The complications associated with dealing with any intracranial space-occupying lesion are also inherent to intracranial infectious lesions. In addition, there are certain issues that need special mention.
Unlike tumors, infectious space-occupying lesions may or may not contain active disease-causing pathogens, and hence spillage of contents into the surrounding normal brain carries risk of intracranial dissemination and should be avoided at all costs.
It should always be borne in mind that surgery is an adjunct to treat the infectious lesion and that the mainstay always remains the antimicrobial or antihelminthic agents. With this dictum, the surgeon should aim at keeping the surgical intervention to a minimum and avoid complications as a rule.
Long-term follow-up is mandated in spite of complete resolution of the infection due to the potential seizure risk in these patients. Scarring of the brain due to perilesional scar tissue formation occurring in infectious lesions acts as the seizure focus.
Pyogenic brain abscess (PBA) is a focal collection of pus within the brain. The incidence of PBAs is 8% of intracranial masses in the developing countries, whereas in the West the incidence is 1% to 2%, with male predominance. The overall occurrence of brain abscess does not appear to have changed significantly in the antibiotic era. The presenting features of brain abscess depend on the size and intracranial location of the lesions, the virulence of the infecting agents, the immunologic status of the host, and the cerebral edema caused by the expanding intracranial mass lesion. The usual treatment combines antimicrobial therapy, serial imaging studies, and surgical drainage. Surgical treatment can be either aspiration of brain abscess content or surgical excision of abscess capsule.
Surgery for PBA is performed with the dual aim of obtaining microbiologic confirmation of the offending organism and decompressing the space-occupying lesion to relieve pressure on the surrounding normal brain. The argument for “craniotomy and excision” versus “stereotactic aspiration” is still contentious. Eloquent and deep location, size, multiplicity, and radiologic characteristics of the abscess play an important role in guiding treatment strategy. Complications arising from the treatment also matter. Aspiration of brain abscess has low surgery-related morbidity and mortality rates; however, this comes at the cost of high postaspiration relapse rates (up to 32%), and such a relapse necessitates reaspiration. Computed tomography (CT)–guided stereotactic aspiration is a modality accurate to within a few millimeters with a diagnostic yield of 95%, is associated with transient morbidity in only 5% of patients, and is highly effective in the definitive drainage of abscesses. Epilepsy is a common posttreatment sequel of brain abscess occurring in 30% to 50% of patients. Seizure frequency is reportedly highest in the fourth and fifth years after diagnosis. Nielsen et al. reported high incidence of seizures with frontal lobe abscesses. Some studies have suggested a trend toward a lower incidence of seizures and other sequelae in those treated by aspiration as opposed to excision.
Intraventricular rupture of brain abscess (IVROBA) is a potentially fatal complication of PBA and can occur iatrogenically during excision or manipulation of the deep wall of the brain abscess. Capsule formation and ring enhancement on imaging studies are generally thinner and less complete on the ventricular side of the abscess, and this may result in a false plane of dissection resulting in inadvertent but disastrous rupture of the abscess into the ventricle. Ill-formed medial abscess wall is probably due to the relatively poor vascularity of the deep white matter and reduced migration of fibroblasts into that area. Mortality rates after IVROBA have been reported to range between 39% and 80%. Individualized approach to iatrogenic IVROBA with intrathecal and intravenous antibiotic therapy, cerebrospinal fluid (CSF) diversion (if under high pressure), and close monitoring of clinical status, CSF reports, and CT scan findings is vital to achieving a satisfactory outcome in such patients.
Standard precautions for avoiding complications while operating on intracranial space-occupying lesions should be adhered to while dealing with PBA. Special care should be taken to avoid spillage of contents into the ventricles to prevent IVROBA, which carries an unacceptably high morbidity and mortality. For stereotactic aspiration, it is imperative to plan an appropriate trajectory to avoid the ventricles. For craniotomy and excision, the medial/deep wall of the abscess deserves special mention. Its thickness and intactness as well as its relation to the ventricular wall should be meticulously studied on the preoperative radiology. If the medial wall is too close (<1 cm) to the ventricular wall, or if it is ill-formed, it would be prudent to proceed with subtotal abscess wall resection to prevent an inadvertent breach in the ventricular wall.
Due to the high incidence of seizures, all patients with supratentorial brain abscess should be given prophylactic anticonvulsant coverage in the perioperative period and should be continued in the postoperative period for at least one year. The anticonvulsant should be tapered if the electroencephalography shows no epileptogenic activity. Patients having intractable seizures may sometime respond to temporal lobe resection or resection of the seizure focus.
Infection of the central nervous system (CNS) by Mycobacterium tuberculosis is invariably secondary to a primary focus elsewhere in the body and is one of the most devastating clinical manifestations of tuberculosis. CNS tuberculosis manifests as meningitis, cerebritis, tuberculous abscesses, or tuberculomas and accounts for approximately 1% of all cases of tuberculosis. Presently, surgery is rarely used as a treatment modality for CNS tuberculosis. With the availability of specific magnetic resonance imaging (MRI) sequences, diagnosis of intracranial tuberculomas can be obtained with reasonable accuracy based on radiology. Hence, indications for surgery/biopsy per se have decreased. The two forms of CNS tuberculosis infections that are most often managed surgically are tuberculomas and tuberculous meningitis with hydrocephalus.
At present, indications for surgery for a suspected case of tuberculoma are: uncertain diagnosis, paradoxical increase in size of the lesion while on medication for tuberculosis, and tuberculomas with mass effect causing raised intracranial pressure (ICP).
Complications and Prevention
With the use of modern techniques, the mortality and morbidity of surgery for tuberculosis are negligible. A trial of antitubercular therapy should always be considered before surgery is attempted, especially in the absence of raised ICP. When surgery is indicated, the approach needs to be conservative rather than risk an undesirable neurologic deficit. The patient should be started on antitubercular chemotherapy, preferably a few days before surgery, if the patient is not already on it. Administration of preoperative corticosteroids is also desirable. No attempt should be made to excise large tuberculomas en masse. Piecemeal removal or initial debulking does not increase the risk of meningitis if the patient is covered with antitubercular drugs. Subtotal or partial excision of lesions situated in or near eloquent areas is justified in order to prevent neurological deficits. No attempt should be made to aggressively excise tuberculomas attached to vital structures like the brainstem or the major dural venous sinuses. Endoscopy has a role in management of associated hydrocephalus and can be used to do third ventriculostomy, fenester the septum pellucidum, break loculations, and reduce the need for multiple shunts.
Cerebral hydatid cysts constitute approximately 2% of all hydatid cysts occurring in the body, and account for approximately 2% of all intracranial mass lesions occurring in humans. Cerebral cysts are mostly solitary (90%) and predominantly supratentorial, with 60% to 70% located in or around the middle cerebral artery territory. Due to their slow growth, the surrounding normal tissue adapts to the chronic compression, and the symptoms are noted only after a prolonged latent period. Chronicity of the illness may also be due to the lack of cerebral edema in the surrounding brain. The average size of a cerebral hydatid cyst ranges from 6 to 10 cm, but 5% reach a diameter of 20 cm. Enucleation of the intact cyst/cysts remains the treatment of choice for cerebral hydatid cysts. The aim of surgery is to excise the cyst intact without spillage of hydatid fluid and to preserve the surrounding brain parenchyma as much as possible. Surgical treatment is complemented with perioperative medical management in the form of albendazole.
Complications of surgery for intracranial hydatid are likely in two settings: very large cyst [giving rise to sudden intracranial decompression on excision and leading to subdural hematoma (SDH), contusions, seizures] and inadvertent rupture of cyst (spillage of hydatid fluid into the surrounding normal brain, leading to dissemination).
Tuzun et al., in their review of 25 pediatric patients operated for cerebral hydatid cysts, review the complications related to cerebral hydatid cyst surgery. Intraoperative cyst rupture occurred in three (12%) patients. Pneumocephalus developed in three (12%) patients. Subdural effusion occurred in five (20%) patients, whereas subdural effusion plus porencephalic cyst occurred in two, hemorrhage in two, epidural hematoma in one, and porencephalic cyst in four patients. After inadvertent intraoperative rupture, the cyst bed was irrigated with 20% saline. No anaphylactic reaction developed. Seizure was not observed. Recurrence of cerebral hydatid cyst was observed in only one (4%) patient who experienced intraoperative cyst rupture and underwent reoperation for the cyst extirpation. However, the location of the recurrence was in a site opposite that of the first cysts.
Intraoperative cyst rupture is the most common and serious complication, which can lead to widespread dissemination followed by severe inflammatory or anaphylactic response. Seizure, subdural effusion, porencephalic cyst, hemorrhage, pneumocephalus, hydrocephalus, stroke, eosinophilic meningitis, and transient neurologic deficits are the postoperative complications that were reported in the literature. Ciurea et al. reported their experience of 27 pediatric cases with cerebral hydatid cyst in 1995. Epilepsy, paresis, subdural effusion, ventricular dilatation, and recurrence were the postoperative complications, and operative mortality was very low with only one death. Subdural effusion or hematoma is a well-known complication of cranial operations that also occurs after surgery for cerebral hydatid cyst. The ICP is high when a hydatid cyst exists in the brain parenchyma. This drops rapidly after the removal of the cyst. This low pressure causes the brain to sag away from the calvarium, opening up the subdural space ( Fig. 25.1 ). Vessels traversing the subdural space get stretched, resulting in transudation of fluid from the intravascular compartment to the subdural space. This is the probable pathogenesis of subdural effusion in such cases.