Page 630 - Concise Pathology for Exam Preparation ( PDFDrive )

23 The Central Nervous System 615

Dura:
Tough fibrous covering of brain, lined on the inside by mesothelium and suspended from

calvarium by denticulate ligament; encloses a space called ‘epidural space’ between
bone and dura.
Subdural space: Enclosed between dura and arachnoid membrane; contains minute

amount of fluid.

CSF

• Seventy percent of CSF is formed in the ventricular choroid plexus by a combined process

of active secretion and ultrafiltration.

• Thirty percent of CSF is formed as interstitial fluid elaborated within intercellular spaces
of the brain and spinal cord.
• Total volume of CSF in adults ranges between 90 and 150 mL.

• Two morphologically distinct blood-brain barriers prevent passage of plasma constituents

into CSF, namely:

1. Capillary endothelium
2. Fenestrated choroidal capillaries enclosed by specialized ependyma found in choroid

plexus epithelium
• Cell content of normal CSF is low (0–4/µL), comprising mainly lymphocytes and mono-
cytes.
• Normal pressure of CSF is 90–180 mm of CSF (60–150 mm of water); it is measured
by allowing CSF to rise in a sterile, graduated manometer tube.
• Normal CSF is crystal clear with an appearance and viscosity comparable to water.
Q. Write in detail on laboratory diagnosis of meningitis.
Ans. Inflammation of meninges is called meningitis. It is of two types:
• Inflammation dura (pachymeningitis): This is usually due to extension of infection
of
from chronic suppurative otitis media (CSOM) or fracture skull.
of
• Inflammation pia-arachnoid (leptomeningitis): The common causes of leptomen-
ingitis include
1. Infection
(a) Acute pyogenic (bacterial/purulent) meningitis

- Infection of pia-arachnoid and of CSF enclosed in subarachnoid space
- May extend to brain, spinal cord, optic nerves and ventricles
Causative organisms:
- Escherichia coli (infects neonates, particularly with neural tube defects)
- Haemophilus influenzae (infects infants and children)

- Neisseria meningitides (infects adolescents and young adults)

- Streptococcus pneumoniae (infects extremes of age; common following trauma)
of
Routes infection:
- Blood stream
- Adjacent focus
- Iatrogenic (during operation/lumbar puncture)
Gross pathology: Normally clear CSF becomes turbid or frankly purulent due to
pus accumulating in the subarachnoid space. Pus may interfere with normal
flow of CSF leading to obstructive hydrocephalus.
Microscopy: Numerous polymorphonuclear leukocytes, prominent around blood
vessels are seen. Gram staining is done to demonstrate specific organisms.
Clinical features:

- Medical emergency; presents with fever, severe headache, vomiting, drowsiness,

stupor, coma and convulsions.

- Stiffness of neck on forward bending, positive Kernig sign (hip flexion causes
pain in the knee) and positive Brudzinski’s sign (neck flexion causes flexion
of knee and hip).
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