OBJECTIVE: The aneurysmal bone cyst (ABC) is included in the group of bone lesions called "pseudo-tumors" because of its clinical and radiological behavior as an expansive tumor with invasive characteristics. It usually occurs in young people and is located in the long bones and vertebrae. It is considered in the differential diagnosis of nasal tumors because of its rare manifestation in the facial bones. Thus, the objectives of this report are to clarify an atypical and important manifestation of this neoplasm in otorhinolaryngology and to report the favorable outcome of a resection and subsequent optic nerve decompression, even in a case with prolonged compression. CASE REPORT: A 19-year-old female patient had sudden eye pain, proptosis, and progressive worsening of visual acuity in the right eye. She was referred to the Department of Otorhinolaryngology, HC-UFMG, and diagnosed with a cystic tumor in the right ethmoid cells, including optic nerve compression and advanced impairment of her ipsilateral visual acuity. During a nasal endoscopy exam, the mass was visualized for ethmoid topography. After an incisional biopsy with inconclusive results, we chose to perform surgical excision by nasal endoscopy. On the first postoperative day, we verified total recovery of visual acuity, confirmed by an ophthalmological examination. CONCLUSION: The ABC can rarely present as a tumor in the nasal cavity. Despite its benign nature, it can cause severe conditions because of its fast growth. From this case, considering the involvement of the optic nerve, it is important to note the finding of the patient's postoperative recovery of her visual acuity despite chronic compression of the optic nerve.
