Background Treatment of cavemous dural arteriovenous fistulas (DAVF) is usually made by a transartedal approach.However,in many complicated patients,treatments via transarterial approaches can not be achieved,and only an operation via a transvenous approach is feasible.We aimed to study the feasibility of transarterial embolJzation of cavous dural arteriovenous fistulas with a combination detachable coils and Onyx to embolize a complicated cavemous DAVF via a transvenous approach.Methods From August 2006 to August 2007,six cases of complicated cavous DAVF were embolized with a combination of detachable coils and Onyx via a transvenous approach.Three cases were male and the other three were female.Their ages ranged from 36 to 69 years old.The fistula was in the right lateral cavous sinus in one case,in the left lateral cavous sinus in another,and in the bilateral cavous sinus in 4 cases.One fistula was fed by the right intal carotid artery and its meningohypophyseal trunk;one was fed by the branches of the left intal carotid artery and left extemal carotid artery;four were fed by the branches of the bilateral intal carotid artery and/or the bilateral extal carotid artery.One case was drained via one lateral inferior petrosal sinus;three were drained via bilateral inferior petrosal sinuses;one was drained via one lateral ophthalmic and facial veins;one was drained via the infedor petrosal sinus and the ophthalmic and facial veins.Four were embolized via the inferior petrosal sinus,and two were embolized via the ophthalmic and facial veins.Results Among six cases of complicated cavous DAVF,four were fully embolized with Onyx by a single operation,and two cases were fully embolized with Onyx following two operations.Transient headache was found after operation in all patients,but was cured after several days by the symptomatic treatments.In one case,the first operation via the inferior petrosal sinus was a failure;the feeding branches of the extal carotid artery were embollzed,and transient facial palsy was appeared after operation.The fistula was fully embolized with Onyx via the inferior petrosal sinus after two months with no complications.One bilateral cavous sinus DAVF was embolized with Onyx via the inferior petrosal sinus by two operations,and transient abducens nerve palsy occurred after embolization.Conclusions Because Onyx may be injected via a transvenous approach and the microcatheter is easily withdrawn,cavous sinus via transvenous catheterization and emboUzation is a safe and efficient way to treat complicated cavous dural arteriovenous fistulas,especially those for which operations via transarterial approaches have failed,or spontaneous cavemous dural arteriovenous fistulas.