Mucocoeles are a consequence of long-standing sinusitis, and arise when any lesion prevents the normal egress of mucus from a sinus cavity. It is an accumulation of the products of secretion, desquamation and inflammation within the paranasal sinuses, with distension of the walls of the sinus. A mucocoele contains tenacious blairy mucus; it causes expansion of the sinus and thinning of its bony walls, and may also cause displacement of the orbit. It is more common in the frontal, ethmoid and sphenoid sinuses than in the maxillary sinus.

This is a case report of a large ‘missed’ mucocoele of the maxillary sinus, causing expansion of the ipsilateral cheek, distorting the lateral nasal wall, and attenuating the floor of the orbit, which was treated initially as a dental abscess, leading to its recurrence.

An endonasal endoscopic approach was employed to enlarge the blocked maxillary sinus ostium, and marsupialise the mucocoele into the nasal cavity. The patient was followed up for 6 months post-operatively, with no recurrence.

Endonasal endoscopic marsupialisation is the treatment of choice for a maxillary sinus mucocoele, with a low risk of recurrence.