Meningitis Case File

Meningitis Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 35

A 7-year-old boy is brought into the emergency room for severe headache, nausea, and fever. His parent states that the patient had been in good health until 2 days previously. Bright lights seem to bother him. On examination, he appears lethargic and ill. His temperature is 102°F. Movement of the neck seems to cause some pain. The heart and lung examinations are normal. The patient refuses to flex his head to enable his chin to touch his chest because the effort is too painful.

⯈ What is the most likely diagnosis?

⯈ What is the most likely anatomical mechanism for this condition?

ANSWER TO CASE 35:

Meningitis

Summary: A 7-year-old boy has a 2-day history of severe headache, nausea, fever, and photophobia. He appears lethargic and ill. His temperature is 102°F, and he has some nuchal rigidity.

• Most likely diagnosis: Meningitis

• Most likely anatomical mechanism: Migration of bacteria through the nasopharynx or through the choroid plexus

CLINICAL CORRELATION

This young child has a 2-day history of fever, headache, nausea, and photophobia. His general appearance suggests sepsis, and the nuchal rigidity suggests meningitis. These symptoms are caused by cerebral inflammation, ischemia, and edema. Increased intracranial pressure may cause lethargy and even seizures. The most common causative organisms are Streptococcus pneumoniae and Neisseria meningitidis. Previously, Haemophilus influenzae was the most commonly isolated organism; however, with the advent of the H. influenzae vaccine, this pathogen has been less of a factor. The diagnosis is made by lumbar puncture. Positive findings would be leukocytes (in particular neutrophils) isolated from the cerebrospinal fluid (CSF), and grampositive organisms. A diffuse erythematous maculopapular rash that becomes petechial is suggestive of meningococcus. Rapid initiation of empiric antibiotic therapy is critical; the medication is aimed at the most common causative organisms and must penetrate through the blood-brain barrier.

APPROACH TO:

Meninges and CSF

OBJECTIVES

1. Be able to identify the meningeal layers

2. Be able to draw the flow of CSF from the choroid plexus to the subarachnoid space

3. Be able to identify sites where infection may spread into the cranial cavity

4. Be able to describe the innervation of the meninges and the pathogenesis of headache

DEFINITIONS

ISCHEMIA: Decrease in blood flow to a tissue, generally due to blockage of the nutrient arteries

EDEMA: Swelling due to accumulation of water in tissue

PETECHIAE: Tiny spots in the skin generally due to broken capillaries

CHOROID PLEXUS: A tissue lining the ventricles of the brain that produces the CSF that fills the ventricles and the subarachnoid space

MENINGITIS: A very serious infection involving the meninges, which may be caused by viruses or bacteria and may lead to long-term consequences or death

DISCUSSION

Within the cranial cavity, the brain is protected by three meningeal layers. The dura mater, a thick fibrous membrane, is the most superficial. Apposed to the deep surface of the dura mater is the arachnoid mater, which is a delicate, thin membrane that is nearly transparent. The pia mater is the thinnest layer, and it is directly apposed to the surface of the brain. Three spaces relate to the three layers. The epidural space lies between the periosteum of the calvaria and the dura mater. Normally, the dura is closely apposed to the bone, so this is a potential space that can be expanded by blood or pus. Similarly, the arachnoid mater is closely apposed to the dura mater. The subdural space between the two layers is also a potential space. The subarachnoid space lies between the arachnoid and pia mater. This space is normally filled with CSF, which is the extracellular fluid of the central nervous system. CSF pooled in the subarachnoid space also serves a protective function by helping to insulate the brain and spinal cord from mechanical shocks.

CSF in the subarachnoid space is produced by the choroid plexus, in the ependyma of the lateral, third, and fourth ventricles. CSF produced in the lateral ventricles flows through the interventricular foramina of Monro into the third ventricle. The cerebral aqueduct of Sylvius then conducts CSF into the fourth ventricle. From there, fluid flows through the foramina of Magendie and Luschka into the subarachnoid space, where it surrounds the brain and spinal cord. The circulatory path ends at the arachnoid granulations, where CSF is resorbed back into the venous system. Most arachnoid granulations are found lining the large venous sinuses, but arachnoid villi may also be present at the roots of spinal nerves.

Meningitis is an inflammation of the meninges, but in practice the term refers to infections of the pia and arachnoid layers, usually involving the CSF (Figure 35-1). Infections reach the meninges by several routes. Most infections seem to be transferred through the vasculature (hematogenous transmission). On the arterial side, bacteria can infiltrate through the choroid plexus into the CSF. On the venous side, there are several routes from the face into the cranium. Normally, the veins drain superficially and inferiorly through the pterygoid venous plexus and facial and retromandibular veins. However, there are also anastomoses with the superior and inferior ophthalmic veins. These veins carry blood from the orbit into the cavernous sinus, which is in the middle cranial fossa. Because veins in the face have no valves, some infections can reverse the normal flow of blood so that pathogens are carried into the cavernous sinus. They can then infiltrate through the walls of the sinus into the CSF. A second route is through the nasopharynx. Mucosal infections can track through the cribriform plate into the anterior cranial fossa.

Figure 35-1. Cross-sectional view of meninges. (Reproduced, with permission, from Waxman SG. Lange’s Clinical Neuroanatomy, 25th ed. New York: McGraw-Hill, 2003:158.)

The severe headaches associated with meningitis are due to increased intracranial pressure, which stretches the dura mater and stimulates pain fibers from cranial nerve V3 (mandibular branch of the trigeminal nerve) traveling with branches of the middle meningeal artery.

COMPREHENSION QUESTIONS

35.1–35.4 Match the following anatomical spaces (A–D) to the descriptions of location.

A. Epidural

B. Subdural

C. Subarachnoid

D. Intraarachnoid

35.1 Between the dura mater and the calvaria

35.2 Between the arachnoid and pia maters

35.3 Between the dura and arachnoid maters

35.4 A 2-month-old baby is noted to have macrocephaly (large head) and developmental delay. On ultrasound, the baby has significant hydrocephalus. The pediatrician is suspicious of congenital stenosis of the aqueduct of Sylvius. Which of the following are the most likely findings in this infant?

	Right Lateral Ventricle	Left Lateral Ventricle	Third Ventricle	Fourth Ventricle
A.	Dilated	Normal	Normal	Normal
B.	Dilated	Dilated	Normal	Normal
C.	Dilated	Dilated	Dilated	Normal
D.	Dilated	Dilated	Dilated	Dilated
E.	Normal	Normal	Dilated	Dilated
F.	Normal	Normal	Normal	Dilated

ANSWERS

35.1 A. The epidural space is between the fibrous dura mater and the periosteum of the calvaria.

35.2 C. The subarachnoid space is between the arachnoid and the pia maters.

35.3 B. The subdural space is between the dura and the arachnoid maters.

35.4 C. The aqueduct of Sylvius is between the third and fourth ventricles; thus, dilation of the lateral ventricles and the third ventricle is seen with aqueductal stenosis.

ANATOMY PEARL

⯈ The three meningeal layers that protect the brain are the dura mater (close to the skull), the arachnoid mater, and the pia mater (adherent to the brain).

⯈ The epidural space is located between the fibrous dura mater and the periosteum of the calvaria, the subdural space is between the dura and pia maters, and the subarachnoid space is between the arachnoid and pia maters.

⯈ CSF is produced by the choroid plexus, which is located in the lateral and fourth ventricles.

⯈ The lateral ventricles connect to the third ventricle through the interventricular foramina of Monro. CSF flows through the cerebral aqueduct of Sylvius into the fourth ventricle and then flows through the foramina of Magendie and Luschka into the subarachnoid space.

⯈ Meningitis is an infection of the pia and arachnoid layers, usually involving the CSF.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:481, 524−526. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:498−501, 865−867, 878−881. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 101, 103−105.

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