Aleukemic T-lymphoblastic leukemia/lymphoma with massive cerebrospinal fluid infiltration

T-lymphoblastic leukemia/lymphoma (T-ALL/LBL) is an aggressive lymphoid malignancy, frequently involving the central nervous system (CNS). However, exclusive CNS infiltration of T-ALL without leukemic presentation at initial diagnosis is extremely rare. Herein, we report the case of a 19-year-old male patient who presented with progressively worsening head and neck pain, dysphagia, and dizziness. No leukemic cells were detected in peripheral blood or bone marrow samples. Computed tomography revealed only a small anterior mediastinal mass and mildly high density in some areas of the bone marrow. Although brain magnetic resonance imaging (MRI) showed no abnormal findings, spine MRI revealed slight contrast enhancement of the cauda equina. A spinal tap revealed massive infiltration of abnormal lymphoid cells that were diagnosed as T-ALL/LBL based on morphological and immunophenotypic findings. Urgent intravenous and intrathecal chemotherapeutic intervention resulted in a rapid reduction in leukemic cells in the cerebrospinal fluid, with relief of symptoms. Since T-ALL/LBL usually exhibits leukocytosis associated with a high frequency of CNS involvement, this case is considered an exceptional presentation. Recognition of such a rare presentation of T-ALL/LBL, which mimics other neurological diseases such as meningoencephalitis and demyelinating diseases, is important to avoid delayed diagnosis and treatment that could result in early death or severe neurological sequelae.