Novel Histopathologic and Immunohistochemical Observations in Explanted Orbital Peri-implant Capsules

To describe the histopathologic and immunohistochemical characteristics of peri-orbital implant capsule and correlate the observed changes with delayed implant extrusion.

Prospective, ex-vivo, histopathologic, immunohistochemical study of peri-implant capsules excised from capsules surrounding a poly-methyl metha acrylate (PMMA) implant. Thirteen capsules were harvested and divided into two groups. Group 1 (implant extrusion group) consisted of capsules harvested from around exposed/extruded implants and Group 2 (implant non-extrusion group) from implants that were surgically exchanged for volume augmentation. Data collected included demography, clinical presentations, etiology of the explantation, age of the capsule in months, inflammatory cells noted/high power field (HPF), CD3, CD20, and CD68, percentage Masson's trichrome staining and mean capsular thickness.

Mean patient age at presentation was 33 ± 13 years. Of the 13 capsules included, 7 belonged to group 1and 6 to group 2. Mean age of the fibro-collagenous membranes were 33 ± 57 months (median 13 months). Median CD3, CD20, and CD68 positivity was 80%, 9%, and 7% denoting a predominant T-lymphocytic response. Mean capsular thickness was 733 ± 422µ (median 678µ). Age of the harvested capsule showed a linear correlation with inflammatory cells/HPF (r = 0.93, p < .0001, 95% C.I. 0.73 to 0.98), with CD3 positivity (r = 0.6, p = .04, 95% C.I. 0.02 to 0.9), with capillary proliferation/HPF (r = 0.85, p = .003, 95% C.I. 0.43 to 0.96) and with percentage of cells showing Masson's trichrome stain positivity (r = 0.71, p = .03, 95% C.I. 0.08 to 0.93). In the extrusion group, the capsules demonstrated high inflammation and low fibrosis.

PMMA orbital spherical implant incites a predominantly T-cell mediated inflammatory response which clinically presents as a peri-implant capsule. Increasing inflammation in the absence of significant fibrosis may be responsible for delayed PMMA implant exposure and extrusion.