Malignant nerve sheath tumor of the spinal accessory nerve: a unique presentation of a rare tumor

Abstract

Background: Malignant peripheral nerve sheath tumors (MPNSTs), sarcomas originating from tissues of mesenchymal origin, are rare in patients without a history of neurofibromatosis.

Case report: We report a case of an MPNST of the spinal accessory nerve, unassociated with neurofibromatosis, which metastasized to the brain. The tumor, originating in the intrasternomastoid segment of the spinal accessory nerve, was removed. Two years later, the patient presented with focal neurological deficits. Radiographic findings revealed a well-defined 2.2×2.2×2.2 cm, homogeneously enhancing mass in the left parieto-occipital region of the brain surrounded by significant vasogenic edema and mass effect, culminating in a 1-cm midline shift to the right. The mass was surgically removed. The patient had nearly complete recovery of vision, speech, and memory.

Conclusions: To our knowledge, this is the first documented case of an MPNST arising from an extracranial segment of the spinal accessory nerve and metastasizing to the brain.

Keywords: malignant nerve sheath tumor; neurofibromatosis; spinal accessory nerve.

Fig. 1

A: Initial MRI performed in 2009 as part of staging for peripheral nerve sheath tumor. T1 weighted axial image post gadolinium injection was negative for abnormal intracranial enhancement. B: Repeat MRI performed August 2010 on admission to neurological intensive care unit. T1 weighted axial image post gadolinium injection revealed 2.2×2.2×2.2 cm, well-circumscribed, homogeneously enhancing lesion identified in the left occipital lobe with extensive vasogenic edema. A midline shift to the right of approximately 1 cm with subfalcine herniation is evident. Mass effect is identified on the occipital horn of the lateral ventricle.

Fig. 2

Contrast-enhanced CT scan of the chest at the time of admission to the neurological intensive care unit. Scan revealed a new 1.1-cm left lower lobe solid nodular density adjacent to the lateral basilar segment artery and bronchus. A stable 0.4-cm nodule was seen peripheral to the left lower lobe.

Fig. 3

A: Photomicrograph of an S-100 immunohistochemically stained slide (magnification ×400) of tissue from the original tumor, which confirms the tumor as an MPNST. B: Photomicrograph of an H & E slide (magnification ×400) of tissue from the cerebral mass. It shows a cellular neoplasm exhibiting storiform architecture with moderate nuclear atypia. Other areas show increased mitotic activity and necrosis. The diagnosis of MPNST was based on expression of similar immunohistochemical staining and nearly identical morphological characteristics shared between the original tumor and the metastatic tumor.