Abstract: Objective To investigate the etiology and early diagnosis of orbital apex syndrome as the initial symptom caused by sinus disease. Methods The medical records of a 74-year-old female patient were reported. She presented with "bilateral upper eyelid ptosis with visual disturbance for more than 4 months, the left eye being more severe", and the patient underwent surgical correction of the left upper eyelid ptosis, which was successful. Two weeks later, the patient presented with decreased vision in the left eye, accompanied by eye pain and headache, and was readmitted for further evaluation. Results The left eye was fixed anteriorly with limited ocular movement in all directions. The left eye was papillary hyperemic and oedematous, with scattered haemorrhages and cotton wool spots at the posterior pole. Orbital and cranial MRI and paranasal sinus CT showed nasal involvement of the orbit and skull base. Nasal biopsy specimens were obtained and sent for pathology, and the final diagnosis was olfactory neuroblastoma secondary to left orbital apex syndrome. The patient died six months after stopping treatment. Conclusion Olfactory neuroblastoma can be found with ocular symptoms as initial symptom. Nasal space occupying lesions should be considered in orbital apex syndrome. Orbital, cranial and paranasal sinus CT or MRI and pathological examination are helpful in the early etiological diagnosis of orbital apex syndrome.

Key words: Orbital apex syndrome, Etiology, Early diagnosis, Ptosis, Nasal malignant tumor