Anaplastic Lymphoma Kinase‐Positive Inflammatory Myofibroblastic Tumor Mimicking Meningioma: A Case Report

A 15-year-old girl presented with intermittent nausea and vomiting, headache, and vision changes. MR imaging of the brain revealed an avidly enhancing infratemporal dural-based mass arising from the tentorium, with hyperintensity on T2WI and transdural extension into the posterior cranial fossa. The well-encapsulated fibrous tumor was resected en bloc after cauterization of its rich tentorial arterial supply. Histologic examination demonstrated pleomorphic myofibroblastic cells admixed with an inflammatory infiltrate. Spindle cells showed strong, diffusely positive immunostaining for anaplastic lymphoma kinase, and genomic sequencing uncovered a tropomyosin 3 gene and anaplastic lymphoma kinase fusion and an activating mutation in the Kirsten rat sarcoma oncogene. A diagnosis of inflammatory myofibroblastic tumor was made. Primary intracranial involvement of inflammatory myofibroblastic tumor is exceptionally rare, and few cases that feature an anaplastic lymphoma kinase translocation have been described. Inflammatory myofibroblastic tumor‐CNS is an important differential diagnosis for dural-based lesions in children and young adults due to its propensity for recurrence and malignant degeneration.