Bacterial meningitis is a severe and life-threatening infection. It is associated with a high rate of complications and neurologic sequelae despite advances in antibiotic therapy and intensive care measures. Recurrence occurs in approximately 1–4.8% of acute bacterial meningitis cases, and is defined as the re-emergence of signs and symptoms of meningitis at least 3 weeks after a sterile culture of the cerebrospinal fluid (CSF) if the pathogen is the same, or a new episode caused by a different pathogen.1

Different predisposing factors for recurrent meningitis have been identified, such as humoral and cellular immunodeficiencies and congenital or acquired structural defects that result in an anatomical communication between the subarachnoid space and the skin, the middle ear or the paranasal sinuses2–4 (Table 1).

The approach to diagnosis must be guided by the medical history, the findings of the physical examination and microbiological test results.5 In many instances, the isolated pathogen gives a clue to the source of meningitis.

We present four cases of paediatric patients with recurrent bacterial meningitis due to congenital anatomical defects in which the causative microorganisms guided the diagnosis (Table 2).

Recurrent bacterial meningitis is a rare disease in children, and few data are available on its incidence. A review of 463 children with bacterial meningitis found 6 patients with recurrent episodes, corresponding to an incidence of 1.3%. The pathogen identified most frequently was S. pneumoniae. An otorhinolaryngological abnormality was confirmed in 2 cases, a primary immunodeficiency in another 2, and no predisposing factor was found in the rest.2 A study of meningitis in 696 adults identified 34 recurrent episodes (4.8%) and estimated their annual incidence at 0.12 cases per 100,000 adults.7

Anatomical defects and primary and secondary immunodeficiencies should be ruled out as underlying causes in patients with recurrent meningitis.8 The identified bacterium can give clues to locate the anatomical defect or to rule out immune defects. In this regard, a review by Trebuegge and Curtis of 132 cases of recurrent meningitis in children and adults from case reports and series published between 1988 and 2008 recommends a diagnostic approach that includes all the investigations performed in the cases presented in this article. The abnormalities described most frequently in the cases reviewed by Trebuegge and Curtis were complement deficiencies, inner ear abnormalities (Mondini dysplasia), dermoid cysts, meningoceles and meningomyeloceles.3

In the cases presented in this article, we describe 4 patients with different congenital anatomical malformations that posed challenges to early detection.

Mondini dysplasia is a defect in cochlear development that occurs in the first trimester of gestation and results in a cochlea with fewer turns than normal, with the apical and middle turns undifferentiated and forming a cystic apex that may cause deafness, vestibular abnormalities and a predisposition for infections of the central nervous system.9 Its radiological diagnosis requires a CT scan of the temporal bone,10 as it may be missed in a cranial CT scan. In case 1, the history of otitis media preceding the episodes, the concomitant unilateral hypoacusis and the repeated presence of a bacterium commonly found in the nasopharyngeal flora called for ruling out this malformation. Its surgical management can be more or less aggressive depending on the previous auditory functioning of the patient, with the purpose of closing the CSF fistula.11 The need for a cochlear implant should only be considered in cases of bilateral deafness, since there is a risk of CSF gusher (perilymph leakage) during the intervention.12,13

When it comes to defects of the cribriform plate, a clinical and anatomical study of spontaneous cerebrospinal fluid rhinorrhoea by Tóth et al. describes 29 patients, of which 4 had malformations at this locus. The study found a correlation between increases in intracranial pressure (intermittent or persistent) and the formation of CSF fistulae in the frontonasal areas, predisposed by the abnormal fusion of the different bony components.14 In the case we present here, anatomical malformations of the inner ear and primary and acquired immunodeficiencies were ruled out. The presence of a microorganism characteristic of the nasopharyngeal area in the CSF prompted a specific radiological examination that led to confirmation of an anatomical defect at the frontonasal level. The patient had abnormal CSF dynamics, so the treatment involved placing a ventriculoperitoneal shunt to reduce intracranial pressure, achieving closure of the fistula, with no further recurrence of meningitis.

Dermal sinuses, involved in the third case, are congenital defects involving incomplete neural tube closure that results in a variety of communications between the skin and the central nervous system. They can be located anywhere between the nasal root and the conus medullaris, and are found most frequently in the lumbosacral region, followed by the occipital region.15 In the latter case the communication is usually intradural, allowing the direct entry of bacteria from the skin flora and the subsequent development of meningitis, most frequently due to S. aureus.16 The presence of hair may pose difficulties to the early detection of occipital dermal lesions. Where such a lesion is found, performance of an MRI is recommended for diagnosis and to determine the extension of the dermal sinus and its potential association with cystic tumours and venous anomalies,17 allowing for early surgical management and for the prevention of future complications. It is frequently associated with dermoid or epidermoid cysts, and more rarely to teratomas. Patients with an occipital dermoid cyst associated with a dermal sinus may develop meningitis and/or abscesses as the earliest clinical manifestation due to the abscessation of the dermoid cyst itself or the formation of secondary abscesses.18,19

There are 25 descriptions of meningitis cases associated to dermoid and epidermoid cysts in the literature. In all these cases, there was a dermal sinus connecting with the central nervous system.20 There are also descriptions of recurrent aseptic meningitis associated to these cysts. Their high keratin content produces an inflammatory reaction that can trigger conditions ranging from mild leptomeningitis to granulomatous meningitis, ependymitis and posterior radiculitis.21 In a review of the medical records of 18 patients with meningitis associated to occipital dermal sinuses, Naderi et al. recommend the prophylactic surgical resection of all cranial dermal sinuses and early resection when the patients are symptomatic.16

In the case presented here, the recurrence of meningitis caused by S. aureus was indicative of craniospinal dysraphism. When the dermal sinus was found, the family history was re-examined, and the mother reported an occipital mass present since birth that had not been examined. The symptoms did not resolve until the dermoid cyst and the dermal sinus were fully resected, and the abscesses were drained while the patient received antibiotic therapy. Drainage and antibiotic treatment alone are not appropriate, as they do not eliminate the source of infection.22

The last case presented, of polymicrobial meningitis caused by gut bacteria, some of them anaerobic, evinces the importance of the prompt determination of the cause of meningitis to avoid severe neurologic sequelae.23

The Currarino syndrome is defined by the following clinical triad: anorectal malformation, in 30% of cases a rectal stenosis (diagnosed a posteriori); sacrococcygeal bony defect, which is pathognomonic in case of a scimitar sacrum; and presacral mass, which is an anterior meningocele in 60% of cases.24 While constipation is the most frequent symptom, it may be associated with recurrent meningitis, which carries a high mortality rate (56%) due to rectomeningeal fistula.25 Fifty percent of cases are due to an autosomal dominant mutation in the HLXB9 gene (7q36). This gene is involved in caudal development and its defects cause the anomalous separation of the neuroectoderm and neuroendoderm before the development of the notochord. Genetic testing for the mutation in family members is recommended.26 In 80% of the cases, the diagnosis is made in the first decade of life by imaging tests. The management of asymptomatic children is conservative, with laboratory monitoring of alpha-foetoprotein due to the possibility of malignisation of the presacral mass. In symptomatic children, the treatment is based on surgical repair of the anatomical defect.24

To conclude, we want to underscore that the close collaboration of clinician and radiologist is essential in cases like the four presented here. The bacterium helps find the source of infection, but knowledge of the various anatomical defects that facilitate the development of meningitis is needed to perform the most appropriate imaging test in each situation, and knowledge of the normal flora of different regions is needed for the prescription of empirical antibiotic treatment. In a patient with recurrent meningitis and a normal evaluation of the immune system, a previous imaging test with normal results should not preclude a more thorough investigation if there is a strong clinical suspicion of an underlying anatomical defect.

Based on our experience with these cases and the cases described in the literature, we conclude that an anatomical defect causing recurrent episodes of meningitis should be treated surgically. At present, there are no studies that demonstrate the efficacy of antibiotic prophylaxis in patients with congenital anatomical defects that cannot be resolved with surgery.

The authors have no conflicts of interest to declare.