NEUROIMAGING / DSA

Balloon Test Occlusion (BTO)

David Goldemund M.D.
Updated on 19/07/2024, published on 29/04/2021

acute internal carotid artery (ICA) occlusion is associated with a high risk of ischemic neurological deficits (20-49%) (Seet, 2012)
- in a meta-analysis of 20 studies of patients with ICA occlusion, the annual risk of stroke was 5.5% (2.1% ipsilateral). Those with hemodynamic compromise on functional imaging had a stroke risk of 12.5% (9.5% ipsilateral)
- the clinical course of ICA occlusion is variable, ranging from asymptomatic lesions to devastating strokes (Klijn, 1997)
a balloon test occlusion (BTO) is performed to determine whether an artery can be temporarily or permanently intentionally occluded without significantly affecting brain perfusion
if the BTO is well tolerated, the risk of subsequent ischemia is significantly reduced, and procedure may be performed
- pharmacologically induced hypotension during BTO further increases the sensitivity of the test
BTO results can be predicted by angiographic findings (CTA, MRA); a small ipsilateral PCOmA, and more significantly, a small AComA (<1.1 mm) can be used to identify patients who are likely to fail BTO (Mendez, 2022)

Indications

functional testing in patients scheduled for ICA occlusion (inoperable aneurysms, glomus tumors, intracranial tumors, tumors in the ENT region)
the Matas test (external CCA compression during angiography) used to be performed; it has been replaced by the more sensitive balloon test occlusion (BTO)

administer allergy premedication (if necessary)
nimodipine 60mg (2 tbl.) every 4 hours can be administered for 24 hours before the procedure to prevent vasospasms
insert a urinary catheter and intravenous cannula
start normal saline solution at 150 mL/h at least 4h before the procedure
ensure the presence of an anesthesiologist for supervision
heparinization during the procedure:
- an initial bolus of HEPARIN 5000 IU IV
- then mix 4mL of Heparin (1ml = 5000jj) + 16mL of NS (20mL solution = 20 000jj) and administer 1-3 mL/h ((1000-3000 IU/h) by IV infusion
- alternatively, additional boluses can be used (1000 to 3000 IU every hour intravenously)
- the target APTT is ~ 2-3x of baseline
flush the distal catheter section above the balloon with normal saline + a low dose of heparin
- 0,5 mL of HEPARIN (500IU) + 500 mL of NS (1mL of solution = 1IU) – via continuous IA infusion 60mL/h (1 IU/min) [Standard, 1995]

the balloon is inflated under fluoroscopic observation, and occlusion is confirmed by a control angiogram
check the neurological status continuously after balloon inflation (continuous verbal dialogue, repeated evaluation of the patient’s muscle strength)
stop the test:
- if neurological deficits develop (BTO if positive)
- if the patient tolerates occlusion for 20 minutes without neurologic deficits (BTO is negative) [Kikuchi, 2014
in addition to a neurological examination, TCCD/TCD monitoring of the MCA may be used [Sorteberg,2008]
- if PSV drops to the max. 65% of baseline, ICA occlusion is safe
- if PSV drops to < 54%, there is an increased risk of hypoperfusion
a 20-minute test with medically induced hypotension may be added
- labetalol IV (bolus 5-20 mg) or sodium nitroprusside (2.5 to 7.5mg/kg/min) are used to lower the mean blood pressure (MAP) to 2/3 of the baseline
- maintain hypotension for ~ 10-20 minutes
- the negative test identifies patients who can safely undergo ICA occlusion with 95% accuracy [Standard, 1995]

extract the balloon after the test is completed
neutralize heparin with PROTAMIN → Neutralization of the anticoagulant drugs
remove the sheath, apply external groin compression or seal the puncture
observe the patient in the ICU for the next 24 hours

assess the contrast filling of ACA (A1-A4 segments) and the MCA (segments M1-M4) on the occluded side (Kikuchi, 2014]
assess the anatomy of the circle of Willis (especially the presence and quality of AComA and PComA, A1 and P1 segments bilaterally)

neurologic complications (due to thrombosis or dissection) : 0-8.3% (average complication rate according to various studies ~ 2.2%) → more here