Contributed by Facundo Las Heras, MD, PhD1, Robert Martuza, MD2, Paul Caruso, MD3, Sandra Rincon, MD3 and Anat Stemmer-Rachamimov, MD4
1Department of Anatomical Pathology, University of Chile Clinical Hospital, and Departments of Neurosurgery2 , Radiology3 and Pathology4, Massachusetts General Hospital
A 24-year-old woman with a 3 year history of multiple sclerosis, for which she was treated with beta interferon, was found to have a T2 intermediate mass (1.3 cm x 0.7 cm) within the left internal auditory canal (Fig. 1) in a follow up MRI. There was no associated mass effect on the adjacent brain parenchyma. In addition, there were numerous T2 hyperintense lesions throughout the supratentorial white matter, consistent with the known history of multiple sclerosis. At the time, she did not have any related symptoms; there was no reported abnormality of hearing or balance, and no facial nerve dysfunction. On examination, visual fields and acuity were normal and cranial nerves II through XII were intact, with normal hearing on both sides. Motor-sensory skills were normal.
The patient underwent surgery (suboccipital approach) with an attempt to preserve hearing and facial nerve function. The surgical intervention was successful, with complete removal of the lesion and preservation of hearing and facial functions.
At gross examination, the lesion was a nodular, well circumscribed mass measuring 1.1.x 0.9 cm. It was tan-white and firm. Histologic examination demonstrated a neoplasm composed of spindled cells with bland, tapered, and at times "wavy", nuclei. The tumor had a biphasic pattern. The predominant pattern is a fascicular growth pattern with focal nuclear palisading around nuclear free areas (Fig. 2, left). The second, minor component shows concentric proliferation of neoplastic spindle cells around one or more axons, with formation of pseudo-onion bulbs (Fig. 2, right). These proliferating cells have elongated to oval nuclei, delicate chromatin, and inconspicuous nucleoli. Mitoses and necrosis are not recognized in either component. Degenerative atypia with nuclear hyperchromasia is focally observed.
Immunohistochemical studies revealed the fascicular component is diffusely positive for S100 protein, while the area with the concentric proliferation of cells was positive for the perineurial markers claudin-1 (Fig. 3) and Glut-1. As expected, the axons surrounded by the concentric rings of cells were highlighted by neurofilament immunostaining (Fig. 4). In addition, antibody anti-CD34 was also focally positive in the tumor (Fig. 5).