INTRODUCTION

Cranioplasty is a surgical reconstruction procedure for individuals who have undergone decompressive craniectomy to manage intractable brain swelling. This procedure is essential for protecting the brain, achieving aesthetic satisfaction, and preventing headaches, seizures, or the syndrome of the trephined [1]. The integrity of the skull can be restored either by reimplanting autologous bone or by using allogenic materials such as polymethyl methacrylate bone cement or patient-specific implants made from titanium or polyether ether ketone (PEEK). The skull flap removed during craniectomy is typically cryopreserved or stored in a subcutaneous pocket in the patient's abdominal wall or thigh. Autologous bone is particularly beneficial as it precisely matches the defect's shape without the need for additional reshaping. Its main advantages include the avoidance of foreign body reactions and cost-effectiveness [2]. Cryopreserved autologous bone is preferred for its straightforward storage process. However, despite these benefits, significant disadvantages exist, including autologous bone flap resorption (ABR) and surgical site infections (SSI) associated with cryopreserved autologous bone [3].

Here, we report a case involving complete lysis of a cryopreserved autologous bone flap accompanied by SSI following cranioplasty, necessitating further surgical intervention.

CASE REPORT

A 24-year-old woman was found unconscious after falling down the stairs following alcohol consumption and was brought to the neurosurgery department of our hospital. A neurological evaluation revealed a Glasgow Coma Scale score of 7, and a brain computed tomography (CT) scan showed an acute subdural hemorrhage with approximately 1.5 cm of midline shift along the left convexity (Fig. 1A). She underwent prompt surgery under general anesthesia, during which a left question mark incision was made, followed by a fronto-temporoparietal craniectomy (Fig. 1B). After the durotomy, the subdural hematoma was adequately removed, careful hemostasis was achieved, and duroplasty was performed. The removed cranial bone flap was cryopreserved at –80 °C for future cranioplasty. After several weeks of intensive care treatment, the patient regained consciousness, and her brain swelling had reduced. Cranioplasty using the cryopreserved autologous bone was performed approximately 3 months after the initial surgery. Postoperatively, there were no significant findings of hematoma or fluid collection on CT scans (Fig. 2), and the patient was discharged after a week of hospitalization. However, she returned to the emergency room within a week due to suspected SSI. Brain CT with contrast revealed an infection around the left temporal-parietal area (Fig. 3). We performed a tissue culture at the site of the skin defect, where a purulent discharge extending to the bone depth was observed. Through this, methicillin-resistant Staphylococcus aureus (MRSA) was detected, raising a suspicion of potential osteomyelitis. Based on previous successful cases of conservative treatment for bone flap-related osteomyelitis after cranioplasty [4,5], we decided to prioritize conservative management to avoid risks such as sinking flap syndrome and direct brain injury, while also considering the possibility of delayed surgical treatment in the future. Additionally, we planned to closely monitor her in the outpatient setting to assess the progression of the osteomyelitis. Therefore, she received 1 month of intravenous antibiotic therapy with teicoplanin and rifampin and was discharged once her wound had healed.

Three months after the initial visit, bone resorption was first observed on a CT scan performed in an outpatient setting (Fig. 4). Subsequent CT scans conducted annually revealed continued bone resorption, leading to discussions with the patient and her guardians regarding the possibility of reoperation. Throughout the follow-up period, no additional signs of infection were detected after the initial cranioplasty. However, 5 years later, she presented at the outpatient clinic with a suspected SSI once again. An abscess was identified around the bone through the skin defect site (Fig. 5A–C), and cultures once again confirmed MRSA. Given the extensive lysis observed at multiple sites of the skull bone (Fig. 5D, E), we opted to remove the remaining fragmented autologous bone graft (Fig. 6). During the removal of the bone flap, MRSA was also found in the culture of the bone fragments. She was treated with an 8-week course of intravenous teicoplanin. Six months later, she underwent a cranioplasty using PEEK material (Fig. 7). After a week of recovery, she was discharged and has since been doing well, with no significant complications reported.

Ethics statement

The patient provided written informed consent for publication of the clinical details and images.

DISCUSSION

The reported incidence of ABR following cranioplasty varies across studies, likely due to differences in the definitions of ABR and the durations of follow-up. Factors including young age, the timing of the cranioplasty, the presence of multiple fractures, and the storage method of the bone graft have been suggested as contributors to the development of ABR, based on small case series and anecdotal reports [6].

Schuss et al. [7] observed that complications such as previous wound healing issues or abscesses following cranioplasty could predict long-term ABR complications in cases of traumatic brain injury, suggesting a possible link between SSI and ABR. Additionally, some research indicates that the cryopreservation methods used for bone storage might facilitate the development of SSI, as bacteria are capable of surviving prolonged freezing while retaining their ability to grow [3,8]. In the case discussed here, autologous bone was cryopreserved for 3 months. MRSA bacteria were detected in the initial SSI wound culture, indicating a potential risk factor for ABR.

Some studies have also suggested that the duration of freezer storage may affect the occurrence of ABR [9]. Storing the bone flap in the freezer can cause bone cell death, characterized by active osteoclasts and non-viable osteoblasts, which may lead to bone resorption and a reduction in flap thickness after cranioplasty [3,8]. Additionally, insufficient flap reintegration could occur if residual fatty bone marrow within the flap acts as a barrier to osteogenesis, potentially resulting in aseptic bone necrosis [10].

Although the exact mechanism of bone resorption remains unclear, strict sterilization of autologous bone before use is crucial, particularly in severe traumatic brain injury cases where open wounds can readily expose the skull bone. Strategies to maintain bone viability include minimizing the time bone is stored in a freezer or, if early cranioplasty is not feasible, storing the bone in a subcutaneous pocket to preserve the viability of bone cells. These considerations are crucial for addressing ABR following cranioplasty and ensuring successful outcomes.

The present case is unusual because MRSA osteomyelitis recurred 5 years after initially successful infection control. The initial SSI may have played a role in the development of bone resorption. Severely lysed and fragmented bone grafts led to a change in pressure gradient, resulting in a condition similar to sunken brain syndrome. This condition could have led to skin erosion and secondary infection, although it is unclear why MRSA was specifically cultured.

ARTICLE INFORMATION

Author contributions

Conceptualization: all authors; Writing–original draft: all authors; Writing–review & editing: all authors. All authors read and approved the final manuscript.

Conflicts of interest

The authors have no conflicts of interest to declare.

Funding

The authors received no financial support for this study.

Data availability

Data sharing is not applicable as no new data were created or analyzed in this study.

Fig. 1.

Brain computed tomography (CT) image of a 24-year-old female patient presenting with traumatic brain injury. (A) The initial brain CT scan showed acute subdural hematoma in the left fronto-temporoparietal area, causing midline shift to the right side of the brain. (B) Brain CT scan showing improvement in the midline shift after emergency decompressive craniectomy.

Fig. 2.

Follow-up computed tomography taken 1 week after cranioplasty using cryopreserved autologous bone.

Fig. 3.

Soft tissue enhancement (arrow) is observed in the left temporo-parietal region on contrast-enhanced brain computed tomography.

Fig. 4.

Circumscribed lysis involving both the internal and external tables of the skull was observed in the bone graft.

Fig. 5.

Imaging showing signs suspicious of surgical site infection (SSI) in the patient and significant autologous bone resorption (ABR). (A, B) Clinical photograph taken in the outpatient setting when the patient exhibited signs suspicious of recurring SSI. A skin defect along the surgical site (circles) was observed, with pus-like discharge noted in the surrounding area. (C) Contrast-enhanced computed tomography (CT) showing soft tissue enhancement with small rim enhancement (arrow) suspicious for an abscess at the site where the initial SSI was observed. (D) CT image taken 5 years later showing progression of ABR to the complete lysis stage at multiple sites. (E) Three-dimensional volume-rendering image provides a clearer depiction of complete lysis of ABR at multiple sites.

Fig. 6.

Computed tomography image after nearly complete removal of the remaining bone fragment.

Fig. 7.

Three-dimensional volume-rendering image taken after cranioplasty using polyether ether ketone material.

REFERENCES

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Figure & Data

References

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