Choice of Procedure
- Image guided aspiration – stereotactic: CT-guided stereotactic puncture and aspiration is the “gold standard” for the treatment of brain abscesses, given its consolidated efficacy, minimal invasiveness, and low rate of complications, especially when compared to abscess excision (13). This procedure can be performed using frame-based stereotaxis or frameless stereotaxis (so-called computer-assisted neuronavigation). Stereotactic aspiration can be conducted at any stage of evolution of the abscess, and a biopsy may yield positive cultures in the early cerebritis stage (94). Stereotactic aspiration technique allows access to multiple and deep-seated abscesses, has a low complication rate, permits a minimal craniotomy, and allows multiple aspirations, if needed (8, 26, 41). Stereotactic aspiration has been demonstrated to have a diagnostic yield of 95% (19).
- Image guided aspiration – free-hand: Free-hand aspiration of the abscess with feedback from various types of real-time imaging can be used to aspirate an abscess. Free-hand aspiration using ultrasound and MRI in addition to CT imaging has been described (80).
- Endoscopic aspiration of abscess: This technique allows the neurosurgeon to inspect and directly view the aspiration of the purulent collection, unlike stereotactic aspiration in which there is a lack of direct visual control (52, 68, 81, 93).
- Craniotomy: Craniotomy for extirpation of the abscess is considered beneficial in some cases of fungal or multiloculated abscesses, and in cases of failed resolution after multiple aspirations (30). It is also considered if the abscess is located close to the surface of the brain where a small craniotomy or bur hole may be used for drainage of the abscess. Craniotomy and excision have been advocated for all cerebellar abscesses, since treatment failures in the posterior fossa can be rapidly fatal (118).
- Aspiration – frame-based stereotaxy: The patient is taken to the operating room where the stereotactic frame is placed with the aid of sedation and local anesthesia. Blockade of supraorbital and occipital nerves can be performed 5 min before the frame is fixed. After imaging has been completed, the patient is returned to the operating room and positioned either supine with the trunk slightly elevated and the head in mild flexion or in a semi-sitting position. The frame is fixed to the operating table.
- Aspiration – frameless stereotactic systems and neuronavigation: Positioning the patient is easier without the presence of the stereotactic frame, so lateral decubitus can also be used when dealing with temporal lesions. The head is usually held in position during the procedure with a head frame.
- Craniotomy: Patient positioning is the same as for any surgical procedure requiring craniotomy for lesions located in temporal, parietal, frontal, or occipital lobes. For cerebellar lesions lateral decubitus or prone position is usually preferred. When using frameless systems, no additional special consideration is needed for positioning the patient except head fixation with pins.
- Scalp incision: The incision will vary with the site of the craniotomy and its extent. There are usually no special considerations for its location.
- Location of craniotomy or bur hole: The location of the opening in the skull will be dictated by both the location of the infections and the structures to be avoided while approaching the infections. Careful planning can result in a smoother postoperative recovery.
- Avoid ventricle when aspirating: While aspirating the abscess, great care should be taken to avoid a needle trajectory through the ventricular system (30).
- Endoscopic removal of abscess: A frameless neuronavigation system can be used to plan the correct trajectory to the abscess. Once the dura is open, a peel-away cannula is inserted through the bur hole and advanced until it encounters the resistance of the outer margin of the abscess’s capsule.
- Frameless stereotaxic (computer-assisted neuronavigation) aspiration: The needle is guided to the image-defined target as it is tracked on the neuronavigational device. Aspiration with a syringe is performed without excessive suction until pus egress stops; thereafter, the abscess cavity can be slightly irrigated. Preoperative stereotactic imaging allows for computation of the abscess volume and provides an estimate of how much material can reasonably be expected to be withdrawn.
- Frame-based stereotactic aspiration (92): The needle is slowly advanced through the frame’s guide sleeve until it reaches the target. Aspiration with a syringe is performed without excessive suction until pus egress stops; thereafter, the abscess cavity can slightly irrigated.
- Ultrasound-guided aspiration: In some cases, the abscess can be drained under ultrasonographic guidance after the craniotomy is performed. This can be done either using guide sleeves attached to the ultrasonic head or free handed. It will require a craniotomy larger than a bur hole so that the ultrasound head can remain in contact with the dura while the needle is being advanced into the abscess. In both situations imaging shows both the needle as it approaches the abscess and the needle’s entry into the abscess. It can then visualize the degree to which the aspiration collapses the liquid center of the abscess.
- CT image-guided aspiration: Under emergent conditions or in the absence of the necessary equipment, aspiration of brain abscesses can be performed in the CT scanner. The CT scan is used to localize the lesion; scalp markers identify the approximate abscess location, size, and depth from the surface; and the biopsy needle is advanced under CT guidance into the abscess cavity. This technique has an accuracy of 4–5 mm and can be useful in these circumstances (13).
- MR fluoroscopic-guided aspiration: The safety and efficacy of aspiration of brain abscesses using a free-hand technique in an open MRI system have been reported in the literature (80). (See images below.)
Craniotomy for aspiration
- Increased size of dural exposure: The increased exposure of dura may be helpful when ultrasonic guidance and imaging are being used concurrently with the passing of an aspirating needle and aspiration of the abscess. It also allows for a cortisectomy and direct approach to the abscess when visualization of the interior is desired, as would be the case for multiloculated abscesses or cerebellar abscesses.
- Endoscopic removal of abscess: Once the internal cavity is reached and spontaneous discharge of purulent material can be observed, specimens are taken for microbiological investigation. A flexible endoscope (4-mm outer diameter and a 3-Fr operative channel) can be introduced into the purulent collection through its trocar, the pus meticulously aspirated, and the cavity then washed with isovolumetric lavages (+/- antibiotic) using the working channel for both irrigation and suction. Irrigation and aspiration should be isovolumetric (93). Hellwig et al. maintained that drainage catheters need not be inserted inside the abscess after endoscopy (for antibiotic infusion and further aspiration during the following days), while Fritsch and Manwaring reported placing them in all cases (52, 68).
Processing of aspirant
- Immediate submission of material to lab: If the abscess is drained, operating room personnel should take the aspirate for culture immediately; waiting for the specimen to be picked up increases the likelihood of a negative culture (55).
- Immediate microscopic examination: Gram-stain, acid-fast stain (AFB stain) for Mycobacterium, a modified acid-fast stain (for Nocardia) looking for branching acid-fast bacillus and special fungal stains (e.g. methenamine silver, mucicarmine) can be considered when examining the aspirant acutely.
- Culturing of aspirant: Routine microbiological culturing, fungal culturing, and culturing for tuberculosis organisms are performed with the aspirated material. The prolonged period of incubation of specimens being cultured for fungal or tuberculous organisms can also result in the identification of fastidious or indolent bacterial organisms.
Irrigation after removal
- Need for antibiotic irrigation not proven: There is no scientific rationale for the instillation of antibiotics into the abscess cavity (104).
- Minimize suture material: Consider monofilament single-layer closure (e.g., 3.0 nylon vertical mattress).