The term intracranial abscess includes the following disorders: cerebral abscess, subdural empyema and epidural empyema. These disorders share many diagnostic and therapeutic similarities and, frequently, very similar aetiologies.
The overall mortality described in six case series of ICA from different countries during the years 1981-1986 ranged from 10 to 36%, with a summed death rate of 22% (142 deaths in 636 patients). Fifteen subsequent studies during the years 1987-1993 suggest that the mortality may have decreased slightly, with a combined death rate of 18% (115 in 634 patients). Summing these 21 studies, the average mortality from ICA was 20%. This was confirmed in the neurosurgical literature in the late 1990's.
Factors possibly responsible for a decrease in mortality include:
(a) earlier and more accurate diagnosis through expanded use of computed tomography,
(b) advances in minimally invasive surgery, e.g. CT-guided fine needle aspiration, and
(c) improved understanding of the bacteriology of ICA, leading to more appropriate antibiotic therapy.
Because of improving mortality, there is a general trend toward a more conservative therapeutic approach in the management of ICA patients. This is reflected in the current international literature. However, patients with certain conditions and complications continue to pose major therapeutic problems. These include patients with:
(a) multiple abscesses,
(b) abscess in a deep or dominant location,
(c) immune compromise, and
(d) no response or further deterioration in spite of standard surgical and antibiotic treatment.
Under these circumstances, adjunctive hyperbaric oxygen (HBO2) therapy may confer additional therapeutic benefit. A number of mechanisms can be postulated by which HBO2 could provide benefit in ICA. First, high partial pressures of oxygen may inhibit the flora found in ICA, the predominance of which are anaerobic. Second, HBO2 can cause a reduction in perifocal brain swelling. Third, HBO2 has the potential to enhance host defence mechanisms. Finally, HBO2 has been reported to be of benefit in cases of concomitant skull osteomyelitis.
Preliminary experience using adjunctive HBO2 to treat patients with ICA has been favourable. To date, 66 such patients have been reported with 1 death (1.5% mortality). These include 16 consecutive patients reported in a series from Germany, 18 patients treated in Austria, 8 patients treated in France (4 with brain abscess; 4 with subdural and epidural empyema), 13 patients treated in Turkey (all with brain abscess and treated with stereotactic aspiration), 5 paediatric patients treated in Austria (1 with single brain abscess, 1 with multi-loculated brain abscesses, 2 with brain abscess and subdural empyema , 1 with brain abscess, subdural empyema, and epidural empyema) and an additional 6 patients treated in several centres in the United States (personal reports collected by Eric Kindwall). A patient with cervical epidural abscess treated in Japan has also been reported. The single death to date occurred in a patient with epidural empyema who had suffered hemispheric venous infarction from superior longitudinal sinus thrombosis prior to referral for hyperbaric oxygen therapy.
Patient Selection Criteria
Adjunct HBO2 should be considered under the following conditions:
1) Multiple abscesses
2) Abscesses in a deep or dominant location
3) Compromised host
4) In situations where surgery is contraindicated or where the patient is a poor surgical risk
5) No response or further deterioration in spite of standard surgical (e.g. 1-2 needle aspirates) and antibiotic treatment.
Hyperbaric oxygen treatment is administered at a pressure of 2.0 to 2.5 ATA, with oxygen administration from 60 to 90 minutes per treatment. HBO2 treatment may be one or two sessions per day depending on the condition of the individual patient. In the initial phase, twice daily treatment may be considered. The optimal number of HBO2 treatments for ICA is unknown. In the largest series of ICA patients treated with HBO2, the average number of HBO2 sessions was 13 in the absence of osteomyelitis. Duration of the HBO2 course must be individualised, based upon the patient's clinical response as well as radiological findings.