Mastoid findings secondary to posterior fossa dural venous sinus thrombosis

In the setting of posterior fossa dural venous sinus thrombosis, mastoid findings can potentially be mistaken as the cause rather than a secondary effect. Obstruction of the mastoid venous drainage can lead to transudation of fluid into the mastoid air cells. We hypothesize that a continuum of the mastoid manifestations secondary to dural venous sinus thrombosis can be seen on MRI and that the difference in venous drainage between the mastoid and middle ears can assist with this important imaging differential.

A retrospective review of acute dural venous sinus thrombosis cases and their follow-up imaging were graded as follows: no involvement; grade 1 mucosal congestion; grade 2, film of fluid; or grade 3, complete opacification. Presence of middle ear fluid was also documented.

Of 22 posterior fossa dural venous sinus thrombosis cases without clinical infectious mastoiditis, 19 had mastoid findings: eight with grade 1, eight with grade 2, and three with grade 3. Middle ear fluid was seen in only one case. There was a statistically significant association between posterior fossa dural venous sinus thrombosis and mastoid findings (chisquare test (n = 22), p < 0.04). Fifteen of 18 cases with follow-up MRI examinations showed lessening of the mastoid findings with resolving dural venous sinus thrombosis.

Acute posterior fossa dural venous sinus thrombosis may present with a spectrum of mastoid findings that should not be misdiagnosed as the cause of the thrombosis. This study illustrates that in the absence of clinical findings of mastoiditis, mastoid fluid with a clear middle ear argues that the mastoid changes are the effect of the dural venous sinus thrombosis rather than the cause.