The results of this study show that the common predisposing conditions of RBM in children are inner ear malformations, dermal sinus tracts, head trauma, meningoencephalocele. Children younger than 3 years old, especially infants younger than 1 year of age, are susceptible population for bacterial meningitis. Underlying conditions should be considered in children older than 3 years old who suffered bacterial meningitis. These conditions include basic anatomical deformities (inner ear deformities, meningoencephalocele), and history of head trauma, asplenia, immune deficiency, etc (Tebruegge et al., 2008). These underlying diseases are also the cause of RBM in children. Of course, infants and young children under 3 years of age who have these conditions can also suffer RBM. Our study showed that congenital anatomic deformities, including inner ear deformities, dermal sinus tracts and meningoencephalocele, accounted for 76.1% of the predisposing conditions of RBM, followed by 16.9% of head trauma. Congenital or acquired anatomical abnormality should be firstly considered in children with RBM.
Our study showed that 79.2% of the inner ear malformations were unilateral malformations. Hearing abnormalities in patients with unilateral malformation were not easily detected by parents or doctors, resulting in delayed diagnosis and treatment. Majority of inner ear malformations could not be correctly diagnosed until one or even several episodes of bacterial meningitis (Lien et al., 2011). Malformation of the inner ear can be easily detected by routine hearing tests. Inner ear malformations in our study were all found by hearing tests, followed by temporal CT scan to make definite diagnosis. In addition, hearing loss is the most common complication and sequela of bacterial meningitis. Therefore, we recommend that all children with bacterial meningitis require routine hearing tests for monitoring the sequela of hearing loss, and also for the potential inner ear malformations.
Our study shows that dermal sinus tracts accounts for 21.1% of children with RBM. The dermal sinus tract is an abnormal development of the ectoderm during the embryonic period. Skin or epithelial tissue remains in the cranial cavity or spinal canal to form a skin-like or epithelial-like cyst. The dermal sinus tracts can often be found by physical examination. The most common site is the lumbosacral region in midspinal line, followed by the chest and occipital region in midspinal line. It is more difficult to find the dermal sinus tracts in occipital region which is covered with hair. So it is necessary to remove the hair during the physical examination, combined with imaging examination to make the right diagnosis. Therefore, RBM in children requires careful physical examination to determine the presence of dermal sinus tracts.
Our study showed that head trauma and meningoencephalocele accounted for 21.1% and 16.9% respectively in children with RBM. Sixty percent and 41% of the patients in these two groups had the symptoms of cerebrospinal fluid leak. So the possibility of skull anatomical defects cannot be excluded in children without symptom of cerebrospinal fluid leak. These patients may show intermittent cerebrospinal fluid leak, especially in case of increased intracranial pressure (such as sneezing) or in forward tilt position (Prosser et al., 2011; Mathias et al., 2016). The liquid is clear and has a salty or even sweet taste, which needs to be distinguished from allergic rhinitis (Ziu et al., 2012). The skull CT and MRI scan should be done for these patients to find the abnormalities (Connor, 2010). The time interval from head trauma to the first occurrence of bacterial meningitis ranges from 3 days to 1.7 years. Therefore, during the history taking of head trauma for RBM, it should not only be limited to history of days to months before the onset of the meningitis, but also the history of trauma years ago.
Our study showed that S. pneumoniae infection is the most common etiology of RBM in children, especially in patients with malformations of the inner ear, meningoencephalocele, head trauma, and innate immunodeficiency, with 62.5%, 46.7%, 66.7% and 50% of patients respectively had at least one episode of S. pneumoniae meningitis. S. pneumoniae is a common colonizing bacterium in the respiratory tract and external ear canal followed by HIB. The anatomic defects of inner ear malformations, meningoencephalocele, and basic diseases of skull trauma result in the communication between the skull and the ear canal, or the nasal cavity or sinuses. Colonizing bacterium can easily invade the skull through local anatomic defects and causes meningitis (Ingels et al., 2014). The 4 patients of immunodeficiency in our study were all antibody-deficient. S. pneumoniae was also the most common etiology. Patients with antibody deficiency are prone to the infection of capsular bacteria (Winkelstein et al., 2006; Ingels et al., 2015; Lopez et al., 2017). S. pneumoniae is a typical capsular bacterium. For that S. pneumoniae is the most common cause of RBM in children, empirical antibiotic treatment of RBM in children should cover S. pneumoniae. In our patients with RBM, HIB is the second etiology only to S. pneumoniae. Patients with dermal sinus tracts had two episodes of E.faecalis meningitis, one episodes of E. coli meningitis, and one episodes of Staphylococcus aureus meningitis. Enterobacteriaceae, enterococci and Staphylococcus aureus should be considered as etiology of RBM in patients with lumbosacral dermal sinus tracts where the deficit is near the perineum, while Staphylococcus aureus meningitis is more common in patients with chest and occipital dermal sinus tracts.
In our study, the rate of positive cultures is low. Some patients had negative cultures, because they had received antibiotic treatment before blood or cerebrospinal fluid was got for culture. As the Implementing of antibiotic stewardship program in China, this problem will be solved.
In summary, predisposing conditions of RBM in children include malformations of the inner ear, dermal sinus tracts, head trauma, meningoencephalocele, and immune deficiency. S. pneumoniae is the most common etiology of RBM in children. Empiric antibiotic treatment should cover S. pneumonia