Introduction: Sphenoid sinus mucoceles comprise 1–2 per cent of paranasal sinus mucoceles. Endoscopic marsupialisation is currently the treatment of choice.

Case report: We present a patient with a sphenoid mucocele whose sphenoid sinus cavity appeared normal on endoscopy due to a horizontal plate of accessory septa, below the sphenoid ostia. The mucocele was in the inferior portion of the sinus below the septa, expanding the sinus inferiorly.

Conclusion: Intra-operative imaging was essential in the successful management of this patient's condition. Although endoscopy offers direct visualisation, endoscopic surgeons must be aware of the anatomical variations in this region. Intra-operative imaging modalities such as image guidance systems and image intensifiers are often vital for safe surgery.