Surgical Indications

Indications for neurosurgical intervention include significant mass effect, intracranial hypertension, progressive neurologic deficit, and pathogen identification.^{Reference Arlotti, Grossi and Pea20} While surgery is generally considered a mainstay of treatment, medical treatment alone may be appropriate. Such instances include small abscesses (<2.5 cm), good initial neurological status, known pathogen, and when the patient is a poor surgical candidate.^{Reference Arlotti, Grossi and Pea20,Reference Mameli, Genoni, Madia, Doneda, Penagini and Zuccotti21}

Although there are no current, widely accepted neurosurgical guidelines for the management of intracerebral abscess, approximately a third of respondents indicated they were aware of general guidelines (e.g., IDSA). Most respondents in this study agreed with the theoretical recommendation that any abscesses larger than 2.5 cm should be operated on. However, few respondents reported implementing this practice for abscesses they recently managed. A patient with a larger abscess may be a candidate for conservative management if there were significant contraindications to surgery, refusal of surgery, or the abscess is in the early cerebritis stage. On the other hand, select abscesses smaller than 2.5 cm may be also be amenable to surgery. The 2.5 cm size cutoff is commonly cited but unfortunately lacks objective evidence to support an impact on functional outcome and overall survival.^{Reference Brook9,Reference Brouwer and van de Beek10,Reference Arlotti, Grossi and Pea20,Reference Brouwer, Tunkel, McKhann and van de Beek1,Reference Mamelak, Mampalam, Obana and Rosenblum22} Respondents also felt that lesion location (e.g., non-eloquent, eloquent, deep, posterior fossa), high suspicion for fungal or atypical bacterial species (e.g., nocardia or tuberculous disease), radiographic appearance, and symptomatic mass effect leading to herniation were also important considerations in the surgical management of intracerebral abscesses.

Surgical Techniques

The optimal surgical technique for management of intracerebral abscess is a topic of ongoing debate.^{Reference Wu, Wei and Yu23,Reference Makwana, Merola, Bhatti, Patel and Leach24} Advantages and disadvantages of each technique have been reported including the challenges and experiences in developing countries.^{Reference Singh, Rohilla and Kumawat25} In the literature, abscess excision has been observed to be associated with decreased recurrence and re-operation rates, decreased duration of antibiotic course, shorter hospital stays, and lower overall cost relative to aspiration.^{Reference Aras, Sabanci and Izgi2,Reference Moorthy and Rajshekhar13–Reference Mut, Hazer, Narin, Akalan and Ozgen16,Reference Ratnaike, Das, Gregson and Mendelow18,Reference Wu, Wei and Yu23} Excision may be preferred in cases of large, superficial, or multiloculated abscesses, when there is significant mass effect, in trauma- and/or foreign body associated abscesses, and those located in the posterior fossa.^{Reference Aras, Sabanci and Izgi2,Reference Ratnaike, Das, Gregson and Mendelow18,Reference Kural, Kırmızıgoz, Ezgu, Bedir, Kutlay and Izci26} We identified further suggestions for excision over aspiration including abscesses in non-eloquent areas of the brain, with suspicion of more resistant pathogens such as fungi, TB, or branching bacteria.^{Reference Brouwer, Tunkel, McKhann and van de Beek1} However, excision has been associated with an increased rate of mortality,^{Reference Ratnaike, Das, Gregson and Mendelow18} intracranial hemorrhage,^{Reference Makwana, Merola, Bhatti, Patel and Leach24} and seizures.^{Reference Aras, Sabanci and Izgi2} Advantages of aspiration include minimally invasive technique, potential to avoid general anesthesia in poor surgical candidates, less potential morbidity and mortality, and use in deep-seated or eloquent areas.^{Reference Aras, Sabanci and Izgi2,Reference Gadgil, Patel and Gopinath14,Reference Ratnaike, Das, Gregson and Mendelow18,Reference Kural, Kırmızıgoz, Ezgu, Bedir, Kutlay and Izci26} The largest drawback of aspiration is that the abscess capsule remains in situ and may lead to higher rates of early recurrence and need for re-operation.^{Reference Aras, Sabanci and Izgi2,Reference Gadgil, Patel and Gopinath14,Reference Wu, Wei and Yu23}

Most of our survey respondents agreed that either aspiration or excision may be an acceptable approach depending on specific clinical and radiographic factors. There remained a preference for less invasive techniques, however, as a much larger proportion of surgeons used aspiration (30.7%) compared to excision (2%) exclusively. Choice of procedure was equivocal if the abscess abuts the ventricle, with more resistant pathogens, and a more radiologically mature capsule. Of particular interest was the discordance in responses between experienced surgeons and residents, those < 10 years into practice, and those managing 0–1 abscesses per month. Specifically, while more experienced surgeons were less likely to excise an abscess in a non-eloquent area, they were more likely to resect an abscess that appears radiologically mature with a “thick” capsule and less likely to use topical antibiotics in the abscess cavity following excision (e.g., vancomycin powder) (Supplementary Table 1).

Additional unresolved issues investigated in this study include intraoperative antibiotic administration and use of synthetic duraplasty in the setting of intracerebral abscess. Some experts advised intra- or postoperative administration of antibiotics into the abscess cavity as penetration through the abscess capsule may be limited during an aspiration procedure.^{Reference Xiao, Tseng, Teng, Tseng and Tsai7} Some authors observed good clinical and radiological outcomes with the use of intracavity antibiotics and suggest their utility in large, poorly resolving abscesses, or those involving more resistant pathogens; however, evidence is limited.^{Reference Broggi, Franzini, Peluchetti and Servello27–Reference Mathisen and Johnson30} In our study, we found that most Canadian neurosurgeons did not routinely utilize intraoperative intracavitary antibiotics unless for repeat procedures.

Approach to Multiple Abscesses

For confirmed intracerebral abscess, the incidence of multiple lesions ranges from 10% to 50%.^{Reference Mameli, Genoni, Madia, Doneda, Penagini and Zuccotti21,Reference Burke, Thawani and Berger31–Reference Mampalam and Rosenblum35} Patient presentation depends on multiple factors: abscess location (i.e., eloquence), size and mass effect, and stage of abscess formation. When there are multiple small brain abscesses (<2.5 cm), Brouwer et al. advocate for diagnostic aspiration of the largest lesion, with subsequent decision to aspirate other abscesses made based on their size, extent of surrounding edema, patient’s symptoms, and response to broad-spectrum anti-microbial therapy.^{Reference Brouwer and van de Beek10} Given the apparent higher mortality rate with multiple abscesses, more aggressive management may be required to achieve source control.^{Reference Dyste, Hitchon, Menezes, VanGilder and Greene33} Mamelak et al. suggest an algorithm with aspiration of all abscesses >2.5 cm on an urgent basis with antimicrobials held until surgical specimens are obtained in the patient with no primary source of infection.^{Reference Mamelak, Mampalam, Obana and Rosenblum22} Interestingly, the conservative cutoff of 2.5 cm for surgical intervention in the nonearly cerebritis phase intraparenchymal abscess was first advocated by Mamelak et al. using Rosenblum et al. finding that solitary abscesses that are 3.0 cm were more likely to require surgical intervention to achieve a cure (p < 0.005).^{Reference Rosenblum, Hoff, Norman, Edwards and Berg36}

Rupture of the intracerebral abscess into the ventricular system either spontaneously or iatrogenically during a surgical procedure is associated with a case fatality rate reported between 84% and 100%.^{Reference Omar and Khu37,Reference Zeidman, Geisler and Olivi38} The spontaneous event is thought to result from a poorly formed abscess capsule on the ventricular wall. The mortality of intraventricular rupture has decreased in recent years with the application of surgical techniques such as intraventricular lavage akin to infective hydrocephalus^{Reference Zeidman, Geisler and Olivi38,Reference Qin, Liang and Xu39} and broader-spectrum antibiotics that can cross the blood–brain barrier. In this survey, many respondents selected a maximally invasive surgical approach to the management of an intracerebral abscess with imaging suggestive of intraventricular rupture (Figure 7B).

Pediatric Considerations

We identified little discordance between the pediatric and adult trained clinicians in the management of intracerebral abscesses. In a recent review of pediatric brain abscesses, Mameli et al. outline recommendations for surgical aspiration versus excision of intracerebral abscesses in children.^{Reference Mameli, Genoni, Madia, Doneda, Penagini and Zuccotti21} Specifically, these authors recommend aspiration for abscesses >2.5 cm, multiple and deep-seated abscesses that may be in eloquent locations and at high risk of complication with excision. Abscesses in children may be considered for surgical excision if located in the posterior fossa, there are multilobulated lesions, or result from a prior cranial trauma.

Limitations

In the present survey study, given the small number of pediatric neurosurgeon respondents, we were unable to identify differences in pediatric compared to adult practice in the management of intracerebral abscesses. Additionally, despite a long data collection period, the response rate was low including some large high-volume centers, therefore the generalizability of the findings to the practices across the country are limited. Recall bias may have influenced respondents estimates of the number of intracerebral abscesses seen in consultation per month.