## 4 Discussion
[PERSON] and [PERSON], in a prospective multi-center study of 251 patients, with a 5-year assessment of safety and aesthetic results after facial soft-tissue augmentation with polyacrylamide hydrogel, recorded a total of 53 adverse events and two serious adverse events related to treatment, thirteen adverse events which were gel indurations and four cases of infection [29]. On the other hand, [PERSON] et al. published a series of unacceptable results following polyacrylamide hydrogel injections: the study evaluated 98 patients who attained unsatisfactory results and complications from injections with Aquamid. The most common adverse events seen were inflammation (52%), asymmetry (32%), irregularity (18%), abscess formation and infection (11%) and product displacement (8%) [30]. Nevertheless, short-, medium- and long-term encouraging results have been published over time, leading us to consider polyacrylamide hydrogel filler a good and safe option in facial wasting rehabilitation [26; 27; 28; 29; 31; 32; 33]. In 2015, [PERSON] et al. presented their 10-year experience with 751 patients, recording indurations in 6.7% of patients and nodules in 3.8%. Five patients (4.8%) had local infections. A further 15 patients with a shorter follow-up (less than 10 years) presented local infections (overall incidence of infection 2.7%); the product had to be withdrawn in three cases [32]. Regarding the tardive swelling that developed in one patient receiving CaHA filler injections, this was already published by [PERSON] as an anomalous case report [34], although it was resolved with 3 days of oral corticosteroids; an acute inflammation of the injected fillers, as recently described for HA fillers, was hypothesized [35]. In the present paper, four patients also received DCA injections in order to reduce buffalo hump in three cases and bullfrog neck in another one. The buffalo hump deformity is a well-described manifestation of HIV-associated lipodystrophy, characterized by dorso-cervical fat pad enlargement [19]. The bullfrog neck deformity is a much rarer clinical condition and is represented by a different degree of cervical fat pad enlargements [36]. After DCA injections, a huge degree of swelling, redness and bruising of the injected area was recorded for a period between 15 and 24 days, and no other complications were recorded. Immediate post-operative swelling, pain and redness lasting 15 to 28 post injective days is the normal course following DCA injections. When DCA is injected into fat, it alters the permeability of fat cell membranes, causing progressive cellular swelling that ultimately results in the breakup of fat cells. This process can take several days to several weeks. After the cellular breakup, macrophages enter the site and eliminate the cytoplasm and cell membrane, while the healing process is carried out through the development of fibrotic tissue. The entire process, including healing, usually takes several months [37; 38]. With the exception of the tardive swelling reported after CaHA injections, complications were recorded just after polyacrylamide hydrogel injections and are coherent with what already published in literature. The main limitation of the present study in represented by the lack of continuous follow-up for all of the patients. Although the patients' satisfaction is beyond the topic of this article, all the patients were happy or very happy with the results. However, when late-onset complications arose, in the two patients who required abscess drainage, their compliance dramatically decreased [39].