Neurilemmoma: A neoplasm that arises from SCHWANN CELLS of the cranial, peripheral, and autonomic nerves. Clinically, these tumors may present as a cranial neuropathy, abdominal or soft tissue mass, intracranial lesion, or with spinal cord compression. Histologically, these tumors are encapsulated, highly vascular, and composed of a homogenous pattern of biphasic fusiform-shaped cells that may have a palisaded appearance. (From DeVita Jr et al., Cancer: Principles and Practice of Oncology, 5th ed, pp964-5)Klatskin's Tumor: Adenocarcinoma of the common hepatic duct bifurcation. These tumors are generally small, sharply localized, and seldom metastasizing. G. Klatskin's original review of 13 cases was published in 1965. Once thought to be relatively uncommon, tumors of the bifurcation of the bile duct now appear to comprise more than one-half of all bile duct cancers. (From Holland et al., Cancer Medicine, 3d ed, p1457)Peripheral Nervous System Neoplasms: Neoplasms which arise from peripheral nerve tissue. This includes NEUROFIBROMAS; SCHWANNOMAS; GRANULAR CELL TUMORS; and malignant peripheral NERVE SHEATH NEOPLASMS. (From DeVita Jr et al., Cancer: Principles and Practice of Oncology, 5th ed, pp1750-1)Scleral Diseases: General disorders of the sclera or white of the eye. They may include anatomic, embryologic, degenerative, or pigmentation defects.