Isolated vein thrombosis of the posterior fossa presenting as localized cerebellar venous infarctions or hemorrhages.

BACKGROUND AND PURPOSE Cerebellar venous infarction or hemorrhage due to isolated venous thrombosis of the posterior fossa is a rare form of intracranial vein thrombosis that can be unsuspected in clinical practice. METHODS We studied 230 patients with intracranial vein thrombosis, identifying 9 (3.9%: 7 women, mean age 34 years) with neuroimaging or histopathologic evidence of localized posterior fossa vein thrombosis causing parenchymal injury limited exclusively to the cerebellum. RESULTS All patients had an insidious presentation suggesting other diagnoses. Intracranial hypertension (n=6) and cerebellar (n=4) syndromes were the main clinical presentations. Intracranial vein thrombosis was idiopathic in 3 patients; associated with puerperium in 3; and with contraceptives, protein C deficiency, and dehydration in 1 case each. CT was abnormal but not diagnostic in 5 patients, showing a cerebellar hypodensity with fourth ventricle compression and variable hydrocephalus in 5 patients, and cerebellar hemorrhage in 2. Conventional MRI provided diagnosis in 6 cases, showing the causal thrombosis and cerebellar involvement; angiography was practiced in 2 of them, confirming the findings identified by MRI. In the other 3 patients, diagnosis was reached by histopathology. Thromboses were localized at the straight sinus (n=4), lateral sinuses (n=3), and superior petrosal vein (n=2). The acute case fatality rate was 22.2% (n=2), 1 (11.1%) patient was discharged in a vegetative state, 1 (11.1%) was severely disabled, and 5 (55.6%) were moderately disabled. CONCLUSIONS Isolated venous thrombosis of the posterior fossa is infrequent and implies a challenging diagnosis. Risk factors for intracranial vein thrombosis and atypical cerebellar findings on CT should lead to further MRI assessment.