A 30-year-old woman with no significant medical history walked into a clinic with what looked like a textbook case of idiopathic intracranial hypertension: a relentless headache, severe vomiting, and blurring vision. Her cerebrospinal fluid opening pressure was elevated, and she was started on acetazolamide, the standard first-line drug for that condition. Instead of improving, she deteriorated over the following weeks, developing projectile vomiting and progressive visual loss in both eyes. What urgent neuroimaging eventually revealed was something far more dangerous, a case so unusual that clinicians have now documented it in a detailed report published in Clinical Case Reports.

The imaging showed extensive cerebral venous sinus thrombosis, a rare form of stroke in which the veins that drain blood from the brain become occluded by clot. CVST accounts for only about 0.5 to 3 percent of all cerebrovascular events, but it disproportionately strikes younger people, particularly women. In this patient, the thrombosis was not confined to one vessel. The superior sagittal sinus, both transverse sinuses, both sigmoid sinuses, and the right internal jugular vein were all involved, effectively shutting down the supratentorial venous drainage system. Even more ominously, the deep venous system, including the internal cerebral veins and the vein of Galen, was thrombosed as well.

Deep venous involvement matters because those vessels drain structures that have almost no collateral blood supply: the thalami, basal ganglia, hypothalamus, and periventricular white matter. When congestion builds in these territories, venous infarction can develop rapidly and carries high morbidity and mortality. Magnetic resonance imaging in this patient confirmed exactly that pattern. T2-weighted and FLAIR sequences showed bilateral thalamic hyperintensity with periventricular edema, and diffusion-weighted imaging demonstrated restricted diffusion in both thalami, the radiological signature of acute venous infarction. Magnetic resonance venography showed absent or markedly reduced flow through the major sinuses, with prominent cortical collaterals suggesting the brain was desperately rerouting its venous outflow.

Complicating the picture further was obstructive hydrocephalus, a rarely reported consequence of CVST. The noncontrast CT scan showed mild dilatation of the lateral ventricles and prominence of the temporal horns, along with a hyperdense cord sign along the superior sagittal sinus, a classic marker of acute sinus thrombosis. Two mechanisms can drive ventricular enlargement in this setting. Elevated venous sinus pressure can impair cerebrospinal fluid resorption across the arachnoid granulations by altering the pressure gradient, while venous congestion and edema in the thalami and adjacent periventricular structures can physically obstruct cerebrospinal fluid pathways. The authors of the report note that their imaging could not pinpoint a single anatomical obstruction site, so the hydrocephalus was considered likely multifactorial rather than attributable to one definitively demonstrated blockage.

The initial misdiagnosis is perhaps the most instructive element of the case. Idiopathic intracranial hypertension and CVST share strikingly similar presentations: progressive headache, vomiting, visual disturbance, and raised opening pressure on lumbar puncture. The key clinical discriminator is the response to treatment. Acetazolamide typically improves idiopathic intracranial hypertension, whereas untreated CVST worsens over time as the thrombus propagates, potentially leading to venous infarction, hydrocephalus, and neurological deterioration. Plain CT can miss venous sinus thrombosis in up to a third of cases, which is why recent recommendations urge that patients with suspected idiopathic intracranial hypertension be screened with MRI and magnetic resonance venography as part of the diagnostic workup. In this patient, progressive symptoms despite acetazolamide therapy were the crucial clue that prompted advanced imaging and the correct diagnosis.

Once the thrombosis was identified, the team turned to the question of why it had happened. Her complete blood count revealed persistent, marked thrombocytosis, with platelet counts repeatedly measured at 1140 × 10^9 per liter, roughly four times the upper limit of normal. A peripheral blood smear showed large platelets, and a bone marrow biopsy demonstrated hypercellularity with megakaryocytic hyperplasia. Molecular testing identified the JAK2 V617F mutation with a variant allele frequency of 14 percent, while CALR and MPL variants and BCR::ABL1 transcripts were absent. The diagnosis was essential thrombocythemia, a myeloproliferative neoplasm in which the bone marrow produces excessive, functionally abnormal platelets.

The JAK2 V617F mutation, present in roughly half to sixty percent of essential thrombocythemia patients, activates the JAK-STAT signaling pathway, driving platelet overproduction and producing platelets that are prone to inappropriate activation. Beyond thrombocytosis, the mutation contributes to endothelial dysfunction, leukocyte activation, and chronic inflammation, all of which amplify thrombotic risk. The result is a hypercoagulable state capable of producing clots at unusual arterial and venous sites. Venous thromboembolism is a recognized complication of essential thrombocythemia, but cerebral venous sinus thrombosis remains a rare manifestation, and the combination of extensive CVST, obstructive hydrocephalus, and JAK2-positive essential thrombocythemia has seldom been described together in a single patient. Current guidelines therefore recommend evaluating for underlying myeloproliferative neoplasms, including JAK2 mutation testing, in any patient with CVST who has no obvious provoking factor.

Treatment proceeded on two fronts. Immediate anticoagulation with low-molecular-weight heparin, enoxaparin 80 milligrams, was initiated on 21 April 2026, and later transitioned to the oral factor Xa inhibitor apixaban at 5 milligrams twice daily in May 2026. Given the extent of the thrombosis and the persistent prothrombotic risk posed by the underlying blood disorder, long-term anticoagulation was deemed appropriate. Cytoreductive therapy with pegylated interferon alfa was also started to bring the platelet count under control, a choice the report highlights as particularly suitable for women of childbearing age because of its disease-modifying potential. A multidisciplinary team spanning neurology, hematology, radiology, and ophthalmology managed the case, with ophthalmological assessment confirming bilateral papilledema and continuous intracranial pressure monitoring instituted. Notably, the hydrocephalus was managed without neurosurgical cerebrospinal fluid diversion; the patient improved with treatment directed at the thrombosis and the hematological disease, underscoring that management must be individualized to neurological status and imaging progression, while recognizing that deterioration may still demand urgent surgery.

The outcome was striking. By a follow-up visit on 2 June 2026, the patient had improved clinically and her platelet count had fallen to 355 × 10^9 per liter, with hemoglobin of 124 grams per liter, hematocrit of 0.41 liters per liter, and a white cell count of 5.6 × 10^9 per liter. Follow-up magnetic resonance venography demonstrated partial recanalization of the right transverse sinus and the posterior portion of the superior sagittal sinus, though recanalization remained incomplete. Susceptibility-weighted imaging showed blooming in the left basal ganglia, suggestive of residual blood products, but no clinically significant bleeding complication occurred during anticoagulation, and no new thrombotic events were observed on subsequent follow-up. The patient remains under combined neurological and hematological care.

The authors are careful to note the limitations inherent in a single-patient report: the temporal relationship and biological plausibility linking JAK2-positive essential thrombocythemia to this catastrophic venous thrombosis are strong, but causality cannot be proven, and generalizability is limited. Still, the clinical lessons are clear. Worsening symptoms in a patient labeled with idiopathic intracranial hypertension should trigger urgent magnetic resonance venography, because delayed diagnosis of CVST allows thrombus propagation with potentially fatal consequences. Once CVST is confirmed, a thorough workup for hidden prothrombotic disorders, including myeloproliferative neoplasms, is essential, since identifying an underlying condition fundamentally changes long-term management. The case also adds to the sparse literature on hydrocephalus as a complication of cerebral venous thrombosis and stands as a reminder that a young brain, given early diagnosis and coordinated multidisciplinary care, can recover even from near-complete occlusion of its venous drainage system.

Subject of Research: Cerebral venous sinus thrombosis with obstructive hydrocephalus caused by undiagnosed JAK2 V617F-positive essential thrombocythemia

Article Title: Extensive Cerebral Venous Sinus Thrombosis With Obstructive Hydrocephalus in a Young Female With Underlying Essential Thrombocythemia: A Case Report

Article References: Nafea, S., Farooq, T., Taher, M. A., Barros, A., Soe, K. N., Ali, F., & Thomas, K. (2026). Extensive Cerebral Venous Sinus Thrombosis With Obstructive Hydrocephalus in a Young Female With Underlying Essential Thrombocythemia: A Case Report. Clinical Case Reports, 14(10), Article e73669. https://doi.org/10.1002/ccr3.73669

Image Credits: AI Generated

DOI: 10.1002/ccr3.73669

Keywords: cerebral venous sinus thrombosis, essential thrombocythemia, JAK2 V617F, obstructive hydrocephalus, myeloproliferative neoplasm, idiopathic intracranial hypertension, venous infarction, anticoagulation, pegylated interferon alfa, magnetic resonance venography, thalamic infarction, thrombocytosis

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