Lateral sinus thrombophlebitis refers to the inflammation of inner lining of the sigmoid sinus which progresses to the formation of thrombus and abscess (due to infection by pyogenic bacteria) . This thrombus then progresses superiorly and inferiorly in the sinus. Release of pus and emboli in circulation causes fever with chills and rigor and gives toxic look to the patient. Besides this, blockade of sigmoid sinus hampers venous return and thus causes increase in CSF pressure and papilloedema. Commonly it is seen in CSOM (unsafe type). Less common causes include acute coalescent mastoiditis and masked mastoiditis. Clinical tests used for the diagnosis of lateral sinus thrombophlebitis are as follows: Crow Beck Test This test refers to observing the effect of manual compression of jugular vein on retinal veins. Patient with already occluded sigmoid sinus will show no change in retinal veins on affected side and engorgement of retinal veins on normal side. Tobey Ayer test involves recording CSF pressure and observing the effect of manual compression of jugular vein. The side with already blocked lateral sirius (due to lateral sinus thrombophlebitis) will show no change in CSF pressure. Greissinger sign swelling in post aural region in area of the mastoid emissary vein (due to thrombosis of mastoid emissary vein)