Multiplicity and Anatomical Distribution of Thrombus in Vaccine-Induced Immune Thrombotic Thrombocytopaenia Following ChAdOx1 nCov-19 Vaccination

Background: A rare prothrombotic syndrome, termed vaccine-induced immune thrombotic thrombocytopaenia (VITT) has been described following administration of the first ChAdOx1 nCov-19 (Astrazeneca) vaccine. Patients present with thrombosis in multiple sites. Targeted imaging is key to diagnosing thrombus in the organ or system of localising symptoms, and early and accurate identification of the extent and multiplicity of occult thromboses in other vascular systems is required to best manage these patients. Methods: We performed a cross-sectional study across the UK to investigate the location, extent and number of thrombi in patients with VITT. All imaging was systematically reviewed by radiologists to determine the presence of cerebral venous sinus (CVST), systemic venous, portal and splanchnic venous (PSV), systemic arterial (SAT) and pulmonary arterial (PE) thrombus. The presenting clinical symptoms and sites of thrombosis were recorded. Results: 40 patients with VITT from seven centres within the UK were included. CVST was the most common diagnosis in 34 cases followed by PE and PSV in 17 and 10 cases respectively. In patients who underwent further screening imaging (30), at least one additional site of thrombosis was identified in 25. 12 patients had radiological evidence of extension of thrombus on repeated imaging during index admission: 8 had progression of known thrombus and 4 with new sites of thrombosis. Conclusions: Patients with VITT are highly likely to present with multiple sites of thrombosis and may develop additional sites and extension of thrombosis after presentation. Moreover some of these thromboses may not be easily discernible through clinical examination. Full body screening contrast enhanced cross sectional imaging may be of value in this patient group.Funding Information: There was no formal funding for this project. Declaration of Interests: The authors do not have any conflict of interests.Ethics Approval Statement: This work is a retrospective audit of data collected as part of routine clinical practice. Formal ethical approval was not required.