Keywords
18F-FDG - lung adenocarcinoma - orbital metastasis - PET/CT
Introduction
Orbital metastases are relatively uncommon, with breast and lung cancers being the most common primary tumors, accounting for 0.7 to 12% of cases.[1]
[2] The choroid is the ocular tissue most frequently affected by metastatic disease, followed by the iris and ciliary body.[3]
[4] In 25% of cases, orbital metastases represent the first manifestation of an unknown primary carcinoma (UPC), where 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) plays a critical role. We present a case of a patient with orbital metastasis incidentally detected by an 18F-FDG PET/CT with lung cancer.
Case Report
A 65-year-old male, a chronic smoker, presented with right eye pain and decreased visual acuity. Initially, this symptom was overlooked. Two months later, the patient developed a chronic cough with hemoptysis, diffuse bone pain, and weight loss. A whole-body CT scan revealed a left pulmonary mass measuring 32 mm × 25 mm, along with suspicious mediastinal lymph nodes.
A biopsy of the lung mass confirmed invasive, moderately differentiated adenocarcinoma, with immunohistochemical markers (TTF1 + ) and an epidermal growth factor receptor (EGFR) mutation (L858R), indicating a bronchopulmonary origin. An 18F-FDG PET/CT scan showed intense uptake in the left lung mass (maximum standardized uptake value [SUVmax] = 6.5), multiple FDG-avid lymph nodes, and lesions in the liver, adrenal glands, and bones ([Fig. 1]A). Notably, there was also intense and suspicious retro-orbital uptake in the right eye (SUVmax = 10.5) ([Fig. 1]B and C).
Fig. 1 (A) Maximum intensity projection (MIP) of our patient showing normal and pathological uptakes. (B) Computed tomography (CT) in axial section of the orbital region showing retro-orbital mass in the right eye (Wight arrow). (C) Fusion image in axial section of the orbital region showing a suspect retro-orbital uptake in the right eye related to a retro-orbital metastasis (Wight arrow).
Ophthalmological examination revealed retinal detachment, suggestive of a tumoral origin. Magnetic resonance imaging showed a 30 × 30 × 22 mm retro-orbital mass (isointense on T1, hyperintense on T2, with diffusion restriction), involving the optic nerve, intraconal fat, ocular rectus muscles, and the sphenoid wing ([Fig. 2]A and B), as well as a lesion in the left cerebellum.
Fig. 2 Magnetic resonance imaging (MRI) of the orbital region showing a 30 × 30 × 22 mm right retro-orbital mass isointense on T1 (A) and hyperintense on T2 with diffusion restriction (B) (Wight arrows), involving the optic nerve, intraconal fat, ocular rectus muscles, and the sphenoid wing.
The patient was treated with targeted therapy (erlotinib 150 mg daily) and radiotherapy for the orbital and cerebral metastases, achieving favorable outcomes.
Discussion
Orbital metastases are rare, comprising 10% of orbital tumors and 3 to 7% of orbital lesions.[5] They typically affect the posterior choroid, with only 5 to 11% involving the ciliary body or iris.[5] Approximately in one-third of cases the primary malignancy is unknown.[6] Common primary sources include breast (39–48%), prostate, melanoma (12%), lung (8%), and kidney (7–11%).[7] Metastatic adenocarcinoma is considered as the predominant histological type.[8]
Orbital symptoms such as proptosis, pain, and chemosis may indicate an undiagnosed primary cancer in 15% of cases.[9] Ocular metastases are often associated with widespread disease, with average survival ranging from 7.5 to 13 months after diagnosis.[10] For symptomatic patients, ophthalmological screening is recommended.[11]
18F-FDG PET/CT is highly sensitive in detecting UPCs and staging disseminated disease. In one study, PET/CT identified primary tumors in 39.5% of cases, with lung cancer being the most common (50%). Sensitivity, specificity, and accuracy were reported as 87, 88, and 87.5%, respectively.[12]
[13]
The treatment for orbital metastases is primarily palliative. Radiotherapy achieves a 79% response rate and preserves vision in 80% of cases.[14] Targeted therapies, such as erlotinib for EGFR-mutated adenocarcinoma, have shown to improve outcomes. Fractionated orbital radiotherapy (30–40 Gy) helps reduce complications like damage to the lacrimal apparatus.[15] The prognosis remains poor, with a 54% mortality rate within 1 year of ocular metastasis diagnosis.[10]
Conclusion
Orbital metastasis can be the first sign of carcinoma in up to 25% of cases. Adenocarcinoma represents 92% of lung cancer-related orbital metastases. Early suspicion and the use of multimodal imaging, such as 18F-FDG PET/CT, are essential for prompt diagnosis and intervention to preserve vision and quality of life. This case highlights the importance of PET/CT in detecting primary malignancies in patients presenting with orbital metastasis.
