INTRODUCTION
Buttock filler injection is a cosmetic procedure used to enhance the shape and volume of the buttocks without requiring invasive surgery, and its popularity has increased substantially in recent years. This procedure is commonly performed to improve self-esteem, achieve a desired body contour, or address age-related volume loss. However, despite its minimally invasive nature, this approach should be critically evaluated in terms of both efficacy and safety, particularly in comparison with established techniques such as implants or autologous fat grafting.
Various techniques for buttock augmentation are available, including implants, fat grafting, and injectable fillers. Despite these options, many patients prefer filler injections due to their convenience and minimally invasive nature. However, the safety of large-volume filler injections has not been fully established. Commonly used fillers can be broadly categorized into nondegradable fillers (e.g., polyacrylamide hydrogel [PAAG], polymethylmethacrylate) and degradable fillers (e.g., non-animal stabilized hyaluronic acid) [1]. Both categories are associated with potential complications, including infection, allergic reactions, nodules, vascular compromise, pseudocyst formation related to biofilm development, and filler migration [2]. While minor filler migration may be managed with massage, manipulation, or hyaluronidase, extensive migration typically requires surgical intervention [3].
We report two rare cases of acute infection and soft-tissue necrosis associated with migration of large biofilm-related pseudocysts following massive PAAG filler injection. Both patients underwent en bloc capsulectomy followed by flap reconstruction, resulting in satisfactory outcomes without complications.
CASE REPORT
Case 1
A 56-year-old female patient underwent Aquafilling (BIOTRH s.r.o.) for bilateral buttock augmentation 10 years prior to presentation. The injected material was identified as Aquafilling based on documentation from the previous clinic, as reported by the patient. Aquafilling is a PAAG-based filler.
Over the preceding 7 months, the patient developed signs of infection at the injection site. She was treated with antibiotics and monitored at another hospital during this period. She also underwent aspiration and incision with drainage at an outside institution; however, purulent discharge persisted, and her symptoms progressively worsened. After 3 months, she noted the development of a soft-tissue defect near the sacrum. Despite daily debridement and betadine irrigation at a local hospital, no clinical improvement was observed. She subsequently presented to our clinic with an advanced sacral defect measuring 6×5 cm. Although no bone exposure was identified, a thin skin flap measuring approximately 0.5–1 cm in thickness covered a wide underlying dead space extending throughout the buttock. Circumferential undermining was present around the wound, involving a substantial portion of the buttock, with a measured diameter of 15 cm. Additionally, pinpoint sinus tracts extended toward both ischial regions. Preoperative magnetic resonance imaging (MRI) demonstrated multiple oval-shaped enhancing lesions within the subcutaneous fat layer (Fig. 1).
Preoperative laboratory testing demonstrated elevated inflammatory markers, including an erythrocyte sedimentation rate (ESR) of 51 mm/hr and a C-reactive protein (CRP) level of 34.7 mg/L. Wound and pus cultures identified Escherichia coli, and targeted antibiotic therapy with sulbactam/ampicillin was initiated. Following surgery, inflammatory markers improved significantly, with ESR decreasing to 17 mm/hr and CRP normalizing to <1.5 mg/L.
During surgery, necrotic tissue was delineated using indigo carmine dye. The dye was applied topically to the exposed raw surface rather than injected, allowing visualization of the superficial pseudocapsular layer. Dissection proceeded beyond the stained layer until healthy tissue demonstrating pinpoint bleeding was identified. Necrotic tissue was excised using a dermatome to preserve flap perfusion. During debridement, yellow, cheese-like material was identified within the subcutaneous fat and gluteus maximus muscle and was completely removed. Following near-total excision of necrotic tissue, sequential irrigation was performed using normal saline, povidone-iodine solution, hydrogen peroxide, and a final saline rinse. The gluteus maximus muscle was then elevated bilaterally from the sacral borders, and the muscle flap was advanced and secured to reconstruct the sacral defect. The remaining skin defect was subsequently covered using a double opposing rotation flap (Fig. 2).
A closed-suction drainage system (Barovac, Seun Medical) drain was placed and maintained for 14 days until drainage decreased. Histopathological analysis revealed foreign body granuloma with necrotic inflammatory tissue. No complications, such as pain or recurrence of infection, were observed during the 4-month postoperative follow-up period (Fig. 3).
Case 2
A 50-year-old female patient underwent Aquafilling filler injections for bilateral buttock augmentation 5 years prior to presentation. Three years before presentation, filler migration led to progressive bulging, erythema, and pain in the right upper lateral pelvic region and medial thigh. She underwent aspiration and incision with drainage at another clinic; however, purulent discharge persisted.
Preoperative MRI demonstrated irregular, lobulated soft-tissue swelling with multiple fluid collections in both pelvic regions. Contrast enhancement was more pronounced on the right side, where the extent of swelling and fluid collections was greater. Notably, the lesion extended from the posterolateral aspect of the right buttock to the medial inguinal-perineal region. Although both sides demonstrated infiltration into the superficial layer of the gluteus maximus muscle, no discrete abscess was identified within the deeper muscle layers (Fig. 4).
Preoperative laboratory testing revealed markedly elevated inflammatory markers, with an ESR >120 mm/hr and a CRP level of 612.5 mg/L. Wound and pus cultures identified Salmonella Group D and Corynebacterium tuberculostearicum. Based on these findings, combination antibiotic therapy with teicoplanin, ceftazidime, and metronidazole was initiated. Postoperatively, inflammatory markers improved substantially, with ESR decreasing to 30 mm/hr and CRP normalizing to <3 mg/L.
An L-shaped incision was planned to address the defect in the right buttock extending to the trochanteric region. An incision was made accordingly, and a subcutaneous flap was elevated. Indigo carmine dye was applied topically to delineate the pseudocapsular boundary of necrotic tissue. Dissection proceeded beyond the stained layer until healthy bleeding tissue was confirmed. Near-total debridement was performed, followed by coverage of the soft-tissue defect using a large local fasciocutaneous flap after capsulectomy (Fig. 5). A closed-suction Hemovac drain was placed and maintained for 10 days. Histopathological analysis revealed foreign body granuloma with necrotic inflammatory tissue.
Postoperative result
Two successful en bloc resections were performed, followed by local flap reconstruction. Postoperative imaging demonstrated removal of most filler-induced granulomatous tissue. Correspondingly, clinical symptoms, including pain and infection, improved markedly (Fig. 3). No additional postoperative complications were observed. These findings indicate a favorable therapeutic response, with sustained symptom resolution and no evidence of recurrence.
DISCUSSION
The gluteal region is increasingly regarded as an important component of physical attractiveness, particularly among women [4]. Desired aesthetic features include a rounded, elevated posterior projection and a smooth inward curvature of the lumbar region [5]. Consequently, demand for buttock augmentation procedures has increased in recent years. This trend reflects broader sociocultural shifts toward body image awareness and aesthetic enhancement. According to the American Society of Plastic Surgeons, buttock augmentation procedures increased by 252% between 2000 and 2017, making them among the fastest-growing cosmetic surgeries [6].
Autologous fat grafting has traditionally been favored as a primary method for buttock augmentation due to its use of natural tissue. However, its long-term volume retention is variable, and it is associated with complications such as fat necrosis, resorption, and, in severe cases, fat embolism [7]. Buttock implants provide a more durable alternative for enhancing contour and volume, with predictable aesthetic outcomes. However, implant-based procedures carry risks, including infection, implant displacement, and scarring, although efforts are made to minimize visible scars [8].
Soft-tissue filler-based augmentation offers a minimally invasive alternative that is theoretically associated with reduced morbidity, shorter recovery time, and fewer complications compared with more invasive procedures such as fat grafting or implant placement [1]. However, nondegradable fillers such as PAAG exhibit high bioactivity, facilitating cellular infiltration and integration into surrounding tissues, which may increase the risk of delayed complications. Notably, many injectable fillers, regardless of degradability, were initially approved but later associated with significant adverse effects. These complications include contour irregularities, infection, allergic reactions, nodules, vascular obstruction, ecchymosis or hematoma, filler migration, and pseudocyst formation [2].
In cases requiring large-volume filler injections, such as in the breasts or buttocks, the risk of pseudocyst formation and filler migration is increased. Pseudocyst formation is associated with biofilm development around the injected material [9,10]. Large-volume procedures typically require multiple injections, increasing the number of needle penetrations and, consequently, the risk of microbial contamination. If sterile technique is inadequate, resident skin flora may be introduced into the injection site, promoting microbial proliferation and biofilm formation [10]. These processes contribute to the development of large pseudocysts within the filler material. Additionally, the substantial weight of injected material may promote filler migration under gravitational forces.
Buttock fillers present additional risks due to the anatomical and functional characteristics of the gluteal region. This area is subject to frequent movement and mechanical stress from activities such as sitting, standing, and ambulation, which may compromise filler stability. Repetitive muscle contraction increases the likelihood of filler displacement or migration [2]. Furthermore, the buttocks are predisposed to infection due to the high density of sweat glands and hair follicles, which may serve as portals of bacterial entry. These factors may negatively affect aesthetic outcomes and contribute to filler migration or absorption. Therefore, meticulous technique is essential in buttock filler procedures.
Mechanical manipulation, trauma, or introduction of additional substances during pseudocapsule formation may activate biofilms. This activation can produce clinical manifestations resembling infection, foreign body granulomas, or inflammatory reactions [11]. Over time, capsular contraction may result in discomfort, contour deformity, and, in severe cases, vascular compromise or tissue necrosis.
Diagnosis involves confirmation of elevated inflammatory markers, such as CRP, through laboratory testing. Ultrasonography enables rapid assessment of pseudocyst size and distribution but may not detect distant filler migration. Therefore, MRI is recommended for comprehensive evaluation and accurate diagnosis. In our cases, MRI demonstrated multiple enhancing lesions extending from the subcutaneous fat layer to the superficial muscular fascia. Differences in the initial locations of the filler injections were also identified. Laboratory findings also played an important role in diagnosis and monitoring. Both patients exhibited markedly elevated ESR and CRP levels preoperatively, reflecting ongoing infection and chronic inflammation associated with biofilm-containing pseudocapsules. Histopathological findings revealed foreign body granulomas with necrotic inflammatory tissue, supporting a chronic foreign body reaction with secondary infection rather than a true cyst. Following en bloc capsulectomy and appropriate antibiotic therapy, inflammatory markers decreased significantly, suggesting that serial ESR and CRP measurements may serve as useful adjunctive indicators of treatment response.
We performed en bloc capsulectomy, a surgical technique aimed at removing the entire fibrous capsule and associated filler material in a single specimen, rather than performing repeated incision and drainage or limited debridement. In this context, “en bloc” refers to circumferential excision along the pseudocapsular plane to the greatest extent anatomically feasible, with the goal of minimizing residual inflamed tissue. This approach was selected for two primary reasons. First, delayed or incomplete removal may result in severe scarring and contour deformity. Second, persistent biofilm-associated bacterial burden can sustain chronic inflammation and recurrent symptoms [10]. The use of indigo carmine dye facilitated accurate delineation of the pseudocapsular boundary, enabling more complete excision. In our technique, the dye was applied topically to the exposed surface to stain the pseudocapsule and guide dissection until healthy tissue with pinpoint bleeding was identified. In addition to surgical management, tissue culture and targeted antibiotic therapy are essential for effective infection control.
Following en bloc capsulectomy, patients were followed for 2.5 and 4 months in the outpatient setting. Postoperative MRI demonstrated residual granulomatous tissue, indicating incomplete removal. However, clinical symptoms improved, and inflammatory markers normalized. Both patients reported high satisfaction and no further complications. These findings suggest that normalization of ESR and CRP may serve as indirect indicators of inflammatory resolution. In this study, recurrence was defined as clinical reactivation of infection, including pain, erythema, wound dehiscence, drainage, or re-elevation of inflammatory markers. Despite residual imaging findings, both patients demonstrated normalized CRP (<1.5 mg/L), normal white blood cell counts, absence of clinical signs of inflammation, and stable wound healing during follow-up. No reintervention was required, and no recurrence was observed during follow-up period.
This study demonstrates that large-volume filler injections, particularly in the breast and buttock regions, are associated with substantial risk. These findings highlight the importance of careful risk assessment and suggest that, when appropriate, the use of degradable fillers such as hyaluronic acid may represent a safer alternative. In addition, strict adherence to aseptic technique and appropriate postoperative care is essential to minimize complications such as infection and pseudocyst formation.
Our cases further emphasize that comprehensive evaluation—including MRI, microbiological culture, and serial inflammatory marker assessment—combined with definitive surgical management is essential for treating complex filler-related complications. These findings underscore the need for increased awareness among clinicians regarding the potential for severe complications associated with large-volume filler injections and support the use of a multidisciplinary approach in management.
Alternative treatment strategies, including repeated drainage, staged excision, or partial capsulectomy combined with prolonged antibiotic therapy, may be considered. However, in patients with extensive pseudocapsular formation, sinus tracts, and failure of prior drainage procedures, a more aggressive excisional approach with appropriate dead-space management may be required. The favorable outcomes observed in our cases likely reflect the combined effects of complete excision, culture-directed antibiotic therapy, dead-space management, and flap reconstruction rather than surgical intervention alone.
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