CHAPTER 7
Nervous Tissue
129
CLINICAL CORRELATION
Figure 7-12C.
Meningitis.
H&E,
3
34; inset
3
147
Meningitis
is an infl
ammatory disease of the meninges
that is largely sequestered in the
SAS
. The infl
amma-
tion is usually caused by infection by
viruses
,
bacteria
,
or
fungal agents
. Signs and symptoms include fever,
headache, irritability, photophobia, neck stiffness
(
meningismus
), vomiting, altered mental status, and
cutaneous hemorrhages (
purpura
). Complications may
lead to deafness, epilepsy, and hydrocephalus. Patho-
logically, the meningitis affects the pia- arachnoid and
the CSF in the SAS and may extend into the cerebral
ventricles. Characteristic ±
ndings include perivascular
cuffs of acute and chronic infl
ammatory cells (
inset,
from red box
), which distend the arachnoid space.
Lumbar puncture
(spinal tap) for CSF is an impor-
tant diagnostic tool. Treatment is usually supportive
for viral meningitis and includes antibiotics or other
agents that can cross the blood-brain barrier for bac-
terial or fungal meningitis.
Arachnoid space
Arachnoid space
filled with
filled with
inflammatory cells
inflammatory cells
and proteinaceous fluid
and proteinaceous fluid
Pia mater
Pia mater
Spinal cord
Spinal cord
white matter
white matter
Spinal cord
white matter
Pia mater
Arachnoid
membrane
Arachnoid space
filled with
inflammatory cells
and proteinaceous fluid
C
Figure 7-12A.
Dura mater, arachnoid, and pia mater.
The leathery outer meningeal layer, the
dura mater
(or
dura
),
consists of elongated ± broblasts and large amounts of extracel-
lular collagen. It is tenuously attached to the
arachnoid barrier
layer
; there is no “subdural space” in the normal state. The dura
is tenaciously attached to the skull at the base of the brain and
at the sutures and is less tightly adherent to the skull in other
regions. The arachnoid barrier layer consist of two to three
layers of cells that are attached to each other by many con-
tinuous tight junctions, hence its “barrier” nature to CSF. The
sub arachnoid space (SAS) is located between the arachnoid
and the pia, contains blood vessels and CSF, and is traversed by
arachnoid trabeculae
. The
pia mater
generally consists of one
to two layers of fl attened ± broblasts that are adherent to the
surface of the brain and spinal cord. Blood vessels located in the
SAS are frequently covered by thin layers of pia. The interface
between the pia and the nervous tissue is characterized by a
glial
limiting membrane
(
glia limitans
), as shown in Figure 7-13A.
J. Lynch
Dura mater
Arachnoid
barrier cells
Pia mater
Nervous tissue
(brain or spinal
cord)
Subarachnoid
space
Blood
vessel
Arachnoid
trabeculum
A
Posterior horn
Posterior horn
Spinal cord
Spinal cord
white matter
white matter
Pia
Pia
Blood vessels
Blood vessels
Dura
Epidural space
Spinal cord
white matter
Posterior horn
Blood vessels
Pia
Arachnoid
Subarachnoid
space
Posterior root
of spinal nerve
B
Figure 7-12B.
Spinal meninges in the region of the
posterior roots.
H&E,
3
34
At spinal levels, the
dura mater
forms a tubular sac enclosing
the spinal cord. However, in contrast to the cranial dura, which
adheres to the skull, the spinal dura is separated from the ver-
tebral bodies by an
epidural space
. Both the spinal and the cra-
nial dura consist of many elongated ± broblasts and abundant
extracellular collagen. The
arachnoid barrier cell layer
is basi-
cally the same at cranial and spinal levels. In the normal state,
the barrier cell layer is attached to the dura, although only
weakly. There is no naturally occurring subdural space; what
appears to be a space here is a tissue preparation artifact. The
pia mater
on the cord is continuous with the
epineurium
on
the posterior root, the latter representing a part of a peripheral
nerve. The
SAS
is located between the pia and the arachnoid
and at this point contains the posterior roots.
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