Purpose: To review the clinical and radiologic characteristics of a group of patients who experienced late enophthalmos after bone-removing orbital decompression. The surgical management of these patients is presented and a hypothesis proposed to explain the idiopathic "imploding antrum" ("silent sinus") syndrome.
Design: Retrospective, noncomparative case series.
Participants: Six patients experienced relative enophthalmos, hypoglobus, and upper eyelid sulcus deformity at between 3 and 6 months after bone-removing orbital decompression for thyroid orbitopathy. Five left orbits and one right orbit were affected.
Intervention: All patients underwent middle meatal antrostomy, together with mobilization and elevation of the collapsed orbital contents by firm packing of the affected maxillary antrum through a buccal antrostomy, the pack being removed about 3 weeks after placement.
Main outcome measures: Symptomatic improvement and reduction in the degree of relative enophthalmos, hypoglobus, and upper eyelid sulcus deformity.
Results: Late-onset enophthalmos after orbital decompression was associated with clinical and radiologic features that resemble the idiopathic imploding antrum syndrome. In all patients, the ethmoidal infundibulum was obstructed by prolapsed orbital fat with secondary antral consolidation, and inward bowing of the maxillary walls was present in five of six patients. After antral drainage and packing, there was an improvement in enophthalmos (mean, 2.7 mm; range, 0-4 mm) and all but one globe returned to within 2 mm of exophthalmometry of the contralateral eye. For recurrent enophthalmos in two patients (minor in one patient and marked in the other), later repair of the orbital floor was undertaken through a lower eyelid swinging flap, using porous polythene sheet, with good cosmetic outcome.
Conclusions: Late-onset enophthalmos after bone-removing orbital decompression seems to be the result of obstruction of maxillary antral aeration, with secondary fluid retention and a subatmospheric pressure in the sinus. This iatrogenic condition, associated in most cases with inward collapse of the maxillary walls, provides a guide to a hypothetical mechanism for the idiopathic imploding antrum (silent sinus) syndrome.