The effect of small filler bolus on intravascular pathways. In the small bolus condition (<0.1 mL), a small amount of filler is carried downstream by blood flow. This may cause limited obstruction that can be bypassed via abundant collateral vessels, unless the region is known to have restricted collaterals (eg, the glabellar region). The clinical effect seen will depend on the presence or absence of adequate collateral circulation in the target tissues.