Abstract

Background: Brain abscesses are a potentially curable but life-threatening medical condition. Their occurrence within brain metastases has been exceptionally reported. In this study, we describe in detail this rare entity.

Case Description: A previously healthy 64-year-old female was referred to our neurosurgical department with right-sided deviation of the oral commissure and a 7-day history of holocranial headache. Magnetic resonance imaging revealed a tumor in the right frontal lobe, exhibiting an iso-intense signal on T1-weighted images with heterogeneous enhancement. On diffusion-weighted imaging, the lesion displayed a hyperintense signal. A body computed tomography scan identified a lung tumor in the left superior lobe and a potential metastasis in the right adrenal gland. Intraoperative findings and histopathological examination revealed metastasis from lung adenocarcinoma. In addition, purulent content was noted within the abscess, and cultures identified Staphylococcus epidermidis and Streptococcus mitis.

Conclusion: Abscess formation within metastases is rarely diagnosed preoperatively, primarily because these lesions do not present with characteristic clinical or radiological features. Early recognition of this entity is crucial for establishing an appropriate treatment plan.

Keywords: Abscess formation, Lung cancer, Metastasis, Neuro-oncology

INTRODUCTION

The formation of an abscess within brain metastasis is an event infrequently reported in the literature. The lack of awareness about this entity leads to misdiagnosis. The development of different sequences of magnetic resonance imaging (MRI), such as diffusion-weighted imaging (DWI) or apparent diffusion coefficient (ADC), and spectroscopy may help to diagnose.[ 4 ]

We report a case of brain metastasis from lung adenocarcinoma with a concomitant abscess formation. This study aims to review the main characteristics of this rare phenomenon.

CASE DESCRIPTION

A previously healthy 64-year-old female was admitted to our Neurosurgical Department due to the discovery of a cerebral tumor on a computed tomography (CT) scan. She had smoked approximately 20 cigarettes/day for 15 years before admission. No other relevant medical conditions were noted, although she had multiple missing teeth. On admission, she presented right-sided deviation of the oral commissure and a 7-day holocranial headache. Fever or neck stiffness was not detected. Physical examination only showed a left flattened nasolabial fold.

A chest X-ray showed a left upper-lobe lung mass. MRI revealed a 25 mm rounded lesion in the right-lobar frontal tumor with an associated hemispheric vasogenic edema and 5 mm displacement of the midline. On T1-weighted images, the lesion presented an iso-intense signal with a heterogeneous center and annular enhancement after gadolinium administration and a heterogeneous signal on T2-weighted images. On DWI, it showed a central slight hyper-intense signal and a halo of hypo-intense signal [ Figure 1 ]. A body CT scan confirmed the presence of the lung mass in the left superior lobe, along with mediastinal and perihilar bilateral adenopathies and bronchogenic seed, as well as a lesion in the right adrenal gland consistent with metastasis. Blood test revealed no significant inflammatory parameters, but carcinoembryonic antigen, CA 15-3, and CA 125 were elevated.

Figure 1:

Magnetic resonance imaging reveals a mass lesion in the right frontal lobe. (a) T1-weighted images reveal a mass lesion in the right frontal lobe that appears iso-intense. (b) Gadolinium-enhanced sequences show irregular enhancement with an annular ring. (c) T2-weighted images demonstrate a heterogeneous signal. (d) Diffusion-weighted imaging (DWI) shows central areas of high signal intensity (restriction) interspersed with peripheral regions of low signal intensity (no restriction).

Due to the extension of the primary tumor, thoracic surgery was declined, but cranial surgery was performed. The tumor was approached through a right frontal craniotomy and a transsulcal approach. During the procedure, the lesion was punctured, and unexpectedly, purulent material flowed from inside and, consequently, was collected. Finally, the tumor was completely removed. Five days after surgery, the patient was discharged without complications. Cultured from the pus isolated Staphylococcus epidermidis and Streptococcus mitis. Pathology revealed epithelial cells with mitotic activity and mucoid cytoplasmic inclusions forming a glandular but irregular pattern, consistent with metastasis from lung adenocarcinoma [ Figure 2 ]. The patient completed a 6-week regimen of ceftriaxone and was followed by whole-brain radiotherapy and systemic chemotherapy. After 8 months of follow-up, the patient remains stable.

Figure 2:

(a) Hematoxylin and eosin stain of the brain lesion (×10). (b) Periodic acid–Schiff stain (×40). Epithelial cells and mucoid cytoplasmic inclusions – arrows – which determine their glandular origin.

DISCUSSION

Approximately 40% of cancer patients develop brain metastases during their disease. Melanoma has the highest propensity to metastasize into the brain, followed by lung and breast carcinomas.[ 3 ] Overall, 50% of metastases arise from lung carcinoma, followed by breast carcinoma.[ 5 , 18 , 26 ] Brain abscesses, on the other hand, are a well-known process and relatively common in daily neurosurgical practice.

Although both brain metastases and brain abscesses are common, their coexistence is rare. This phenomenon has been reported mainly in pituitary adenomas, meningiomas, gliomas, and rarely in craniopharyngiomas, Rathke’s cleft cyst, and primary central nervous system lymphoma.[ 8 - 10 , 12 - 14 , 24 ] To our knowledge, abscess formation within metastases has been documented in only eight patients.[ 1 , 4 , 16 , 19 , 21 , 23 , 27 ]

Pathophysiology of abscess formation in metastases

It is remarkable how some cancers metastasize to the brain, despite the blood–brain barrier (BBB) being the tightest barrier in the body. The current studies have shown that non-small cell lung carcinomas overexpress proteins involved in interactions between metastatic cells and endothelial cells, as well as in angiogenesis and reprogramming of glial cells toward an immunosuppressive state.[ 30 ] The process of abscess formation involves several mechanisms, including hematogenous co-metastasis of bacteria and tumoral cells, over-infection from distant infection, or a single coincidental event. Metastatic cells passing through the BBB induce endothelial cell impairment, which makes it easier for the penetration and proliferation of bacterial agents.[ 1 ] This process may be further facilitated by the optimal environment provided by tumoral necrosis and immunosuppressive conditions, such as diabetes mellitus, steroid use, chronic diseases, or other acquired immunodeficiencies.[ 1 , 27 ] No known predisposing factors were identified in our patient, although her immunological status was not assessed.

Bacteriology

Up to 50% of cultures of abscess material in brain tumors are negative. Gram-positive bacteria are more common in metastatic tumors, though cases with Salmonella, diphtheroids, or Acinetobacter have also been reported.[ 11 , 16 , 19 , 23 ] In our patient, S. epidermidis and S. mitis were isolated from the pus. S. mitis is a member of the Streptococcus viridans group, which is involved in almost two-thirds of brain abscesses.[ 15 ] Both S. mitis and S. epidermidis are oral commensals that can cause polymicrobial brain abscesses.[ 20 , 22 ] The disruption of the tooth-tissue interface in our patient may have facilitated their entry into the bloodstream, leading to abscess formation.

In pathological studies, although bacteria are not usually observed, some inflammatory features, such as pus or leukocytes, may be seen.[ 14 , 17 ]

Clinical presentation and blood test findings

Abscess formation within tumors rarely causes the classic triad of abscess symptoms, which includes fever, meningeal signs, and altered levels of consciousness. Clinical features vary depending on the location of the metastasis. Intracranial hypertension symptoms and symptoms secondary to mass effect, such as headache, focal neurologic deficit, or ataxia and gait disturbance in metastasis located in the posterior fossa, are common.[ 4 , 11 , 19 ]

Particularly, pyrexia is as frequent as focal deficit in abscess formation in meningiomas, while sellar tumors often with chronic headache, visual impairment, and hypopituitarism symptoms.[ 6 , 14 ]

In cases of abscess formation, infectious signs such as fever or meningismus, as well as inflammatory parameters in blood tests, may be absent. These features may be missing even in the presence of a brain abscess due to the lack of overt systemic infection, which complicates diagnosis.[ 8 , 28 ]

Radiological features

Metastases, gliomas, and abscesses are frequently confused on conventional MRI.[ 2 ] These lesions generally present with hypo-intense signals on T1-weighted, resulting from intratumoral necrosis, with peripheral enhancement after contrast administration. On T2-weighted images, they display heterogeneous or hyperintense signal. All of these lesions may exhibit a ring-enhancing pattern, although this is more typical in brain abscesses.

Recent advances in MRI, including DWI and ADC techniques, have greatly improved the diagnosis of a brain abscess. On DWI, brain abscesses show homogenously hyper-intense signals because of restricted diffusion, along with a significantly reduced ADC, reflecting their high viscosity and cellularity. In contrast, metastases and gliomas commonly exhibit unrestricted diffusion within the lesion and restricted diffusion in their borders on DWI, with low signal on ADC. In the present case, the lesion exhibited mixed features on DWI, which have previously been associated with irregular densities of pus, tumor cells, necrosis areas, or hemorrhage.[ 14 , 29 ]

In brain spectroscopy, brain abscess shows a high level of lactate, alanine, cytosolic acid, and acetate, which originate from the enhanced glycolysis and fermentation of the infecting micro-organisms. However, these findings are inconsistent. A high choline/creatine ratio is often observed in metastatic tumors, whereas this ratio tends to be lower in cerebral abscesses.[ 2 , 7 ] However, the mixed signal pattern in cases of brain metastases with abscess formation can create overlapping features, making the diagnosis challenging.[ 14 ]

Treatment and outcome

Without surgical intervention, abscess formation within metastases may lead to acute neurologic deterioration and death. Unexpected abscess formation may be overlooked during surgical excision if the purulent content is not collected and cultured, often being mistaken for a necrotic liquefied cyst.[ 4 ] Therefore, total tumor resection followed by specific antibiotic therapy is essential.

The overall survival rate has significantly improved with recent advances in immunotherapy and chemotherapy. The presence of brain metastases remains a critical factor for poor prognosis, being the median overall survival in these cases being approximately 12 months.[ 25 ] Nevertheless, the concurrence of abscess formation within brain metastases does not significantly impact prognosis.[ 11 , 19 ]

CONCLUSION

Abscess formation within metastases may be easily misdiagnosed, as it does not present characteristic clinical and radiological features. Therefore, it is often an unexpected intraoperative finding. Despite being a rare event, this entity should be recognized to optimize disease management.

Ethical approval:

Institutional Review Board approval is not required.

Declaration of patient consent:

Patient’s consent not required as patient’s identity is not disclosed or compromised.

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.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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