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.