NF2 and Melnick-Needles syndrome: Separately, sporadic MNs are the most common primary intracranial tumors in adults, with ∼50% having biallelic, somatic inactivation of NF2. Benign MNs (World Health Organization grade I) are most common; however, they often cause severe neurologic morbidity and mortality because of compression of adjacent brain or spinal cord.