In some examples, an aspiration catheter system includes an outer catheter and an inner catheter configured to be positioned within the outer catheter lumen, and an alignment element. The outer catheter defines an outer catheter lumen and an outer catheter distal opening. The inner catheter defines an inner catheter lumen, an inner catheter distal opening, and a plurality of sidewall openings proximal to the inner catheter distal opening. The alignment element is configured to indicate a predetermined position of the inner catheter relative to the outer catheter when the inner catheter is received within the outer catheter distal opening. When the inner catheter is at the predetermined position, at least one sidewall opening of the plurality of sidewall openings remains positioned within the outer catheter lumen and at least one other sidewall opening of the plurality of sidewall openings is positioned distal to the outer catheter distal opening.
