Pediatric high-grade diffuse B-cell non-Hodgkin lymphoma mimicking a deep neck space infection with internal jugular vein and sigmoid sinus thrombosis: a diagnostic dilemma

Pediatric head and neck lymphomas may occasionally mimic deep neck space infections, creating substantial diagnostic challenges. The coexistence of lymphoma with extensive venous thromboembolism—specifically cerebral venous sinus thrombosis (CVST) and internal jugular vein (IJV) thrombosis—is uncommon and introduces profound diagnostic dilemmas. We report a case of high-grade diffuse B-cell non-Hodgkin lymphoma initially mistaken for an infectious deep neck process. A previously healthy 12-year-old girl presented with a two-month history of persistent left-sided headache, progressive orbital swelling, and proptosis. During the diagnostic workup, she received multiple alternative diagnoses, including typhoid fever and migraine, before developing a left cervical mass. Following a tonsillectomy and biopsy of a parapharyngeal mass, she experienced acute clinical deterioration characterized by respiratory distress, severe dysphagia, dysarthria, and an isolated lower motor neuron hypoglossal nerve (CN XII) palsy. Initial contrast-enhanced computed tomography demonstrated extensive left sigmoid sinus thrombosis, left internal jugular vein thrombosis, and a deep neck mass. Although initially managed as a presumed deep neck space infection complicated by venous thrombosis, and later misinterpreted histopathologically as Histoplasmosis, expert slide re-evaluation and immunohistochemical characterization definitively established the diagnosis of high-grade diffuse B-cell non-Hodgkin lymphoma, showing diffuse CD20 positivity and a Ki-67 proliferative index of approximately 90%. Anticoagulation therapy was successfully managed, and the patient was referred for definitive oncological care. This case illustrates the ability of pediatric lymphoma to closely mimic deep neck infections clinically, radiologically, and histopathologically, with venous thrombosis arising from tumor-associated hypercoagulability and direct mechanical compression. Persistent headache, cranial neuropathies, cervical masses, or cerebral venous thrombosis in children should prompt consideration of underlying malignancy, particularly when clinical, radiological, and pathological findings are discordant. Early multidisciplinary reassessment and expert pathological review are essential to avoid diagnostic delay and ensure timely oncological management.