Anaplastic lymphoma kinase-positive primary CNS anaplastic large cell lymphoma in a pediatric patient: illustrative case.

Background: Anaplastic lymphoma kinase (ALK)-positive primary CNS anaplastic large cell lymphoma (ALCL) is an extremely rare pediatric malignancy. Its radiological appearance often mimics infectious or glial lesions, complicating diagnosis and delaying treatment.

Observations: The authors report the case of a 10-year-old immunocompetent female who presented with absence seizures and vomiting. Brain MRI revealed a left frontal lesion with peripheral contrast enhancement and diffusion restriction, suggestive of a cerebral abscess. She was started on antibiotics and underwent resection. Histopathology confirmed ALK-positive primary CNS ALCL. The patient was treated with NHL-BFM (non-Hodgkin lymphoma-Berlin-Frankfurt-Münster) chemotherapy, the ALK inhibitor lorlatinib, and focal cranial radiotherapy (18 Gy/22 fractions). She remains in complete remission at 18 months. A systematic review of 15 pediatric ALK-positive CNS ALCL cases revealed male predominance, supratentorial location, and inconsistent treatment protocols. Methotrexate-based chemotherapy was most common treatment; the role of radiotherapy and surgery varied.

Lessons: ALK-positive primary CNS ALCL should be considered in the differential diagnosis of pediatric intracranial masses with atypical imaging. Early histological confirmation is essential. While chemotherapy remains central to treatment, targeted therapies and radiation-sparing approaches require further investigation to improve outcomes and reduce long-term morbidity in children. https://thejns.org/doi/10.3171/CASE25522.