I don't think there is a code for this, so you'll have to use an unspecified code or else query the provider for more information. An occlusion of the vein codes to thrombosis, which would lead you to the pulmonary embolism codes, but given the severity of that diagnosis, I would not assign it without first getting further clarification from the provider. Otherwise, my inclination would be to use I99.8 - Other disorder of circulatory system, although I87.9 - Other specified disorders of veins would also work.