An intracranial mass is removed from a 33-year-old patient. The mass is composed of cells that have elongated, wavy nuclei. A biphasic pattern of growth is identified, consisting of areas of dense cellularity interspersed with less dense myxoid regions. The cells show diffuse S-100 immunoreactivity. Which of the following is the most likely diagnosis?
Schwannomas are tumors of the peripheral nervous system that arise from Schwann cells. Microscopically, they appear biphasic with highly cellular areas (Antoni A pattern) intermixed with myxoid regions of low cellularity (Antoni B pattern). The Antoni A areas are composed of spindle cells with elongated, wavy nuclei that form palisading patterns with interspersing nuclear-free zones called Verocay bodies. Schwannomas are universally S-100 positive due to their neural crest cell origin. Another important S-100 positive tumor is melanoma (also derived from the neural crest).
Schwann cells are to the peripheral nervous system as oligodendrocytes are to the central nervous system: both protect and insulate axons. The transition from oligodendrocytes to Schwann cells occurs within a few millimeters from the surface of the brain and spinal cord. Therefore, schwannomas can occur within the cranial vault and spinal canal. Schwannomas may arise from any cranial nerve except the optic nerve (CN II) and olfactory nerve (CN I), which are not covered by Schwann cells.
The most common site of intracranial schwannomas is the cerebellopontine angle at CN VIII. Schwannomas in this particular location are also called acoustic neuromas, and can present with tinnitus, vertigo, and sensorineural hearing loss.
(Choice A) Glioblastoma is a highly aggressive primary brain tumor that consists of bizarre-looking glial cells with multiple mitotic figures, pseudopalisading necrosis, and abundant neovascularization and hemorrhage. It commonly occurs in the frontotemporoparietal white matter and grows along the white matter tracts across the corpus callosum to affect the opposite hemisphere.
(Choice B) Meningiomas are typically slow-growing extra-axial tumors that arise from the meningothelial cells of the arachnoid. Meningiomas most commonly appear as cells arranged in lobules or whorls with or without psammoma bodies (laminar calcifications).
(Choice C) Brain metastases are the most common cause of intracranial tumors in adults. Lung, breast, skin (melanoma), and renal cancer are particularly likely to metastasize to the brain. Metastatic brain lesions typically form well-circumscribed masses along the grey-white junction. Histologically, there is often necrosis with surrounding areas of reactive gliosis and edema.
(Choice D) Optic glioma is a form of glioma that affects the optic nerve. It is often found in association with neurofibromatosis type 1. Histologic findings are usually consistent with pilocytic astrocytoma and include tumor cells with hairlike processes, microcystic areas, and Rosenthal fibers (elongated or corkscrew intracytoplasmic eosinophilic bundles).
Educational objective:
Schwannomas present histologically with a biphasic pattern of cellularity (Antoni A and B areas) and S-100 positivity (indicating neural crest origin). Schwannomas can arise from the peripheral nerves, nerve roots, and cranial nerves (except CN II and CN I). Acoustic neuromas are the most common type of intracranial schwannoma and are located at the cerebellopontine angle at CN VIII.