Early cerebritis (first ~5 days): Represents early focal infection with localized polymorphonuclear leukocytes (PMNs), edema, scattered necrosis, and petechial hemorrhage. Toxic changes in neurons with perivascular infiltrates are present. The lesion is poorly demarcated from surrounding brain.
Late cerebritis (5–14 days): Reticular matrix formation begins leading to a rim of thin granulation tissue at the periphery. Necrotic foci also coalesce leading to the development of a necrotic center.
Late capsule (several months): The lesion wall thickens and contains collagen, granulation tissue, and macrophages. The central cavity begins to shrink as the wall of the abscess thickens. The lesion also induces peripheral gliosis at this stage.
Because a cerebral abscess can occur anywhere in the brain, the general surgical approach that would be most useful is a stereotactic-guided minicraniotomy for evacuation and drainage. The goals and advantages include
Image-guided needle aspiration combined with antibiosis has significantly improved the outcomes for patients with intracerebral abscesses (Fig. 114.1 A-C).
Fig. 114.1 (A) Axial view showing patient positioning and stereotactic frame in place with site of skin incision determined based on the trajectory location and entry point as determined on preoperative imaging studies. Eloquent structures are avoided. A stereotactic biopsy and aspiration can be obtained to determine the offending organism and decompress a deeply located abscess. (B) Oblique front view of the same setup and positioning described in (A). (C) A minicraniotomy may also be performed in select cases with frameless stereotaxy and a guided small thin ultrasound probe can be driven down to the location of the abscess to better determine the nature of the lesion and achieve decompression. SI, S-shaped skin incision; CS, coronal suture.
Preoperative CT/MR images should be obtained including a stereotactic protocol. These films should be studied to plan the trajectory. This will aid in positioning, pin placement, as well as incision type and location. Patients should be placed under general anesthesia and then positioned where the planned craniotomy is facing up and toward the surgeon. Pins should be placed far out of the way of the operative site. An incision should be planned in a way that it can be extended if necessary. The hair should also be shaved or clipped in an adequate manner to accommodate this eventuality. The reference star or frame for neuronavigation should be placed directly on the headholder in a tight fashion so as to not migrate during the procedure. Once the system is registered and active, this can be used to further guide incision and approach plan.
Once a detailed “time out” is performed outlining the procedure type and site, local anesthetic can be injected into the planned incision site. One technique is to make a “lazy S” incision that is about one and a half times to twice the size of the planed craniotomy. Next, a 10-blade scalpel can be used to make the skin incision. Further tissue dissection can be performed using the Bovie electrocautery. A self-retaining retractor can be used such as a cerebellar retractor. Then, the image guidance probe should be used to redefine the minicraniotomy site. One or two burr holes are usually sufficient. These can be made with a high-speed drill. One should try to hide the burr holes under an area that can be covered with overlying muscle if possible. Now, a Penfield #3 dissector can be used to strip the dura from the underside of the bone that is to be removed. A side cutting apparatus/drill attachment can be used to turn a bone flap, which is passed off the field with care.
Once the bone flap is taken off and the dura exposed, the reference probe should be used to reconfirm the path to the abscess. The bone edges should be waxed and, depending on how large a craniotomy made, a few dural tack-up sutures are placed. One option is to open the dura in a cruciform fashion such that the opening can be extended if needed. The dura is opened using a 15-blade scalpel. The dural leaves are held off the field with 4-0 Nurolon suture. The operative microscope should be brought in at this point, and the Greenberg retractors (or other self-retaining retractor system) can be placed in case these become necessary. The image guidance should be used to guide entry into the brain parenchyma to minimize brain trauma. Once the abscess is encountered, one should keep in mind that the capsule can be rather resilient and may need to be opened with a scalpel (in cases of larger abscesses that need to be drained prior to resection). An attempt should be made to remove the abscess cyst in its entirety (in an “en-bloc” fashion). If this cannot be done safely then that cyst should at least be drained and a specimen sent to a microbiology laboratory for identification. The purulent fluid obtained from the abscess should be sent for routine aerobic and anaerobic cultures as well as fungal elements and acid-fast bacilli. Care should be taken not to rupture the abscess into the ventricle if it is located near that area (Fig. 114.2).
Once resection/removal are complete, copious irrigation should be used with or without antibiotics (depending on the surgeon’s preference, as certain antibiotics have been shown to be neurotoxic). Meticulous hemostasis should be completed using the bipolar cautery and absorbable gelatin powder (GelfoamTM powder, Pfizer Inc., New York, NY) with thrombin. Strips of absorbable hemostat (SurgicelTM, Johnson & Johnson Inc., New Brunswick, NJ) can be placed in the resection cavity. The dura is reapproximated with 4.0 Nurolon. The bone flap is replaced and held in place with titanium microscrews and plates. The scalp flap is then closed using inverted 2.0 Vicryl suture for the galea, followed by staples for the final skin closure.
If a lesion is not fully accessible or complete removal is not possible, then the surgeon should try to remove as much lesion as safely possible and then abort the procedure. At least a specimen can be obtained and will guide specific treatment management.
If the craniotomy made was too small and does not offer adequate access, it can always be enlarged, but this eventuality should be anticipated at the onset of the procedure when choosing the incision type and location.
Patients have the best outcomes when the abscess is discovered early, a pathogen is identified, antibiotics are tailored, and the patient does not have significant comorbidities such as a compromised immune system.
3 Cavusoglu H, Kaya RA, Türkmenoglu ON, Colak I, Aydin Y. Brain abscess: analysis of results in a series of 51 patients with a combined surgical and medical approach during an 11-year period. Neurosurg Focus. 2008;24(6):E9
4 Shachor-Meyouhas Y, Bar-Joseph G, Guilburd JN, Lorber A, Hadash A, Kassis I. Brain abscess in children - epidemiology, predisposing factors and management in the modern medicine era. Acta Paediatr. 2010