AVM are challenging conditions that may require emergency intervention when bleeding occurs in high-risk areas in contiguity to the main airway, like face and tongue. To achieve efficient embolization an ideal agent should travel distally from the point of injection and fill the whole nidus of dysplastic vessels, as opposed to occluding the supplying arteries alone (Yakes, 2004).
NBCA-MS is an embolic agent with large evidence of safety and efficacy in this and many other settings (Rosen & Contractor, 2004; Raffi et al., 2007; Pedicini et al., 2017). NBCA-MS is mixed with Lipiodol to make it radiopaque and to adjust its polymerization time. However, mainly due to its rapid polymerization and the inability to blend with other fluids, its behavior may prove unpredictable during injection and cause permanent damage if non-target embolization occurs (Lanza et al., 2014; Li et al., 2005). These risks should be foreseen by the operator and appropriate measures to avoid them should always be put in place. For instance, NBCA has been proven to induce coughing once deployed (Pelz et al., 1995), as it occurred in the present case; the use of deep general anesthesia could have prevented the reported complication, although the routine use of such an approach is not supported by any guideline or position paper. Other potential risk factors for failing the correct delivery of the embolic agent include the early retraction of the microcatheter during injection, lack of operator experience and highly diluted embolic compound.
NCBA-MS has shown several benefits compared to traditional cyanoacrylates and may be preferred for its slower polymerization time, which makes it more flexible. Moreover, the addition of MS has been reported to lower cytotoxic and inflammatory effect due to the milder exoteric traction (Loffroy et al., 2009; Loffroy, 2016).
Recent papers suggest that the deployment of Onyx Liquid Embolic System (Medtronic Neurovascular, Irvine, CA, USA) in an intracranial embolization setting correlates with a lower risk of neurological complications (Choo & Shankar, 2016). It is possible that Onyx’s high manageability due to its viscosity could have theoretically prevented the non-target embolization (Romero et al., 2009). Nevertheless, in an unstable setting of a not paralyzed patient under conscious anesthesia, the same feature could have also led to an early reflux into the common carotid artery during coughing, possibly with even more dramatic consequences considering the non-resorbability of all its components.
After reviewing the literature, where Onyx has been associated with higher costs, longer fluoroscopy times (Velat et al., 2008) and poorer visualization in case of reflux in small arteries (Katsaridis et al., 2008), our group is still endorsing the use of NBCA-MS. To overcome some limitations of Onyx, PHIL (MicroVention, Tustin, California) is a new generation non-adhesive liquid embolic agent comprised of a biocompatible polymer dissolved in dimethyl sulfoxide (DMSO) linked to an iodine agent, triiodophenol, for radiopacity purpose (Vollherbst et al., 2018).
In this adverse event our expectations about the evolution of the neurological status were far from optimistic since we expected permanent brain damage; instead, there was a complete resolution of the initial neurological impairment and radiological findings. This clinical condition, characterized by a NIHSS≤3, MRS ≤ 2 and initial positive DWI findings has been referred as minor stroke (Fischer et al., 2010). We suppose that, as opposed to the major stroke mechanism in which a large embolus blocks a proximal artery, we observed a more scattered and incomplete peripheral arterial embolization, which has probably allowed for compensation from adjacent vessels to take place (Romero et al., 2009). Consistently with the progressive neurological improvement, we may speculate that the majority of the displaced emboli was made of Lipiodol, which was more represented in the compound and is, unlike NBCA-MS, a slowly-resorbable embolic agent (Ethiodized oil - DrugBank, 2019).