The case involves a 49-year-old Malay male who works as a medical health officer with a history of childhood asthma, allergy to seafood and nonsteroidal medication, and single-vessel coronary artery disease treated by percutaneous transluminal coronary angioplasty 3 years prior. He was on dual antiplatelet therapy for a year, followed by 6 months of single antiplatelet drug therapy; subsequently, he became non-compliant. Other than that, he is a nonsmoker, enjoys running (~ 4 km/day), and has a healthy body mass index of 22. The patient received the first dose of subcutaneous mRNA COVID-19 vaccine (EP2163, Pfizer/BioNTech) on March 1, 2021 and reported mild symptoms of soreness at the injection site and myalgia that lasted for 24 h. Sixteen days later (March 17), the patient complained of a new-onset of mild to moderate headache and giddiness, which initially was thought from the exertion of working. The symptom persisted, requiring a hospital visit 5 days later (March 21). The systemic and neurological examinations were unremarkable, while routine laboratory tests for full blood count, coagulation profile, C-reactive protein, and hepatic and renal function tests were normal. Notably, the platelet was 302 × 109/L, international normalized ratio of 0.98 (0.86–1.14), prothrombin time of 13 s (12.6–15.7), activated partial thromboplastin time of 38 s (30–45.8) and D -dimer of 0.2 (reference value, < 0.5).

A noncontrast computed tomography (CT) of the brain showed cordlike hyperattenuation within the left transverse and sigmoid sinus suggestive of cord or dense clot sign (Fig. 1a,b). The patient elected to ignore the radiological finding and persevere with the symptoms. On March 22, he received the second dose of the vaccine (EP9605, Pfizer/BioNTech). Due to unresolved and somewhat worsening symptoms, the patient agreed to CT cerebral venography 2 days later. The finding confirmed a long segment-filling defect and empty delta sign within the superior sagittal sinus (SSS), extending into the torcula Herophili, left transverse sinus, and sigmoid sinus to proximal internal jugular vein (Fig. 1c,d). He was immediately started on therapeutic subcutaneous Clexane (1 mg/kg twice daily) and antiplatelet therapy (clopidogrel 75 mg). The autoimmune test and thrombophilia screening returned normal. The symptoms had gradually improved. Repeated CT cerebral venogram 2 weeks post-treatment shows residual cerebral VST (Fig. 1e). Filling defects within the proximal section of the superior sagittal sinus, left transverse sinus, and left sigmoid sinus were present (Fig. 1f). Opacification were visualized at the distal part of the superior sagittal sinus, torcula Herophili, and left internal jugular vein. Throughout these imaging techniques, no cerebral infarct or edema was seen. Following that, the clexane was switched to apixaban (5 mg twice daily).