Epidermoid cyst and abscess following titanium mesh cranioplasty: A rare case report

Abstract

Background:

The development of a slowly enlarging epidermoid cyst (EC) near a scalp incision following titanium mesh cranioplasty (TMC), with subsequent progression to an epidural abscess after resection, represents an exceedingly rare iatrogenic complication.

Case Description:

A 68-year-old male, who had undergone decompressive craniectomy followed by staged bilateral TMC 5 years earlier for traumatic brain injury, presented with a solitary scalp mass that had been noted 1 year prior. Six months after the mass was resected, the patient developed an epidural abscess. Pathological examination confirmed the diagnosis of an EC, chronic inflammation, and Staphylococcus epidermidis growth.

Conclusion:

This case suggests that the EC and subsequent abscess were likely related to the prior TMC, highlighting this clinical course as a rare but serious iatrogenic complication of the procedure.

INTRODUCTION

Titanium mesh cranioplasty (TMC) is associated with significant complications, with rates reportedly as high as 15.0% in a recent study (Hauerberg et al., 2024).[2] We have previously proposed[11] that cranioplasty failure using materials such as silicone and titanium mesh may be due to the body’s persistent rejection reaction to the allogeneic implant. To our knowledge, the occurrence of an epidermoid cyst (EC) and abscess following TMC, as described here, represents the first such reported case. Nonetheless, it constitutes the fifth reported case of iatrogenic complications in neurosurgery [Table 1].

Table 1:

Diagnosis of iatrogenic epidermoid cysts.

CASE DESCRIPTION

A 68-year-old male patient underwent bilateral decompressive craniectomy due to severe traumatic brain injury 5 years earlier, followed by staged secondary bilateral TMC. Approximately 1 year before presentation, a noticeably raised, gradually enlarging mass measuring approximately 20 × 20 mm developed along the medial edge of the left frontal surgical scar. The mass was soft in consistency and demonstrated nonrebounding depression upon digital pressure [Figure 1a]. Computed tomography [Figure 1a] and contrast-enhanced magnetic resonance imaging [Figure 1b and c] findings were consistent with a preliminary diagnosis of a subcutaneous intracranial penetrating cyst. Findings from other routine examinations were unremarkable.

Figure 1:

Preoperative imaging: (a) Noncontrast computed tomography scan, arrow indicating localized soft tissue bulging in the left forehead; (b and c) Contrast-enhanced magnetic resonance imaging, arrows pointing to a spherical cystic lesion in the left forehead with mild wall enhancement, half of the cyst located intracranially.

With approval from the Ethics Committee (No. 202528), under general anesthesia, initial needle aspiration of the mass was performed, revealing gray-white, caseous, paste-like material. The mass was then completely excised by dissecting along its well-defined capsule. It was soft in consistency and extremely tightly adherent at its base to the titanium mesh, with extension through the mesh pores into the epidural space as a dumbbell-shaped lesion, which was firmly bound to the underlying thickened dura mater. The titanium mesh was incised to accomplish total resection, and the cyst wall was meticulously separated from the dura using sharp micro-dissection [Figure 2]. The surgical field was thoroughly irrigated to prevent residual cyst contents. The wound healed primarily, and the patient was discharged. Notably, because the patient remained completely asymptomatic during the 5-year postcranioplasty interval, no routine radiological surveillance was performed until the recent appearance of the scalp mass; hence, baseline historical scans capturing chronological enlargement rates were unavailable.

Figure 2:

Intraoperative photograph during the second surgery, revealing inflammatory granulation and mass tissues tightly adhering to and eroding through the pores of the previously implanted titanium mesh, extending into the underlying epidural space.

Unfortunately, 6 months later, the patient developed an epidural abscess at the surgical site, which required surgical evacuation and antibiotic therapy. The wound healed by secondary intention, and the patient was discharged. No new symptoms were observed during a 6-month follow-up period.

Final pathological diagnosis revealed that the outer layer of the cyst wall consisted of dense fibrous connective tissue with proliferative small blood vessels. The cyst wall was lined by stratified squamous epithelium, which from external to internal showed basal layer, spinous layer, and granular layer in sequence. The cyst lumen contained eosinophilic, lamellar-arranged keratinous debris.

The aspirated gray-white, caseous material was consistent with keratin, confirming the diagnosis of an EC. Bacterial culture of this specimen yielded no growth.

Microbiological culture of the tissue obtained during the second surgery grew Staphylococcus epidermidis. Histopathological examination revealed focal inflammatory cell infiltration with no residual EC tissue identified. Detailed morphological features are shown in Figure 3.

Figure 3:

Clinical and histopathological presentation of the mass. (a) Scalp mass presenting as a raised, soft lesion protruding along the previous surgical incision scar, displaying nonrebounding indentation upon digital pressure. (b) Gross appearance of the aspirated gray-white, caseous, paste-like cyst contents (red arrow). (c) Histopathological examination of the cyst contents stained with hematoxylin and eosin, revealing characteristic eosinophilic, lamellar-arranged keratinous debris (Scale bar = 100 μm). (d) Histopathological view of the cyst wall with hematoxylin and eosin (H&E) staining, showing distinct stratified squamous epithelial layers from inner to outer: the stratum corneum (yellow arrow), granular layer (green arrow), spinous layer with densely arranged cells (red arrow), and the basal layer with cells arranged in a palisade pattern (blue arrow) (×20; scale bar = 100 μm).

DISCUSSION

ECs are characterized by a wall of mature squamous epithelium and contain keratinous material. They most commonly occur on the face, neck, and upper trunk and are generally attributed to damage or disruption of the pilosebaceous unit. Clinically, they present as slow-growing, dome-shaped, cystic nodules on the skin surface and can be completely excised surgically.

However, for a diagnosis of iatrogenic EC (IEC), a direct causal relationship with a preceding medical procedure must be established, as detailed in Table 1. To our knowledge, only five cases of IEC managed within the field of neurosurgery have been reported [Table 2]. Case 6 in the table should not be classified as an IEC but rather represents iatrogenic cerebral vasospasm triggered by intraoperative rupture of a preexisting EC and subsequent spillage of its contents[4]; it is therefore more accurately categorized as a distinct iatrogenic complication.

Table 2:

Iatrogenic epidermoid cysts reported in neurosurgery.

The other five cases[1,3,6-8] meeting the diagnostic criteria for IEC demonstrate a clear cause-and-effect relationship between a medical procedure and the complication. Even minimally invasive interventions, such as lumbar puncture, can breach the skin barrier. If this manipulation inadvertently implants epidermal keratinocytes (particularly basal layer cells) into deeper tissues, these cells may persist, proliferate, and undergo keratinization within the dermis or subcutaneous layer. This process leads to the gradual formation of a cystic wall that encloses accumulating keratin debris, eventually resulting in cyst development.

In the context of TMC performed in neurosurgery, potential etiologies for IECs may include excessive surgical traction, inadvertent use of sharp instruments, or implantation of epidermal cells via electrocautery-induced splattering. Notably, electrocautery may cause damage to follicular structures, potentially obstructing the normal excretion of sebum and keratin. In addition, surgical flap elevation can compromise scalp perfusion; resultant local ischemia may adversely affect the tissue repair process and lead to aberrant healing. Furthermore, a pro-inflammatory microenvironment could alter the local niche, potentially enhancing the survival and proliferation of implanted epidermal cells.

The mechanisms underlying the progression of ECs, including their enlargement and associated bacterial infections, have not been fully elucidated. Zhao et al.[10] reported an intradermal EC that expanded through an osteolytic mechanism, eroding through the calvarium. Yufeng et al.[9] documented an EC within the cranial diploë, with culture of its contents yielding Staphylococcus aureus. Kohno et al.[5] described a case of an intracranial epidural EC in the right parasellar region. Three years after the initial surgery, the patient underwent a second procedure for recurrence in the right parasellar area and a right temporal brain abscess. Unfortunately, the patient succumbed to bacterial meningitis and encephalitis 11 months later despite aggressive antibiotic treatment.

Based on the present case, in which an EC developed following TMC for traumatic brain injury and an epidural abscess emerged 6 months after EC surgery, we propose a pathogenetic hypothesis. We suggest that ECs possess a degree of local invasiveness. Given their documented capacity to erode through cortical bone and expand into the diploë over years or even decades, forming large mass lesions, traversing the pores of a titanium mesh would likely be a straightforward process. The development of an abscess following EC surgery has a multifactorial etiology, which may be related not only to the disease process itself but also to factors of clinical management.

CONCLUSION

The development of an IEC and subsequent epidural abscess is a rare but severe delayed complication of TMC. This case demonstrates that inadvertently implanted epidermal cells can not only proliferate over years but also utilize the pores of the titanium mesh as a conduit to extend into the epidural space, thereby predisposing the patient to deep infections. To mitigate this risk, neurosurgeons must emphasize meticulous tissue handling, avoiding unnecessary thermal or mechanical trauma to the skin flap during initial and reconstructive procedures. Furthermore, any delayed, progressively enlarging mass overlying a cranial implant should raise high clinical suspicion for an iatrogenic lesion, warranting prompt and complete microscopic resection to prevent secondary central nervous system infections.

Ethical approval:

The research/study was approved by the Institutional Review Board at The Medical Ethics Committee of Zhangjiagang Third Hospital, number 202528, dated June 18, 2025.

Declaration of patient consent:

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given consent for their images and other clinical information to be reported in the journal. The patient understands that the patient’s names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship:

Nil.

Conflicts of interest:

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation:

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

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