Enlarged translesional pressure gradient drives recruitment of leptomeningeal collaterals in medically treated patients with symptomatic middle cerebral artery stenosis

Aims: Evolution patterns and contributing factors of leptomeningeal collaterals (LMCs) in symptomatic intracranial atherosclerotic stenosis (sICAS) remain elusive. Methods: Patients with atherosclerotic M1 middle cerebral artery (MCA-M1) stenosis (50%–99%), who were treated medically and had CT angiography (CTA) at baseline and 1 year, were recruited. LMC status was determined by the laterality of distal vessels in anterior and posterior cerebral artery territories in baseline and 1-year CTA. Computational fluid dynamics models were constructed based on baseline and 1-year CTA, to quantify post-stenotic to pre-stenotic pressure ratio (PR) in MCA-M1 lesions. Decreased PR over 1 year indicated enlarged translesional pressure gradient. Results: Among 33 patients (median age 62 years), 18 (54.5%) and 15 (45.5%) had good and poor baseline LMCs; 11 (33.3%) and 22 (66.7%) had good and poor 1-year LMCs. Twelve (36.4%), 16 (48.5%) and 5 (15.2%) patients had worse, similar and better LMCs at 1 year versus baseline. Sixteen (48.5%) patients had decreased PR over 1 year, associated with good LMCs at 1 year (adjusted odds ratio 6.40; p=0.038), independent of baseline LMC status. Conclusion: LMCs may evolve over time in medically treated sICAS patients, when an enlarged translesional pressure gradient may be a driving force.