Extensive Cerebral Venous Sinus Thrombosis in a Young Male With Severe Hyperhomocysteinaemia: An Unusual Presentation With Early Diplopia.

Cerebral venous sinus thrombosis (CVST) is a rare cause of stroke, particularly in young adults, and often presents with nonspecific symptoms that may delay diagnosis. Hyperhomocysteinaemia is a recognized but frequently overlooked prothrombotic risk factor. We report a case of a 25-year-old previously healthy male who presented with sudden-onset severe unilateral headache and projectile vomiting. Neuroimaging with magnetic resonance imaging and venography revealed extensive thrombosis involving the superior sagittal, left transverse, and left sigmoid sinuses with cortical veins involvement. Laboratory evaluation showed markedly elevated serum homocysteine levels, with no other identifiable risk factors. The patient was treated with therapeutic anticoagulation, osmotic agents, and vitamin supplementation for hyperhomocysteinaemia. During treatment, he developed early horizontal diplopia due to left abducens nerve palsy, attributed to evolving intracranial hypertension. Acetazolamide with Fresnel prism eye glasses led to stabilization and gradual improvement of symptoms. This case emphasizes the importance of evaluating metabolic risk factors such as hyperhomocysteinaemia in young patients with CVST and highlights the need for vigilant clinical monitoring for neurological deterioration even after initiation of appropriate therapy.