Cerebral Venous Sinus Thrombosis Revealing ALK-Positive Anaplastic Large-Cell Lymphoma in a Patient with Inherited Thrombophilia and Concomitant Infection: Case Report and Narrative Review.

Cerebral venous sinus thrombosis (CVST) is an uncommon cerebrovascular disorder with heterogeneous manifestations and may occasionally precede the diagnosis of an underlying malignancy. We report the case of a 24-year-old man who presented with recurrent fever, headache, pharyngodynia, and systemic inflammation initially attributed to a sinonasal or odontogenic infectious process. He subsequently developed binocular horizontal diplopia, left abducens nerve palsy, papilledema, severe headache, and nausea. Neuroimaging demonstrated extensive CVST involving the left internal jugular vein, bilateral transverse sinuses, and superior sagittal sinus, without ischemic, hemorrhagic, or tumoral brain parenchymal lesions. Thrombophilia testing identified heterozygous prothrombin G20210A as the only established inherited thrombophilic factor. Despite initial neurological stabilization, the patient developed a rapidly recurrent frontal calvarial, epicranial, and cranio-dural lesion extending toward the superior sagittal sinus, without brain parenchymal involvement or imaging evidence of leptomeningeal disease. Initial morphological assessment suggested Langerhans cell histiocytosis. However, comprehensive histopathological and immunohistochemical reassessment demonstrated diffuse strong CD30 expression, nuclear and cytoplasmic ALK positivity, CD43 expression, and focal epithelial membrane antigen and granzyme B positivity, while CD1a and S100 were negative. These findings established the diagnosis of systemic ALK-positive anaplastic large cell lymphoma with secondary extra-axial cranio-dural involvement. Systemic staging demonstrated disseminated nodal disease and a noncontiguous cranio-dural extranodal lesion, consistent with stage IV disease. Treatment with anticoagulation and six cycles of brentuximab vedotin combined with cyclophosphamide, doxorubicin, and prednisone resulted in a favorable neurological and oncological outcome, with no metabolically active or residual enhancing disease on follow-up imaging. This case emphasizes the importance of continued etiological investigation in young patients with extensive CVST and an atypical clinical course, even when plausible infectious and inherited thrombotic risk factors coexist.