Eggshell-like Intraosseous Cyst of the Ethmoid Perpendicular Plate: Imaging Clues and Endoscopic Management

Intraosseous cysts of the ethmoid perpendicular plate are rare and anatomically distinctive lesions. Because such lesions may clinically resemble septal deviation, inflammatory sinonasal disease, or other osseous septal masses, preoperative imaging recognition is essential. We describe a 36-year-old man with recurrent postnasal drip, headache, and snoring, in whom nasal endoscopy revealed a smooth superior septal bulge compressing the adjacent middle turbinate. Computed tomography showed a sharply marginated expansile cyst centered within the ethmoid perpendicular plate and surrounded by a thin eggshell-like osseous shell. Magnetic resonance imaging demonstrated a non-enhancing cystic lesion with low T1 and high T2 signal intensity, supporting a benign intraosseous process. Complete endoscopic excision of the cyst wall and its delicate bony shell was performed, together with correction of septal deviation and treatment of concomitant sinonasal inflammation. Histopathology confirmed a benign respiratory epithelium-lined intraosseous cyst with chronic inflammation. Postoperatively, the patient's symptoms improved, and endoscopic follow-up at 6 months showed good mucosal healing and no visible residual or recurrent lesion. This case emphasizes that an eggshell-like, non-enhancing cystic lesion centered in the ethmoid perpendicular plate represents a distinctive CT-MRI pattern that can guide accurate diagnosis, distinguish this entity from more common septal or sinonasal lesions, and facilitate complete endoscopic treatment.