Isolated oculomotor nerve palsy caused by an Onodi cell mucocele: a case report of a rare presentation

Introduction and importance: Onodi cell (OC) mucoceles are a rare subtype of paranasal sinus mucoceles that can compress adjacent neurovascular structures due to their anatomical proximity to the orbital apex. Isolated oculomotor nerve palsy (CN III) resulting from an OC mucocele is exceptionally uncommon and poses diagnostic challenges, especially in patients with vascular comorbidities. Case presentation: We present a rare case of a 71-year-old man with a 5-day history of left eyelid ptosis and diplopia. The patient had a background of well-controlled hypertension and diabetes. Physical and ophthalmologic examinations revealed isolated left CN III palsy without optic nerve involvement. Magnetic resonance imaging was inconclusive, but CT imaging showed complete opacification and expansion of the left OC. The patient underwent endoscopic sinus surgery, revealing a mucocele in the OC. Postoperative recovery was marked by rapid improvement in ptosis, with complete resolution of nerve palsy within 1 month. Clinical discussion: This case highlights the importance of considering OC mucoceles in the differential diagnosis of atypical cranial neuropathies. Delayed diagnosis may result from nonspecific presentations and confounding vascular risk factors. Imaging is critical in detecting these lesions and guiding timely intervention. Conclusion: OC mucoceles that cause CN III palsy are extremely rare. Imaging plays a crucial role in detecting these lesions, and timely surgical decompression is essential for achieving optimal recovery of neural function. This may also aid in accurately assessing these lesions.