 He did his internship and surgical residency at Montefiore Medical Center in the Bronx and his neurosurgical residency at New York University-Bellevue Medical Center, while serving in the Army reserves, under the tutelage of Joseph Ransohoff.In 1983, he was named professor of neurosurgery at New York University (NYU) and two years later director of the division of pediatric neurosurgery by Ransohoff, his former mentor.It was there that he saw the resemblance of operable tumors in the cerebellum and, until then, inoperable ones in the brain stem.