Imaging and Clinical Features of an Intra-Axial Brain Stem Schwannoma

Abstract

SUMMARY:A 68-year-old man presented with a highly symptomatic brain stem tumor originally thought to be a brain stem glioma. Intraoperative MR imaging guidance was used to resect the tumor, and real-time evoked potentials improved during surgery. Pathology findings unexpectedly indicated that the tumor was an intra-axial brain stem schwannoma, a condition reported, to our knowledge, only 6 times previously in the literature. The patient made an excellent recovery with reversal of his symptoms. We report an unusual case of a highly symptomatic intra-axial schwannoma that was successfully treated surgically. Case ReportA 68-year-old man developed gait imbalance, coughing, and hiccups during a 2-month period. The symptoms progressed, and he developed nausea, vomiting, intermittent diplopia, and weakness in his right arm.Physical examination revealed an alert well-oriented patient, with normally reacting pupils and intact extraocular movements. Positive findings included bilateral nystagmus on lateral gaze, right facial weakness, hoarse voice, and weakness in the right upper and lower extremity (4 of 5 weaknesses on the 5-point strength scale). Swallowing and motor speech assessment showed severe pharyngeal phase dysphagia with noneffective and unsafe swallowing.MR imaging showed a cystic septate lesion involving the midbrain, pons, and medulla (Fig 1). The upper extent was in the left midbrain in the anterior pretectal region. The inferior extent was from the left medulla up to the anterior pyramids. The lesion was hypointense on T1 (not shown), hyperintense on T2 (Fig 2), and had enhancing septa on gadolinium-enhanced images (Fig 1). The cerebellar peduncles and anterior cerebellum on the left were also involved, showing fluid-attenuated inversion recovery signal-intensity abnormality (not shown).The patient underwent a craniotomy with intraoperative MR imaging and sonography, with microscopic dissection guided by motorevoked potentials. The surface of the brain stem where the tumor came to the surface was abnormal, but there was no extension along any cranial nerve. A biopsy showed a pure spindle cell tumor. Pathologic considerations at the time were either meningioma, schwannoma, or tanycytic ependymoma. There were no mitotic figures. Xanthochromic intratumoral cyst fluid was found to be under moderate pressure. The tumor was resected but had to be coagulated medially and inferiorly at the brain stem attachment where dissection was difficult. Multiple septa were fenestrated and resected. Right-sided evoked potentials returned immediately once the cyst was decompressed. A gross total resection was achieved.Pathologic results after the surgery showed a spindle cell neoplasm. Additional special studies were performed on permanent tissue. A positive tumor reactivity was seen in tumor cells with S-100, but they were negative for glial fibrillary acidic protein and epithelial membrane antigen. Studies for MIB-1 showed rare labeled tumor nuclei. A diagnosis of schwannoma was made. The patient's neurologic status improv...

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