Pathology of Meningitis and Ventriculitis in Children

Pathophysiology

Spine infections in children

• Multiple potential routes for infection: Infections reach the spine via the blood stream, Batson’s venous plexus, extension from adjacent nidus, dermal sinus tracts projecting to the spine, direct infection via surgical procedures, or penetrating trauma. Pediatric spinal infections differ from adult infections due to anatomic characteristics (76, 77).
• Limited to disk space: Pyogenic spinal infections in children tend to be limited to the disk space, whereas in adults infections originate at the vertebral body. With aging, vasculature to the vertebral disk regresses, leaving the disk avascularized, whereas the pediatric disk retains vasculature. Moreover, extensive anastamoses exist between the intraosseous spinal arteries precluding metaphyseal end plate destruction when septic emboli lodge in the metaphyseal artery (76, 77).
• Two forms – pyogenic and nonpyogenic: Spinal infections are classified as either pyogenic or nonpyogenic. The pyogenic infections are further subcategorized into vertebral osteomyelitis and diskitis. The nonpyogenic infections can be subcategorized as parasitic, fungal, and tuberculous (76, 77).

Spinal epidural abscesses in children

• Most hematogenous inoculation: Spinal epidural abscess may arise by direct spread of infection (e.g., vertebral osteomyelitis) or from hematogenous spread from a distant site through Batson’s venous plexus. The latter appears more commonly in childhood (20, 21).
• Most common site thoracolumbar: The usual location for spinal epidural abscesses is the lower thoracic or lumbar spine, owing to the narrowing of the spinal cord at these levels. This narrowing results in a large dorsal extradural space that contains a rich venous plexus. This venous plexus is the route of infection, with blood from the inferior vena cava communicating with the extradural space (19, 38).
• Epidural space contains septations limiting infection: The epidural space is not uniform in its structure or contents. It is divided into septated segments with differing amounts of adipose and vascular tissue. These septa are thought to be responsible for both limiting infectious extension and preventing communication between the anterior and posterior epidural spaces (22).
• Epidural abscesses more extensive in children: Maturation of the epidural space and spinal vasculature may predispose children to extensive posterior epidural abscesses. First, children have more posterior and less segmented epidural fat than adults do. Second, vertebral vasculature changes with age, which may affect perfusion and hematogenous spread of pathogens to the epidural space (39–41).

Spinal subdural abscesses in children

• Most associated with dysraphism: The majority (53%) of spinal subdural infections in children are found in the setting of spinal dysraphism or otherwise congenitally abnormal spines (126). Of the 39 recorded cases in which patients harbored a dysraphism, only six patients presented after 4 years of age. Children with dermal sinus tracts appear most apt to develop infections of the subdural space, as the tract provides a pathway for organisms to seed this otherwise relatively remote anatomic compartment.
• Relative rarity: Several explanations have been proposed to account for the relative infrequency of these infections in both the adult and pediatric populations. Compared to the intracranial compartment, in which infection often spreads via the sinus cavities, the spinal column possesses no such sinuses (122). Cranial infections may also spread from extracranial sources hematogenously due to the rich, centrifugally flowing blood supply of the cerebrum (122). In contrast, blood flows centripetally within the spine (122). An additional etiology of cranial abscess or empyema is post-procedural contamination, and it is well known that the number of operations in which the dura is violated in the cranium far surpasses the number of operations in which the spinal dura is accessed. (118).
• Mid to lower spine location: Infections involving only a single region of the spinal cord outnumbered those that comprised multiple regions by a ratio of 3:2. Of the 43 single-region infections, more than half (53.5%) involved the thoracic spine and 40% involved the lumbar spine. Of the 29 cases where the infection was located in more than one spinal region, 13 (44.8%) involved lumbosacral segments. The cervical subdural space was rarely infected (7%).

Intramedullary spinal cord abscesses in children

• Spread from contiguous infection: In children an intramedullary abscess most commonly forms by contiguous spread from the skin to the intramedullary compartment via congenital communications between the spinal cord and skin. Indeed, 53% of patients with intramedullary spinal cord abscesses had such a communication diagnosed either before (37%) or after (13%) presenting with signs of abscess formation. Once infection develops within the intramedullary space, it tends to spread longitudinally along the fibers of the cord.
• No capsule: These abscesses probably never form a heavy wall or capsule (24).

Microbiology

Spine infections in children

• S. aureus most commonly isolated organism: S. aureus is the most commonly isolated organism in both diskitis and osteomyelitis (78).
• Bartonella henselae: The presence of B. henselae can be an atypical manifestation. Serologic testing should be performed if the patient has a history of feline contact (78).

Spinal epidural abscesses in children

• S. aureus most common organism: The predominant pathogen in spinal epidural abscesses is S. aureus. Review of the literature confirmed its role in abscesses in both children and adults (22, 28, 29, 42). The emergence of methicillin resistance in this organism is increasingly important. In the few studies describing its role in spinal abscesses, 15–18% of all isolates were MRSA (17, 43, 44). Community-acquired MRSA has been recognized in children (45, 46). Other isolates include Aspergillus flavus, group B streptococci, Pseudomonas, and Proteus (21).

Spinal subdural abscesses in children

• Streptococcus and Staphylococcus when dermal sinus present: In the presence of a dermal sinus, methicillin-sensitive S. aureus is the commonest offending organism, and Proteus mirabilis has also been reported (25). Nine distinct pathogens were identified in children with dysraphisms or congenital anomalies of the spine: Streptococcus sp.. (n=6), Staphylococcus spp. (including S. albus) (n=4), M. tuberculosis (n=4), E. coli (n=4), Bacteroides (n=2), Proteus (n=2), Klebsiella (n=1), and diphtheroids (n=1) in the review by Sandler et al. (126).

 

• Echinococcus and TB if nondysraphic spine: In the 34 patients with normal spines, only five different causative pathogens were identified, with E. granulosus the commonest (n=14) organism followed by M. tuberculosis (n=13), Staphylococcus spp. (n=4), Streptococcus spp. (n=1) and T. solium (n=1) (126).

 

Intramedullary spinal cord abscesses in children

• Staphylococcus most common organism: Staphylococcus spp. are, by far, the most common causative organisms in intramedullary spinal cord abscesses, with P. mirabilis second. This pattern seems to hold whether the intramedullary spinal cord abscess appears in the setting of a spinal dysraphism such as dermal sinus tract or whether no concomitant anatomic abnormality has been found. E. coli, Schistosoma mansoni, B. abortus, and M. tuberculosis have also been isolated from intramedullary spinal cord abscesses in children (64).