PMC9247645_01
Neuroblastoma-like schwannoma, cat, subcutaneous mass. The mass is composed of multiple lobules that are separated by variably thick bands of dense connective tissue (arrow). Note the hypercellular peripheral nerve fascicles (asterisk) in the vicinity of the mass, which is partially encapsulated by the epineurium. H&E stain (A). The lobules are composed of multiple, tightly packed, 5-300-mum-in-diameter, fibrillar, giant rosettes that exhibited a characteristic cellular polarity with a peripheralized nucleus and centrally oriented cytoplasm. Note that there is nuclear palisading. H&E stain (B). Each individual giant rosette is characterized by radially-arranged fusiform cells with round to oval, lymphocyte-like nuclei and eosinophilic fibrillary cytoplasm. H&E (C). Giant rosettes contain a centralized collagen core (in blue). Masson's trichrome stain (D). Each fibrillar and eosinophilic cytoplasmic neoplastic process, similar to each Schwann cell in healthy peripheral nerves (asterisk), diffusely and strongly immunoreacts to laminin. Immunohistochemistry for laminin (E). Each neoplastic cell is coated by a well-formed, continuous, 50 nm thick, electron-dense basal lamina investing long and interdigitating cytoplasmic processes. The cytoplasm contains a flattened, often invaginated nucleus, microfibrils and sparse organelles with a few mitochondria, ribosomes, and lysosome-like granules. TEM micrograph (F).
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F1
The stretched capsule surrounding the mass consisted of epineurium and a few residual nerve fibers (Figure 1A). Each rosette was characterized by radially-arranged, fusiform cells with indistinct cell borders, and twisted nuclei stacked in one to 10 layers at the periphery with often prominent nuclear palisading (Figures 1B,C). The center of the rosettes was composed of various amounts of trichrome-positive collagen fibrils (Figure 1D) and of indistinct fibrillar and eosinophilic cytoplasmic processes, which were laminin immunoreactive (Figure 1E). Ultrastructural examination of neoplastic cells corroborated a well-formed, continuous basal lamina investing long and interdigitating cytoplasmic processes (Figure 1F). Multifocally, variable amounts of collagen fibrils were deposited extracellularly (Supplementary Figure 1). Re-examination of the initial cytological smear (Supplementary Figure 1) confirmed the pattern of giant rosettes with piling of elongated nuclei at the periphery and centrally-oriented, fibrillary processes.
Neuroblastoma-like schwannoma, cat, subcutaneous mass. Immunohistochemistry. Neoplastic Schwann cells cytoplasmic processes diffusely and strongly immunoreact to periaxin (A). One hundred percent of nuclei of neoplastic cells are strongly positive for Sox-10 (inset) (B). Neoplastic Schwann cell cytoplasmic processes immunoreact to S-100 (C). Neoplastic fibrillary cytoplasmic processes are strongly labeled with glial fibrillary acid protein (D). Immunohistochemistry for synaptophysin confirms lack of immunoreactivity of neoplastic cells (E). Approximately 10% of the cells display nuclear ki-67 (MIB-1) immunostaining (F).
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F2
Additional immune markers revealed that neoplastic cells were also strongly immunoreactive to GFAP, S-100, periaxin, and Sox-10 but with no immunoreactivity to synaptophysin and SMA (Figures 2A-F).
PMC9247645_02