Background

Brain abscess is a condition characterized by the formation of an abscess within the cerebral parenchyma due to suppurative infections reaching the brain. Although less common, brain abscesses can also result from fungal or protozoan infections. These abscesses commonly occur secondary to rhinogenic, odontogenic, and otogenic infections, as well as post-trauma and post-endovascular interventional procedures. Brain abscesses can occur at any age but are more prevalent among young adults. The incidence of brain abscesses during pregnancy is low, and Actinomyces meyeri-induced brain abscess rupturing into the ventricle during pregnancy is even less common, with no previous reports of such a case available in the literature to date. The symptoms of brain abscesses are usually nonspecific, and the condition is severe, posing a significant threat to the lives of both the mother and the infant. Consequently, the mortality rate is exceedingly high. Here we report a case of a pregnancy-associated brain abscess caused by Actinomyces meyeri.

Case presentation

The patient was a previously healthy 38-year-old primipara at 8 weeks of amenorrhea. She was admitted to the emergency department at our hospital due to a 4-day history of fever and vomiting that exacerbated in the 8 h prior to admission. The patient experienced a sudden loss of consciousness 4 h before arrival to the unit. On physical examination, the patient had a body temperature of 39.0 °C, blood pressure of 131/69 mmHg, and a heart rate of 80 beats/min. The patient was in a coma with a Glasgow Coma Scale score of 6 (1 + 1 + 4). Pupillary examination revealed a diameter of 0.4 cm and 0.2 cm for the right and left pupils, respectively, with neither showing direct nor indirect light reflexes. Cardiac examination did not reveal any significant abnormalities. Her abdomen was flat and soft, without tenderness or noticeable abdominal muscle tension. No movement was observed in the limbs, and there was no voluntary motor response. Her leukocyte count was slightly elevated at 16.6 × 109/L, while the C-reactive protein concentration was within the normal range.

Cranial computed tomography (CT) revealed a large low-density shadow in the right parietal–temporal lobe, suggestive of cerebral swelling. The suprasellar cistern appeared compressed and narrowed, displaying an irregular shape, although brain herniation still needed to be ruled out (Fig. 1). Cranial magnetic resonance imaging (MRI) revealed abnormal signals in the right parietal–temporal lobe, which may have been due to an abscess rupturing into the ventricle and sulcus. The presence of a tumor had yet to be excluded. There were signs of increased intracranial pressure, with compression of the right lateral ventricle and a shift in midline structures to the left. Additionally, a mass was identified in the right temporal–occipital region, accompanied by a midline shift and severe cerebral edema (Fig. 2).

Fig. 1
figure 1

Axial cut of CT scan of the brain. A: A patchy low-density shadow was observed in the right temporal–parietal lobe. The right lateral ventricle was compressed and flattened. B:The suprasellar cistern was compressed and narrowed, displaying an irregular shape. Brain herniation needed to be excluded. C: The brainstem was compressed, and the boundaries were unclear. Brain swelling may have occurred

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Fig. 2
figure 2

Magnetic resonance images of the brain abscess. TIW = T1-weighted; T2W = T2-weighted; DWI = diffusion weighed imaging. A patchy abnormal signal was observed in the right parietal–temporal lobe, with a low signal on T1-weighted imaging surrounded by annular high signals, and a high signal on T2-weighted imaging surrounded by annular low signals around the lesion. Diffusion-weighted imaging showed high signals with patchy long T1 and long T2 signals around the lesion; the lesion appeared to be connected to the right lateral ventricle

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Emergency interventions were initiated, including the administration of mannitol (150 ml) and dexamethasone (5 mg) injections to treat cerebral edema and reduce intracranial pressure, respectively. Empirical antibacterial treatment with ceftriaxone sodium injections (2 g) was initiated. A lumbar puncture was successfully performed, revealing cerebrospinal fluid (CSF) pressure above 300 mmH2O. The CSF sample was sent for bacterial examination, and the results indicated a bacterial infection. The CSF sample had a reddish, turbid appearance. Routine biochemistry in the CSF revealed that glucose levels were 4.29 mmol/L (normal range: 2.2–3.9 mmol/L), and protein levels were 554 mg/dL (normal range: 15–45 mg/dL). The leukocyte count was 150/µL (normal range: 0–10/µL), with 70% neutrophils and 30% lymphocytes observed.

Upon completion of preoperative preparations, emergency procedures were performed, including examination with craniotomy and removal of the right temporal–occipital mass, decompressive craniectomy, implantation of an intracranial pressure monitoring device, and external ventricular drainage. During the operation, approximately 7 mL of yellowish pus was aspirated. Post-operative pathology revealed a brain abscess, purulent inflammation of the brain tissue. The CSF culture identified the presence of Actinomyces meyeri. However, no drug sensitivity test was performed.

After surgery, the patient was administered a regimen of linezolid injections at a dose of 0.6 g q12h, meropenem injections at 2 g q8h, and mannitol injections at 150 mL q8h to mitigate intracranial pressure. The patient’s vital signs remained stable post-operation. After two weeks, the treatment was supplemented with intravenous drip of ornidazole at 0.5 g q12h for anti-infection purposes. Two months post-operation, the treatment was continued with linezolid tablets at a dosage of 0.6 g q12h orally for four weeks for anti-infection purposes. During hospitalization, the outcome of multidisciplinary consultations was that pregnancy should be terminated at an appropriate time following further control of the systemic infection. With informed consent from the patient’s family, a B-ultrasound-guided intra-amniotic injection of rivanol was performed, resulting in the intact delivery of the fetus.

Following the surgery, the patient exhibited obvious signs of hydrocephalus, and a hydrocephalus shunt was performed several months later. Six months post-craniotomy, a follow-up cranial MRI (Fig. 3) was conducted. A follow-up cranial CT scan (Fig. 4) was also performed one year after the surgery. Both examinations indicated no recurrence of the brain abscess. However, the patient remained in a coma vigil state.

Fig. 3
figure 3

Magnetic resonance images of the brain abscess. TIW = T1-weighted; T2W = T2-weighted. Patchy abnormal signals were observed in the right occipital lobe, with low signals on T1-weighted imaging and high signals on T2-weighted imaging, possibly indicating post-operative changes. Formation of local encephalomalacia and post-operative changes of communicating hydrocephalus were observed

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Fig. 4
figure 4

Post-operative changes were observed in the right skull and left frontal bone. Patchy low-density shadows were observed in the right parietal–occipital lobe with unclear boundaries (axial cut of CT scan of the brain)

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Discussion

Brain abscess is a rare complication during pregnancy, with only 20 cases reported in the literature in English to date [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. The clinical symptoms, abscess location, etiology, antibiotic treatment, delivery method, maternal and infant morbidity, and mortality rates of these cases are shown in Table 1. Clinical manifestations of brain abscesses during pregnancy are often non-specific and related to the size, number, and location of the lesions; to pathogen toxicity, and to the immune response of the host. Mental state changes are commonly observed, while only 20% of patients with brain abscess display typical symptoms such as fever, headache, and focal neurological deficits. The abscesses are commonly located in the frontotemporal lobe, followed by the parietal lobe, occipital lobe, and brainstem. Manifestations of the abscess are often associated with increased intracranial pressure caused by the mass, which can lead to neurological symptoms. The most concerning complications include brain herniation and abscess rupture. In this particular case, the patient initially exhibited only minor symptoms, including low fever and vomiting. Unfortunately, due to the fact that the patient was experiencing an early pregnancy and that the initial symptoms of brain abscesses exhibit some similarities with common early pregnancy reactions, they were overlooked. As a result, the patient did not receive timely medical attention, leading to a missed opportunity for optimal treatment. Eventually, rapid progression of the condition led to the rupture of the abscess into the ventricles and brain herniation. To the best of our knowledge, this is the first reported case of Actinomyces meyeri-induced brain abscess during pregnancy.

Table 1 Reported cases of pregnancy-associated brain abscess in the medical literature
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Brain abscesses associated with pregnancy predominantly originate from pyogenic infections at neighboring sites. These include rhinogenic, otogenic, and odontogenic brain abscesses, as well as hematogenous, traumatic, and cryptogenic brain abscesses. Rhinogenic brain abscesses account for approximately two-thirds of all brain abscesses, and are primarily caused by Streptococcus viridans and β-streptococcus. In contrast, otogenic brain abscesses are often attributed to proteobacteria and anaerobic bacteria. Hematogenous brain abscesses are most frequently caused by Staphylococcus aureus, while traumatic brain abscesses are commonly caused by Staphylococcus aureus and Enterobacteriaceae bacteria. Our patient, who was previously healthy and 8 weeks pregnant, had no medical history of congenital heart disease, chronic otitis media, or arteriovenous fistula of the lungs. Moreover, the patient had not used steroids, and all her regular prenatal check-ups had shown no abnormalities. However, the emergency scout view of CT revealed dental caries in the second molar. Thus, the possibility that the infection may have originated from this source cannot be ruled out. Previous literature indicates that approximately 7% of brain abscesses are caused by dental infections and procedures. Dental conditions can lead to systemic diseases and other severe complications, especially during pregnancy, when immune function is compromised [17]. In this specific case, the pus culture suggested an uncommon Actinomyces meyeri infection.

Actinomyces is a genus of anaerobic gram-positive filamentous bacteria commonly found in the oral cavity and the upper respiratory, gastrointestinal, and genitourinary tracts. Endogenous infection may occur in individuals with a compromised immune system or poor oral hygiene, or after tooth extraction or oral mucosal damage, leading to actinomycosis. This condition typically affects the face and neck, and can also extend to the gastrointestinal tract and lungs, leading to infection of these structures [21]. Typical characteristics include a hidden course of the disease, formation of thick wood-like abscesses, presence of sulfur-like granules, and fistula formation [21]. Actinomyces meyeri is one of many Actinomyces species found in the human microbiota. It was first isolated in 1911 from a patient with pyothorax, and has been reported in the literature in English only 30 times to date [22].

Actinomyces meyeri exhibits a tendency to invade and disseminate diseases [1]. These infections are strongly associated with the presence of dental plaque and caries [1]. The bacterium can penetrate deep tissues and readily invade the human central nervous system, leading to severe infections [21, 23]. However, our understanding of the specific virulence mechanisms used by Actinomyces meyeri to achieve tissue invasion remains limited. To date, only ten cases of brain abscesses associated with Actinomyces meyeri infection have been reported in the literature [22,23,24,25,26,27,28,29,30,31,32], and these are summarized in Table 2.

Table 2 Published cases of A. meyeri cerebral abscesses
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Laboratory tests for diagnosing brain abscesses associated with Actinomyces meyeri infection lack specificity. Lumbar puncture is not recommended, as it provides limited diagnostic assistance and can potentially induce brain herniation in patients with intracranial hypertension. On the other hand, cranial CT or MRI imaging can aid in the diagnosis, with MRI and diffusion-weighted imaging being more sensitive than CT scans. Actinomycotic brain abscesses manifest as one or more peripherally enhanced lesions on MRI. These lesions may display high-signal edges on T1-weighted non-contrast images and exhibit grape-cluster patterns on T2-weighted low-signal images at the borders [29, 32].

The treatment of Actinomyces meyeri-induced brain abscesses requires a combination of antimicrobial drugs, surgical intervention, and elimination of the primary focus of infection. Detecting the etiology of the infection is crucial for the administration of more effective and targeted antimicrobial therapy. Although the positivity rates in CSF and blood sample cultures are relatively low [22], which may be attributed to antibiotic usage and testing methods, the acquisition of specimens for culture and for Gram staining remains particularly important. The replacement of traditional microbiology detection methods by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) technology has the potential to enhance bacteria detection rates. Before utilizing advanced detection technology, it is beneficial to rely on general knowledge about bacteria originating from various sources of infection. This knowledge can help predict the most probable pathogens responsible for the abscess, which in turn can facilitate the selection of the most appropriate antimicrobial therapy. Additionally, it is imperative to select drugs that can readily cross the blood–brain barrier and penetrate the abscess wall. In case of large diameter abscesses, aspiration or surgical removal can be considered. In our case, as the abscess had ruptured into the ventricles and led to brain herniation, craniotomy decompression and removal of the focus of infection were performed. Additionally, drainage tubes were inserted, and mannitol and steroids were administered to reduce intracranial pressure.

The duration of antibiotic treatment for Actinomyces meyeri brain abscesses remains unstandardized. A review of the literature indicates that the typical approach to the treatment of Actinomyces infections involves administering intravenous penicillin at a daily dose of 18 to 24 million units for a period of 2–6 weeks, followed by oral penicillin or amoxicillin for 6–12 months [22]. For abscesses caused by Actinomyces meyeri, the preferred antibiotic regimen consists of penicillin G in combination with metronidazole, with the duration of treatment varying from six weeks to one year. When clinically appropriate, intravenous medication may involve broader spectrum antibiotics such as piperacillin–tazobactam, cefoxitin, ceftriaxone, or carbapenems. In patients that are allergic to penicillin, alternative drugs such as clindamycin, which has good penetration into abscesses, as well as macrolides, doxycycline, tigecycline, and chloramphenicol should be considered [33]. It is important to note that these drugs differ in their ability to penetrate the central nervous system.

Considering the severity of this particular case, which involved subsequent multiple systemic infections, a treatment regimen consisting of meropenem, linezolid, and ornidazole was chosen and administered over three months. This combination provided broad coverage against both aerobic and anaerobic microorganisms. No recurrence of the abscess was registered at the one-year follow-up. Successful treatment of Actinomyces meyeri-associated brain abscess has previously been reported with a continuous infusion of 24 million units of benzylpenicillin and 36 million units of dexamethasone as adjunctive for one month. No recurrence was observed in the patient after a year of follow-up [24]. However, the conventional recommendation of 6–12 months of antibiotic treatment may not be suitable for all patients. Moreover, the treatment duration, to some extent, depends on factors such as the initial disease burden, the effectiveness of the surgical removal, and the patient’s response to treatment.

The prognosis of Actinomyces meyeri-associated brain abscesses is generally poor, with most patients experiencing residual neurological deficits. Among comatose patients, the mortality rate can be as high as 89% [11]. However, with the advancement of medical science, the mortality rate from cerebral edema during pregnancy has noticeably decreased in recent years, and the overall prognosis has gradually improved. Several factors contribute to the poor prognosis of brain abscesses, including abscess rupture within the ventricles, presence of hydrocephalus, and depth of the abscess. In this particular case, the patient did not receive early diagnosis and treatment, leading to rupture of the abscess into the ventricles. Despite undergoing surgical abscess removal and receiving aggressive anti-infection treatment, the patient experienced significant post-operative hydrocephalus. Although the patient’s life was saved, serious neurological damage ensued. The patient did not regain consciousness after surgery and remained instead in a coma, requiring the induction of labor. The prognosis in cases like these is significantly influenced by the type of bacterial infection, the extent of the brain damage, and the overall response to treatment. Moreover, brain swelling caused by Actinomyces meyeri typically exhibits a less pronounced headache, and symptoms such as fever and vomiting can be easily mistaken for early pregnancy reactions, resulting in delayed treatment and poorer prognosis.

Conclusion

During pregnancy, a decrease in immunity can result in a heightened susceptibility to severe infections, even from bacterial species normally present in the body. Despite the low incidence of Actinomyces meyeri-associated brain abscesses during pregnancy, they pose a significant threat to the health of both the mother and fetus, necessitating complex treatment approaches and multidisciplinary collaboration. However, the advancement of neuroimaging techniques, antimicrobial drugs, treatment protocols, and neurosurgical technologies has significantly reduced the mortality rate and led to an overall improved prognosis for patients. In this case, the patient displayed atypical initial symptoms that included only mild fever and vomiting, which were initially misinterpreted as early pregnancy reactions and consequently overlooked, resulting in a missed opportunity for timely intervention. Hence, it is crucial to promptly consult with healthcare professionals when symptoms such as fever, headache, altered mental state, and neurological deficits arise during pregnancy to rule out the possibility of a brain abscess. Prognosis can be further compromised if a brain abscess worsens or if it eventually ruptures into the ventricles, which may lead to brain herniation.

In summary, the rupture of an Actinomyces meyeri-associated brain abscess during pregnancy is rare and typically linked to underlying etiologies. Therefore, it is advisable to eliminate potential dental sources of infection and improve oral hygiene before pregnancy. To the best of our knowledge, this is the first reported case of a woman in early pregnancy with an Actinomyces meyeri-induced brain abscess in whom no apparent predisposing factors were observed except for dental caries detected on radiographic images. Additionally, the decreased immunity during pregnancy may have heightened the risk of abscess formation and contributed to the atypical clinical course and symptoms of the infection.