (could be corrected): alterations of coagulation,
sepsis,
renal failure.
- Presence of a vascular communication of the pseudoaneurysm with vital structures.
- Contraindication for treatment with a percutaneous injection of thrombin: difficult access to the lesion (poor visualization),
infection,
wide neck of the pseudoaneurysm [ Fig. 17 ],
and arteriovenous fistula.
3.3.
What are the most appropriate treatments?
The selection of the therapeutic option will depend on the location,
risk of rupture,
clinical symptoms,
and comorbidities.
A) INTERVENTIONAL TECHNIQUES:
A1.
Eco-guided compression:
- Mainly performed in pseudoaneurysms of extremities.
- Description of the technique: the compression is performed with the ultrasound probe with direct and continuous visualization of the vessels and the flow behavior with the Doppler.
- Compression point: It is done on the neck of the pseudoaneurysm.
If it is not visible or accessible,
it is directly done on the pseudoaneurysm itself.
- Degree of compression: it must be energetic enough for the flow inside the pseudoaneurysm to disappear,
but to allow arterial flow in the adjacent vessels.
- Time: an initial period of 10-20 minutes.
These cycles can be repeated up to a total period of 1 hour.
- Technical considerations:
- The success of the procedure decreases if the patient is anticoagulated.
If possible,
anticoagulation should be stopped.
- Other factors to consider that affect the technical success are obesity,
the pseudoaneurysm’s size (> 4cm),
aneurysmal neck at the inguinal / suprainguinal level and evolution time superior to one week (chronic).
- The compression can be extremely painful,
so it is advisable to administer analgesics.
A2.
Intra-aneurysm thrombin injection:
- It is the technique of choice for accessible PSA.
The success rate of the procedure decreases substantially if the patient is under anticoagulating treatment.
- Description of the technique: it consists of the percutaneous injection of thrombin inside the sac guided by ultrasound,
being able to use maneuvers to control the blood flow inside the aneurysmal sac/neck.
The end of the needle is placed as far as possible to the neck of the pseudoaneurysm.
The thrombin is injected continuously,
with US monitoring,
until the beat inside the sack ceases.
Then,
US-Doppler confirms the absence of flow inside the sack.
[ Fig. 18 ]
- Other substances such as NBCA (N-butyl 2-cyanoacrylate) can also be used.
This glue can cause adhesion to the tip of the catheter to the arterial wall.
- Pathophysiology: thrombin converts inactive fibrinogen into fibrin and produces pseudoaneurysm thrombosis.
Under conditions of normal blood flow,
the clotting factors (which are activated by minimal endovascular trauma) are removed from the site of trauma by blooding flow and are inactivated by the liver or by natural thrombolytic mechanisms.
However,
when there is relative blood stasis (as in PSA),
activated clotting factors such as thrombin are less washed away,
facilitating the thrombus formation.
- Injected amount: a concentration of 1000 U/ml is usually used.
Low concentrations of 100U / ml can also be used.
- Material: 21G intramuscular needle (4 cm long).
- Time: Thrombosis of the pseudoaneurysm is achieved in about 10 seconds with very small volumes of thrombin (0.5-1 ml).
- Technical considerations:
- Thrombin should not be injected into the neck because of the risk of distal embolization.
It is necessary that there is a narrow and controllable aneurysmal neck so that there is no thrombin leakage.
- If we see flow inside the neck we will have to perform a check in 24 hours to see if it has thrombosed (which is what usually happens).
[ Fig. 19 ]
- We should look at pulses before and after the procedure.
- The success rate of this technique is superior to echo-guided compression even if the patient has anticoagulant and/or antiplatelet treatment.
- In cases of difficult flow control inside a pseudoaneurysm,
this technique can be combined with a pseudoaneurysmal neck occlusion (angioplasty balloon,
embolization with coils).
- Precautions to consider:
- Verify that the patient has no allergy to thrombin (skin test).
- Verify that the patient does not have an arteriovenous fistula associated with the pseudoaneurysm.
- Analyze the possible risk in patients with critical ischemia or infection of limbs if complications occur.
A3.
Endovascular techniques:
- The goal is to exclude the pseudoaneurysm from circulation.
- Description of the technique: two techniques are used (they can be combined): embolization and stenting.
- There are 4 possible scenarios (according to the location of the pseudoaneurysm) which depend on whether the artery in which it sits is dispensable or not:
- Dispensable artery,
without collateral circulation: Embolization of the afferent artery.
[Fig 20c]
- Dispensable artery,
with collateral circulation: proximal and distal embolization (to avoid the re-entry of blood into the pseudoaneurysm through collaterals).
[Fig 20d]
- Essential artery,
with a secure pseudoaneurysmal neck (narrow): Selective embolization of the pseudoaneurysmal sac with conventional or controlled release coils.
[Fig 20b]
- Essential artery,
with a pseudoaneurysmal neck difficult to control (wide): Selective embolization of the pseudoaneurysmal sac with controlled release spirals.
Variants of the technique:
- Covered stent [Fig 20e]: they require an accessible vessel segment,
straight vessels segments and parameters that are appropriate to the commercially available covered stent.
It may not be feasible to place a stent in special cases such as vascular tortuosity or distal location.
- "Remodeling" with an uncovered stent or temporary occlusion balloon [Fig 20f]: it consists of the placement of these devices prior to the release of the coils,
with the aim of avoiding the migration of the coils to the artery,
due to the high risk of migration through the wide neck of the PSA.
Fig. 21: Endovascular techniques algorithm.
Fig. 20: Different pseudoaneurysms treatment possibilities. (a) Percutaneous or intravascular injection of cast-forming agents. (b) Selective embolization of the aneurysmal sac (sac-packing technique) in an essential artery with a narrow neck. (c) Embolization of the afferent artery in a dispensable artery without collateral circulation. (d) Proximal and distal embolization of the parent vessel (sandwich technique) in a dispensable artery that presents collateral circulation. (e) Covered stent excludes the pseudoaneurysm (with a wide neck) in an accessible, straight and essential artery (if the parameters of the commercially available covered stent are adequate). (f) An uncovered stent is placed prior to the release of coils to the pseudoaneurysm (with a wide neck) in an essential artery.
B) REGARDING THE SURGICAL TREATMENT:
- There are certain entities that make surgical repair difficult and greatly increase the associated morbidity and mortality,
impeding the performance of the surgical technique.
- Although it has been the gold standard in the treatment of pseudoaneurysms,
it remains of choice in cases in which percutaneous treatment has failed,
PSAs with a mass effect that causes ischemia/inflammation of limbs/neuropathy,
and in infected PSAs.
- It includes bypass resection,
arterial ligation,
and partial or total organ removal.
- It has a high morbidity and mortality compared with minimally invasive techniques.
- Associated complications: bleeding,
infection,
lymphocele formation,
radiculopathy,
perioperative myocardial infarction,
and death.
3.4.
What are the complications associated with the treatment?
A1) Eco-guided compression:
- Venous thrombosis.
- Necrosis of the skin.
- Local arterial thrombosis and distal embolization.
- Rupture of the pseudoaneurysm.
A2) Percutaneous thrombin injection:
- Distal arterial thrombin thromboembolism:
- Small PSA usually asymptomatic and spontaneously lysed.
- Minor symptoms: Heparin.
- Symptoms of severe ischemia: Angiography.
If the suspicion is confirmed: aspiration thrombectomy + intra-arterial thrombolysis.
If not enough: add surgical exploration.
- Venous thrombosis.
- Allergic reaction (urticaria and anaphylaxis).
- Cellulitis,
abscess.
- Rupture.
A3) Endovascular techniques:
- Arterial embolization due to spiral migration (ischemia-infarction).
- Arterial thrombosis.
- Rupture of the pseudoaneurysm:
- Early (by manipulation).
- Late (recanalization of an embolized aneurysm through collaterals).
- Abscess-sepsis.