Venous sinus thrombosis after whiplash possible?

Unlikely: Trauma can lead to vascular injuries but thrombosis do the sinus would be unlikely after a minor injury classified as "whiplash".

Unlikely: This is unlikely in an isolated whiplash injury. However, if there is a skull base fracture at the back of the head, it is possible to have a thrombosis of the transverse sinus(a large venous structure). The likelihood of this is greater, the larger the fracture is. With the fracture, there is injury to the underlying transverse sinus which can lead it to clot-ie. Thrombose.

If just whiplash,: Virtually impossible to occur. But if head trauma open or closed head injury, may be a consequence.