IPLab:Lab 9:Bacterial Meningitis

Clinical Summary

This 45-year-old white female with a history of psychiatric illness sustained self-inflicted third degree burns over 49% of her body surface. After initially doing well under treatment, she developed severe respiratory distress and became comatose. Antemortem blood cultures were positive for Pseudomonas aeruginosa.

Autopsy Findings

At autopsy the principal findings were in the lungs and brain. Bronchopneumonia was present in all lobes of both lungs. The brain weighed 1450 grams and the leptomeninges contained a thick yellow purulent exudate most prominent over the frontoparietal areas and at the base of the brain.

Images

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  This gross photograph of the autopsy specimen from this case demonstrates the purulent exudate (arrows) in the leptomeninges.

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  This is a low-power photomicrograph of brain section. Note the exudate (1) in the meninges and congestion of the vessels (2) in the leptomeninges.

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  This is a higher-power view of a congested blood vessel. Inflammatory exudate is present within the vessel and throughout the leptomeninges.

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  This higher-power photomicrograph of a sulcus shows the congested vessels and the inflammatory exudate in the leptomeninges.

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  This is a higher-power photomicrograph of inflammatory exudate in a sulcus. The majority of cells in this exudate are neutrophils. There is also abundant fibrin (arrows) and red blood cells are present in the congested vessels.

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  This is a high-power photomicrograph of a blood vessel from the previous image. The vessel is surrounded by neutrophils (arrows).

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  This is a high-power photomicrograph of exudate from the leptomeninges which has been Gram-stained. Note the Gram-negative bacteria (arrows) throughout this section.

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  This photomicrograph of brain tissue demonstrates diffuse edema.

Study Questions

• What is the most common etiologic agent that causes bacterial meningitis?

The specific etiologic agent varies with the age of the patient:

• in neonates: the organisms include Escherichia coli and the group B streptococci;
• in infants and children: S. pneumoniae and N. meningitidis pervade in immunized children (H. influenzae type b (Hib) vaccine is routine in the U.S.), while Haemophilus influenzae is more prominent in non-immunized children;
• in adolescents and in young adults: Neisseria meningitidis;
• in the elderly: Streptococcus pneumoniae and Listeria.

• What organism caused meningitis in this case and why?

Burn patients are at high risk for developing Pseudomonas infections. In this case, the patient was debilitated due to the extensive severe burn and developed a Pseudomonas septicemia which then led to the Pseudomonas meningitis.

• Why is there fibrin in these lesions?

Because of the acute inflammatory reaction, there is extravasation of fibrin as well as the recruitment of neutrophils.