Discussion
Subdural empyema is a rare and fatal intracranial complication of chronic otitis media with a mortality rate of 12.2% to 28%.11,17 The predisposing risk factors include neglected middle ear infections, lack of access to health care and availability of imaging modalities such as CT scan and/or MRI, immunosuppression, and poor economic status.7,10,18,19Over the past years, the incidence of complications of otitis media have decreased with the use of antibiotics, improved imaging studies, the introduction of the pneumococcal vaccine, and multidisciplinary management.6,7
Clinical presentation : The symptoms and signs in patients with subdural empyema are due to pus collection and the mass effect on the brain. The classical triad of presentation which include headache, fever and vomiting is present only in 36% to 50% of the patients. Showing that the triad is not very sensitive in diagnosing subdural abscess. To emphasise this fact, as was already mentioned above in the case study, the patient had only fever from the so called ‘classic triad’. Therefore, it is generally agreed that the symptom complex of fever, headache, vomiting, and altered mental status is rather more precise.8,16,20 Even with this, due to the rarity of the condition, the diagnosis is often delayed if not missed. Therefore, physicians need to have a high index of suspicion in patients who have history of COM.
Investigation : Radio-imaging using CT scan or MRI is required to confirm the diagnosis. In the early stages of the disease however, CT scan can be normal in 63% of the cases.8 As MRI can identify intracranial edema better than CT scan, it is more preferable to use MRI for earlier diagnosis of intracranial complication.6 Similarly MRI is better in recognizing the extension of the empyema into the interhemispheric fissure and the posterior fossa.14 Hence, in suspected cases of intracranial subdural empyema for accurate diagnosis MRI is the gold standard with a sensitivity of 93%.8,12 Laboratory analysis of blood shows elevated WBC, ESR, and C-reactive protein.6 Culture and sensitivity of intraoperative pus should be done, even though often empyema is sterile and has no yield in 50% of the cases.6,8,16 It was similar in our case. This is due to the administration of antibiotics before the diagnosis is made.
Management : The mainstay treatment of subdural empyema includes the use of antibiotics and surgical evacuation of the pus. There should be immediate initiation of broad spectrum antibiotics. A combination of oxacillin/nafcillin, a third-generation cephalosporin and metronidazole covers the most common pathogens. Due to the increasing presence of penicillin resistant Streptococcus pneumoniae andStaphylococcus aureus the use of vancomycin instead of oxacillin is preferred.6,8,15,16,21 This was done in our case and the outcome was satisfactory. Most recommend a minimum 2 weeks of IV antibiotics while others suggest continuation for 6 weeks. In our case, the two weeks of IV antibiotics were found to be adequate. But almost all agree that IV antibiotics must be followed by 6 weeks of oral antibiotics.6,8,15,22
Surgical drainage of the subdural pus is the next crucial step following the initiation of antibiotics. The surgical procedure can either be craniotomy or burr whole. Craniotomy is preferred as it allows adequate exploration; complete removal of pus, loculations, and the possible calcifications on the abscess wall, and effective decompression of increased intracranial pressure.8,11,14,16 Moreover, recurrence of subdural empyema is more common in Burr hole (almost 40%) as compared to craniotomy.15,16,20 However, in the weak patients or those in septic shock or when the empyema is parafalcine, Burr hole is the preferred procedure. The surgical intervention should be done as soon as possible, since any delay results in worsening of outcome. Disability reaches as high as 70% in those who were operated after 72 hours of presentation as compared to the 10% in those who were operated within 72 hours.11,15,17
Administration of prophylactic anticonvulsants is advised as seizures occur in 32% to 44% of patients with subdural empyema.15,16,20 Moreover mannitol should be given preoperatively and postoperatively to reduce the increased intracranial pressure.6,15,21 After the patient stabilizes the chronic otitis media and mastoiditis should be properly treated by the ENT specialists.3,6,10 Similarly our patient was later on transferred to the ENT department where her chronic otitis media was properly addressed.
Factors such as age of the patient, delay in presentation, extent of the sepsis, and the subdural empyema along with level of consciousness at presentation significantly affect the outcome of the patient.16 Morbidities such as sensorineural hearing loss, residual neurological deficits including seizures and hemiparesis are seen in about 28% of the survivors.3,11 Therefore to achieve good results early diagnosis, immediate surgical intervention, and appropriate antibiotic therapy are of paramount importance.