We describe a young man who noticed a postauricular mass and was subsequently diagnosed with adenocarcinoma of the parotid gland. Four years after the initial diagnosis and multiple treatments, he developed acute visual loss in one eye, followed by visual loss in the fellow eye one month later. Neuroimaging eventually revealed metastatic osseous lesions involving both optic canals. This case underscores that metastatic bony involvement of the optic canal, although rare, can cause acute optic neuropathy and may be challenging to detect on neuroimaging.

A 24-year-old man noticed sudden, painless visual loss in the left eye (LE). He had a four-year history of poorly differentiated adenocarcinoma of the left parotid gland, which was previously treated with total left parotidectomy with facial nerve preservation and adjuvant radiotherapy with a total dose of 70 Gy in 33 fractions. He was then found to have metastases in the pituitary fossa, calvarium, sternum, spine, scapulae, ribs, clavicles and abdominal lymph nodes and was treated with several courses of chemotherapy consisting of cisplatin, gemcitabine and zoledronic acid. Of note, the previous neuro-ophthalmic examination six months prior was normal.

Visual acuity was 20/25 in the right eye (RE) and 20/30 in the LE. There was a left relative afferent pupillary defect (RAPD) and dyschromatopsia in the LE on Ishihara testing. He had full extraocular motility, and anterior and posterior segment examination of each eye was normal. Optical coherence tomography of the peripapillary retinal nerve fiber layers and macular ganglion cell complex was normal. A contrasted CT scan of the brain demonstrated known metastatic lesions and heterogeneous marrow involving most of the calvarium and skull base including the sphenoid bones and the right aspect of the dorsum sellae. The mass in the dorsum sellae was suspected to be slightly larger when compared to the latest brain MRI performed seven months ago, but it did not approach the visual apparatus. MRI orbits with contrast also demonstrated diffuse osseous metastases involving the calvarium, skull base, mandible and cervical vertebrae. Lesions had increased in size compared with the prior study, most notably at the right dorsum sellae and bilateral anterior clinoid processes. No abnormal enhancement of the optic nerves or brain parenchymal involvement was seen.

One week later, he noticed further worsening of vision in the LE, which was now only counting fingers. Posterior segment revealed slightly elevated optic discs in each eye. Formal visual field testing showed a nonspecific defect with a mean deviation (MD) of −7 dB in the RE and diffuse depression with an MD of −29 dB in the LE.

Further review of the orbital MRI demonstrated infiltrated and expanded bone marrow adjacent to both optic canals, severely narrowing them, more prominently on the left side; thus, bony metastasis along the optic canals was considered the most likely cause of visual loss (Figure 1). A pituitary hormone showed an elevated cortisol level. He was treated with bicalutamide, dexamethasone and radiation therapy for clivus lesions.

Figure 1.

(A–B) Axial Fluid Attenuated Inversion Recovery (FLAIR) and post-contrast coronal T1 images demonstrating no bony metastasis along the optic canals in November 2024. (C–F) MRI in June 2025 shows replaced T1 and enhancing marrow signal surrounding the optic canals, which are narrowed from the bony expansion.

One month later, vision further worsened to 20/400 in the RE and hand motions in the LE. Left RAPD was still present, and now both optic nerves appeared pale. Formal visual field testing revealed severe generalized depression in each eye. Ganglion cell analysis of the macular complex showed severe thinning bilaterally. A follow-up MRI of the orbits after radiation therapy demonstrated a slight reduction of the extraosseous soft tissue metastasis and near-complete resolution of pituitary stalk thickening. It was concluded that bony metastasis into the optic canals and their expansion were the cause of the bilateral visual loss. Radiotherapy was planned; however, the patient passed away three weeks later due to hypoxia and respiratory failure. Patient’s parents provided consent for this publication.

This man had a rare malignancy (salivary gland carcinoma), which affected him at a very young age that is atypical for this disease. Salivary gland cancers have a worldwide incidence of approximately 0.5–3.0 per 100,000 per year and usually affect patients in their sixth decade of life. ^{Reference Alvi, Chudek and Limaiem1} Salivary adenocarcinoma subtype accounts for only 14% of salivary gland malignancies but carries the highest mortality rate when regional node metastasis is present. ^{Reference Xiao, Zhan, White-Gilbertson and Day2} Twenty percent of patients with salivary gland cancer develop distant metastases, with bone metastasis being the second most common site. ^{Reference Ali, Bryant and Palmer3}

Metastasis to the optic canal represents a very rare form of osseous metastasis. Of the cancers that metastasize to the optic canal, adenocarcinoma of the prostate gland is the most frequent, followed by lung cancer, with a mean age at diagnosis of 66 years. ^{Reference Kelkar, Findakly and Wang4,Reference Saito, Hiruta and Naruse5} Detection of bony metastasis along the optic canal on MRI remains challenging due to the inherently low signal of cortical bone, the small size and complex anatomy of the canal and frequent susceptibility artifacts from adjacent air-containing sinuses. Early metastatic infiltration confined to the bone marrow may produce only subtle or nonspecific signal changes, often indistinguishable from normal variation or fatty marrow replacement. Consequently, MRI has limited sensitivity for early osseous involvement, particularly in the absence of a soft tissue component. This limitation is further compounded by the fact that patients with metastatic disease are typically followed with brain MRI protocols rather than dedicated orbital imaging. Such studies often lack high-resolution pre-contrast T1-weighted images of the orbits to adequately assess bony marrow and may also not have post-contrast fat-saturated sequences that are critical for evaluating the optic canal region. High-spatial resolution CT bone window images may help detect bony irregularities along the optic canal suggestive of underlying metastasis. In this patient, the disease radiologically extended over seven months to involve both optic canals and the bilateral anterior clinoid processes, resulting in acute visual impairment.

In summary, the optic nerve is especially vulnerable to compressive lesions affecting the optic canal, given its very small space, and metastasis to the optic canal, while rare, can occur. Their diagnosis can be difficult, and high-spatial resolution CT and positron emission tomography/CT are preferred imaging modalities for assessing subtle osseous changes, while MRI of the orbits is preferred for evaluation of soft tissue lesions extending into the optic canal.