19.1 Introduction

Postinfectious hydrocephalus is the most common cause of hydrocephalus in developing countries.1 It occurs, most commonly, after acute bacterial meningitis resulting in obstruction of the cerebrospinal fluid (CSF) pathways and its absorption. Even when treated, infectious hydrocephalus is associated with high rates of morbidity and mortality. Although CSF diversion remains the principle management goal, the altered CSF dynamics in this type of communicating hydrocephalus can affect the success of surgical strategies. Endoscopic third ventriculostomy (ETV) is increasingly being used to treat infectious hydrocephalus with reported good outcomes; however, its superiority over shunting remains controversial (Video 19.1).

19.2 Pathophysiology

Intracranial infection may result from a variety of microorganisms that can spread to the brain via three methods: hematogenous, direct, and retrograde spread. The hematogenous route is the most common as pathogens from the blood can penetrate the vascular cell layer of the blood-brain and blood-CSF barriers, enter the CSF fluid, and produce meningitis by subarachnoid bacterial growth (Video 19.1).2

Acute bacterial meningitis is the most common form of intracranial infection that results in postinfectious hydrocephalus. Several studies have shown that the causative microorganisms vary depending on the age group, geographical distribution, and season.

The types of bacteria causing meningitis overall in Europe are Neisseria meningitidis (22%), Streptococcus pneumoniae (18%), Staphylococcus aureus (10%), Group B Streptococcus (GBS) (5%), and Escherichia coli (5%).3

There is slight variation in the United States, where Streptococcus pneumoniae was the predominant infective species (58%), followed by GBS (18.1%), N. meningitidis (13.9%), Haemophilus influenzae (6.7%), and Listeria monocytogenes (3.4%) between 2003 and 2007.4 In other developed countries a similar epidemiology to this is also found. Different bacteria also predominate in different age groups as outlined in Table 19.1 .

Source: Data obtained from Centers for Disease Control and Prevention.45

In countries with the highest annual temperatures, Group A Meningococcus is the most frequent causative agent of meningitis. It accounts for an estimated 80–85% of all cases in the meningitis belt of sub-Saharan Africa.5 There is a striking absence of group B Streptococcus in many studies in the developing world.1 Staphlococcus aureus is a rare cause of meningitis in adults. Usually it occurs postoperatively, after bacteraemia or a major underlying disease, and therefore it is predominantly found in nosocomial infections. It is associated with a higher mortality rate than the common causes of pyogenic meningitis.6,7

With HIV, a resurgence of tuberculosis (TB) has been observed in Western countries.8 Tuberculous meningitis is also still common in certain parts of the world such as sub-Saharan Africa, India, and Latin America, where TB remains a burden.9 Cryptococcal meningitis (CM), caused by the fungus Cryptococcus neoformans, is an opportunistic organism that has a predilection for immunocompromised hosts.10 Hydrocephalus is a well-described sequelae after CM and can occur both during the acute infection as well as a delayed complication presenting weeks to months after infection.11 Other CNS infections that may be accompanied by, and complicated by, hydrocephalus include parasitic cysts and toxoplasmosis.

Meningeal, ependymal, and arachnoidal inflammation occur due to the release of proinflammatory toxic bacterial compounds (Video 19.1).12 Cytokines generated during this inflammatory process lead to disruption of the blood-brain barrier and thus increase vascular permeability. Consequentially there is an inflammatory exudate that blocks the subarachnoid cisterns causing hydrocephalus (extraventricular intracisternal obstructive hydro-cephalus). This is more prominent in tuberculous meningitis (Fig. 19.1).13

As observed in neuroendoscopic findings, there is ependymal and choroid plexus scarring after meningitis, as well as aqueductal obstruction due to intraventricular deposits of pus and hemosiderin.14 Contrast-enhanced neuroimaging often reveals meningeal enhancement representing ventriculitis and arachnoiditis (Fig. 19.2). Studies have shown that this reactive inflammation could result in decreased CSF flow due to reduced absorption leading to communicating hydrocephalus (Video 19.1).12

The overall risk of postinfectious hydrocephalus as a consequence of meningitis is around 7.1%.15 It is less frequent (3–5%) in adults following community-acquired bacterial meningitis.16,17 The risk is considerably higher in the pediatric population, and in neonates is up to 31%.1,18 Moreover, the presence of postinfectious hydrocephalus has been shown to be a predictor of severe neurologic sequelae in meningitis.19 The risk of hydrocephalus is much higher in TB meningitis (85%).20 In such cases, hydrocephalus tends to develop in the acute phase of the infection rather than at a later stage as in pyogenic meningitis. In CNS TB, hydrocephalus may also be of the noncommunicating type due to aqueductal stenosis.

19.3 Clinical Features

Meningitis presents classically with fever, headache, neck stiffness, and signs of cerebral dysfunction. Although the above signs may individually have low sensitivity, the absence of any two can rule out meningitis with a negative predictive value of 95%.21 The clinical features may, however, depend on the age group as well as the underlying pathogen. For instance, young children may not show nuchal rigidity,22 as compared with adults in which it is the most sensitive clinical sign (45%).21,23 In neonates, clinical features can also include bulging fontanelles, irritability, and hyperreflexia. Clinical features of systemic compromise can also be present depending on the severity of the infection. These carry prognostic significance for an unfavorable outcome.23