Intraparenchymal Brainstem Schwannomas in Pediatric Patients: Two Unusual Case Reports

Background: A schwannoma is a tumor that originates from the myelin sheath of peripheral nerves. Intracranial schwannomas constitute 8-10% of primary brain tumors with many of these tumors associated with the vestibular nerve. Less than 1% of schwannomas are intraparenchymal with development unrelated to cranial nerves. Four pediatric cases have been previously documented in the English literature. Many developmental and non-developmental theories have been proposed to explain the histogenesis of these tumors; however, their origin is still largely unknown. This report details the cases of two children with intraparenchymal brainstem schwannomas both without neurofibromatosis and discusses the radiographic and pathologic characteristics of the lesions. Case Information: A previously healthy 8-year-old female presented with a history of ataxia, visual impairment, right hemiparesis, and school decline for approximately three months. Magnetic Resonance Imaging (MRI) revealed a fairly well-circumscribed lobulated mass arising from the right dorsal and lateral mesencephalon. The patient underwent a posterior fossa craniotomy with telovelar approach, and the intramedullary midbrain tumor was completely resected. Pathology best classified the tumor as schwannoma (WHO Grade I). Testing for neurofibromatosis was negative. There were no obvious immediate complications postoperatively; however, the following day the patient developed secondary hydrocephalus and later a right occipital ventriculoperitoneal shunt was internalized. Postoperatively, she had left hemiparesis, cranial nerve three and four palsies, aphasia, and hypertonia. Four years after the total resection, the patient had no evidence of residual tumor and remained with spastic hemiparesis, seizure disorder, and the presence of cerebrospinal fluid drainage problem. The second patient, a previously healthy 15-year-old female, arrived in the emergency department with diplopia and a headache which began the previous night. Anisocoria and ataxia were also noted; however, she did not present with a fever, vomiting, or history of a head injury. MRI revealed a complex partially cystic and partially enhancing posterior fossa lesion involving the midbrain and pons. The patient underwent a left subtemporal craniotomy with gross resection of the tumor and a small residual cyst remained deep in the fourth ventricle with no evidence of immediate complications. The tumor was best classified as schwannoma (WHO Grade I) and genetic work up for neurofibromatosis was negative. Postoperatively, she experienced right hemiparesis, dystonic tone in her neck, and was very somnolent and labile. Six months postoperative, MRI showed no evidence of disease recurrence with a stable decompressed cyst; however, she continued to experience ongoing right hemiparesis and neuropathic pain. Her muscle strength and diplopia gradually improved. Conclusions: Further investigation is necessary to determine the exact origin of these tumors and to explain their unusual location. Also, considering the rarity of these tumors, they should always be considered during workup. Furthermore, it is important to obtain an intraoperative frozen section to obtain good patient outcomes as gliomas appear similar to schwannomas on MRI and are more likely to be found in the brainstem. Lastly, complete resection is more difficult in the brainstem; therefore, a partial resection and intracapsular decompression also may obtain favorable outcomes.