Formation or presence of a blood clot (THROMBUS) in the LATERAL SINUSES. This condition is often associated with ear infections (otitis media or mastoiditis) without antibiotic treatment. In developed nations, lateral sinus thrombosis can result from craniocerebral trauma; brain neoplasms; neurosurgical procedures; thrombophilia; and other conditions. Clinical features include headache; vertigo; and increased intracranial pressure.