848
SECTION III
NEUROSURGERY
CHAPTER VII
EXPERIMENTAL
STUDY OF PROBLEMS OF INFECTION OF THE CENTRAL NERVOUS SYSTEM AND THE TREATMENT THEREFOR a
During
the existence of the Army Neurosurgical Laboratory the original plan of
investigation was developed and extended. In some lines of activity
progress was achieved,
while in other phases no definite advances were made. The work of the
laboratory is summarized
in this chapter.
HYDROCEPHALUS 1
One
of the most frequent of the sequelae of meningitis (particularly of the
chronic type)
is the development of an internal hydrocephalus. The experimental
production of the condition
was found to be possible in both adult cats and kittens. Previous
investigators had been able to
reproduce the condition by blocking the intraventricular passages of
the cerebrospinal fluid; in
this laboratory the experimental obstruction to the normal escape of
the fluid was caused by a
lesion in the meninges and not by blockage in the ventricular system.
The method used for this
purpose was the injection into the subarachnoid space of a 5 to 10
percent solution of lampblack
in Ringer's solution. The carbon particles thus introduced either
mechanically blocked the
meningeal passages of the cerebrospinal fluid or occasioned a sterile
meningitis which, in turn,
accomplished a similar obstruction. 2
Such
subarachnoid injections of suitable amounts of lampblack in adult
animals caused
an almost immediate lethargy and sleepiness; the more acute cases
remained in this condition for
several days. In the milder cases the animals were a little more quiet
than normal, with the
progressive development of a lethargy. The lesion at autopsy in such
adult cats was a typical
hydrocephalic enlargement of the lateral ventricles.
The
younger animals (kittens), in which the ossification of the skull was
not yet
complete, showed even more striking abnormalities after such injections
of lampblack. Not only
did the ventricles enlarge enormously at the expense of cerebral
cortex, but the whole head
became bulging and relatively enormous. The fontanelles opened widely;
in some animals in
which the cranial bones were already united by bony union, the
fontanelles were reformed. The
clinical and pathological pictures were typically those of an infant
with an internal
hydrocephalus.
As
soon as it was found possible to reproduce this pathological condition
invariably,
therapeutic measures aiming at its relief were undertaken. A certain
degree of amelioration
followed the creation of an artificial connection between the
subarachnoid space and the superior
sagittal sinus.
a Report
of Investigations conducted at the Army Neurosurgical Laboratory,
Baltimore, Md. By Capt. Lewis H.Weed, M. C.
849
CISTERN
PUNCTURE 3
Difficulty
in obtaining cerebrospinal fluid by lumbar puncture in laboratory
animals led
to the adoption of puncture through the occipitoatlantoid ligament as a
convenient method
(Dixon and Halliburton). The technique for performing this puncture
proved to be quite simple,
and with a little practice the needle may be inserted into the fluid
reservoir, lying just beneath the
ligament, without injury to the structures of' the medulla. The use of
this operation greatly
facilitates the obtaining of spinal fluid from the cadaver. It should
prove of value in man when
there is a block in the spinal subarachnoid space due to meningitis
adhesions; it should be
serviceable likewise in irrigations of the spinal subarachnoid space
for the removal of the pus
and débris due to infection. With the increase in experience in the use
of this puncture the route
may prove of value for the introduction of serum in early cases of
epidemic meningitis. It was
found that a much better spread in the basilar cisterns and over the
convexity of the brain was
obtained when a suspension of india ink was injected by the
occipitoatlantoid route than when it
was introduced in the lumbar region.
EFFECT OF
INTRAVENOUS INJECTIONS OF SOLUTIONS OF VARIOUS CONCENTRATIONS
UPON CEREBROSPINAL FLUID PRESSURE 4
Research
in the Army Neurosurgical Laboratory demonstrated that the intravenous
injection of hypertonic solutions exerted a marked effect on the
pressure of the cerebrospinal
fiuid. Hypotonic solutions, when injected intravenously into an
etherized animal, caused an
enduring rise in the pressure of the fluid as determined in a manometer
connected with the
subarachnoid space. On the other hand, the intravenous injection of a
strongly hypertonic
solution brought about an initial rise in the pressure of the
cerebrospinal fluid followed quickly
by a marked fall, often to negative values. The employment of a
solution isotonic with the blood
occasioned no lasting change in the pressure of the cerebrospinal
fluid. The logical explanation
of the alterations in the pressure of the cerebrospinal fluid following
the intravenous injection of
hypotonic and hypertonic solutions, seems naturally to be related to
the experimental change in
the osmotic value of the blood. Data regarding the absolute or relative
osmotic values of the
body fluids were not obtained, but it appeared that the alteration in
the salt-content of the blood
produced experimentally could only be compensated by fluid
readjustments within the tissues.
ALTERATION
OF BRAIN VOLUME. 5
Investigations
on cats showed that the intravenous injection of a strongly hypertonic
solution (30 percent NaCl or saturated NaHCO3) was followed
by a marked decrease in the size
of the brain. This change in cerebral volume occurred in the unopened
skull; but if the skull was
trephined and the dura opened, the brain after such injection could be
seen to fall away several
millimeters from the inner surface of the skull. Intravenous injection
of a hypotonic solution
(water) caused a marked swelling of the brain,. Such increase in brain
bulk was noted in the
intact cranium; if the skull was opened, tense herniae of the cerebral
substance, protruding
several millimeters, invariably
850
resulted from the experimental procedure.
Animals subjected to these experimental procedures
promptly became normal on recovery from the anesthetic.
These
changes in brain bulk were independent of the volume of the fluid
injected, as was
demonstrated by control injections of Ringer's solution, which did not
alter the size of the brain.
The age of the animal was found to playa noticeable part in this
phenomenon, the brains of old
cats failing to respond readily to such intravenous injections,
especially of hypotonic solutions.
No histological changes were demonstrated in the brains of animals
subjected to experimental
alteration of brain bulk but with opened skulls (removal of
restrictions to change in volume). In
those animals which were not trephined, internal changes, recognizable
microscopically, were
found quite constantly. The clinical application of this phenomenon of
volume-change of the
brain should be of value in cases of increased intracranial tension,
cerebral herniation, cerebral
edema in acute infections or injuries.
BRAIN
ABSCESS 6
The
methods by which brain injuries and local infections were produced in
experimental
animals varied much in detail, but the investigation was primarily
related to the study of the
general principles underlying the spread of infection and the
possibility of the experimental
control of the process. In every instance the dura was perforated; in
some of the experiments,
parts of the cortex were removed; in others, perforations communicating
with the lateral
ventricles were made, while in others only the most superficial layers
of the brain were injured.
Foreign bodies of bone or metal were sometimes introduced into the
wound; while at other
times the skull was fractured, with puncture of the central nervous
system. In a word, attempts
were directed toward reproduction of cerebral wounds similar to those
occurring at the
battlefront. It was early discovered that an abscess in the brain of a
cat developed only with great
uncertainty unless a massive dose of bacteria was introduced into the
wound. Simple puncture
wounds were found to heal per primam although no efforts were made to
sterilize the
instruments or tract. The animal's resistance to infection even after
puncture of the dura seemed
quite remarkable. Gross examination of such infected brains showed
principally great swelling,
with necrosis of the tissue and protrusions through the wound opening.
In about one-half of the
cases recorded a generalized meningitis was present at death, either
from direct or indirect
infection of the lateral ventricles in the region of the wound and
subsequent spread to the
meninges through the foramina of Magendie and Luschka. A complete
restoration of the
destroyed nervous tissue was never attained, although function might
have been taken over by
other cells; and in some instances a normal individual, to all intents
and purposes, was preserved.
An attempt was made by the tissue to combat the process of destruction
instituted by the
infecting organism; this defense. as well as the removal of the debris
by large phagocytic cells, could be seen microscopically. The tendency of the infective process to
invade the subarachnoid
space from the point of injury was not marked, but in a third of the
animals the infection entered
the subdural space, forming there a subdural abscess.
851
These
acute traumatic lesions were very different from the more slowly
growing
abscesses, extending from the cranial air sinuses. The latter,
occurring frequently in man, may be
differentiated by the relatively slight swelling and dislocation of the
cerebral substance, and by
the development of a definite connective tissue capsule between the
infective focus and the
sound parenchyma. The traumatic abscess in the experimental animal
extended rapidly along
the fiber tracts. No encapsulation could be demonstrated in any of the
observations. Healing took
place by the ingrowth of connective tissue.
ACTION OF
ANTISEPTICS UPON THE CENTRAL NERVOUS SYSTEM 7
The
toxicity of certain antiseptics upon the central nervous system was
tested by direct
injections into, or irrigation of, the subarachnoid space. Practically
all of the chemical bodies
employed possessed definite intraspinous toxicity, so that, unless
given in suitable dilution and
amount, immediate death of the animal ensued. With chlorainine and
flavine on subarachnoid
injection, in addition to the initial toxicity, death in five to ten
days was brought about in
consequence of the direct injury to the central nervous system. With
injection of small amounts
of a suitable dilution the animals remained apparently normal but all
showed at autopsy
pathological changes in the meninges. The lesions consisted of a more
or less complete
obliteration of the meningeal (subdural and subarachnoid) spaces with
serofibrinous exudate; in
the more severe cases the nervous system became involved in a process
of destruction by direct
continuity from the meninges. The blocking-off of the subarachnoid
space by this exudate was
complete in one case, as demonstrated by the subsequent injection of
india ink; it was not,
however, sufficient for the localization of an infection. The
subarachnoid injection of lysol and
potassium permanganate, in the presence of an otherwise fatal meningeal
infection, did not
prolong the life of the animal.
SUBARACHNOID
IRRIGATIONS 8
In
the earlier experiments the irrigation was limited to the spinal canal,
and for this
operation the first puncture needle was inserted into the subarachnoid
space through the
occipitoatlantoid ligament, and the second in the lumbar region.
Between these needles fluid
could be passed through the spinal subarachnoid space in either
direction, although the
descending route (from cervical to lumbar) was, as a rule, selected.
Later, in order to include the
cerebral meninges in the irrigation, needles were introduced into the
subarachnoid space in the
vertex area; from there the flow could be conducted either to an
occipitoatlantoid or to a lumbar
needle.
Irrigations
of the spinal and cerebral subarachnoid spaces were well tolerated by
cats if
the irrigating fluid was composed of sodium chloride, potassium
chloride, and calcium chloride
in proper proportions (modified Ringer's solution). If, however, the
irrigations were made with
isotonic solutions of sodium chloride alone, various toxic effects
became very apparent. Many of
these animals died during or immediately after the irrigation; if this
immediate toxicity was
survived, convulsive seizures and acute mania were almost invariable.
Recovery from such
attacks was frequent. Single irrigation of infected
852
meningeal spaces with modified Ringer's
solution prolonged the life of the animals as compared
with the controls. The period of survival in many cases was doubled as
a result of this washing
out of the infected meninges. Multiple irrigations were not attempted.
EPIDURAL
COMPRESSION OF THE SPINAL CORD 9
The
method employed to produce compression of the cord was the injection of
paraffin
into the epidural space; subsequently the spinal fluid above and below
the area of compression
was examined. As a result of such epidural compression of the spinal
cord a partial transverse
myelitis, manifested chiefly as incomplete paraplegia, resulted. In
these cats the spinal fluid
obtained from below the area of compression usually differed greatly
from that above; the former
showed almost constantly a greater protein-content, was usually scanty
in amount. and
frequently of a yellow color, and at times clotted rapidly and
completely. The fluid taken from
above was uniformly normal. As in man, the fluids which clotted and
contained the greatest
amount of protein were found in the animals showing greatest symptoms
of pressure upon the
spinal cord. The protein associated with the mild aseptic meningitis
present in these cases was
relatively insignificant as demonstrated by the fact that the fluid,
obtained from the cisterna
magna, often contained white cells equal in number to those from the
lumbar region, but showed
only slight increase in protein. In some cases a well-marked vascular
engorgement of the pial
vessels below the area of compression was demonstrated as was also an
abnormal amount of
serum in the subarachnoid space at the level of compression.
Transudation into the lumbar sac
was apparently the pathological process operative in the formation of
these fluids so rich in
protein.
EXPERIMENTAL
CRANIOPLASTY 10
Experiments
were undertaken to determine the relative value of various kinds of
bone for
bridging experimental defects in the skull, the protection of the
underlying structures, and the
return of the contour of the head to its normal convexity. The problems
of cranioplasty could not
be met entirely by the experience obtained from osteoplastic work on
long bones. The logical
material for use in crainioplasty consisted of plates of cranial bones
as the requirements of
protection for the brain and restoration of the shape of the head could
be immediately
accomplished and the formation of exostoses was avoided. Animal
experimentation (on cats)
indicted that either living or dead grafts could he used effectively in
the head. In the case of dead
grafts, the bone might be removed during routine autopsies, sterilized
by boiling or in the
autoclave, and kept until needed for the operation. In man living
grafts were recommended: but
if they were not available, plates of sterilized cranial bone were
preferred to any other tissue.
LETHARGIC ENCEPHALITIS 11
The
initial investigation of an outbreak of lethargic encephalitis in Camp
Lee, Va., was
intrusted to the staff of this laboratory. Nine cases of this disease
were examined with complete
pathological studies of four. The onset of
853
symptoms was always insidious--headache,
malaise, weakness, and vertigo being commonly
complained of. Early symptoms of probably greater significance were
sore throat, diplopia, and
invariable fever. It was unusual to find signs of organic nerve disease
in the first week of illness,
hut by the second week--sometimes later still--a widespread organic
neurological disorder became
evident, when cerebral symptoms appeared. Drowsiness occurred in almost
every case,
frequently developing into coma, and at times alternating with at state
of irritability or anxiety.
In spite, however, of an apparently clouded mental condition,
orientation and cerebration were
usually unaffected until just before death. Long projection fiber
tracts to arms and legs showed
pro-found disturbance in seven cases as indicated by ataxia,
spasticity, and clonus. The only
symptoms and signs of a focal character were referable to the
brainstem, and these were present
in all. Diplopia was complained of in seven of the nine cases, although
oculomotor palsy was
seldom seen, doubtless because of its transitory nature. The second
most frequent disorder was
weakness of the facial muscles, usually one-sided, a condition seen in
five cases.
Macroscopically,
all the brains examined appeared alike. A great degree ofen gorgement
of all vessels was conspicuous, and free blood was present in the
meninges as evidenced by a
pink tint to the pia. The chief seats of the lesions were the brain
stem and basal ganglia. The
essential pathologic processes were found to be a perivascular
exudation and a diffuse
infiltration of parenchyma. While both types of lesion varied greatly
in intensity, extent, and
symmetry, they occurred especially in the gray matter about the canal,
fourth ventricle, and
aqueduct, though deeper tissues were also affected and the white matter
was not spared. The
cells concerned in both types of lesion were all mononuclear; a small
mononuclear cell and at
large mononuclear cell, frequently phagocytic, together with the
lymphocytes and plasma cells,
were recognized. Polymorphonuclear leucocytes were absent even in the
cases of short duration.
That the diffuse infiltrating exudate was not necessarily related to a
destructive process was
borne out by the normal or only slightly changed appearance of nerve
cells in its midst: however,
when the exudate was excessive, marked nerve cell changes, including
neuronophagia, resulted. Hemorrhages were few in nunber and very small.
Blood vessel changes were of two types. There was almost constant
evidence of proliferation of the intima in vessels in areas of
exudation, those in unaffected territory usually showing no
abnormality. The second type of
lesion noted was infiltration of the vessel walls (especially
intra-adventitial), with mononuclear
cells, chiefly lymphocytes and plasma cells. The cord and organs in
cases examined appeared
essentially normal. Lesions in the cerebral cortex were in all cases
either nonexistent or
negligible. No organisms were seen and cultures from the cerebrospinal
fluid and from the
nervous system post mortem were negative.
EXPERIMENTAL
MENINGITIS
One
of the chief problems presented for investigation in the Army
neurosurgical
laboratory was that of meningitis. In general it was not proposed to
deal with the meningococcic
infections but rather to ascertain whether the pyogenic,
nonmeningococci forms of meningitis
could be treated successfully
854
by measures other than serum therapy. The
first need in such an investigation was that of
standardization of the infection; i. e., the experimental production of
a uniformly fatal
meningitis. It was hoped that an organism capable of bringing about
meningeal infections in the
laboratory animals in numbers analogous to those causing infection in
man could be found.
Previous work on meningitis in animals had, almost without exception,
dealt with the sub-arachnoid injection of very large doses of organisms
(one-half to four agar slants). The infections
under such circumstances were hardly uniform, even in the monkey.
The
search in this laboratory for an organism highly virulent within the
meninges of
experimental animals was successful. The investigation necessitated the
testing of many strains
of bacteria within the meninges and the later accentuation of the
pathogenicity of those which
possessed "natural virulence." Later the major portion of the work
became centered about the
study of the factors which favored the invasion of the meninges from
the blood stream; the
production of such hematogenous meningitides was investigated from many
angles. The results
of the subarachnoid injection of the various organisms will be detailed
first and the study of
infections of the meninges by organisms circulating within the blood
stream will be given later.
MENINGITIS PRODUCED BY SUBARACHNOID INOCULATION 12
Practically
all of the experiments dealing with the direct subarachnoid injection
of
organisms were done on cats, the inoculations being made into the
meninges through the
occipitoatlantoid and lumbosacral ligaments. Organisms, possessing no
natural virulence within
the meninges of the cat, were discarded after a few trials. If the
organism seemed to possess
some pathogenicity, but too large a number, on initial injection, was
required to produce a fatal
meningitis, the virulence was raised by passage through the meninges of
a series of animals.
The
reaction caused by the growth of an organism in the meninges was
determined by the
clinical manifestations of the animal, characteristic changes in the
cerebrospinal fluid, and the
pathological lesions of the central nervous system at necropsy.
Although the clinical
manifestations varied somewhat, the more acute cases were characterized
by general weakness,
convulsions, extensor rigidities of the muscles, accompanied by
frequent spontaneous out-cries.
These signs of cortical irritation appeared in paroxysms, so that, were
the animal observed
during a quiescent period, little could be noted unless there actions
were elicited by appropriate
stimuli. Chronic meningitis exhibited signs of neuromuscular
disturbance--ataxia, variations in
gait (spasticity),weakness and paralysis of certain muscle groups-which
were probably the result
of permanent destructive lesions in the central nervous system.
The
microorganisms which generally cause a fatal meningitis in man
(meningococcus,
pneumococcus, streptococcus, staphylococcus, influenza, etc.) were
found to possess but slight
natural pathogenicity for the meninges of a cat. This animal also
proved to be comparatively
insusceptible to these organisms on intravenous inoculation, especially
if they were of human
origin. Another group of organisms (miscellaneous bacilli) was found to
be capable
855
of the production of a fatal meningitis upon
the injection of massive doses into the subarachnoid
space, but their virulence could not be raised markedly. A third group
of organisms was found
to possess great virulence within the meninges of the laboratory
animals used. Of this group (B.
pyocyaneus, B. coli, B. paratyphosus-B., and the mucosus capsulatus
group) a strain of B. lactis aerogenes possessed the
greatest natural virulence for the meninges.
The chief disadvantages of
this organism were related to its extreme virulence, the difficulty
experienced in producing an
immune serum, and its relative infrequency as a meningeal invader in
man; these characteristics
made it difficult of use in the investigation of certain other phases
of the study of experimental
meningitis, although for the purpose of this laboratory it was
invaluable. This strain of B. lactis
aerogenes was virulent within the meninges of all the common
laboratory
mammals; in cats, the
subarachnoid injection of as few as 20 organisms (as determinel by
plating) produced a
meningitis causing death within 24 hours. The organism was originally
obtained at autopsy from
the heart's blood and lungs of a man dying of bronchopneumonia.
The
routine culturing at necropsy of the heart 's blood of animals dying of
experimental
meningitis revealed certain interesting facts in regard to the transfer
of infection between the
meninges and the blood stream. In all cases of meningitis caused by the
injection of organisms
into the subarachnoid space, cultures of heart 's blood showed the
presence of the same bacteria
with which the animal had been inoculated intraspinously.
THE PATHOLOGY OF EXPERIMENTAL MENINGITIS 13
The
study of the meningeal reaction produced by subarachnoid inoculation of
a large
number of organisms, was made largely upon formalin-hardened material.
The meningitis
resulting from such subarachnoid inoculation could be grouped into
three pathological types.
The first, a focal subacute meningitis, showed small accumulations of
exudate in isolated foci,
especially in the deeper layers of the pia. Organisms were usually
absent from the meninges and
the blood, both culturally and on microscopic examination. The second,
an acute, low-grade,
exudative meningitis, was characterized by a scanty or a considerable
exudate, of
polymorphonuclear or lymphocytic cells. Organisms, if present, were but
few in number and
were considered to possess only mild subarachnoid virulence. The third
group consisted of those
cases of massive acute meningitis, in which there was evidence of
extreme virulence and
proliferation of the organism. In this type alone was death considered
to be due primarily to the
meningitis.
In
the cases of acute fulminating meningitis the exudate soon passed
beyond the
subarachnoid space into the ventricles, and a little more tardily
invaded the substance of the
brain and spinal cord. In 24 hours approximately one-half of the
specimens showed such
involvement of the central nervous system; this invasion usually
occurred by direct extension
from the ventricles and canal. The exudate also spread outward with the
nerve roots, and a
patchy or diffuse epidural infection then resulted. The dura itself
became infiltrated at areas of
root "perforation." The blood stream was early infected in such acute
856
meningitis, as seen on section and on
culture, and it is likely that this septicemia played an
important role in the death of the animal. In the less acute forms of
meningitis, the arachnoid
membrane more or less effectively limited the spread of infection from
without and from within.
FORMATION OF MACROPHAGES BY THE CELLS LINING THE SUBARACHNOID CAVITY 14
In
the course of the study of the processes involved in the localization
of an infection
within a focus in the nervous system, certain physiological reactions
of the cells lining the
subarachnoid space were noted. When active or inert particles of matter
were injected into the
subarachnoid cavity of a living animal, the cells lining the space
hypertrophied, lost their normal
attachments, and engaged in removing the debris. The importance of such
a formation of free
cells from fixed elements in any process involving destruction and
repair in the meninges
(infection, hemorrhage, etc.), seemed great. The reaction of the
cellular membrane to such
particulate matter was a slow one and appeared to be well under way
only after the first 24
hours; dead bacteria might betaken up and removed by the leucocytes
before the arachnoid cells
showed any signs of activity. The most striking results occurred after
subarachnoid injection of
laked blood, due probably to the fact that it had no toxic effect on
the cells and could be utilized
by them.
This
reaction of the cells lining the subarachnoid space apparently plays a
part in the
defensive process against infection. Many of the earliest cases of
meningitis (six hours) showed
a marked proliferation of these cells: the exudate frequently was
largely mononuclear. In other
cases roughly half of the cells were mononuclear while the remainder
were polymorphonuclear.
On section the cell borders of the arachnoidea (particularly the
trabeculae) seemed to be high and
proliferating; the origin of at least a considerable portion of the
mononuclear elements in the
exudate seemed certain. The proper control of such a defensive cellular
reaction will ultimately
accomplish much in the therapy of infectious processes.
THE CEREBROSPINAL FLUID IN
MENINGITIS 15
In
meningeal infections there is always a cellular and protein exudate in
the cerebrospinal
fluid. With different bacteria and etiological factors, such
pathological conditions within the
meninges cause ialso variations ill the concentrations of glucose, of
sodium chloride, and of
urea, and perhaps other changes both in organic and inorganic
constituents. The increased
cellular and protein constituents of the cerebrospinal fluid must,
however, be considered as
giving greatest indication of a reaction caused by the injection of a
known microorganism into
the subarachnoid space.
The
number of cellular elements in the normal cerebrospinal fluid of the
experimental
animals was found to be rather variable; in a series of routine
examinations the counts of the
white cells ranged from 0 to 10 per c. mm. No erythrocytes were
demonstrated in the
cerebrospinal fluid from normal cats in a large number of examinations.
The protein content
varied from 0.1 to 0.5 grams per liter, 0.25 grams being a low normal
and 0.5 grams a high.
bordering
857
on a pathological fluid. The colloidal
gold reaction of a number of normal fluids gave a
similar curve to that obtained by normal fluids from man. In acute
meningitis the cerebrospinal
fluid of the cat was found to contain from200 to 22,400 white blood
cells, 2 to 17 grains of
protein to a liter, and to give are action in any of the three zones in
the gold sol test. The
cerebrospinal fluid. of chronic meningitis in a cat proved to be
practically normal, with
exception of the gold sol reaction, in which a change to the paretic or
luetic zones was recorded.
In some of the chronic cases there was a slight increase in the number
of white blood corpuscles
and in the content of protein. The colloidal gold reaction was of
service in demonstrating a
pathological cerebrospinal fluid but showed no specific zone reaction,
except to a slight extent in
the cerebrospinal fluids from animals with chronic meningitis. There
was indeed a great
similarity in the Lange test as applied to the cerebrospinal fluids
from cases of experimental
chronic meningitis and those of general paresis in human patients. It
was suggested that reaction
in the paretic or even the luetic zone denotes the presence of a small
amount of protein, as in a
chronic lesion of the central nervous system.
INTRAMENINGEAL VIRULENCE OF MICROORGANISMS 16
In
determining the natural virulence of 102 strains of 24 groups of
microorganisms, it
was found that certain bacteria or groups of bacteria were more capable
than others of producing
a fatal infection when injected directly into the meningeal spaces. The
term "natural” virulence
has been used to denote the pathogenicity of recently isolated strains
of microorganisms, before
increase in virulence by animal passage. It was found necessary to
enhance the natural
intrameningeal virulence of strains of B. mucosus capsulatus,
hemolytic streptococcus,
meningococcus and B. paratyphosus, as after being kept
for some time on the ordinary
laboratory media their virulence so far decreased as to render them of
little value for
experimental work. Failure to increase the intrameningeal virulence
(though the intravenous
pathogenicity was raised considerably) by successive intravenous
injections of the culture in cats
caused the trial of "animal passage " by means of inoculation directly
into the meninges. It, was
found possible by this method of direct subarachnoid inoculation to
increase the virulence of
four strains of microorganisms, representing as many groups, to the
degree indicated: B. lactis aeroqenes, 0.000,000,000,01 c. c. of a 24-hour broth culture
killing in 24 hours (cats); B. paratyphlosus-B., 0.0001 c. c. (cats):hemolytic streptococcus
(cats), 0.001 c. c., and (rabbits),
0.0005 e. c.; meningococus (rabbits), 0.001 c. c. By such passage, the
intravenous virulence was
hardly increased; the intrameningeal and intraperitoneal virulence
increased to the same degree.
By combined intraperitoneal and intrameningeal methods, approximately
the same degree of
pathogenicity was developed with streptococcus in rabbits. The
intrameningeal virulence became
at least 500 times greater than the intravenous. The ratio of the
intrameningeal and intravenous
pathogenicity of B. lactis aerogenes, of B.
paratyphosus-B., of streptococcus on cats and on
rabbits, and of meningococcus became, respectively, 10,000,000 to 1:
10,000 to 1; 1,000 to 1;
500 to 1, when the intrameningeal method of animal passage was employed.
858
HEMATOGENOUS MENINGITIS 17
The
marked virulence of the B. lactis aerogenes within the
meninges of the cat led to its
use in other laboratory mammals. For all of these (guinea pig, white
rat, rabbit, monkey) the
same intraspinal pathogenicity held. Later, experiments leading to
another end were undertaken. These concerned the intravenous injection
of this organism in doses of from 0.5 to 1 c. c. of a
24-hour broth culture. None of these cats developed meningitis, but
remained normal throughout
the period of observation. In one case, shortly after such experimental
injection into the blood
stream, cerebrospinal fluid was removed by puncture. The next day the
animal showed signs of
meningeal irritation, and a second puncture, with withdrawal of
cerebrospinal fluid, was made.
This fluid was definitely turbid, contained 5,800 white blood cells,
and yielded a positive culture
of B. lactis aerogenes. In the film preparation from
this fluid many bacilli were present. The
animal died in 28 hours, and at necropsy atypical exudative meningitis
was found.
Experiments
on cats were immediately devised to test out the possible relationship
of this
withdrawal of cerebrospinal fluid during an artificial bacteremia to
the later production of a
meningitis.18 The series were so arranged that the control
animals were given double the
intravenous dose of B. lactis aerogenes (usually 0.5 c.
c. of a 24-hour meat infusion broth
culture). These control cats remained normal and showed no signs of
meningeal infection, and
were usually killed at the end of a month for histologic control. The
other cats in the series were
given the unit dose of organisms intravenously (usually 0.25 c. c. of
the same culture), and two
minutes afterward, cerebrospinal fluid was withdrawn. In the routine
experiment, from 1 to 2 c.
c. of fluid was permitted to escape, and the animal then allowed to
recover from the anesthetic. As contrasted the next (lay with the
control cat, which, though receiving double the intravenous
dose, was normal and active, the punctured cat would exhibit signs of
meningeal infection.
Customarily within 24 hours, the typical signs of such meningeal
involvement were present; the
animal was somewhat hyper-sensitive, ill, and cautious, and moved only
on urgent necessity.
The tendency toward convulsions became more outspoken as time elapsed,
and spontaneous
seizures were noted. During such a spasm death often occurred, or the
animal went into a coma
and died without further signs of meningeal irritation. Pathologically,
an acute exudative
leptomeningitis was invariably found.
The
experimental procedure outlined above was repeated in scores of
animals; the
production of meningitis by intravenous inoculation followed by release
of cerebrospinal fluid
was so certain and so regular that it became the chief method for the
experimental production of
the infection. The work was controlled in many ways, in addition to the
routine method of giving
one animal in the series an intravenous injection of double the amount
of the culture but without
puncture.
The
release of cerebrospinal fluid was brought about by either lumbar
oroccipitoatlantoid
puncture. Approximately the same amount of fluid was withdrawn by
either method; the end
result was identical. Release of fluid by both procedures, with proper
dosage of the organism
within the blood stream, resulted invariably in infection of the
meninges.
859
That
this phenomenon of an acute meningitis following intravenous
inoculation with
release of cerebrospinal fluid was not peculiar to eats was
demonstrated by a series of
experiments on rabbits, guinea pigs, white rats, and monkeys. In each
of these species, the
control was given the same or double the intravenous dose as the animal
from which the
cerebrospinal fluid was removed at the height of the artificial
bacteremia. In every case, the
control remained well and normal until killed, while the animals from
which spinal fluid was
removed promptly developed a typical meningitis with death in 96 hours
or less. In the two
monkeys at our disposal, the same procedure was carried out; the
control (receiving only the
intravenous injection) remained normal for seven months, while the
monkey receiving the
intravenous injection, followed by release of cerebrospinal fluid, died
in 54 hours with typical
signs of meningitis. The two monkeys were subjected to cistern puncture
48 hours after the
initial injection; in the control, the cerebrospinal fluid contained no
white cells and the culture
was negative, while the fluid of the other had 14,000 white blood cells
and gave a positive
culture.
The
time relations between the withdrawal of cerebrospinal fluid and the
intravenous
injection of organisms were found to be of importance. In no case did
meningitis develop when
the cerebrospinal fluid was released 30 or more minutes before the
intravenous inoculation. If
the puncture were done, however, only a few minutes before the
inoculation into the blood
stream, infection of the meninges occurred as in other observations in
which routine withdrawal
of fluid was accomplished immediately after the intravenous injections
of organisms.
During
the height of a suitable artificial bacteremia, the release of spinal
fluid invariably
caused a meningitis. In one series of experiments, the punctures were
delayed for various periods
after the intravenous injection. Animals from which cerebrospinal fluid
wats removed within
three hours after the intravenous injection developed meningitis. But
also animals receiving
somewhat larger intravenous doses could not be punctured five hours
afterwards without developing infection of the meninges. Hence a
striking time relation between the degree of the
artificial bacteremia and the withdrawal of cerebrospinal fluid seemed
established. It must be
assumed that following the intravenous injections of B.
lactis aerogenes the number of bacteria
in the circulating blood was constantly diminishing so that in
practically all cases of simple
intravenous injection the blood was sterile in 24 hours. Consequently
delay in removing
cerebrospinal fluid became comparable to the initial administration of
a smaller intravenous dose
of organisms. Apparently the number of organisms circulating in the
blood stream at the time of
puncture is one of the crucial factors in determining the infection of
the meninges.
Other
observations were made to determine how soon the infection of the
meninges
occurred after the release of cerebrospinal fluid during the height of
the bacteremia with B. lactis
aerogenes. In these typical experiments the animals were killed in
one hour, two hours, four
hours, and six hours after the injection and puncture. The membranes of
the central nervous
system were then examined in the fresh by means of smears taken from
the subarachnoid space,
and the findings later controlled by histologic sections. In the
one-hour
860
case, after repeated search one or two large
bacilli, morphologically identical with B. lactis
aerogenes, were found in the cerebral leptomeninges but not
elsewhere within the meninges.
The two-hour specimen yielded bacteria only in the cranial portion of
the pia-arachnoid, but in
considerable numbers. Practically no cellular exudate was found. Many
polymorphonuclear and
mono-nuclear cells were present in the four and six hour animals; the
infection seemed to be
largely within the cerebral meninges, but apparently to a lesser degree
the spinal portion of the
subarachnoid space was involved. These findings indicated that the
infection of the meninges
occurred almost immediately after the release of cerebrospinal fluid
during the bacteremia.
Pathologically,
the meningitis produced by this means was comparable to infection of
the
meninges in man. In a great majority of cases (particularly those under
48 hours' duration) the
gross distribution of the exudate was almost entirely cerebral; but in
a small percentage of the
early cases, the exudate was wholly confined to the spinal meninges. In
the more prolonged
infections, the involvement of the subarachnoid space was customarily
universal. Microscopically the exudate consisted of polymorphonuclear
leucocytes, large mono-nuclear cells, a
few phagocytes, and the infecting organisms.
It
was essential to determine whether the meningitis produced by
intravenous
inoculation and release of cerebrospinal fluid was the result of
infection due to a possible
leakage of blood along the track of the needle into the subarachnoid
space. The evidence was
strongly in favor of the idea that the determining factor in the
infection was the reduction of the
pressure of the cerebrospinal fluid, with associated vascular changes.
With
such results following the intravenous injection of B. lactis aerogenes with
release
of cerebrospinal fluid, experiments were undertaken to ascertain if the
same procedure, but with
other organisms, would produce meningitis. The difficulty here was that
with the ordinary
cultures in a laboratory, the intravenous toxicity was high in
comparison to the intraspinal.
However, it was possible to repeat these experiments and confirm the
finding on the cat with two
other organisms, B. pyocyaneus and B. paratyphosus-B.
On rabbits a similar result has been
obtained with strains of meningococci and of streptococci, procured
from an Army camp.
The
facilitation of infection of the meninges from. the blood stream by the
release of
cerebrospinal fluid seemed established as a biological factor by the
production, in this
laboratory, of a typical meningitis with five different organisms. The
conditions for the
successful production of such an experimental meningitis concerned two
factors, both apparently
of determining importance. In the first place, it was demonstrated that
the organism used must
possess relatively great virulence within the meninges and be capable
of multiplication there,
even when in small numbers. The strain of B. lactis
aerogenes best fulfilled this requirement
when introduced into the subarachnoid space of the common laboratory
mammals; its virulence
in these animals was comparable to that of organisms causing meningitis
in man. The other
important condition dealt with the number of organisms circulating in
the blood stream at the
time of release of the cerebrospinal fluid; if this was not great
enough, no infection took place.
861
It
must not be assumed from the statements made that a meningitis could
not be produced
by B. lactis aerogenes after simple intravenous
injection. Such a meningitis was caused by the
introduction within the blood stream of massive doses of the organism.
The amount necessary to
produce such a meningitis was many times the customary intravenous
injection; such animals
were killed usually by the septicemia and not by the meningitis. Many
of these animals died
from the overwhelming intravenous injection without development, as
shown by later necropsy,
of any meningeal infection at all.
Practically
all of the data indicated that the infection of the meninges by
organisms
circulating in the blood stream, following removal of cerebrospinal
fluid, was due to alteration in
the pressure of the cerebrospinal fluid and the associated vascular
changes within the cranium. It
was assumed that the withdrawal of the spinal fluid was partially
compensated by an immediate
vascular dilatation, particularly on the venous side. This vascular
readjustment really involved a
slowing of the blood flow through the cerebral vessels; it was thought
possible that this slowing
of the flow might facilitate in growth of organisms from the blood
stream into the meninges.
Experiments
to test this hypothesis were carried out.19 In the first
group, the retardation
of cerebral blood flow was brought about by digital compression of the
jugular veins and
adjacent tissues of the neck for two minutes; in the second series, the
heart was completely
stopped for 30 seconds by excessive administration of ether. Both
series were subjected to the
necessary controls; every animal was given a suitable intravenous
injection of organisms before
the secondary facilitating procedure was carried out. In the two
series, a fatal meningitis
occurred in 50 per cent of the animals; the clinical manifestations of
the disease were typical.
These
experiments seemed to indicate strongly that the infection of the
meninges from
the blood was closely associated with cerebral vascular changes. That
only one-half of the
animals developed a fatal meningitis could well be accounted for by the
necessary variability of
the experimental procedures employed. It did appear, however, that the
removal of the
cerebrospinal fluid was more certain than these other procedures as a
facilitating factor. At this
time, experiments dealing with the effect of intravenous injections of
solutions of different
concentrations upon the pressure of the cerebrospinalfluid were being
conducted in this
laboratory. It was found, as recorded in a foregoing paragraph, that
the intravenous injection of a
strongly hypertonic solution markedly lowered the pressure of the
cerebrospinal fluid, often to
negative values. Such intravenous injections were immediately combined
with suitable
intravenous injections of organisms, virulent within the meninges; a
fatal meningitis invariably
occurred as in the experiments in which the pressure of the
cerebrospinal fluid was reduced by
withdrawal of fluid. The relation of the low pressure of the
cerebrospinal fluid and its associated
vascular changes was thereby demonstrated.
Further
observations were made to determine the effect of preliminary
subarachnoid
injections of protein (autologous, homologous, and heterologous)upon
the intrameningeal
lodgment of organisms circulating within the bloodstream. Flexner and
Amoss had earlier
demonstrated that poliomyelitis
862
could be experimentally produced by
intravenous injection of the virus, provided that the
permeability of the meninges had previously been altered by
intraspinous injection of serum, salt
solution, etc. Subsequently Austrian applied this same procedure to
experimental meningococcic
meningitis in rabbits. Austrian recorded the production of a fatal
meningitis in three out of
twenty rabbits given intravenous injections of meningococci after
preliminary intraspinous
injections of serum. In this laboratory preliminary injections of serum
into the subarachnoid
space were given and later suitable intravenous injection of B.
lactis aerogenes was made. In 6
out of 39 cats, a typical fatal meningitis was produced; the other
animals remained normal in
every way. As a facilitating mechanism the preliminary subarachnoid
injection of serum has
been found to be by no means as effective as the reduction in the
pressure of the cerebrospinal
fluid and the associated vascular changes.
The
interpretation of these many and varied experiments is necessarily
related to the
mechanism of facilitation of the infection of the meninges from the
blood stream. The
intravenous injection of suitable dosage of an organism virulent within
the meninges did not of
itself produce meningitis; such an injection had to be combined with an
experimental procedure
which facilitated invasion of the subarachnoid space by bacteria. Of
these various procedures,
withdrawal of cerebrospinal fluid by puncture or reduction of its
pressure by intravenous
injection of strongly hypertonic solutions was most efficacious.
Measures slowing the
intracranial blood flow (cerebral venous congestion or stoppage of the
heart) caused infection of
the meninges in only half of the cases. Preliminary subarachnoid
injections of serum resulted in
infection of the meninges in but 6 out of 39 experiments.
PATHOLOGY OF HEMATOGENOUS MENINGITIS 17
In
this acute hematogenous meningitis, there occurred a more or less
wide-spread
distribution of purulent matter throughout the subarachnoid space,
obliterating all characteristic
markings and obscuring contours. With the discoloration due to pus and
hemorrhage, there was
associated a fairly constant swelling of the nervous system itself,
rendering tense the dura of
both brain and spinal cord. In a great majority of cases (particularly
those under 48 hours'
duration) the gross distribution of the exudate was almost entirely
cerebral; but in a small
percentage of the early cases, the exudate was wholly confined to the
spinal meninges. Evidence
favored the view that the cortical meninges were the site of earliest
infection, with rapid spread
to other portions of the subarachnoid space and to the cerebral
ventricles. The invasion of the
ventricles occurred early in all fatal cases. Infection of the
ventricles and canal led to
involvement of the substance of the brain and cord. The exudate which
accompanied all the
meningeal infections was polymorphonuclear or mononuclear in character
and its distribution
followed closely that of the organisms. In the earlier cases, the
exudate was often slight, but in
those of longer duration it became massive, imparting to the entire
meninges a discolored
appearance. Extension outward from the subarachnoid space occurred in
many cases and two
methods of the accomplishment of this process have been observed. One
was through apparent
adhesions of arachnoid and dura with infiltration by
863
leucocytes and swelling at this point. A more
common site of extension was in the area where
the dura is "pierced" by the nerve roots, the exudate frequently
accompanied both the anterior
and posterior roots outward for a short distance, invading the dura and
sometimes passing
through it to its external surface. With the strains of B.
lactis aerogenes, meningococcus, and
streptococcus employed, there was produced an acute
hemorrhagic-purulent meningitis, in which
the bacteria appeared to be rapidly increasing in number. With B.
pyocyaneus and B. paratyphosus-B., a mild acute meningitis resulted, with very few
organisms to be seen. Control
animals receiving inoculations alone showed no pathological lesion of
the central nervous
system or merely a mild "febrile reaction," recognizable only
microscopically.
PRODUCTION OF PANOPHTHALMIA BY INFECTION
FROM
THE BLOOD STREAM.20
The
microorganism, B. lactis aerogenes, which proved so
extremely virulent in the
central nervous system, exhibited a similar pathogenicity for the eye.
The release of fluid from
the anterior chamber of the eye, and the congestion of the cerebral
circulation during an
experimental bacteremia, resulted in the production of a purulent
panophthalmia. It is interesting,
however, that in the course of several hundred experiments on
meningitis in which this
bacterium was inoculated into the blood stream of cats, an ophthalmia
was produced only once.
When procedures analogous to the withdrawal of spinal fluid were
carried out on the eye, the
infection was limited to the one organ operated upon, the opposite eye
and the central nervous
system being unaffected. The close correspondence between the
anatomical and physiological
processes in the eye and central nervous system was emphasized by this
production of
panophthalmia by intravenous inoculation followed by facilitating
measures.
LUMBAR PUNCTURE AS A FACTOR IN THE
CAUSATION
OF MENINGITIS 21
A
series of cases was observed in the base hospital at Camp Jackson by
members of the
staff of this laboratory for the purpose of determining the
relationship, if any, of diagnostic
lumbar puncture, in the presence of a septicemia, to the subsequent
occurrence of meningitis. To
this end, blood cultures were taken at the time of the lumbar puncture
and the cases were
followed subsequently with reference to the development of meningitis.
In a number of cases in
which a septicemia was present, the first diagnostic lumbar puncture
yielded a clear and normal
cerebrospinal fluid in which no organisms could be demonstrated; later
fluids from these cases
were turbid and contained the organism isolated from the blood culture.
Two cases of
pneumococcus septicemia developed a meningitis, subsequent to
diagnostic lumbar punctures
yielding normal fluids. In one of meningococcic septicemia, a negative
spinal fluid at the time
when the blood culture was positive, was obtained; the presence of an
early meningitis was
observed at autopsy. The case suggested a possible relationship between
the release of
cerebrospinal fluid during the septicemia and the subsequent
meningitis. Three other patients
with meningococcic septicemia were observed; lumbar puncture in all
three yielded initial
negative
864
fluids. Within 48 hours two of the three had
developed a definite meningitis. Interpreted from
the standpoint of the experimental work in this laboratory, the
relationship of the withdrawal of
cerebrospinal fluid during a septicemia to the development of a
meningitis was indicated.
To
prevent the possible accidental production of a meningitis as the
result of diagnostic
lumbar puncture, it was recommended that careful consideration be given
the bacteriological
study of the blood before such punctures were attempted; and that in
acute diseases, in the
absence of definite signs of irritation of the central nervous system,
lumbar puncture should be
avoided unless it was first conclusively shown that the blood stream
was free of infection.
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