Using MRI angiography, sinus thrombosis was diagnosed in a 42-year old
female patient who had been treated with intravenous heparin for 18 d
ays because of a symptomatic stenosis of the internal carotid artery.
Moreover, thrombosis was also found in both the common carotid artery
and external carotid artery, and the platelet count dropped from 526/n
l to 111/nl. Once heparin application was stopped, giving warfarin for
anticoagulation instead, platelet levels quickly returned to normal v
alues. Symptoms, blood findings and clinical course suggested the diag
nosis of heparin-induced thrombocytopenia with thrombus formation (HAT
type II) in this patient, which could be confirmed by specific labora
tory tests. in HAT type II, heparin-dependent IgG-antibodies against p
latelets and endothelial cells are formed, causing intravasal aggregat
ion of platelets with subsequent blood clotting in both arteries and v
eins. Given an incidence of 0.5-5%, these immunologically caused throm
bocytopenias are among the rare side effects of heparin therapy.