Patients who received the J&J COVID-19 vaccine (or any adenovirus vector COVID vaccine) can develop Cerebral Venous Sinus with thrombocytopenia. The reason for the pause in vaccination with the J&J vaccine was to determine and disseminate how to treat (especially with anticoagulation) this clotting issue.
Working with Neurology, a guidance document was created for how to treat CVST, with or without thrombocytopenia.
The short version:
For more detail, see this link: Anticoagulation for Central Venous Thrombosis (CVT) / Central Venous Sinus Thrombosis (CVST)