Introduction
Splenic artery embolization (SAE) effectively increases hematologic indices in patients with hypersplenism; particularly in patients who are not good candidates for splenectomy.
In addition to cirrhotic liver disease, SAE has been utilized to treat several hematologic, vascular and rheumatologic disorders.
Embolization may be performed alone or in combination with other interventions, such as retrograde transvenous variceal obliteration. ​

Indications
  • Hypersplenism: Large spleen with portal hypertension (e.g. from cirrhosis or portal vein thrombosis), thrombocytopenia (< 60,000) and normocellular bone marrow. Uncommon causes in children include Gaucher disease and biliary atresia.
  • Major sequelae of portal hypertension include GI bleeding and hepatic encephalopathy.
  • Specific portal hypertension related indications include unresponsive hepatic encephalopathy and GI bleeding with splenic vein thrombosis where TIPS may not be effective.
  • Splenic injuries:
    • Hemodynamically unstable patients are often managed surgically (Table 1).
    • Stable patients are evaluated with CT scan.
    • Splenic artery embolization is based on the clinical and imaging findings.
    • In a hemodynamically stable patient, contrast extravasation, presence of pseudoaneurysm or arteriovenous fistula, decreasing hematocrit, active contrast extravasation, AAST III grade or higher injury and large hemorrhagic ascites are indicators for urgent angiography and embolization.

Other less frequent indications
  • Thrombocytopenia from chemotherapy.
  • Thalassemia, sickle cell disease.
  • Hereditary spherocytosis.
  • Autoimmune hemolytic anemia.
  • Idiopathic thrombocytopenic purpura.
  • Idiopathic hypersplenism.
  • Pre-splenectomy.
  • Splenic artery aneurysm.
  • Splenic artery steal syndrome.
  • Refractory ascites.
  • Hypersplenism with leukopenia and/or thrombocytopenia causing intolerance to immunosuppression in renal transplant recipients.
  • Splenic lymphoma, CLL, myelofibrosis, myeloid leukemia.
  • Felty syndrome (rheumatoid arthritis, splenomegaly and leukocytopenia with increased risk of infections and ulcers).
  • Hemodialysis with thrombocytopenia and splenomegaly.
 ​

Contraindication
  • No absolute contraindication.
  • Relative contraindications include hepatofugal flow, severe infection, severe coagulopathy and decompensated liver failure.

Pre-Procedure
  • History including indication and prior procedures.
  • Imaging
    • Abdominal CT or MRI is useful to establish a splenic volume baseline and to screen for portal or splenic vein thrombosis. Alternatively an ultrasound can be used.
  • ​​Splenic volume is measured.
  • ​The planned percent of distal embolization is calculated.
  • The percentage of devascularization formula: % devascularization = 1-(blush area after embolization)/ (initial blush area).

Vaccination
  • SAE and splenectomy may increase the risk of infection by encapsulated organisms including are S. pneumoniae (pneumococcus), H. influenzae, and N. meningitis (meningococcus).
  • Vaccines may reduce the risk of:
    • Pneumococcus Polysaccharide (Conjugate, Polysaccharide Pneumovax 23 at 8 weeks and 5 years)
    • Meningococcus (Conjugate ACWY + Recombinant B +, repeated at 8 weeks, Conjugate ACWY at 5 years)
    • Haemophilus influenzae type b (Conjugate Hib vaccine)
    • Influenza Annually

Medication
Patients on small molecule multi-tyrosine kinase inhibitors with anti-VEGF activity (Sorafenib, Sunitinib and Regorafenib), significantly lymphopenic, or on Avastin: discontinuing these medications should be discussed with oncology. SAE may be considered with 2 weeks of antibiotics.

Anticoagulation
SAE of massive spleen is associated with splenic/portal venous thrombosis. Short-term anticoagulation with 2-weeks of Enoxaparin and antibiotics should be considered.

Labs
  • CBC
  • PT/PTT
  • Liver Function Tests
    • Ammonia, renal function, serum amylase tests.

Technique
  • Consent the patient for
    1. Splenic Artery Embolization
    2. Possible portomesenteric pressure measurement.
    3. Possible paracentesis.
    4. Bilateral thoracentesis and drainage.
    5. Possible embolization/sclerotherapy of GI varices.

Prophylactic antibiotics
  • Risk of infection depends on the extent of ischemia created; 16% when greater than 70% of the spleen is infarcted, as opposed to 3% when 50%–70% of the spleen is infarcted.
  • No consensus on best choice of antibiotics or length of treatment with various protocols for peri-operative prophylaxis.
  • For proximal splenic artery embolization (PSAE)
    • ​Pre-procedural antibiotics: 1-2 hrs before the procedure
    • Post-procedural antibiotics for 5 days: controversial
  • For distal/selective splenic artery embolization (DSAE):
    • Pre-procedural antibiotics: 1-2 hrs before the procedure
    • Post-procedural antibiotics for 5 days.
​
Practical choice of antibiotics for proximal splenic artery embolization (PSAE):
  • Pre-procedural IV Cefazolin or Ceftriaxone 1-2 hrs before the procedure.
  • Post-procedural PO Amoxicillin-Clavulanic acid (Augmentin) for 5 days.

Practical choice of antibiotics for distal partial splenic artery embolization (DSAE):
  • Pre-procedural IV Cefazolin or Ceftriaxone 1-2 hrs before the procedure.
  • Post-procedural IV Cefazolin or Ceftriaxone for 5 days.

General Protocol
  • General Anesthesia, Foley catheter, Prep both groins.
  • Prep abdomen or chest if planning to do paracentesis or thoracentesis.
  • Arterial access via the common femoral, radial or brachial artery.
  • Size of the sheath depends on the embolization technique and agents o Distal splenic artery embolization (DSAE).
  • 5-(or 4) Fr sheath for particles, glue or Gelfoam.
  • 5-(or 4) Fr 0.038” Vertebral, Cobra or MPA catheter to access the splenic artery. Sos or Simmons can also be considered.
​
Proximal splenic artery embolization (PSAE)
  • 5 -6 Fr sheath with or without guiding catheter.
  • Glucagon (for transient reduction of bowel motion during abdominal angiography, particularly the venous phase).
  • Glucagon 10 mcg/kg (max 500 mcg or 0.5 mg) IV given 1 minute before injection. Glucagon can be repeated after 10 minutes.
  • Abdominal aortogram with a sizing 4 or 5 Fr pigtail catheter.
  • Celiac and splenic angiography is performed to evaluate the splenic and hepatic arterial and venous anatomy but also potential collaterals to the spleen, including the left gastric, gastroepiploic and pancreatic arteries.
  • Identification of major pancreatic branches (e.g. dorsal pancreatic artery and greater pancreatic artery) is crucial.
  • ​Coaxial catheter combination (e.g. 4 Fr Vertebral via 5 Fr Envoy) provides additional support.


Proximal splenic artery embolization (PSAE)
In PSAE, embolization is performed distal to the dorsal pancreatic artery. This is equivalent to splenic artery ligation where splenic perfusion is maintained through collaterals. Used frequently for trauma.

Distal splenic artery embolization (DSAE)
  • Superselective distal embolization.
  • For non-traumatic indications such as hypersplenism.
  • Embolization is done with a microcatheter advanced further to distal splenic artery branches. It preserves perfusion to the remainder of the spleen.
  • The middle or lower pole splenic branches are usually superselected due to lower risk of pulmonary complications such as atelectasis, pneumonia and pleural effusion, or pain, which are more common with upper lobe embolization.
  • DSAE may miss bleeds controlled by spasm; may have a higher failure rate, may cause more frequent and larger splenic infarcts.

Embolic agents
  • Polyvinyl alcohol particles: (Contour, PVA) of 500-700 μm or 300- 500 μm or larger. Particles are suspended in contrast 10-20 mL of contrast (or contrast-saline).
  • Tris-acryl gelatin microspheres: (Embosphere) of 500-700 μm or (300- 500 μm or larger sizes).
  • Gelfoam slurry: One Gelfoam pad (2x6x7 cm) is cut into small parts which are then placed into a 10-mL syringe connected via three-way stopcock to a second 10-mL syringe was filled with 10 mL of contrast (or contrast-saline). The mixture is exchanged between syringes only 3-4 times to maintain a coarse consistency.
  • Gelfoam pledgets: One Gelfoam pad (2x6x7 cm) is cut into small parts (e.g. 1x1x5 mm).
  • Amplatzer plugs: (St. Jude): Choose AVP (type 2 or 4) with a diameter 30-50% larger than the artery.

AVP 2
  • Diameter 3-22 mm (Length 6-18 mm), 135 cm wire.
  • Diameter 3-8 mm: ID 0.056”  Diameter 10-12 mm: 0.070”
  • Diameter 14-16 mm: 0.086”  Diameter 18- mm: 0.098”

Sheaths
  • 5-8 Fr sheaths: e.g. 45-cm Flex-or Check-Flo Introducers or Bright-tip sheath. 6 Fr sheath can deliver up to a 12-mm diameter.
  • Envoy Guiding Catheter 90 cm:
    • 5 Fr ID 0.056” (1.4 mm)
    • 6 Fr ID 0.070” (1.8 mm)
    • 7 Fr ID 0.078”
  • The guiding catheter or sheath is advanced into a straight segment of the proximal splenic artery coaxially over the 4-5 Fr catheter.

AVP 4
  • Diameter 4-8 mm (10-13.5 mm). Can be deployed using 0.038” catheter (e.g. 4 or 5 Fr Cobra).
  • AVP is advanced into the proximal third of the splenic artery where it is held in place while catheter is slowly withdrawn.
  • Wait 5 min with the device still attached, then do a contrast test.
  • With complete occlusion, AVP is released.
  • With partial occlusion after 15 min, AVP is released, and a second AVP or coil is added.
  • Completion splenic arteriogram or aortogram is repeated.

Coils
(e.g. 2D Interlock 18 Fibered IDC coils in 2D Helical and Diamond shapes, 2 mm-14 mm with variable lengths).
  • Interlock 18 coils require microcatheter with an inner diameter of 0.021" (e.g. Renegade STC 18 Microcatheter with 3 Fr proximal OD to 2.4 Fr distal tip).

Embolization Volume
  • SAE of 30–70% of the splenic parenchyma is safe. Devascularization of > 70% splenic volume increases complications. Reduced-volume embolization (30%–40%) may decrease morbidity but a second embolization may be needed in 1 month. Between 50 and 70% volume appears to the ideal balance between achieving effect and minimizing complications.
  • The percentage of devascularization formula: % devascularization = 1-(blush area after embolization)/ (initial blush area).

​Figure

Celiac artery angiography visualizing the anatomy of splenic vasculature
Splenic artery angiography (pre-embolization)
Splenic artery angiography (post-embolization using Amplatzer 4 plug and 30 cm Penumbra packing coil) 

Complications
  • Sepsis, splenic abscess, splenic rupture, splenic vein thrombosis, portal vein thrombosis, pneumonia, pleural effusions that require thoracentesis, paralytic ileus and pancreatitis.
  • Pulmonary Complications: include atelectasis, pleural effusion, pneumonia and pleurisy. Typically left sided and can be reduced by avoiding embolization of the upper splenic pole.

Post-Procedure
  • Admission: to the hospital for about 4-6 days for complicated medical history.
  • Post embolization syndrome (fever, left upper abdominal pain, nausea, and anorexia) is very common after DSAE.
  • Pain Control:
    • Patient-controlled analgesia (PCA) to all patients
    • NSAID: Ketorolac
    • IV paracetamol
    • Steroid: Methylprednisolone (Medrol) for rebound pain for 5 days.
    • Intra-arterial 2-chloroprocaine (Nesacaine)
    • Epidural anesthesia
  • Anticoagulation: Consider Enoxaparin (Enoxaparin, 1 mg/kg SC q12hr) for 2 weeks to prevent thrombosis in patients with hepatofugal flow, splenic vein thrombosis, and massive splenomegaly.
  • Incentive spirometry to prevent atelectasis and pneumonia is recommended.
  • Continue prophylactic antibiotics for 5 days.
  • Post embolization syndrome is frequent, with some nausea, loss of appetite, intermittent fever, left upper abdominal pain and leukocytosis. Generally resolving without issues.
  • Prolonged (> days) or high fever (>39), prolonged leukocytosis or severe pain should be investigated promptly with CT scan, CXR and labs including pancreatic enzymes. CT scan should be repeated at low threshold with concerns for splenic abscess, splenic vein thrombosis, pneumonia /pleural effusions and pancreatitis.
  • May consider vaccination according to recommendations for splenectomy if spleen is largely devascularized. Pneumococcal vaccine is ideally given > 2 weeks before procedure or 2 weeks post-procedure.
  • Lifelong antibiotic prophylaxis: Prophylactic antimicrobial therapy is generally recommended for asplenic children younger than 5 years of age and may be considered for older children and adults during the initial 1 to 2 years after splenectomy, with lifelong prophylaxis for persons who have had an episode of postsplenectomy sepsis.

Follow-up
Clinical & Laboratory Follow-up
  • Platelets: Platelet count rises 12-24 h after SAE, peaks at 1 or 2 weeks, stabilizes in 2 months at about 2 times higher than that before SAE and correlates with volume of spleen infarction. Stable may be lower than peak and may remain significantly high for up to 8 years.
  • White blood cell: Transient elevation of WBCs is a normal response after splenectomy. It could be found at POD 1, may reach peak at POD 3. Prolonged elevation of WBCs may imply an infection. After SAE, WBCs increase markedly: around 50% at 1 month and 30% at 6 months.
  • Red blood cells: RBCs destruction occurs almost exclusively in the enlarged spleen. Rise in the RBC count may be found 3 months after SAE, significantly increased at 6 months after the procedure - even up to normal level, remaining increased for up to 7.5 years.
  • Alteration of hemodynamics: SAE improves the local hyperdynamic state in the splenic area in cirrhosis. It may increase hepatic arterial and superior mesenteric blood flow.
  • Reduction of splenic volume: Nonembolized volume can be used to predict the functional outcome of SAE. Spleen will shrink gradually in months. CT scan is the practical method to measure splenic infarction.
  • Improvement in gastric mucosa.
  • Improved liver perfusion and function.
  • Improvement in hepatic encephalopathy.
  • Improvement in hepatopulmonary syndrome.

Imaging Follow-up
  • CT of the abdomen and pelvis with contrast 1 day after DSAE: Evaluate the extent of splenic infarction.
  • Low threshold to repeat CT of the abdomen with concern for splenic abscess.
  • For DSAE, follow-up CT scan at 3-6 months. Further CT as indicated. IR OV in 3-6 months (right after CT scan), can be combined with OVs with GI and surgery if needed.

References
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  2. Madoff DC, et al. Splenic Arterial Interventions: Anatomy, Indications, Technical Considerations, and Potential Complications. RadioGraphics 2005; 25:S191–S211.
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  4. Davis KA, et al. Improved success in nonoperative management of blunt splenic injuries: embolization of splenic artery. pseudoaneurysms. J Trauma 1998; 44:1008–1013; discussion, 1013–1015.
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