GBM is a highly malignant brain tumor with a poor prognosis. GBM constitutes approximately 17 and 6.5% of intracranial neoplasms in adult and pediatric populations, respectively [10, 11].
Currently, standard care to improve GBM patient survival begins with surgical removal followed by radiation and chemotherapy [2]. Despite optimal treatment, most patients die of the disease, and the median overall survival time is 12–15 months [1, 12]. The main parameters associated with long-term survival are younger age (<40 years), good performance status, and the ability to undergo gross total resection, followed by radiotherapy and chemotherapy [2, 10, 13]. GBM can easily metastasize within the neuroaxis (i.e., the meninges or spinal cord) via the CSF occurring in approximately 20% of GBM patients [14]. GBM metastases outside the central nervous system are rare [15], but may be found in the extraocular muscles, limbus, or orbit [16, 17]. Systemic chemotherapy is the only treatment that considerably prolongs overall survival times [12], which seem not to differ regardless of GBM developing extracranial metastasis.
The most common tumor of the optic nerve is optic nerve glioma, which represents approximately 66% of all primary optic nerve tumors. Approximately 90% of optic gliomas occur in children and most cases are relatively benign [18]. Malignant optic gliomas are rare, and mostly present in middle aged men [19]. From 1900 to 2015, only 22 cases of pathology proven optic nerve glioblastomas were recorded among 66 cases of primary malignant optic gliomas [7, 8]. At onset, 70% patients with malignant optic nerve gliomas present with symptoms of acute unilateral visual loss, spreading rapidly over the chiasm and leading to total blindness typically within 3 months [8].
Neuroradiologic findings are unspecific and typically described as contrast enhancement and thickening of the optic nerve, chiasm, or tract, with lesions having hypo- to iso-intensity on T1-weighted images [20]. Biopsies continue to be necessary to confirm a diagnosis [7].
The current standard therapy consists of surgical resection or biopsy as feasible, followed by radiotherapy and/or temozolomide chemotherapy for high grade astrocytomas [7, 21]. The prognosis of a malignant optic glioma is fatal and most patients die within 1 year [7, 8].
Our case was challenging; diagnosis was difficult before biopsy because the optic nerve tumor appeared 7 years after brain GBM and visual function was initially normal. In addition, the complications of radiotherapy were a concern. The relationship between delayed radiotherapy and the progression and extension of the optic nerve tumor was unclear. Fortunately, BCVA and VF in the fellow eye remained unchanged despite the chiasm becoming involved 1 year after the symptom onset. Compared with previous reports, the progression of the optic malignant tumor was slower and the prognosis was better.
In summary, malignant optic tumors may appear >5 years after brain GBM. Regular ophthalmic examinations and brain MRIs are recommended for early diagnosis. Additional studies should evaluate the role and optimal timing of early adjuvant radiotherapy before visual function decreases. Young age, good health, and the ability to undergo CCRT can palliate the clinical course and preserve visual function in the fellow eye.
