Silicone has been used in surgery for over 30 years in procedures such as joint replacement and breast augmentation. Initially, it enjoyed a reputation as being a biologically inert substance. Over the past 15 to 20 years, however, concerns over the safety of silicone implants have culminated in several well-publicised legal cases and negative media reports. Its use has been curtailed for fears of association with granulomatous reactions and, in rarer cases, malignancy [1, 2]. Injections of free silicone into breast tissue have long been abandoned in the United States following the development in some women of disfiguring complications such as gravitational migration through the soft tissues to distant sites [1, 3].
Silicone is a non-biodegradable prosthetic material which elicits relatively little local inflammation in most people due to its low tissue immunogenicity [3]-[6]. It is composed of dimethylsiloxane polymers which can result in differing properties and products according to the variation in their chain lengths and cross-links [4, 7]. Liquid silicone consists of short chains, and gels are made from long chains [4].
Despite its initial reputation as a biologically inert substance, it has been associated in the literature with numerous, albeit rare, complications including local and systemic granulomatous inflammatory reactions affecting breast tissue, lymph nodes, joint capsules, the heart, liver and kidneys. In addition, it has been suggested that silicone may be a causative factor in the development of adult respiratory distress syndrome (ARDS), various connective tissue and autoimmune diseases and human adjuvant disease [4, 8, 9]. At present, the mechanism of such complications is uncertain and in some cases, proof of such a relationship remains a source of controversy [2, 9]-[11]. Malignant lesions including lymphoma and cancers of the breast and lung have arisen in those with silicone prostheses although again there has yet to be any firm proof of its carcinogenicity. Indeed, some papers have shown a reduced relative risk of breast cancer in women with breast implants [1, 4, 12]. The inflammatory reaction is thought to be more pronounced in the lymph nodes than in connective tissue [1, 8].
Silicone particles can migrate through tissues following either rupture or erosion of a silicone-containing surface or through continued leakage through an intact surface [1, 3, 4, 6, 8]. The risk of rupture and/or leakage increases with increasing age of the implant, the site of implantation (retroglandular as opposed to submuscular), the presence of local tissue contractures and/or symptoms and the type and/or manufacturer of the implant used [6, 7, 13]. The average age at rupture varies between studies but is in the region of 10 to 13 years and it is best diagnosed with magnetic resonance imaging (MRI) scanning [4, 14]. Rupture itself is normally a relatively harmless condition which only rarely progresses and becomes symptomatic [15].
When leakage does occur, silicone can cause fibrosis and foreign body granulomatous reactions, especially when combined with certain fatty acids, resulting in pain and contractures [4, 6]. Once silicone particles have breached the confines of their prosthesis and passed through any local fibrotic reaction, they may be transported to regional lymph nodes by macrophages in the reticulo-endothelial system [1]. The resulting granulomatous reactions may present as lymphadenopathy and, when sited in the axilla, malignancy of the ipsilateral breast is a diagnosis which needs to be excluded. Indeed, it is not impossible for both silicone granulomata and breast cancer metastases to coexist in the same lymph node [6].
Silicone lymphadenopathy has been reported more frequently following joint surgery than following breast augmentation either by silicone gel implants or silicone injection [1, 6]. When associated with breast augmentation, it primarily affects the axillary nodes but cases have been reported involving intramammary, internal mammary and supraclavicular nodes [3, 5].
Fine needle aspiration (FNA) of affected lymph nodes has been shown to be a cost effective and accurate method of excluding malignancy and diagnosing implant disruption in patients with silicone prostheses presenting with an axillary mass [6]. Under such circumstances, fine needle aspiration cytology (FNAC) shows a foreign body reactive lymphoid background with numerous giant cells [1, 6]. Specifically, one sees cystic spaces with multivacuolated macrophages but relatively few multinucleated giant cells [1, 8]. Other granulomatous processes can be excluded if birefringent particles are found in the macrophages whereas in silicone reactive macrophages, the vacuoles contain refractile, homogenous and faintly yellow non-birefringent material [1, 3, 6].
Some papers have suggested that a conservative approach involving excision of the axillary nodes is favourable. The rationale for this is that silicone granulomata have been found as incidental findings in axillary nodes removed at mastectomy for breast cancer in the presence of intact breast prostheses [1]. Also it has been suggested that silicone may dilute the cellular elements within the node and thus mask the presence of cancer cells [1]. If intramammary nodes are affected, then excision has been recommended as mammography is unable to differentiate between benign and malignant pathology [5].
