Answer: EBV-associated smooth muscle neoplasm

Histology: The lesion is a cellular spindle cell tumor with elongated nuclei arranged in intersecting fascicles. The fascicles are punctuated by areas of hyalinized collagen with a stellate shape, similar to but thinner than the amianthoid fibers that are described in palisaded myofibroblastoma. Tumor is strongly immunoreactive for alpha smooth muscle actin and demonstrates nuclear reactivity for the EBER early transcript of Epstein-Barr virus. S100 and EMA immunostains were negative.

Discussion: The current lesion is an excellent mimic of schwannoma in that it features nuclei which are spindled and wavy, variable cellularity, and sclerosis. However, the lesion is non-reactive for S100, which excludes schwannoma. Fibrous meningioma is a consideration, though the current tumor’s nuclei lack the characteristic ovoid shape and intranuclear inclusions of meningioma, and the tumor was EMA negative. Palisaded myofibroblastoma features amianthoid fibers, however, the lesion is typically intranodal and is not associated with EBV infection.

Smooth muscle neoplasms associated with Epstein-Barr virus are classically seen the setting of immunodeficiency (transplant patients, congenital immunodeficiency, and HIV), particularly in children. These tumors are often multifocal, and involve visceral sites. In situ hybridization for Epstein-Barr virus is a sensitive assay for this tumor. The current case shows an unusual histology including collagen deposition resembling amianthoid fibers, which to our knowledge has not been described in this neoplasm.