Authors: İlhan Aydın, Fikret Öztürk, Fatih Ekşi, Berkay Kef, Melih Üçer, Orhun Mete Çevik
Categories: Case Lesson, brain abscess, sinusitis, opportunistic pathogens, Gemella morbillorum, Kocuria rosea, case report, CRP = C-reactive protein, ENT = ear, nose, and throat, ESR = erythrocyte sedimentation rate
Source: Journal of Neurosurgery: Case Lessons
Doi: 10.3171/CASE25950
Authors: İlhan Aydın, Fikret Öztürk, Fatih Ekşi, Berkay Kef, Melih Üçer, Orhun Mete Çevik
Brain abscesses typically arise from streptococcal, staphylococcal, or gram-negative pathogens, but low-virulence commensals may occasionally cause severe intracranial infection when anatomical barriers are disrupted. Gemella morbillorum and Kocuria rosea are rare opportunistic organisms that are seldom implicated in CNS disease and are usually associated with immunosuppression, chronic otolaryngological pathology, or postoperative states. Their simultaneous isolation from a single intracranial abscess has not been previously reported.
A previously healthy 23-year-old man presented with progressive somnolence and persistent headache following recent sinusitis. Neuroimaging revealed a multilobulated left frontal abscess with extensive vasogenic edema. Initial surgical aspiration yielded purulent material, and culture grew G. morbillorum and* K. rosea*. Despite 1 month of broad-spectrum intravenous antibiotics, follow-up MRI demonstrated recurrence, necessitating reoperation with complete excision of the abscess capsule. The patient recovered fully after 6 weeks of antimicrobial therapy.
This case highlights that rare commensal organisms can cause aggressive intracranial infection even in immunocompetent individuals. Accurate microbiological diagnosis is essential when evaluating sinus-derived abscesses, as atypical pathogens may influence treatment decisions and risk of recurrence. Multiloculated abscesses may require complete excision when aspiration and antibiotic therapy are insufficient for durable infection control.
https://thejns.org/doi/10.3171/CASE25950
Brain abscess is an uncommon but potentially life-threatening intracranial infection, with an annual incidence of approximately 0.9 per 100,000 individuals and a 1-year mortality approaching 20%.^1^ Despite improvements in neuroimaging and antimicrobial therapy, long-term neurological morbidity, including chronic seizures, cognitive decline, and focal deficits, remains significant.^2^ Large epidemiological and clinical series underscore the importance of early recognition, timely surgical intervention, and pathogen-directed therapy in reducing complications and improving outcomes.^3^^,^^4^
The spectrum of causative organisms is broad. While streptococci, staphylococci, and gram-negative bacilli account for most cases, anaerobic bacteria, fungi, and opportunistic pathogens also contribute, particularly in patients with immunosuppression, systemic illness, or healthcare-associated exposures.^5^^–^^9^ Contemporary guidelines emphasize integrating imaging features, classical microbiology, and molecular diagnostic platforms to identify fastidious or anaerobic organisms, including streptococcal species such as Streptococcus constellatus and mixed anaerobic flora.^9^^,^^10^ These diagnostic approaches are especially relevant in infections arising from sinus or dental sources, where polymicrobial or unusual pathogens are more frequently encountered.
Gemella morbillorum, a commensal organism of the oral and upper respiratory tract, is rarely implicated in CNS infections. Reported cases typically involve sinusitis, odontogenic infections, shunt-associated meningitis, or chronic ear, nose, and throat (ENT) pathology.^11^^–^^14^ Kocuria sp., including Kocuria rosea and Kocuria varians, are similarly low-virulence commensals traditionally regarded as contaminants, yet they have been associated with bacteremia, meningitis, and, in rare cases, brain abscess, most often in immunocompromised or postoperative patients.^15^^–^^19^ A comprehensive narrative review highlights increasing recognition of Kocuria sp. as an emerging opportunistic pathogen in vulnerable populations.^19^
Despite scattered reports of each organism independently causing CNS infection, there are no documented cases describing the coexistence of G. morbillorum and K. rosea in a single intracranial abscess. We present a multilobulated frontal lobe abscess occurring after sinusitis in a previously healthy, immunocompetent young adult, in whom cultures revealed simultaneous growth of both organisms. This case expands the known pathogen spectrum of sinus-related intracranial abscesses and underscores the importance of considering atypical commensal organisms—even in immunocompetent patients—when evaluating brain abscess of presumed ENT origin.
A 23-year-old previously healthy male presented with several days of progressive somnolence and persistent headache. Three weeks earlier, he had been treated for acute sinusitis with moxifloxacin and anti-inflammatory medication, after which most symptoms resolved except for ongoing headache. On admission, he was somnolent but oriented and cooperative, with a Glasgow Coma Scale score of 15 and preserved motor strength. His temperature was 37.5°C. Laboratory evaluation showed elevated inflammatory markers (C-reactive protein [CRP] 38 mg/L, erythrocyte sedimentation rate [ESR] 51 mm/hr). Serological testing for HIV, hepatitis, brucellosis, hydatid disease, syphilis, and borreliosis was negative. Immunological evaluation, including serum IgG, IgA, IgM, complement levels (C3, C4, CH50), and lymphocyte subset analysis, was normal. Antiedema and antiepileptic therapy were initiated, and the patient was admitted to the intensive care unit for close monitoring.
Initial noncontrast brain CT demonstrated multiple hypodense lesions in the left frontal lobe with surrounding vasogenic edema. Subsequent contrast-enhanced brain MRI was performed for confirmation and further lesion characterization, revealing a multilobulated ring-enhancing abscess with central diffusion restriction and significant mass effect. CT and MRI of the paranasal sinuses demonstrated mucosal thickening, hypodense intraluminal material, and focal bony irregularity, consistent with active sinusitis (Fig. 1). FIG. 1.A and B: Paranasal sinus images demonstrating the presumed source of infection. Axial (A) and sagittal (B) CT scans showing focal bony defect along the sinus wall. C–F: Preoperative sagittal (C) and axial (D–F) brain MR images demonstrating a multilobulated left frontal abscess. The lesion is hypointense on T1-weighted imaging and hyperintense on T2-weighted imaging, with a thick ring-enhancing capsule following contrast administration. Marked surrounding vasogenic edema with associated mass effect is present.
The patient was taken to the operating room on hospital day 2, after completion of preoperative evaluation and preparation. A bicoronal skin incision and left frontal craniotomy measuring approximately 3 × 3 cm were performed. Because stereotactic or neuronavigation-guided aspiration was not consistently available at our institution, intraoperative ultrasonography was used as the primary guidance modality. Ultrasonography identified multiple hypoechoic abscess cavities, enabling accurate localization and aspiration of the multiloculated lesion. The aspirated material was thick, greenish, and foul smelling (Video 1), and specimens were sent for microbiological and pathological examination. Postaspiration ultrasonography confirmed marked reduction in the abscess cavities. Postoperative CT demonstrated no procedure-related complications, and the patient remained neurologically intact.
Cultures from the aspirated material grew G. morbillorum and K. rosea, both uncommon commensal organisms capable of causing invasive infection. The patient was treated with intravenous vancomycin, ceftriaxone, and metronidazole for 1 month. Otolaryngology evaluation with nasal endoscopy revealed no residual sinus infection.
At the end of the 1st postoperative month, while the patient was still hospitalized and receiving intravenous antibiotic therapy, neurological examination remained normal and inflammatory markers had partially improved (CRP 20 mg/L, ESR 34 mm/hr). However, with the development of progressively worsening headache, repeat brain CT and MRI demonstrated a recurrent capsulated ring-enhancing abscess in the left frontal lobe with surrounding edema (Fig. 2). FIG. 2.A: Axial contrast-enhanced T1-weighted MR image showing a recurrent ring-enhancing lesion in the left frontal lobe. B: Coronal T2-weighted MR image demonstrating surrounding vasogenic edema with interval enlargement. C: Sagittal contrast-enhanced T1-weighted MR image depicting the craniocaudal extent of the recurrent lesion. D: Sagittal CT scan showing a focal posterior frontal sinus wall defect. E: Axial CT scan confirming the focal bony defect with intracranial extension.
An otolaryngology (ENT) consultation was obtained before the second operation. Endoscopic nasal examination revealed no indication for active endoscopic drainage or surgical intervention of the affected paranasal sinuses. The ENT team recommended continuation of systemic antibiotic therapy supported by saline nasal irrigation. On preoperative follow-up imaging obtained prior to the second neurosurgical procedure, brain CT and MRI demonstrated spontaneous drainage and interval resolution of the purulent sinus content, with no evidence of persistent sinus empyema, skull base defect, or ongoing intracranial-sinus communication. Accordingly, additional sinus-directed procedures such as cranialization, debridement, or sealing were not indicated, and surgical management was limited to complete excision of the intracranial abscess.
Reoperation was performed through the previous bicoronal incision, with extension of the initial craniotomy. A well-defined capsulated abscess cavity containing dark purulent material was encountered, and the abscess capsule was completely excised (Fig. 3). FIG. 3.A and B: Intraoperative photographs obtained during the second surgery showing the excised multiloculated abscess capsule after removal. The specimen demonstrates a thick, well-formed capsule containing dark purulent material. C: Intraoperative view of the surgical cavity following complete excision of the recurrent abscess.
Postoperative MRI confirmed complete excision of the lesion with no residual enhancement or recurrent fluid collection (Fig. 4). The patient remained neurologically intact. Intravenous antimicrobial therapy continued for a total of 6 weeks, followed by 3 weeks of oral antibiotics and ongoing antiepileptic medication. At discharge, he was asymptomatic with normalized inflammatory markers, and he experienced no complications during follow-up. FIG. 4.Postoperative multimodal imaging following surgical drainage of a frontal sinus–related intracranial abscess. A–C: Postoperative MR images demonstrating the residual surgical cavity in the left frontal lobe with decreased mass effect and surrounding edema. D and E: Diffusion-weighted image and ADC map showing no significant residual diffusion restriction. **F and G:**CT bone window images demonstrating the frontal sinus wall defect with postoperative intracranial changes.
The necessary informed consent was obtained in this study.
Brain abscesses arise from a diverse range of pathogens, and their clinical course depends greatly on early recognition and appropriate therapeutic intervention.^2^^,^^3^ Although pyogenic organisms are most common, fungal abscesses, filamentous bacteria such as Nocardia, and anaerobic species, including organisms from the Streptococcus anginosus group, play important roles in selected patient populations.^8^^–^^10^^,^^18^ These pathogen categories differ in their typical sources, host characteristics, preferred intracranial locations, and surgical considerations, as summarized in Table 1. Recent diagnostic studies have emphasized the role of anaerobic cultures and molecular methods in identifying fastidious organisms, particularly in sinus or dental origin abscesses where mixed infections are common.^10^ TABLE 1.Comparative overview of pathogen categories associated with brain abscesses, including the present caseCategorySourceTypical HostCommon LocationSurgeryOutcomeStreptococciOdontogenic, sinusitis, hematogenous dissemination (endocarditis)Often immunocompetent; poor dentition or chronic sinus diseaseFrontal most common; temporal also frequent; may be multipleAspiration commonly sufficient; excision if recurrenceGenerally good w/ antibiotics & surgery; mortality 5–15% Staphylococcus aureusPostneurosurgical infection, trauma, hematogenous spread from skin/soft tissueHealthcare-exposed, postop patients; device-related infectionsVariable; often near surgical hardware or prior op siteDrainage or excision frequently requiredMortality 10–20%; higher relapse riskGram-negative bacilliOtitis/mastoiditis (Pseudomonas sp.), urinary or abdominal infectionsOlder or healthcare-associated infectionsTemporal or cerebellar regionsAspiration, sometimes repeated; ENT source control essentialMortality 10–20%, varies by comorbidityAnaerobesOdontogenic & sinus infectionsPoor oral hygiene; chronic sinus diseaseFrontal predominanceAspiration + prolonged antibioticsOutcomes comparable to those for streptococci if treated promptlyOpportunistic pathogens (Nocardia sp., fungi, others)Pulmonary sources (Nocardia sp.), sinonasal (Aspergillus sp.), systemic infectionsImmunocompromised, transplant recipients; malignancy; HIVDeep-seated or multiple lesionsOften requires repeated drainage or excisionHigher morbidity/mortality depending on immune statusPresent Gemella + Kocuria spp.Sinonasal origin (frontal & maxillary sinusitis)Immunocompetent young adult (23-year-old male)Lt frontal multilobulated abscessInitial aspiration → recurrence → complete excisionComplete recovery; no recurrence
Multiloculated brain abscesses represent a distinct surgical challenge, as their compartmentalized architecture is associated with higher rates of incomplete drainage, recurrence, and need for repeat intervention when managed with aspiration alone. Large surgical series have demonstrated that while stereotactic or burr hole aspiration may be effective for uniloculated lesions, multiloculated or encapsulated abscesses frequently require open excision to achieve durable source control.^2^^–^^4^ In a landmark series of 973 patients, Nathoo et al.^3^ reported significantly higher failure rates following aspiration in multiloculated abscesses, often necessitating subsequent craniotomy and excision. Similarly, systematic reviews and contemporary guidelines emphasize that failure of clinical or radiological response despite appropriate antimicrobial therapy constitutes an indication for reoperation, particularly in cases with progressive mass effect or edema.^2^^,^^4^^,^^6^
In the present case, despite 4 weeks of broad-spectrum intravenous antibiotic therapy following ultrasound-guided aspiration, the patient developed progressive headache accompanied by radiological enlargement of the multilobulated abscess and worsening vasogenic edema. This constellation is consistent with treatment failure, for which early surgical reintervention with total capsular excision is recommended to prevent further neurological deterioration and recurrence.^2^^,^^4^^,^^6^
Reports of CNS infection due to G. morbillorum remain rare and are usually associated with sinusitis, dental disease, or otolaryngological conditions.^11^^–^^14^ Similarly, Kocuria sp.—once dismissed as contaminants—have been increasingly recognized as opportunistic pathogens capable of causing meningitis, bacteremia, and brain abscess, particularly in immunocompromised hosts or following neurosurgical procedures.^15^^–^^18^ The narrative review by Ziogou et al.^12^ highlights the emerging pathogenic potential of Kocuria sp., noting that clinical recognition of these organisms is increasing as microbiological techniques improve.
Our case is notable for several reasons. First, the patient was young and immunocompetent, with no systemic disease or immunological abnormalities that typically predispose to opportunistic infection. Second, the infection appears to have originated contiguously from acute sinusitis—a mechanism far more commonly linked to streptococci or anaerobic pathogens than to Gemella or Kocuria sp.^5^^–^^9^^,^^11^ Third and most importantly, there are no previously published cases documenting the co-isolation of G. morbillorum and K. rosea from the same intracranial abscess. The multilobulated structure of the lesion, its sinus origin, and its recurrence despite appropriate broad-spectrum antimicrobial therapy underscore the invasive potential of these organisms when anatomical barriers are compromised.
Additionally, as demonstrated in major clinical series, multiloculated abscesses often respond incompletely to aspiration alone and may require complete excision to achieve durable source control.^4^ This aligns with our case, in which recurrence after aspiration necessitated total capsular excision.
This case provides several important clinical lessons. First, clinicians should maintain a broad microbiological differential when evaluating sinus-derived brain abscesses, even in immunocompetent patients. Uncommon commensals such as G. morbillorum and K. rosea may act as invasive pathogens when local anatomical barriers are breached. Second, given that fastidious or atypical bacteria may be underrecognized, meticulous microbiological sampling, including aerobic, anaerobic, and, when appropriate, molecular diagnostic techniques, is critical for accurate pathogen identification. Third, recurrence may occur despite prolonged antibiotic therapy, particularly in multiloculated or encapsulated abscesses. In such cases, repeat surgical intervention with complete capsular excision may provide more definitive control. Overall, this case highlights the potential for rare commensal organisms to cause aggressive intracranial infections and underscores the importance of individualized surgical and antimicrobial management supported by thorough microbiological evaluation and vigilant postoperative follow-up.
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The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.
Conception and Aydın, Öztürk. Acquisition of Aydın, Öztürk. Analysis and interpretation of Aydın, Ekşi, Kef. Drafting the Aydın, Öztürk, Kef, Üçer, Çevik. Critically revising the Aydın, Ekşi, Kef, Çevik. Reviewed submitted version of Aydın, Ekşi, Kef, Çevik. Approved the final version of the manuscript on behalf of all Aydın. Statistical Kef. Administrative/technical/material Ekşi, Üçer, Çevik. Study Aydın, Öztürk, Üçer.
Video 1. https://vimeo.com/1163293702.
İlhan Aydın: Istanbul Bakırköy Prof. Dr. Mazhar Osman Training and Research Hospital for Mental Health and Neurological Disorders, Istanbul, Türkiye. ilhanaydinmd@gmail.com.