Brainstem Cavernous Malformation Mimicking Glioma in Neurofibromatosis Type 1: A Rare Diagnostic Pitfall

Background and Objectives: A cerebral cavernous malformation (cavernoma) is a lesion composed of clustered abnormal capillary channels lacking normal brain parenchyma between them. Most cerebral cavernomas are sporadic but up to 20% have familial autosomal dominant inheritance pattern. They are extremely rare, with an annual incidence of approximately 0.15-0.56 per 100,000 population. The treatment ranges from observation for asymptomatic patients to surgical resection. Case Description: A 20-year-old patient with type I neurofibromatosis (NF1) and bilateral optic pathway gliomas since infancy underwent radiotherapy at age seven for an enlarging right medullary lesion, radiologically diagnosed as a glioma. In 2025, he developed intermittent headaches, limited cognitive function, and altered speech. MRI in July 2025 showed enlargement, contrast enhancement, and a cystic component of the right medullary lesion with fourth ventricle compression. Suboccipital craniotomy, performed for presumed medullary glioma, revealed a hemorrhagic vascular lesion; histopathology confirmed a cerebral cavernous malformation and excluded glioma. Because the lesion predated radiotherapy and the availability of susceptibility-sensitive imaging in 2012 is uncertain, its relationship to irradiation cannot be established. The case therefore illustrates a pre-existing or occult cavernous malformation with subsequent radiological evolution. The postoperative course was uneventful, and the patient remains clinically stable. Conclusions: It is possible for cerebral cavernous malformations to mimic gliomas on imaging, particularly in patients with pre-existing CNS lesions such as type I neurofibromatosis. Susceptibility-weighted imaging (SWI) together with post-contrast T1-weighted imaging may aid in distinguishing vascular malformations from primary brainstem tumors.