Anterior Clinoid Mucocele Causing Peripheral Visual Field Defect: Case Report, Pathogenesis, and Surgical Treatment

Background Mucoceles are benign cystic lesions that involve mainly the frontal and ethmoid sinuses, containing mucoid sterile secretions produced by entrapped respiratory epithelium. Mucoceles of the paranasal sinus are a well-described entity; however, anterior clinoid mucoceles have seldom been described, with only 18 cases described to date. The pathogenesis of these lesions is not fully understood.

The most common clinical presentation is orbital symptoms (ipsilateral retro-orbital pain and progressive monocular vision loss) or diplopia. The diagnosis is suggested with neuroimaging.

Case Report An 18-year-old woman presented with dull headache for 6 months associated with right periorbital pain and progressive blurry vision, despite corrective lens. On physical exam, the confrontational visual field exam showed a right nasal field defect and no other abnormalities on neurologic exam. MRI and CT exams were suggestive of a right anterior clinoid mucocele with the ipsilateral optic nerve displaced medially. A right pterional craniotomy with an extradural approach to the anterior clinoid was performed, and we identified the cystic cavity with hypertrophic mucosa and secretion. A communication with the sphenoid sinus was identified through the optic strut. An anterior clinoidectomy was completed and the optic nerve was decompressed.

The pathology report confirmed the presumed diagnosis and described the specimen as a fragment of benign sinonasal mucosa, admixed with acellular proteinaceous debris without acute inflammation.

In the most recent follow-up at 6 months postoperative, the patient had no new neurological deficits and no defects in confrontational exam of the visual field. The Humphrey’s visual field test showed improvement to the preoperative exam, but still a defect mainly in the inferior nasal quadrant.

Discussion There are two theories regarding the pathogenesis of anterior clinoid mucocele. The first postulates that a pneumatized anterior clinoid process becomes obstructed. The second postulates that an aberrant inclusion of ectopic mucinous tissue within the developing bone produces mucoid secretion without any outlet and the mucocele develops.

Despite an anecdotal report of a case describing successful treatment with antibiotics alone, early surgical decompression is the treatment most authors advocate, either using an endonasal or a transcranial approach, with the position of the optic nerve being the main deciding factor.

A lateral approach was chosen in this case because the optic nerve had been displaced medially and an endonasal approach would require its manipulation, increasing the risk of worsening the patient’s visual deficit and possibly it would not be effective in resecting the entire mucocele.

Conclusion Although anterior clinoid mucocele is a rare entity, it must be considered as a possible diagnosis for patients with monocular visual field defects and orbital pain. A timely diagnosis and surgical decompression allow a full visual recovery, whereas a delay could lead to a permanent visual defect.

The data we have reviewed and our case analysis further support surgical decompression as the ideal treatment. We suggest that the approach used be dictated by the mucocele position to the optical nerve, favoring an endonasal approach when medial and a transcranial approach when lateral.