Benign and malignant intra-axial tumors of the mesencephalon; pons; or medulla oblongata of the BRAIN STEM. Primary and metastatic neoplasms may occur in this location. Clinical features include ataxia, cranial neuropathies (see cranial nerve diseases), nausea, hemiparesis (see hemiplegia), and quadriparesis. Primary brain stem neoplasms are more frequent in children. Histologic subtypes include GLIOMA; hemangioblastoma; ganglioglioma; and ependymoma.