Extensive Temporal Bone Necrosis in Petrous Bone Cholesteatoma Complicated by Actinomycosis: A Case Report

Introduction

Temporal bone necrosis is a rare pathologic process, most frequently caused by previous radiation therapy, necrotizing otitis, or prolonged bisphosphonate treatment. Cholesteatoma is defined as a keratinizing squamous epithelial lesion, which can grow in different areas of the temporal bone. Under certain conditions, particularly in the presence of secondary infections of the ear, cholesteatoma can contribute to the development of temporal bone necrosis and to the formation of bony sequestra.

We report a case of extensive temporal bone necrosis with intracranial involvement in a patient affected by mastoid and petrous apex cholesteatoma, further complicated by Actinomyces infection. The association between cholesteatoma and actinomycosis leading to the formation of an osseous sequestrum is exceptionally rare and clinically significant, given the risk to critical structures within and adjacent to the temporal bone.

The uniqueness of this case lies in the extent of the necrosis and in the clinicopathological features of our patient, including an immunocompetent status, which differ from those typically observed in classical necrotizing malignant otitis. Another noteworthy aspect is the excellent postoperative outcome, marked by the absence of disease recurrence and long-term sequelae.

Case Report

A 47-year-old woman presented to the Department of Sense Organs at Sapienza University of Rome with severe right-sided conductive hearing loss, persistent otorrhea, and localized pain in the right mastoid region. Symptoms had been present for approximately 2 months with a gradually progressive course. The patient reported that she initially underappreciated their significance. Her presentation to our department was further delayed while she completed an unsuccessful course of oral amoxicillin–clavulanate and corticosteroid otic drops prescribed by an outside otolaryngologist.

In the weeks preceding presentation, she also had intermittent episodes of dizziness and vertigo, although no neurological deficits were observed on clinical examination. Her medical history was negative for previous otologic diseases or ear surgeries, with no evidence of diabetes mellitus or immunodeficiency. She was not undergoing bisphosphonate therapy and had not received radiotherapy, thereby excluding osteoradionecrosis from the differential diagnosis.

Otoscopic examination revealed a whitish mass obstructing the right external auditory canal accompanied by purulent otorrhea. Facial nerve function was preserved, with a House-Brackmann grade I score. Physical assessment identified a small retroauricular cutaneous fistula on the right side, draining necrotic material and purulent exudate. The fistula and the otoscopic findings raised concern for extensive osseous involvement and prompted urgent imaging with high-resolution CT of the temporal bone and contrast-enhanced magnetic resonance imaging (MRI).

A high-resolution computed tomography (CT) scan of the temporal bone demonstrated a destructive lesion involving the right middle ear, with extension into the mastoid process and retroauricular soft tissues. The lesion also involved the ossicular chain and the bony canal of the facial nerve (Figure 1A–1C).

MRI revealed a hypointense lesion on both T1- and T2-weighted sequences, with diffusion restriction on diffusion-weighted imaging (DWI) and marked contrast enhancement. Necrotic tissue was present in the right external auditory canal, mastoid air cells, middle ear cavity, and internal auditory canal. In addition, the enhancing tissue was located adjacent to the basal turn of the cochlea and the lateral semicircular canal. MRI further identified a second fistulous tract spreading antero-medially from the mastoid bone toward the parapharyngeal space, in close proximity to the internal carotid artery. Evidence of thrombophlebitis involving the right sigmoid and transverse sinuses was also described, along with osteomyelitic changes in the apex of the petrous portion of the temporal bone (Figure 1D–1F).

Given the patient’s clinical and radiological findings, surgical intervention was indicated. An extended petrosectomy was performed under general anesthesia. Intraoperative findings revealed a destructive necro-inflammatory process extending through the soft tissues of the retroauricular region, the mastoid bone toward its tip, the middle ear, and the petrous portion of the temporal bone. Notably, the ossicular chain and the fallopian canal were eroded up to the geniculate ganglion. Dehiscence of the tegmen tympani was identified, with exposure of the dura mater of the middle cranial fossa. All necrotic caseous material was meticulously debrided and submitted for histopathological and microbiological analysis (Figure 2).

Histological examination of the excised sample confirmed the clinical diagnosis of cholesteatoma (Figure 3A). In addition, it revealed fragments of bone tissue with empty osteocyte lacunae, as in osteonecrosis (Figure 3B). Bone tissue showed extensively scalloped surfaces (Figure 3C). Acute inflammation associated with keratinous debris and colonies of Actinomyces spp. were also observed (Figure 3C, 3D).

In contrast, microbiological cultures of the operative specimen yielded no growth, and Actinomyces spp. were not isolated.

The patient remained hospitalized for 1 month after surgery to complete a course of intravenous antibiotic therapy based on penicillin G, administered at 20 million units per day, delivered as 5 million units every 6 hours, for a total of 28 days. The dose selection was based on published recommendations for actinomycosis [1]. She then received adjuvant treatment with multiple sessions of hyperbaric oxygen therapy to promote revascularization and osteogenesis, and was subsequently discharged in good general and local clinical status.

At 1-year follow-up, no evidence of recurrence on radiologic evaluation was observed. The retroauricular cutaneous fistula was now completely healed and the patient no longer had right-sided otorrhea or otalgia. However, she continued to report occasional, self-limiting episodes of dizziness, most likely attributable to residual peripheral vestibulopathy secondary to the preoperative extent of disease. Remarkably, no postoperative facial nerve deficit was observed, despite the significant erosion of its bony canal noted during surgery.

Discussion

Cholesteatoma is a keratinizing squamous epithelial lesion capable of inducing significant bone resorption and sequestrum formation within the temporal bone through multiple, interrelated mechanisms. Osteoclastogenesis promoted by the inflammatory cytokines TNF-α, IL-1, and IL-6, as well as the activation of enzymes such as collagenases and matrix metalloproteinases (MMPs), enhance bone demineralization. It has been demonstrated that variations in cellular expression of MMPs and their endogenous inhibitors contribute to the pathophysiology of cholesteatoma, suggesting an imbalance between matrix degradation and regulation [2].

In addition to its biochemical effects, the growth of cholesteatoma exerts a destructive mass effect due to the pressure on the adjacent structures of the temporal bone [3–5]. This pressure can compromise blood flow, resulting in ischemia and subsequent necrosis of bone tissue. As the necrotic bone loses its blood supply, it can become separated from the surrounding healthy bone, forming a sequestrum. The latter is defined as a fragment of necrotic, devitalized bone that becomes isolated from the surrounding viable osseous tissue.

A necrotic sequestrum can facilitate secondary microbial colonization. The bacterial infections, in turn, intensify the osteolytic process by promoting granulomatous response [6]. This cyclical interplay between infection, inflammation, and necrosis underlies the severity of advanced cholesteatomatous disease, especially in the tympanic part of the temporal bone. This area is particularly susceptible to necrosis formation due to its precarious blood supply, its superficial location, and communication with the microbial flora of the upper airway [7].

Actinomycosis is a chronic suppurative infection caused by Actinomyces species, a group of facultative anaerobic, gram-positive, filamentous bacteria. Although typically saprophytic and considered part of the normal commensal flora of the oropharynx, gastrointestinal tract, and genitourinary system, Actinomyces can become pathogenic under specific conditions, particularly following mucosal disruption. The cervicofacial region is the most frequently involved site and otologic manifestations are exceedingly rare [1].

Actinomycosis alone is less frequently associated with temporal bone necrosis when compared to cholesteatomas. Nevertheless, when cholesteatoma and bacterial infection coexist, like in our reported case, their combined effects facilitate the mechanisms of bone resorption and chronic inflammation, thus impeding the normal healing processes. Over time, the progressive compromise of temporal bone integrity leads to osteonecrosis, and its extension can result in an increased risk of severe complications, such as facial nerve palsy, labyrinthine fistula, and intracranial involvement [1,3,4].

Actinomycosis of the middle ear is an uncommon disease, with fewer than 50 cases documented in the literature to date [8]. In a case reported by Modi et al, middle ear actinomycosis was initially suspected to be a cholesteatoma due to the presence of ossicular chain erosion on high-resolution CT. However, unlike our patient, histopathological examination revealed no evidence of keratinizing squamous epithelium, which ultimately excluded the diagnosis of cholesteatoma [9].

To the best of our knowledge, this is the only documented case of a temporal bone sequestrum associated with concomitant cholesteatoma and actinomycosis in an immunocompetent patient, without prior irradiation of this region. Another distinctive feature is the discordance between negative intraoperative cultures and the histopathological demonstration of Actinomyces colonies within the necrotic bone specimen. This highlights that actinomycosis can be culture-negative and that, in such circumstances, clinical suspicion together with histopathological examination is crucial to establishing the correct diagnosis [10,11].

It is important to delineate the differences between our case and the more typical osteomyelitis of the temporal bone, which usually occurs as a complication of necrotizing malignant otitis. This condition is an aggressive, invasive bacterial or fungal infection, most commonly caused by Pseudomonas aeruginosa, which typically affects elderly, diabetic, or immunocompromised individuals.

Management of temporal bone osteomyelitis complicated by necrosis and sequestrum formation typically requires prolonged courses of culture-directed intravenous antibiotics and surgical debridement with sequestrectomy to remove devitalized tissue and prevent further complications [12]. Our reported case necessitated the same treatment, with particular attention to monitoring the facial nerve, which was extensively dehiscent along its tympanic and mastoid segments. Hence, the postoperative preservation of facial nerve function was particularly remarkable in this patient.

Radiological imaging plays a crucial role in diagnosing temporal bone necrosis. HRCT scans reveal cortical bone erosion and the presence of bone sequestrum appearing as a homogeneous, dense, sclerotic fragment of bone with irregular margins, often surrounded by a lucent rim of granulation tissue or purulent material. MRI is more accurate for describing soft tissue involvement and intracranial invasion. In addition, MRI is particularly efficient for assessing abnormalities of the medullary cavity of bone. The necrotic bone appears hypointense on T1-weighted images and often hypointense on T2 due to low water content and dense mineralization [12–14].

Postoperative hyperbaric oxygen therapy is an adjuvant treatment indicated for extensive necrosis of the temporal bone. It elevates the partial pressure of oxygen within the wound microenvironment, thereby enhancing the oxidative killing capacity of phagocytes against microorganisms and facilitating angiogenesis and osteogenesis [15].

Conclusions

The occurrence of temporal bone necrosis caused by cholesteatoma and actinomycosis, although very rare, is a critical topic in otology and neurosurgery, especially for the complications that can arise intracranially and to the facial nerve. The recommended management is meticulous surgical debridement, followed by adjunctive hyperbaric oxygen therapy and a prolonged course of intravenous antibiotics postoperatively. This case report demonstrates that bone necrosis can develop and severely damage the temporal bone even in the absence of the most common risk factors associated with this condition.