Abstract
Purpose: To describe the management of a case of an arachnoid cyst of the optic nerve.
 Methods: Here, we report a 27-year-old female patient who was diagnosed with arachnoid cyst of the left sheath optic nerve, drained in several occasions, and came to our service because of progressive blurring in the left eye.
 Outcomes: Due to the location of the lesion, excision could not be performed; so we performed a microsurgical incision with drain by nasal superior transconjunctival approach. After that, the visual acuity (VA) was 0.7, and we could observe that the size of the cyst was smaller than previous examinations with magnetic resonance imaging (MRI). Nowadays, the patient keeps the same asymptomatic VA. So medical appointments are planned to closely follow-up, and periodically, we perform new scan images and visual fields.
 Conclusions: Arachnoid cysts of the optic nerve are rare, benign, slowly progressive conditions. They can be asymptomatic lesions, especially smaller ones, or may result in proptosis and loss of vision because of the compression. The best imaging examination for their follow-up is MRI. They should be differentiated from optic nerve sheath meningioma and other conditions.
Highlights
Arachnoid cyst of the optic nerve is a rare benign entity, which is a proliferation of normal fibrovascular tissue that comprises the leptomeninges in the location they are found
The pupils and slit-lamp examination were normal. She did not present with exophthalmos. Her ocular fundus showed normality in the right eye, and in the left eye, we could observe transparent papilla at the level of the excavation, where there was liquid behind a hyperpigmented zone
Magnetic resonance imaging (MRI) with and without contrast was performed, and both demonstrated that this cyst was bigger in size than a previous examination done two years earlier in another medical centre (Figs. 1 to 3)
Summary
Arachnoid cyst of the optic nerve is a rare benign entity, which is a proliferation of normal fibrovascular tissue that comprises the leptomeninges in the location they are found. The cyst had smaller size than in previous examinations, with diameters of 13 × 18 mm and 1.7 cm[3] currently compared with previous ones of 14 × 19 mm and 2.0 cm[3] (both measurements taken in the same plane and sequence for better correlation). It kept the same aspect by image, without pathological enhancement The most important change we have noticed is the improvement in the VA
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