Imploding antrum (silent sinus) syndrome has clinical features of enophthalmos and hypoglobus after a downward collapse of inferior orbital wall with an ipsilateral volume decrease of maxillary sinus. We present a case of imploding antrum syndrome after an orbital decompression surgery.

A 26-year-old female underwent inferomedial wall orbital decompression surgery through a caruncular approach to reduce exophthalmos. At 14 months after surgery, her right eye showed 2 mm of enophthalmos and orbital CT scan revealed both maxillary sinusitis. At 28 months after surgery, 3 mm of enophthalmos and hypoglobus of the right were observed, and an orbital CT scan was taken. Orbital CT scan showed a downward collapse of inferior orbital wall, a volume decrease and inward bowing of the maxillary sinus, and a maxillary opacification on the right side, which are typical findings of imploding antrum (silent sinus) syndrome.

Imploding antrum (silent sinus) syndrome after orbital decompression surgery is a rare complication. Considering that any prolapsed orbital fat after orbital decompression surgery could result in imploding antrum syndrome with hypoventilation of a maxillary sinus, care should be taken to keep the maxillo-ethmoidal interface (bony strut) intact, which helps maintain maxillary aeration.