Schwannoma

Overview

Schwannomas are benign, encapsulated tumors that arise from a Schwann cell cylinder (the myelinating peripheral nerve cell) and grow within the parent nerve (ie, they do NOT infiltrate the surrounding tissue).

Note that Schwann cells myelinate peripheral nervous system axons whereas oligodendrocytes myelinate central nervous system axons.

Schwannomas commonly originate from CN 8, the vestibulocochlear nerve (called acoustic schwannoma or vestibular schwannoma) at the cerebellopontine angle or the dorsal (sensory) nerve roots.
Vestibular schwannomas are most common in patients in their 40s and 50s and present with expected clinical findings: hearing loss and/or tinnitus, early on, and cerebellar signs, if they grow large enough to compress the surrounding cerebellar peduncles and cerebellum.

Histopathology

Biphasic appearance: Antoni A (densely cellular, think: pAcked*) and Antoni B (less cellular (paucicellular)).

Verocay bodies comprises palisading rows of elongated nuclei with clear a cellular zones in between.
Verocay bodies are most commonly found in spinal schannomas (rather than acoustic schwannomas) and are characteristic but not pathognomonic of schwannomas (they are found in other tumors, as well).

Antoni B regions comprise a less cellular, loose stroma with thin, wispy-appearing cells.

Schwannoma and NF-2

Bilateral acoustic schwannomas are characteristic of Neurofibromatosis, Type 2 (NF-2).

Schwannoma vs Neurofibroma

Both types form benign peripheral nerve sheath tumors.
Schwannomas form an eccentrically located tumor within the nerve that displaces normal nerve fibers whereas neurofibromas infiltrate and expand the width of the nerve and entrap and distort the related nerve fibers.
Schwannomas can be resected (because they form a tumor within the nerve) whereas neurofibromas cannot because they infiltrate the nerve and entrap the nerve fibers.

References

Adesina, Adekunle M., Tarik Tihan, Christine E. Fuller, and Tina Young Poussaint. Atlas of Pediatric Brain Tumors. Springer, 2016.

Bland-Sutton, John. Tumours, Innocent and Malignant; Their Clinical Characters and Appropriate Treatment. New York?: Funk, 1911. http://archive.org/details/tumoursinnocentm1911blan.

Gray, Frangoise, Charles Duyckaerts, and Umberto De Girolami. Escourolle and Poirier’s Manual of Basic Neuropathology. OUP USA, 2013.

“Neuropathology for the Neuroradiologist: Antoni A and Antoni B Tissue Patterns | American Journal of Neuroradiology.” Accessed July 9, 2018. http://www.ajnr.org/content/28/9/1633.

Newton, Herbert B. Handbook of Brain Tumor Chemotherapy, Molecular Therapeutics, and Immunotherapy. Academic Press, 2018.

Orkin, Stuart H., David E. Fisher, A. Thomas Look, Samuel Lux, David Ginsburg, and David G. Nathan. Oncology of Infancy and Childhood E-Book. Elsevier Health Sciences, 2009.

Rodriguez, Fausto J., Andrew L. Folpe, Caterina Giannini, and Arie Perry. “Pathology of Peripheral Nerve Sheath Tumors: Diagnostic Overview and Update on Selected Diagnostic Problems.” Acta Neuropathologica 123, no. 3 (March 2012): 295–319. https://doi.org/10.1007/s00401-012-0954-z.

Image References

Nasimudeen, Dr Roshan. English: Neural Tumour with Cut End of Nerve Affected by It on Both Ends. March 24, 2017. Department of Pathology, Government Medical College, Kozhikode. https://commons.wikimedia.org/wiki/File:Schwannoma.jpg.

Nephron. English: Intermediate Magnification Micrograph of a Schwannoma. HPS Stain. [object HTMLTableCellElement]. Own work. https://commons.wikimedia.org/wiki/File:Schwannoma_-_Antoni_A_and_B_-_intermed_mag.jpg.
Nephron. English: Very High Magnification Micrograph of the Herringbone Pattern in a Malignant Peripheral Nerve Sheath Tumour, Abbreviated MPNST. [object HTMLTableCellElement]. Own work. https://commons.wikimedia.org/wiki/File:Malignant_peripheral_nerve_sheath_tumour_-_very_high_mag.jpg.