A nonagenarian right-handed patient with a past medical history of atrial fibrillation and pulmonary embolism presented with global aphasia, right-sided facial droop, hemianopsia and hemiparesis, with a National Institutes of Health Stroke Scale (NIHSS) score of 22. Review of the patient’s chart revealed a remote contrast-enhanced CT scan performed a few years prior, during which the patient experienced an anaphylactic reaction to iodinated contrast. Given the hyperacute nature of the case, an iodinated contrast-enhanced CT angiogram (CTA) with perfusion imaging of the head and neck was performed under emergency consent. The non-contrast CT of the head revealed evolving infarcts in the left middle cerebral artery (MCA) territory, with an Alberta Stroke Programme Early CT Score of 4 (Supplementary Figure 1). The CTA demonstrated an occlusion in the left distal M1 MCA with good collateral circulation (Supplementary Figure 2). Intravenous thrombolysis was contraindicated due to the patient’s use of a twice-daily direct oral anticoagulant (Apixaban), with the last dose most likely taken within the preceding 48 hours. Following the CTA, the patient developed tachypnea and hypoxia, requiring emergent oxygen therapy and intramuscular epinephrine for an anaphylactic reaction to iodinated contrast dye. A decision was made to proceed with endovascular therapy using intra-arterial gadolinium-based contrast (GBC). Under monitored conscious sedation, an 8-French short sheath was used for femoral access, followed by placement of a BOBBY Balloon Guide Catheter (MicroVention, USA) into the left internal carotid artery. With intra-arterial gadobutrol, digital subtraction angiography (DSA) confirmed an occlusion in the distal left M1 MCA with good collaterals (Figure 1, Supplementary Video S1). A Solumbra technique was performed using a Solitaire 4 × 40 mm (Medtronic, USA) and RED 62 (Penumbra, USA). Complete reperfusion thrombolysis in cerebral infarction-3 was achieved after the first pass (Figure 1, Supplementary Video S2). A total of 50 mL of gadobutrol (Gadavist, Bayer Healthcare, USA), diluted 1:1 in normal saline – approximately 0.93 mmol/kg in this 54 kg patient – was used during the procedure. To minimize contrast administration, DSA runs were restricted to a single intracranial acquisition with the guiding catheter positioned in the cervical internal carotid artery and two post-thrombectomy acquisitions, since the first was compromised by patient motion. The patient experienced no acute or delayed complications. Post-procedure, the patient regained movement in the right extremity, with only mild residual weakness, and had an NIHSS of 3 at discharge to a stroke rehabilitation facility.

Figure 1. Anteroposterior digital subtraction angiography runs with intra-arterial gadobutrol demonstrate a left M1 occlusion (left) and a final TICI (Thrombolysis In Cerebral Infarction) score of 3 after a single pass (right).

Anaphylactic reactions to iodinated contrast are rare, with an incidence of approximately 0.04%. ³ In such cases, intra-arterial GBC has been previously reported for use in endovascular treatment of acute stroke, ^{Reference Male, Mehta and Tore1,Reference Albóniga-Chindurza, Ortega-Quintanilla, Alcalde-López, Zapata-Arriaza and González4} acute coronary syndrome ^{Reference Guragai, Roman and Vasudev5} and acute aortic syndrome. ^{Reference Ganga, Goyal, Ojha, Kumar and Sharma6} However, routine use of GBC in angiography remains limited due to risks, including nephrogenic systemic fibrosis ³ and cardiac arrhythmias, ^{Reference Kalsch, Kalsch, Eggebrecht, Konorza, Kahlert and Erbel7} , especially at high or undiluted doses. Most commercially available GBCs recommend a dose of 0.2 mL/kg or 0.1 mmol/kg, with some exceptions (Table 1), based on data from the US Food and Drug Administration. ^{Reference Food and Administration8} Gadobutrol (Gadavist) has the highest reported maximum dose of approximately 1.5 mL/kg (1.5 mmol/kg), while gadopentetate dimeglumine (Magnevist, Bayer Schering, Germany), now discontinued, had one of the lowest maximum doses at 0.2 mL/kg up to a maximum of 20 mL. In this case, we used 0.93 mmol/kg of Gadavist, while other reports have documented doses ranging from 0.37 to 0.77 mL/kg ^{Reference Albóniga-Chindurza, Ortega-Quintanilla, Alcalde-López, Zapata-Arriaza and González4} to 0.56 mmol/kg, ^{Reference Ganga, Goyal, Ojha, Kumar and Sharma6} without resulting nephrogenic complications.

Table 1. Different commercially available gadolinium-based contrast dyes with their recommended and available maximum reported doses based on publicly available US Food and Drug Authority (US FDA) product labels

We conducted a systematic review, which was not registered in any database (e.g., PROSPERO), using PubMed/MEDLINE with the following search strategy: (“thrombectomy”[Title/Abstract] OR “mechanical thrombectomy”[Title/Abstract] OR “endovascular thrombectomy”[Title/Abstract]) AND (“gadolinium”[Title/Abstract] OR “gadolinium-based contrast”[Title/Abstract] OR “gadolinium-based contrast agents”[MeSH] OR “gadolinium”[MeSH]). This search yielded 26 results. We included case reports or case series that explicitly described the intra-arterial use of gadolinium-based contrast agents during stroke thrombectomy procedures in humans. After screening titles and abstracts, two relevant articles were identified. ^{Reference Male, Mehta and Tore1,Reference Albóniga-Chindurza, Ortega-Quintanilla, Alcalde-López, Zapata-Arriaza and González4} Reference list screening of these articles yielded no additional case reports. In Supplementary Table 1, we summarize the key points of all published case reports. In all three cases, gadobutrol (Gadavist) was used successfully and uneventfully at undiluted doses up to 110 mL. While standard practice encourages minimizing radiation and contrast exposure (iodinated or gadolinium-based), emergent procedures such as endovascular thrombectomy may necessitate higher-than-recommended contrast doses. Given this context, a compiled list of reported gadolinium contrast doses, as shown in Table 1, may be beneficial for neurointerventionalists treating patients with contraindications to iodinated contrast.

In conclusion, intra-arterial gadolinium-based contrast is a viable alternative for emergent endovascular procedures in patients with known hypersensitivity or anaphylaxis to iodinated contrast. While only a few case reports exist, gadolinium-based agents – particularly Gadavist – have been used safely in doses exceeding traditional recommendations.