Small spheno-ethmoidal meningoencephalocele versus ethmoidal mucocele in spontaneous intracranial hypotension

Background: Meningoencephalocele is defined as an abnormal sac of brain tissue and meninges extending beyond natural skull margins, often leading to cerebrospinal fluid (CSF) leakage. When this condition arises in the sphenoethmoidal region, the diagnosis becomes more challenging as it can be mistaken for other nasal pathologies, such as mucocele.Research question: We show in this case report a non-congenital sphenoethmoidal meningoencephalocele causing rhinoliquoral fistula and spontaneous intracranial hypotension.Results: this 65-year-old woman presented with sporadic rhinoliquorrhoea associated with orthostatic headache, nausea and dizziness. Brain MRI revealed a small lesion of an ethmoidal sinus, which was successfully treated with endoscopic endonasal surgery. Histology confirmed the presence of meningoencephalic tissue positive for S100 protein on immunohistochemistry.Conclusions: When dealing with lesions of the paranasal sinuses in contact with the anterior skull base, rhinoliquorrhoea presence suggests meningoencephalocele. In dubious cases, a proper workup, including a thorough clinical history and neurological examination, specific imaging, and a direct search of CSF-like markers, is essential to support the differential diagnosis. In such cases, a transnasal endoscopic surgical approach is rec-ommended to obtain a final histological diagnosis and to perform eventual dural plastic surgery.