Peripheral Nerve Sheath and Central Nervous System Tumors
Neurofibroma, the most common peripheral nerve sheath tumor, is a slow-growing tumor that consists of a mixture of endoneurial fibroblasts, Schwann cells, and axons. Neurofibromas may be circumscribed but are not encapsulated. They are firm and rubbery. Microscopically, the spindle-shaped cells have slender, wavy nuclei. These nuclei are arranged in ribbons and cords in a matrix of myxoid tissue and collagen that contains axons. Cytogenetic studies indicate that the most frequent structural rearrangements involve chromosome arm 9p.
Isolated neurofibromas do not necessarily indicate a systemic syndrome, but they are more common in neurofibromatosis 1 (NF1). The plexiform type of neurofibroma is considered pathognomonic for NF1 (Fig 14-16). Plexiform refers to an intricate network, or plexus, classically described as a “bag of worms.” Studies indicate that a limited number of pathways are potentially involved in tumorigenesis of the plexiform neurofibroma. The CCN1 gene may be a useful diagnostic or prognostic marker and may serve as the foundation for new treatment strategies. The CCN1 and related gene products are cysteine-rich proteins that have been shown to play a role in intracellular signaling in the extracellular matrix.
Figure 14-16 Plexiform neurofibroma. A, Clinical photograph depicting the typical S-shaped deformity of the upper eyelid. B, Note the thickened, tortuous nerves (arrows) with proliferation of endoneurial fibroblasts and Schwann cells.
(Part A courtesy of Sander Dubovy, MD.)
Liu K, DeAngelo P, Mahmet K, Phytides P, Osborne L, Pletcher BA. Cytogenetics of neurofibromas: two case reports and literature review. Cancer Genet Cytogenet. 2010;196(1): 93–95.
Pasmant E, Ortonne N, Rittié L, et al. Differential expression of CCN1/CYR61, CCN3/NOV, CCN4/WISP1, and CCN5/WISP2 in neurofibromatosis type 1 tumorigenesis. J Neuropathol Exp Neurol. 2010;69(1):60–69.
A neurilemoma (also spelled neurilemmoma; also called schwannoma) arises from Schwann cells of peripheral nerves. These are the most common nerve sheath tumors found in the orbit of adults. Slow growing and encapsulated, this yellowish tumor may show cystic spaces and areas of hemorrhagic necrosis. It may be solitary or associated with a genetic syndrome such as neurofibromatosis or schwannomatosis. Histologically, neurilemomas can demonstrate one or more characteristic growth patterns. The Antoni A pattern consists of slender spindle cells in which the nuclei are arranged in palisades that may form intervening Verocay bodies (collections of fibrils resembling sensory corpuscles) (Fig 14-17). The Antoni B pattern is made up of stellate cells set in a mucoid stroma. Vessels are usually prominent and thick walled, and no axons are present. IHC analysis of neurilemoma is relatively nonspecific, and typically the tumor is positive for S-100 protein and vimentin.
Figure 14-17 Neurilemoma (schwannoma). A, The Antoni A pattern. Spindle cell nuclei are arranged in linear palisades. B, Palisading of nuclei may form a Verocay body (asterisks).C, The Antoni B pattern consists of a loosely arranged, mucoid stroma and represents degeneration within the tumor.
(Parts A and B courtesy of Nasreen A. Syed, MD.)
Meningiomas are found in the CNS as they are derived from the meninges. Most meningiomas that affect the orbit are actually primary tumors of the intracranial cavity that invade through the orbital bones, typically the sphenoid bone, and behave as an infiltrative mass lesion in the orbit. A minority of meningiomas found in the orbit arise from the optic nerve sheath primarily. These tumors tend to stay within the sheath and result in compression of the optic nerve. For further discussion of meningioma and other CNS tumors occurring in the orbit, see Chapter 15.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.