Bacterial(Purulent) Meningitis Histology and Explanation

A variety of bacteria can cause meningitis, but several are more common, and have an incidence more frequent at certain ages:

ORGANISM	PEAK AGE INCIDENCE	GRAM STAIN
Escherichia coli	Neonates	Gram negative rods
Hemophilus influenzae	Infants and Children	Gram negative coccobacilli
Neisseria meningitidis	Adolescents and Young adults	Gram negative diplococci
Streptococcus pneumoniae	Older adults or Children	Gram positive cocci in chains

One cause for acute swelling is infection. The yellow-tan clouding ofthe meninges seen here is due to an exudate from acute meningitis.

This is another case of acute meningitis. It is important to make the diagnosis and begin antibiotic treatment as soon as possible. Clinical signs may include: headache, neck stiffness (from irritation of spinal nerve roots), fever, and clouded consciousness.


Here is another example of an acute meningitis from bacterial infection. The cerebrospinal fluid (CSF) in such cases typically has a low glucose, high protein, and many PMN's. A gram stain should be done to identify organisms.


Microscopically, a neutrophilic exudate is seen involving the meninges at the left, with prominent dilated vessels. There is edema and focal inflammation (extending down via the Virchow-Robin space) in the cortex to the right. This acute meningitis is typical for bacterial infection.
This edema can lead to herniation and death. Resolution of infection may be followed by adhesive arachnoiditis with obliteration of subarachnoid space leading to obstructive hydrocephalus.



Microscopically, a gram stain reveals gram negative diplococci within a neutrophil, typical for Neisseria meningitidis. Gram stain and culture can be performed on cerebrospinal fluid obtained via lumbar puncture.