Pan Arab - Brain Abscesses

INTRODUCTION

There has been a good improvement in the mortality and morbidity rates of brain abscess during the last few decades. This has been due primarily to the development of diagnostic procedures ie. computed tomography (CT) scan and magnetic resonance imaging (MRI), along with the improved effectiveness of antibiotics and the development of neurosurgical technology and instrumentation.

Age and sex distribution
There is an increase in the incidence of brain abscess at both ends of the human span of life (Table 1).

It was noted about 30% of the cases were under the age of 12 years while approximately 26% were elderly patients. This presumably is because of the vulnerable immune status in the mentioned age groups. As regards the male to the female involvement, there is about 63% (so generally approximately 2/3 of the patients were male), as is shown in Table 2 and Figure 1.

Table 1

Table 2

Age in years	No. of Patients
Under 2 years	9
2-12	12
12-20	10
20-30	6
30-40	5
40-50	7
50-60	7
60-70	11
Total	68

Age in years	Male	Female
Under 2 years	5	4
2-12	8	4
12-20	7	3
20-30	4	2
30-40	3	2
40-50	4	3
50-60	4	3
60-70	4	3
Total	43	24

Causes and causative organisms
Brain abscesses may occur via one of the following routes:

1. Haematogenous spread: In this route the brain abscesses could be multiple in about 21% of the cases.

	In infants and children: Primary sources of infection are cyanotic heart diseases, arteriovenous fistula, and rarely bacterial endocarditis. The causative organisms are usually gram-negative in infants and haemophilus influenza in children.
	In adults: Primary sources of infection are lung and pelvic abscesses and empyema. The causative organisms are gram-negative bacilli and staphylococci.

It is worthwhile to note that no source of primary infection could be found in approximately 28% of the cases that occurred via this route.


	Figure 1

2. Contiguous spread: Purulent paranasal sinusitis, middle ear and mastoid infection could often cause brain abscesses. Streptococcus (anaerobic) as well as staphylococcus aureus and streptococcus viridans (aerobic) could be found.

3. Penetrating cranial trauma: Post-neurosurgical procedures tend to be commonly staphylococcus aureus.

It was noted that when the immune state of the patient is suppressed or various types of antibiotics were used prior to the clinical onset of the brain abscess, the flora of the primary disease would be replaced by other less common and more unusual organisms.

Histopathological Staging

1. Cerebritis: A small area of pus surrounded by an area of severe oedema (toxic changes in neurons and perivascular infiltration).

2.Thin-walled abscess: Pus spots that may be only partially or completely surrounded by a thin wall (reticular networks).

3. Thick-walled abscess: Well-developed capsules such as collagen capsules, necrotic centre, and gliosis around the capsule.

figure 2

Figure 2 - Cerebritis stage abscess

figure3

Figure 3 - Thin-walled abscess

figure 4

Figure 4 -Thick-walled abscess

Clinical presentation
There is a great variety of clinical presentations which depends on location, size and the speed of abscess formation in addition to the brain tissue reaction and the degree of neurons destruction by the inflammatory process. The immune state of the patient has its effect as well as the age of the patient.

Clinical syndromes for brain abscesses are quite diverse and generally, a raised intracranial pressure; in addition to various degrees of neurological deficits with or without a toxic inflammatory process. We shall summarise the common symptoms and signs which we found in our group of patients in the following table.

Table 3

Symptoms and signs	No. of patients	%
Headache	47	70
Nausea	44	65
Vomiting	40	60
Papilloedema	27	40
Alteration of Conscious level	44	65
Hemiparesis	27	40
Seizures	23	35
Pyrexia	27	40
No symptoms or signs of infection	27	40
Ataxia and cerebellar signs	23	35
Cranial nerves involvement mainly III, VI, VII	13	20

Figure 5

Figure 5 - Malignant glioma

Figure 6

Figure 6 - Hydatid cyst

Diagnosis:

	Good clinical history and bedside examination.
	Haematology: ESR was raised; WBC was above 15,000 in 38% of the cases.
	Lumbar puncture: Is contraindicated when brain abscesses are suspected to avoid herniation. Although CSF findings are abnormal in over 90% of the cases, its culture is rarely positive.
	Cerebral angiography: Showed a localised avascular mass.
	CT scan showed the following: Cerebritis: A thin ring of enhancement but lack of delayed decay. Capsule: Could be a faint rim, a thin enhancement ring or a thick diffuse ring.
	MRI usually shows a different thickness of capsule depending on the stage of the abscess, necrotic centre with oedematous surrounding brain tissue. Sometimes we need to use gadolinium to ensure a good diagnosis.

The differential diagnosis
Malignant glioma, metastatic neoplasm, tuberculoma, some types of cerebral infarction and cerebral hydatid cyst.

The treatment:
There is no definite strategy to treat all brain abscesses, so decisions must be made for every individual case, taking into consideration several points.

The medical treatment:

We limit ourselves to the medical treatment when:

	The brain abscess is in the cerebritis stage.
	When there are multiple or small abscesses less than 2.5 cm.
	When a short clinical duration and good response to antibiotics within the first few days are observed.

Antibiotics: Antibiotics must be started as early as possible. These antibiotics must have a wide spectrum of effects, as well as an acceptable penetration of the blood brain barrier. Usually, we start with the combination of Vancomycin, Cefotaxime and Metronidazole.

We could change the antibiotics, according to the clinical and bacterial situation. The patient must be under clinical and CT scan or repeated MRI evaluation. Antibiotics must continue for 4-6 weeks duration.

Steroids: Recommended for deteriorating patients because of oedema and mass effect.

The surgical treatment
A brain abscess is usually a surgical emergency. The type of surgery depends upon the degree of the patient�s illness. Decision for surgery is taken if one of the following factors exists:

1.	There is a large brain abscess with a mass effect.
2.	The clinical condition of the patient is deteriorating.
3.	When there is doubt about the diagnosis.

Types of surgical treatment
1. Needle aspiration: We do tend to go for abscess aspiration when the abscess is in the early capsular stage or in case of multiple or deep abscesses. A wide spectrum of antibiotics was started, awaiting the result of material culture and sensitivity and soft catheter was left in situ, for intermittent irrigation and drainage.

2. Total excision: The aim of excision must be the complete removal of the abscess with minimal damage to the surrounding oedematous brain tissue. Otherwise, aspiration is selected as the initial step and radical excision is the early secondary procedure under cover of an early start of a wide spectrum of antibiotics.

If we follow this way, the recurrence rate is usually less, in addition to the fact that the course of the antibiotic treatment is much shorter (6-10 days), if total excision was performed.

In the next table we summarise the type of treatments we followed in our patients. The needle aspiration was selected in 41% of our cases and early secondary total excision was perfomed in only 12% of the cases.

Table 4

Type of treatment	No. of treated cases	%
Medical treatment alone	12	18
Aspiration	28	41
Secondary excision	8	12
Primary excision	20	29

Table 5

Type of deficits

No. of patients

Hearing problems and emotional disturbances

Children	40
Adults	10

Hemiparesis

Focal or generalised seizures

Other neurological disabilities

Figure 6

Figure 6 - Excised cerebral abscess

Follow-up and recurrence rate
After treatment has been conducted a repeated clinical examination and CT scan or MRI should be made repeatedly to evaluate the result of the treatment.

The reason for brain abscess recurrence is either an incomplete control of the septic infection of the abscess, or failure to eradicate the primary cause of the cerebral abscess, either nearby infection: (paranasal sinus, middle ear and mastoid infection) or remote infection (thoracic, heart, or pelvis).

PROGNOSIS

Although the mortality rate has declined following the introduction of recent antibiotics, CT scan and MRI, the rate remains 10-15%. The state of consciousness of the patient usually gives some indication as to the end result of the treatment.

Factors that influence the prognosis

	Delay in diagnosis and profound conscious level, very ill patients on admission.
	The degree of cerebral oedema.
	Brain stem compression.
	The abscess has ruptured into ventricle.
	The presence of meningitis.

During the surgical treatment we missed a loculation of one of the small abscesses.

The cerebellar abscesses have higher mortality rate (about 20%) because of their proximity to the brain stem ventricles. They are also usually multiloculate, which makes their treatment difficult.

Generally, the mortality rate is between 10 and 15% of all patients. While the morbidity rates are summarised in Table 5.