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Presentation type	Oral presentation
Title	Silent Sinus Syndrome Presenting as Apparent Contralateral Proptosis: A Diagnostic Pitfall

Purpose	To describe a case of silent sinus syndrome presenting as apparent contralateral proptosis.
Methods	31-year-old male presenting with apparent proptosis of the left eye, noticed by relatives over 1 week.
Results	We report a 31-year-old male, with asthma and chronic sinusitis, referred for perceived visual loss after relatives noticed apparent left-eye proptosis and lowering of the right eye. Best-orrected visual acuity was 1.0 bilaterally, with normal colour vision, pupillary reactions, fundus and OCT, excluding optic neuropathy. Thyroid function was normal and there was no history of trauma. Hertel exophthalmometry showed only mild asymmetry (16 mm right, 17 mm left), yet a deepened right lid sulcus and restricted right eye elevation with upgaze diplopia suggested true displacement of the right globe rather than contralateral proptosis. Orbital CT showed chronic maxillary sinusitis with atelectasis of the sinus, including downward displacement of the orbital floor. The increase in orbital volume produced 1.5 mm hypoglobus and 3 mm enophthalmos, consistent with silent sinus syndrome. He was referred for endoscopic sinus surgery, with orbital floor reconstruction reserved for persistent enophthalmos.
Conclusion	Silent sinus syndrome is a rare cause of spontaneous enophthalmos and hypoglobus, resulting from chronic maxillary sinus hypoventilation and orbital floor resorption. Literature describes frequent diagnostic delay, as the condition is typically painless and patients often lack nasal complaints. This case illustrates a further pitfall: the enophthalmic eye may be overlooked when attention is drawn to apparent proptosis of the fellow eye. Mild Hertel asymmetry does not exclude significant displacement and warrants imaging.
Conflict of interest	No

Authors 1

Last name	RENARD
Initials	N
Department	AZ Sint-Jan
City	Brugge

Authors 2

Last name	VAN DE VEIRE
Initials	S
Department	AZ Sint-Jan
City	Brugge