Malignant Optic Glioma of Adulthood (MOGA), or Malignant Optic Nerve Glioma (MONG), is an extremely rare but fatal neoplasm arising in the anterior visual pathway and optic chiasm, typically extending beyond the visual pathway. It was first reported by Hoyt et al. in 1973.
Optic gliomas in children are pathologically benign pilocytic astrocytomas. In contrast, the adult type is a malignant tumor showing the same histological features as malignant gliomas arising in the cerebrum, and the nature of the two is fundamentally different.
Optic gliomas account for 66% of primary optic nerve tumors and 0.6–1.2% of all brain tumors. Ninety percent of optic gliomas occur in children, and most are benign. MOGA/MONG is very rare and is said to occur predominantly in middle-aged men. There are 89 reported cases in the literature, but only 57 have been pathologically proven. The mean age at diagnosis is 62 years, and the gender difference is inconsistent across reports (some suggest male predominance, others no difference).
Pediatric optic glioma is a benign pilocytic astrocytoma, especially when associated with NF-1, often requiring no treatment, and the prognosis is good. The adult type (MOGA/MONG) is a malignant tumor with the same histological features as cerebral malignant gliomas, and most patients die within one year of diagnosis, making it a fatal disease.
The frequency of fundus findings is shown below.
| Finding | Frequency |
|---|---|
| Papilledema | Approximately 40% |
| Hemorrhage | 30% |
| Optic atrophy | 14% |
The pattern of findings varies depending on the lesion location.
In 70% of cases, this disease presents with rapidly progressive unilateral vision loss, leading to bilateral blindness within weeks to months. Screening for intracranial tumors in cases of acute unilateral vision loss may help preserve vision in the contralateral eye and prolong survival. Early consultation with an ophthalmologist and neurologist is important.
MOGA/MONG manifests as anaplastic astrocytoma (AA, WHO grade III) or glioblastoma (GBM, WHO grade IV). It arises from glial cells of the optic nerve and extends beyond the optic nerve and chiasm to other sites.
The main sites of origin and their frequencies are shown below.
| Site | Frequency |
|---|---|
| Hypothalamus | 50% |
| Temporal lobe | 22.5% |
| Basal ganglia | 15% |
In adults, tumors may extend continuously to the area near the hypothalamus.
MOGA/MONG pose a major diagnostic challenge due to their rarity and the similarity of symptoms and imaging findings to more common diseases.
MRI Findings
T1-weighted imaging: Heterogeneous thickening of the optic nerve, chiasm, and optic tract with low to isointense signal. May be accompanied by cystic areas.
T2-weighted imaging: Shows high signal intensity.
DWI/ADC map: May show suggestive findings.
Contrast-enhanced MRI (temporal changes): Changes from initial local contrast enhancement to rapid progression and extensive nerve hypertrophy, serving as a reliable diagnostic indicator.
Histological Criteria
The following four findings are required for histological confirmation of MOGA/MONG.
Necrosis
Vascular proliferation
Nuclear pleomorphism
Mitoses
Optic nerve thickening and contrast enhancement are nonspecific findings and can also be seen in demyelinating optic neuritis, perioptic neuritis, low-grade optic glioma, lymphoma, leukemia, and metastatic tumors. In MOGA/MONG, the absence of calcification on MRI is useful for differentiation from optic nerve sheath meningioma.
For a definitive diagnosis, a biopsy of the optic nerve itself, rather than the optic nerve sheath, may be necessary.
Differential diagnoses include optic neuritis, vascular lesions (cavernous hemangioma, ischemic optic neuropathy, CRVO), compressive lesions, neurosarcoidosis, lymphoma, and metastatic tumors.
MRI findings are non-specific and can resemble many diseases such as optic neuritis and lymphoma. Definitive diagnosis requires histological criteria (necrosis, vascular proliferation, nuclear pleomorphism, mitotic figures), and a biopsy of the optic nerve itself may be necessary.
There is no established standard for the timing or method of treatment. For each case, observation, surgery, chemotherapy, or radiotherapy is selected based on tumor location, size, extent, degree of visual impairment, proptosis, and cranial nerve symptoms.
Currently, the prognosis is extremely poor, and most patients die within one year of diagnosis. Chemoradiotherapy may extend median survival by 2 to 3 months, but no curative treatment has been established.
Glioma destroys adjacent optic nerve tissue, causing visual field defects corresponding to the damaged area.
If the tumor extends to the optic chiasm, it may cause a contralateral superior temporal visual field defect via Wilbrand’s knee. Wilbrand’s knee is an anatomical phenomenon where inferonasal crossing fibers curve forward 1–2 mm into the contralateral optic nerve before returning to the chiasm and proceeding to the optic tract.
Without treatment, it almost certainly progresses to the contralateral optic nerve, leading to bilateral visual impairment.
In adults, 17% of intracranial neoplasms are GBM, and 20% of these metastasize within the central nervous system via cerebrospinal fluid. MOGA/MONG can arise de novo or appear after cerebral GBM. Therefore, regular ophthalmic examinations and brain MRI are recommended after GBM.
When occurring after GBM, it often appears more than 5 years after the initial lesion, highlighting the importance of long-term ophthalmic follow-up [5].
