A 9-year-old child presented with a 4-week history of headache, diplopia and mastoid pain. She was diagnosed with mastoiditis, received intravenous antibiotics and underwent mastoidectomy. Headache and diplopia persisted and the neurology service was consulted. Examination revealed right sixth nerve palsy and bilateral papilloedema. MRI demonstrated mastoid opacification and inflammation, and ipsilateral jugular and sigmoid venous sinus thrombosis (fig 1). The patient received low-molecular-weight heparin and acetazolamide, with prompt resolution of headache, diplopia and papilloedema.

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Figure 1 (A, B) MR venography demonstrates signal void in the right sigmoid sinus and jugular vein (arrow). (C) T1 weighted MRI demonstrates opacification of the right mastoid (arrow) and the venous hyperintensity (dotted arrow) indicates that absent flow-related signal on venography is due to acute clot, not sinus hypoplasia.

Sinovenous thrombosis (SVT) is a known complication of acute mastoiditis,1 and although the incidence of SVT has declined in the antibiotic era, it remains an important diagnostic consideration.2^–4 In most cases, treatment of SVT includes aggressive hydration and anticoagulation, which has been associated with improved cognitive outcome and a trend to lower mortality3 without an increase in intracranial haemorrhage.3 4 The clinical improvement may occur long before the thrombosis improves on imaging and may be related to improved microcirculatory venous drainage. Delay in diagnosis and initiation of treatment with anticoagulation may increase morbidity, including permanent visual deficits.