Congenital midline nasal fistula with extensive nasal septal dermoid cyst: a case report.

Nasal dermoid sinus cysts (NDSCs) are often misdiagnosed as superficial masses in young children; however, extensive intranasal invasion involving the entire nasal septum is extremely rare in adults. Here, we report the case of a 25-year-old man who presented with a six-month history of nasal congestion and pain, accompanied by an external opening at the nasal base. Computed tomography (CT) and magnetic resonance imaging (MRI) revealed a large cystic lesion in the perpendicular plate of the ethmoid bone, extending from the crista galli to the nasal tip, without intracranial extension. For such extensive lesions in adults, achieving a balance between radical excision and preservation of nasal structure is challenging. The cyst was located proximate to the cribriform plate, and its surgical removal may have caused significant structural damage; therefore, an endoscopic marsupialization combined with limited external resection was performed. Histological examination demonstrated the presence of hair and sebaceous glands, confirming the diagnosis of a dermoid cyst. This combined approach provided a durable drainage pathway while preserving nasal integrity and achieving satisfactory aesthetic outcomes. No symptomatic recurrence was observed during the 6-month follow-up, and the patient recovered smoothly.