1. Introduction {#sec0005}
===============

The management of intracranial tumors differs greatly from that of abscesses, including the operative procedure. Therefore, precise preoperative discrimination between these two lesions is of great importance [@bib0005]. Because neuroimaging and the clinical picture cannot always differentiate between a brain abscess and a necrotic cyst within a brain tumor, preoperative differentiation remains challenging, and numerous reports have described approaches to accurately differentiating between cystic brain metastasis and brain abscess, based on comparisons of pre-operative images and post-operative histological findings [@bib0005; @bib0010; @bib0015; @bib0020; @bib0025].

If a lesion possesses the imaging characteristics of both a tumor and an abscess, it is necessary to conduct tissue sampling during surgery for pathological and microbiological testing, which can distinguish a brain metastasis from an abscess and thereby ensure the most appropriate therapeutic course. However, five reported cases had abscesses within metastatic brain tumors, and these required multidisciplinary and comprehensive strategies using both anti-cancer chemotherapy and antibiotics [@bib0030; @bib0035; @bib0040; @bib0045].

A brain abscess within a brain neoplasm is a small entity. There are only about 20 cases of abscesses associated with intracranial tumors in the literature [@bib0030; @bib0035; @bib0040; @bib0045; @bib0050; @bib0055; @bib0060; @bib0065; @bib0070; @bib0075; @bib0080; @bib0085; @bib0090; @bib0095; @bib0100; @bib0105; @bib0110; @bib0115; @bib0120; @bib0125]. However, this combination is generally fatal. Treatments for combined conditions in cases with the imaging characteristics of both a tumor and an abscess should not be delayed. Early diagnosis facilitates early treatment employing surgical management and antibiotic administration. We report a case harboring a brain abscess within a metastatic brain tumor. The relevant literature is also reviewed.

2. Case presentation {#sec0010}
====================

Two years prior to the current presentation, a 56-year-old man had been admitted to our neurosurgical department with nausea accompanying an intraventricular hemorrhage which was treated conservatively. During this short hospital stay, an aortic aneurysm and bile duct cancer were revealed, and he underwent open abdominal surgery on two subsequent occasions. As the bile duct cancer metastasized to the lung and abdominal lymph nodes, adjuvant ambulant oral chemotherapy (TS-1; tegafur, gimestat, and otastat potassium at a molar ratio of 1:0.4:1) was administered.

The patient had presented with feelings of bodily instability, an indication of truncal ataxia. Computed tomography (CT) and magnetic resonance (MR) imaging revealed two cystic lesions, one in each of the cerebellar hemispheres ([Fig. 1](#fig0005){ref-type="fig"}). The small lesion in the left hemisphere had a cystic pattern with hypo-intensity on T1-weighted images and hyper-intensity on T2-weighted images, but showed neither surrounding edema nor any ring enhancement with gadolinium. The other, larger, lesion was in the right hemisphere and was heterogeneous on T2-weighted imaging. This lesion showed surrounding edema, which was accompanied by ring enhancement with gadolinium.

Initially, we considered these lesions to be metastases, but the right lesion showed high intensity on diffusion-weighted images (DWI) ([Fig. 1](#fig0005){ref-type="fig"}), raising the possibility of a brain abscess. MR spectroscopy revealed elevated lactate, slightly elevated amino acids (0.9 ppm), and a relatively low choline peak, which also suggested an abscess ([Fig. 2](#fig0010){ref-type="fig"}). Although laboratory studies were unremarkable in terms of indicators of infection, the patient had received five operative treatments in the prior 30 years including left frontal craniotomy due to trauma and recent abdominal surgeries which also raised the possibility of a brain abscess.

To relieve the neurological symptoms and obtain a diagnosis, we performed echo-guided aspiration of the right lesion. After surgical puncture, we identified a viscoid purulent exudate. We canceled the craniotomy for lesion removal and instead inserted a drainage tube. Pathological examination of the exudate indicated large numbers of inflammatory cells but no malignant cells were detected after Papanicolaou staining, and the exudate was thus, confirmed to indicate an abscess ([Fig. 2](#fig0010){ref-type="fig"}). Because microbiological tests including anaerobic cultures were negative, we commenced intravenous administration of broad-spectrum antibiotics.

However, the lesion wall gradually grew over a period of two months, necessitating lesion extirpation. The lesion was relatively hard with numerous fine feeding arteries, and the histopathology indicated a well-differentiated adenocarcinoma ([Fig. 3](#fig0015){ref-type="fig"}). Taking these observations together with the initial findings, we diagnosed the lesion as an abscess within a cerebellar metastasis. Subsequently, we performed stereotaxic radiosurgery on the tumor cavity, and resumed anticancer drug administration. There was significant symptomatic relief of ataxia, and the patient was discharged from our hospital three months after admission with a Karnofsky performance status of 100%. The left lesion was not diagnosed pathologically and remained unchanged in size, but the number of cysts gradually increased in the following months, suggesting metastatic tumors. Ultimately, stereotactic radiosurgery was also performed on these lesions.

3. Discussion {#sec0015}
=============

The coexistence of a brain abscess and a brain tumor is rare except for intrasellar lesions where direct extension of microbial flora from the sinuses occasionally results in this complication. We reviewed the global medical literature related to brain tumors in association with abscesses using MEDLINE and found 20 reports in English, excluding those associated with trauma and neurosurgical procedures [@bib0030; @bib0035; @bib0040; @bib0045; @bib0050; @bib0055; @bib0060; @bib0065; @bib0070; @bib0075; @bib0080; @bib0085; @bib0090; @bib0095; @bib0100; @bib0105; @bib0110; @bib0115; @bib0120; @bib0125]. The clinical characteristics of these cases and our case are outlined in [Table 1](#tbl0005){ref-type="table"}. Other reported tumors associated with an abscess were 12 gliomas, five meningiomas, and five brain metastases.

The first report in the global literature of a brain abscess within a brain metastasis described an embryonal carcinoma plus seminoma in the testis with brain metastases, complicated by a *Salmonella* brain abscess [@bib0045]. The reported cases of abscess formation within a brain metastasis all had different primary lesions and infectious organisms, and due to the coexistence of a brain abscess and brain metastasis being uncommon, most of these cases were diagnosed unexpectedly after lesion removal, fluid drainage, or post-mortem examination. It may be important to consider this combined pathology in cases with the imaging characteristics of both a tumor and an abscess [@bib0030; @bib0035; @bib0040; @bib0045].

Except for direct extension of microbial flora, the pathogenesis of abscess formation within a brain tumor is considered to be related to deterioration of the systemic immune system and the blood--brain barrier [@bib0060; @bib0080; @bib0090]. Ichikawa et al. reported an intratumoral abscess with hematoma and speculated that steroid therapy, the absence of the blood--brain barrier, and poor nutrition promoted abscess formation via sepsis following phlebitis [@bib0060]. Five of the reported cases of abscess formation within a brain metastasis were regarded as having a secondary infection of a pre-existing cerebellar metastasis via hematogenous bacterial emboli from an infected site or sepsis [@bib0030; @bib0040; @bib0045]. In the present case, the patient presumably had the potential for immunodeficiency due to the chemotherapy, and this could have allowed abscess formation in a cerebellar metastasis with no blood--brain barrier.

The preferred treatment is complete surgical removal of both the tumor and the intracranial infection. Targeted antibiotic therapy for an appropriate duration is also essential [@bib0070; @bib0130]. Modern diagnostic tools such as DWI and MR spectroscopy are reportedly reliable for differentiating brain abscesses from brain tumors, including brain metastasis, and these modalities were found to be useful in our current case [@bib0015; @bib0020; @bib0025]. However, if preoperative differentiation is difficult and complete removal is considered during a second surgical operation, it may be sufficient to initially drain the abscess content to relieve symptoms, followed by tissue culture. If pus or abscess fluid is evident during complete removal, the postoperative course could become unstable during hospitalization, due to widespread pyogenic meningitis, ventriculitis, and/or sepsis. Therefore, preoperative preparation is important whenever the coexistence of an abscess and a brain neoplasm is a possibility.

In cases with high-grade glioma and metastatic brain tumors, further oncotherapy is frequently necessary [@bib0065; @bib0070; @bib0115]. Chemotherapy and radiotherapy are beneficial for brain neoplasms. However, the risk/benefit ratio of the concomitant immunosuppressive effect is unclear. As the patient's immunity is compromised, the risk of infection is increased. Therefore, chemotherapy and radiotherapy could be used to treat residual or recurrent tumor progression after ensuring that there are no signs of infection. In the present case, we resumed chemotherapy to treat lymph node metastasis eight weeks after surgery when the patient had no signs of intracranial infection.

The pathophysiological processes underlying the coexisting abscess and metastasis were unknown in our patient, but immunodeficiency due to the immunosuppressive agent given for cancer treatment and his medical history of numerous surgeries could have contributed to this diagnosis. This case highlights the importance of considering intratumoral abscesses. If we encounter a brain tumor with the imaging characteristics of both tumors and abscesses, differentiation between the two is especially important due to the different management methods for such lesions. However, we should also consider the treatment of cases with both conditions. Acquiring tissue from the lesions for both pathological and microbiological examinations to differentiate a brain tumor from an abscess is useful, and preoperatively considering the possible coexistence of both with appropriate preparations could improve the patient's outcome.

4. Conclusion {#sec0020}
=============

This case highlights the importance of considering the coexistence of two diseases prior to surgery. Preoperatively considering the possibility that a brain tumor and a brain abscess may coexist, when we encounter cases with imaging characteristics of both lesion types, may improve treatment outcomes.

Conflict of interest {#sec0025}
====================

All authors have nothing to declare about this.

Funding {#sec0030}
=======

All authors have nothing to declare about this.

Ethical approval {#sec0035}
================

Authors had obtained patient's consent on paper, and this case report fulfills ethicalapproval.

Author contribution {#sec0040}
===================

Yukihiro Goto: surgeon of the patient, data collection, writing paper. Toshihiko Ebisu: surgeon of the patient, data analysis and interpretation. Katsuyoshi Mineura: concept and design.

Consent {#sec0045}
=======

Authors had obtained patient's consent on paper. Medical information about the patient in this case report had completely changed to anonymous patient. This case report does not obtain personally identifiable information. Information has been kept strictly base on the compliance of information management about medical record in Kyoto Prefectural University Graduate School of Medicine. Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal upon request.

Guarantor {#sec0050}
=========

Authors do not receive any research grant.

![MR images on admission demonstrating two different types of lesions in each cerebellar hemisphere. The right lesion shows ring enhancement with gadolinium and hyper-intensity on DWI, whereas, the left lesion does not. Left: T1-weightedimages, center: T1-weighted images with gadolinium, right: diffusion-weighted images.](gr1){#fig0005}

![Upper: MR image showing slightly elevated amino acids (0.9 ppm) and a relatively low choline peak. Lower: pathological examinations of the exudate showing a collection of inflammatory cells (left: Papanicolaou stain × 10; right: Papanicolaou stain × 200).](gr2){#fig0010}

![Right lesion showing progression over two months; pathological examinations after the second surgery confirmed well-differentiated adenocarcinoma. Left: T1-weighted images with gadolinium three weeks after surgery (upper: axial images, lower: sagittal images). Center: T1-weighted images with gadolinium eight weeks after surgery (upper: axial images, lower: sagittal images). Right: pathological examinations after the second surgery (upper: hematoxylin--eosin stain × 10, lower: hematoxylin--eosin stain × 200).](gr3){#fig0015}

###### 

Clinical summary of abscesses associated with brain tumors.

  Author                          Year   Age/sex   Tumor                  Region              Symptom                          Organism                                                        Means of spread   Outcome
  ------------------------------- ------ --------- ---------------------- ------------------- -------------------------------- --------------------------------------------------------------- ----------------- -------------------------------------------
  Sharma et al. [@bib0100]        1986   32/M      High-grade glioma      Temporal            Elevated intracranial pressure   *Salmonella typhi*                                              Bacteremia        Favorable
  Rodriguez et al. [@bib0045]     1986   28/M      Metastatic carcinoma   Parietal            Fever, headache, nausea          *Salmonella enteritidis*                                        Bacteremia        --
  Noguerado et al. [@bib0090]     1987   78/M      High-grade glioma      Occipital           Aphasia, hemiplegia              *Salmonella enteritidis*                                        Bacteremia        Death
  Ichikawa et al. [@bib0060]      1992   46/F      High-grade glioma      Frontal             Aphasia, fever, hemiplegia       *S. aureus*                                                     Bacteremia        Favorable
  Shimomura et al. [@bib0105]     1994   64/F      Meningioma             Parasagittal        Fever                            *B. oralis*                                                     Bacteremia        Favorable
  Ng and Lozano [@bib0040]        1996   79/F      Metastatic carcinoma   Posterior fossa     Nausea, truncal ataxia           *Haemophilus parainfluenza*                                     Bacteremia        Death[b](#tblfn0010){ref-type="table-fn"}
  Nassar et al. [@bib0085]        1997   2/M       Ependymoma             Posterior fossa     Meningitis                       Unidentified                                                    Meningitis        Death
                                         78/F      Meningioma             Parasagittal        Hemiplegia                       *E. coli*                                                       Bacteremia        Death[b](#tblfn0010){ref-type="table-fn"}
  Eisenberg et al. [@bib0055]     1998   78/F      Meningioma             Parasagittal        Hemiplegia                       *Proteus mirabilis*                                             Bacteremia        Moderately disabled
  Sarria et al. [@bib0095]        2000   58/F      High-grade glioma      Frontal             Hemiplegia, meningitis           *Salmonella enteritidis*                                        Bacteremia        Death
  Bansal et al. [@bib0050]        2001   11/F      Glioma                 Parieto-occipital   Seizure                          *Pseudomonas aeruginosa*                                        Bacteremia        Death
  Yeates et al. [@bib0120]        2003   38/F      Meningioma             Convexity           Seizure                          *B. fragilis*                                                   Bacteremia        Favorable
  Kovacic et al. [@bib0030]       2004   66/M      Metastatic carcinoma   Posterior fossa     Nystagmus, gait disturbance      *P. acnes*                                                      Bacteremia        Death
                                         72/M      Metastatic carcinoma   Posterior fossa     Headache, gait disturbance       *S* spp.                                                        Bacteremia        Death[b](#tblfn0010){ref-type="table-fn"}
  Mohindra et al. [@bib0080]      2004   9m/M      Ependymoma             Posterior fossa     Vomiting, fever                  *Enterobacter aerogenes*                                        Bacteremia        Death
                                         35/M      Low-grade glioma       Posterior fossa     Nystagmus, vomiting, headache    Unidentified                                                    Bacteremia        Favorable
                                         42/M      Medulloblastoma        Posterior fossa     Elevated intracranial pressure   Unidentified                                                    Bacteremia        Favorable
  Lind et al. [@bib0075]          2005   78/F      Meningioma             Anterior falx       Personality change               *Citrobacter koseri*                                            Bacteremia        --
  Young et al. [@bib0125]         2005   38/M      Meningioma             Sphenoid ridge      Headache, fever                  [a](#tblfn0005){ref-type="table-fn"}spp.                        Bacteremia        Favorable
  Kalita et al. [@bib0070]        2008   57/F      High-grade glioma      Occipital           Monoparesis                      *S. aureus*                                                     Bacteremia        Favorable
  Tsai et al. [@bib0110]          2008   52/M      Low-grade glioma       Temporal            Aphasia                          *S. aureus*                                                     Bacteremia        Favorable
  Moiyadi and Shetty [@bib0035]   2010   36/F      Metastatic carcinoma   Frontal             Elevated intracranial pressure   *A. baumannii*                                                  Unknown           Favorable
  Jho et al. [@bib0065]           2011   53/M      High-grade glioma      Temporal            Headache, hemiplegia, aphasia    *A. iwofii, P* spp., [a](#tblfn0005){ref-type="table-fn"}spp.   Bacteremia        Favorable
  Tsugu et al. [@bib0115]         2012   45/M      High-grade glioma      Temporal            Elevated intracranial pressure   *Bacilli* spp.                                                  Bacteremia        Favorable
  Present case                    2012   58/M      Metastatic carcinoma   Posterior fossa     Truncal ataxia                   Unidentified                                                    Bacteremia        Favorable

F: female, M: male, m: month, A: Acinetobacter, B: Bacteroides, E: Escherichia, P: Propionibacterium. S: Staphylococcus. spp.: species.

Streptococcus.

Neurologically favorable just after surgery, but died due to systemic disease.
