Cysts of several different types
may develop within the spinal canal and may come to medical attention by causing
myelopathy or radiculopathy or as incidental findings. Intraspinal ganglion
cysts and synovial cysts, thought to be rare in 1985, are encountered not
infrequently in current neurosurgical practice.
There is some element of
confusion in the classification of spinal cysts, and several schemes have been
used. Part of the confusion comes from the various terms that have been applied
to the same entities by different authors, and part comes from the imprecise
description of the cysts in some of the case reports.
Another source of confusion is
our incomplete knowledge of the origins of some of these lesions. As an example,
intraspinal epithelial cysts that are lined by a single layer of cuboidal
epithelium could be of neurenteric or neuroepithelial origin. In some of the
reported cases, standard light and electron microscopic techniques have not been
sufficiently precise to make this differentiation. At present it is possible to
supplement such assessments by immunohistochemical studies which have the
potential of permitting more accurate classification.
A final source of confusion is
the fact that there is some degree of overlap between the groups. For example,
there is a continuum of cases from spinal epidermoid cysts at one end to spinal
teratomatous cysts at the other, and a similar continuum from simple spinal
neurenteric cysts at one end to spinal teratomatous cysts at the other. Another
area of overlap is among spinal perineurial cysts, meningeal diverticula along
spinal nerve roots, and lateral spinal meningoceles.
Discussion here does not
consider syringomyelia or hydromyelia; cysts associated with astrocytomas,
ependymomas, or hemangioblastomas of the spinal cord; or meningoceles and
meningomyeloceles that extend out of the confines of the spinal canal.
Spinal Extradural Cysts
Spinal extradural diverticula
and cysts are of various types, but those that develop spontaneously, have
connective tissue walls, and contain cerebrospinal fluid are probably variations
on a theme. They can be grouped as congenital extradural spinal cysts, spinal
perineurial cysts (Tarlov cysts), spontaneous meningeal diverticula along spinal
nerve roots, and occult intrasacral meningoceles. The congenital extradural
spinal cysts (also called developmental extradural arachnoidal cysts or
extradural arachnoid cysts) typically come to medical attention during the
second decade of life, whereas the other three types are diagnosed most often
during the middle of life.
Congenital Extradural Spinal
Between 1898 and 1970, at least
115 cases of congenital extradural spinal cyst were described in the medical
literature, and since then many additional cases have been reported. These cysts
are most often located in the thoracic area and are diagnosed most frequently in
patients under 30 years of age. The male/female ratio of occurrence is about 4:
3. Scheuermann's kyphosis dorsalis or kyphosis without epiphysitis has coexisted
in almost half the cases overall and in two-thirds of the patients between 11
and 20 years of age (all of whom had cysts in the thoracic region).
Cysts in the lumbar and cervical
regions tend to occur in persons past the age of 20, suggesting that the cysts
arising within the relatively small thoracic spinal canal become symptomatic
earlier in life than those arising within the larger cervical or lumbosacral
The congenital extradural spinal
cyst, also referred to as an extradural arachnoid cyst, is attached by a narrow
pedicle to the dura mater, usually either in the midline posteriorly or
posterolaterally at the attachment of the dural sleeve covering a dorsal nerve
root. The cyst may or may not communicate with the subarachnoid space. Several
such cysts may be present in the same patient, though they usually are solitary.
Microscopically, the cyst may be lined by a flattened layer of cells resembling
arachnoidal cells, but the rest of its wall is composed of avascular collagenous
Most of the reported cases have
been sporadic rather than familial. Several hypotheses have been advanced to
explain their origin, all of which imply a congenital defect of some sort. No
matter what their exact origin, such cysts appear to enlarge by hydrostatic
pressure and CSF pulsations (perhaps with a ball-valve mechanism) until for some
reason their communication with the spinal subarachnoid space becomes
The clinical course of the
patient with a congenital extradural cyst in the thoracic or cervical region is
one of spastic paraparesis or quadriparesis of fluctuating but progressive
severity. Sensory and autonomic functions are usually involved to a lesser
degree than motor function. A congenital extradural cyst in the lumbar area may
present with pain, especially pain of a radicular nature.
As the cyst enlarges, it causes
enlargement of the spinal canal, which can be identified radiographically.
Myelography will reveal an extradural defect. and occasionally the contrast
medium will enter the cyst through its pedicle. CT scanning after Myelography
enhances the value of the study. MRI is also valuable in establishing the
The overall prognosis of
surgically treated cases is good. Usually the cyst can be excised or resected.
and the dural defect closed. If the associated cord compression is not too
severe or too longstanding, recovery is likely. The key is early recognition
Spinal Perineurial Cysts (Tarlov
Although such cysts were noted occasionally during the first
four decades of the twentieth century, their nature was not elucidated until
Tarlov's investigations, first published in 1938. At that time Tarlov was
conducting an anatomic study of the filum terminale in about 30 human subjects
for another purpose. and in five of the subjects he discovered cysts on the
sacral or coccygeal posterior nerve roots in the region where they passed
through the dura mater. By studying these and subsequent cases, Tarlov defined
the nature of spinal perineurial cysts.
The spinal perineurial cyst arises between the arachnoid that
covers a nerve root (perineurium) and the outer surface of its pia
(endoneurium), and its walls are formed of these elements. The cyst may extend
around the circumference of the nerve or into the substance of the nerve root
and dorsal ganglion. It is filled with a clear fluid that probably initially is
CSF in communication with the CSF within the spinal subarachnoid space; later
this communication may close. Although a spinal perineurial cyst involves a
single nerve at first, it may enlarge to the point where it compresses adjacent
nerve roots as well.
These cysts typically involve the sacral nerve roots, and
they usually were discovered incidentally during myelography, CT scanning, or MR
imaging for the evaluation of another condition. However, in at least 60 cases
reported between 1948 and 1970, a spinal perineurial cyst has been thought to be
the cause of symptoms (especially radicular pain) and signs of nerve root
In the rare instance in which a single Tarlov cyst is causing
significant symptoms, surgical excision of the cyst (and its parent root if a
water-tight dural closure cannot be achieved otherwise) may provide relief.
Since most of these cysts are asymptomatic and are found incidentally, treatment
is otherwise not necessary.
Spontaneous Meningeal Diverticula along Spinal Nerve Roots
Meningeal diverticula along spinal nerve roots are not
uncommon findings on myelography, CT, or MRI examinations, or during detailed
postmortem studies. Like perineurial cysts. these occur in adults of either sex
and project laterally into the dorsal root ganglia. They appear to be
arachnoid-lined outpouchings that communicate freely with the spinal
subarachnoid space. Although they occur along the length of the spine, there is
a cervicosacral size gradient. the more cephalad cysts being smaller than those
located more caudad (probably a hydrodynamic effect in the upright human being).
On rare occasions a meningeal diverticulum may produce
symptoms of nerve root compression. especially in the sacral region. Treatment
under this circumstance would be the same as for a symptomatic Tarlov cyst.
However. most meningeal diverticula along spinal nerve roots are incidental and
do not require treatment.
Occult Intrasacral Meningoceles
The term intrasacral meningocele is actually inaccurate,
since a meningocele is ordinarily defined as a herniation of the meninges
through a defect in the skull or vertebral column. However, in common usage it
denotes a sac composed of fibrous tissue resembling dura mater that is usually
lined by arachnoid, lies within an enlarged sacral spinal canal. and is attached
to the caudal termination of the dural sac by a narrow or broad pedicle that
usually permits the free flow of CSF from the tip of the subarachnoid space into
At least 44 cases of occult intrasacral meningocele were
reported between 1932 and 1972. Most of these meningoceles did not become
symptomatic until adult life. which suggests that this lesion enlarges with
time. probably because of the hydrodynamic effects of the CSF within it.
The intrasacral meningocele displaces the adjacent sacral
nerve roots and compresses them against the bony walls of the sacral canal,
which is enlarged about the meningocele. This nerve root compression is
apparently the cause of the patient's symptoms. The most common complaint is
pain in the back with radiating pain and paresthesia in the sciatic distribution
of one or both legs. At times hypoesthesia is noted in the same sciatic
distribution or in the perineal area. There may also be weakness in one or both
legs. Urinary or fecal incontinence or retention are common symptoms and
impotence has also been reported. Ordinarily the enlargement of the sacral canal
can be seen or suspected on plain roentgenograms and confirmed by myelography,
CT or MRI.
Surgical treatment consists of ligating and dividing the
pedicle of the meningocele and deflating its sac. Such treatment should relieve
the sacral nerve root compression. If the meningocele is associated with
tethering of the spinal cord. that condition should also be treated by division
of the filum terminale.
Meningeal Diverticula at the Site of Avulsed Spinal Nerve
After traumatic avulsion of one or more cervical nerve roots
from the spinal cord, meningeal diverticula are commonly demonstrated by
myelography, CT, or MRI at the levels of injury. Such a pseudomeningocele
results from a tear of the dura mater and arachnoid with subsequent loculation
of the CSF or from a tear in the dura with herniation of the arachnoid through
the defect. It may be confined within the spinal canal. but ordinarily it
extends out through the intervertebral foramen along the course of the spinal
nerve. Usually the traumatic meningeal diverticulum marks the level of the
avulsed nerve root, but rarely the pseudomeningocele occurs around or adjacent
to an intact nerve root. or an avulsed nerve root exists in the absence of a
myelographically demonstrable dural injury.
This same type of traumatic diverticulum can occur in the
lumbosacral region in association with avulsion or traction-disruption of one or
more of the lower lumbar or upper sacral nerve roots. Traumatic lumbosacral
diverticula of this sort are usually seen in association with a fractured
pelvis. They are much less common than those in the cervical region.
When one or more meningeal diverticula are demonstrated
radiologically after a traction injury to the brachial, lumbar or sacral plexus,
this usually indicates not only which nerve root(s) are involved but the fact
that the nerve injury is complete and permanent and is not amenable to surgical
treatment. The pseudomeningocele(s) themselves ordinarily do not require
Postoperative or Post-Traumatic Spinal Meningeal Diverticula
A postoperative spinal meningeal diverticulum is ordinarily
the result of an intentional or accidental opening of the dura mater land
usually of the arachnoid as well) during an operation on the spine, without a
watertight closure of the dura at the end of the operation. The CSF leaks out
into the planes of operative dissection and becomes encysted by connective
tissue as a pseudomeningocele. A post-traumatic spinal meningeal diverticulum
may occur in association with any penetrating wound or fracture-dislocation that
disrupts the dura mater and arachnoid.
The diverticulum may increase in size because of the direct
hydrostatic pressure of the CSF it contains. Most of the reported postoperative
diverticula have been in the lower lumbar area, which may simply reflect the
distribution of the original condition that was treated surgically (e.g., a
ruptured lumbar disc) or may also indicate the importance of CSF pressure in the
development of these fluid-filled sacs. As the diverticulum enlarges, it may
compress, distort, or entrap the adjacent neural structures. The resulting
symptoms and signs will vary according to the specific structure that is
compressed. In some cases the CSF enters the diverticulum to such an extent that
when the patient assumes an upright position, postural headaches and even
syncope may result.
If the presence of a postoperative or post-traumatic spinal
pseudomeningocele is suspected, the diagnosis can be verified radiologically.
Myelography with postmyelographic CT is the procedure of choice, but MRI may be
helpful as well.
The key to the management of postoperative meningeal
diverticula is their prevention by avoidance of dural tears and by watertight
closure of dural defects at the initial operation. Closure of such defects with
gelatin sponge, oxidized cellulose, muscle stamps, and the like is far less
effective than the direct reapproximation of the dural edges with sutures. If
prevention fails, the successful treatment of the symptomatic diverticulum is
secondary closure of the dural defect, combined with deflation of the
Spinal Ganglion Cysts and Spinal Synovial Cysts
There are two types of cyst that
arise from periarticular tissue throughout the body. One has a synovial lining
and is called a synovial cyst. The other has no specific lining and is called a
ganglion cyst. Such cysts contain viscid or gelatinous material that can range
from clear and colorless to turbid or grumous and colored (white to brown).
In 1968, Kao et al. reported two
cases of ganglion cyst arising in the extradural periarticular tissues of the
lumbar spine. In 1973, Sypert et al. described a patient with a true synovial
cyst of a facet joint (which was unusual in that it seemed to be post-traumatic
in origin). Since 1968, numerous additional examples of both types of cyst have
Usually the cyst is unilateral
and is located in the posterolateral epidural space, attached to or adjacent to
a facet joint. At times it may be adherent to the ligamentum flavum, or rarely,
within the interspinous ligament. Most often it occurs in the lumbar area
(especially at the L4-L5 level) and comes to medical attention by compressing
one or more spinal nerve roots. Spinal ganglion cysts or synovial cysts have
been described in bilateral locations and in other areas of the spine, but both
situations are unusual.
On myelography a spinal ganglion
or synovial cyst produces a posterolateral extradural mass effect. CT scanning
or MR imaging shows a rounded posterolateral extradural cystic mass that may
contain peripheral calcification. On occasion, such a cyst can be seen to
contain gas, perhaps originating from a facet joint. A cyst that communicates
with the facet joint (synovial diverticulum) can be imaged by vertebral
arthrography, although this technique is not ordinarily required in the
management of the usual case.
The standard treatment of a
symptomatic spinal ganglion or synovial cyst involves the surgical excision of
the cyst. a straightforward operation that usually provides relief. However.
two percutaneous CT-guided approaches to treatment have been reported. The first
involves the opacification of a synovial diverticulum by vertebral arthrography.
followed by the instillation of a corticosteroid preparation. The second
involves the percutaneous biopsy and aspiration of the cyst. It is not yet known
whether such approaches will provide better long-term results than surgical
Miscellaneous Spinal Extradural
Other spinal extradural cysts
are rarely encountered in current neurosurgical practice and are mentioned here
only for completeness. They include multiple posterior diverticula into the
laminae and spinous processes in the lumbosacral region in patients with
ankylosing spondylitis, aneurysmal bone cysts (occurring more often in the
neural arch than in the vertebral body). extradural spinal hydatid cysts t
spinal echinococcosis), etc.
Spinal Intradural Cysts
During the normal development of
the human embryo. a trilaminar germ disc is formed during the third week of
development. The outer layer, the ectoderm faces the amniotic cavity. The inner
layer, the endoderm faces the yolk sac in the opposite direction. Between these
lies the mesoderm. The mesodermal cells that will give rise to the notochord
pass forward from Hensen's node under the ectodermal surface. By the eighteenth
day, the floor of this tubular notochord and the underlying endoderm
disintegrate. The notochordal canal, now known as the neurenteric canal.
connects the yolk sac and the amniotic cavity through the blastopore. Thus there
is a temporary direct connection between the anlagen of the spinal cord, spine
and gastrointestinal tract.
Knowing this, one would predict
that malfunctions at this stage of development might result in combined
anomalies of the spinal cord, spine and gut. In fact, such combined anomalies
have been recognized since the nineteenth century and were classified by Feller
and Sternberg in 1929. In 1960, Bentley and Smith
unified to some degree the previous hypotheses of the origin of neurenteric
malformations, especially those of Feller and Sternberg 1929 and Saunders (
1943), under the label the split notochord syndrome.
On the basis of different
embryologic information. one would expect to occasionally encounter neurenteric
cysts within the spinal canal, and such is the case. Between 1926 and 1972, at
least 47 intraspinal neurenteric cysts (also known as enterogenous cysts,
endodermal cysts, archenteric cysts, gastrocystomas, intestinomas, cystic
teratomas, foregut cysts. etc.) were reported. Wilkins and Rossitch
subsequently reviewed 72 additional cases of a similar nature. Of the 119
patients. 76 were male and 43 were female. In some instances.
abnormalities were noted at birth. The diagnosis was established during the
first decade in 41 (34 percent) patients and in the second decade in 27 (23
percent) patients. Only eight of the patients were 50 years old or older.
Of the 119 cysts. 63 were
totally or partially in the cervical spinal canal. 53 were totally or partially
in the thoracic spinal canal. and 27 were totally or partially in the
lumbosacral canal (cysts at the cervicothoracic junction were counted in both
cervical and thoracic categories. and cysts at the thoracolumbar junction were
counted in both thoracic and lumbosacral categories). The most common cervical
or thoracic cyst location (in 57 cases) was anterior or anterolateral to the
spinal cord, perhaps with intramedullary involvement as well.
Pathologically, these cysts vary
in composition and complexity and form a spectrum that merges with intraspinal teratomas on the one hand and intraspinal dermoids and epidermoids on the other.
The simplest examples of intraspinal neurenteric cysts are those lined by a
single layer of simple. pseudostratified. or stratified cuboidal or columnar
epithelial cells. with or without cilia, lying on a basement membrane and
supported by a layer of more or less vascular connective tissue. Varying numbers
of the epithelial cells can be demonstrated to contain mucin by appropriate
stains. The more complex types have a similar epithelial lining but, in
addition, they have one or more of the other elements found along the course of
the gastrointestinal tract or tracheobronchial tree.
Intraspinal neurenteric cysts
cause the neurological symptoms and signs and the radiologic features one would
expect from any slowly enlarging intraspinal mass. Pain in the affected region
of the spine is a common and prominent symptom. which may be accompanied by
appropriate radicular pain or by meningismus. Unless an early diagnosis is made,
the total course of the illness is usually prolonged over many years, often
marked by remissions and exacerbations.
postmyelographic CT and/or MRI are the best techniques at present for
visualizing intraspinal neurenteric cysts and their coexisting vertebral
abnormalities. In addition, plain roentgenograms and tomograms may add to the
identification and depiction of the vertebral abnormalities. such as anterior or
posterior spina bifida, widened vertebral bodies, fused vertebrae,
hemivertebrae, and diastematomyelia.
The treatment of intraspinal
neurenteric cysts is surgical. They are frequently adherent to the spinal cord
or cauda equina to the extent that complete excision is not feasible. but even
so. evacuation and partial resection of these lesions is usually followed by the
same good results as complete excision. In either case, neurological function
usually improves and recurrence after partial resection may take years to
Epidermoid and Dermoid Cysts
Epidermoid and dermoid cysts are
also dealt with elsewhere. They
account for 0.2 to 2 percent of the primary spinal tumors seen by neurosurgeons.
Among children, however, epidermoid and dermoid cysts comprise 3 to I3 percent
of such spinal tumors. and if only the spinal tumors presenting within the
first year of life are considered. the incidence rises further to 17 percent.
The epidermoid cyst represents
one end of a scale of increasing complexity, with the tridermal teratomas at the
other end. The wall of an epidermoid cyst is composed of a connective tissue
capsule lined by stratified squamous epithelium. The wall of a dermoid cyst is
similar, but also exhibits dermal appendages (e.g.. hair follicles, hair,
sebaceous glands, and occasional sweat glands). In the walls of both types of
cysts, calcium deposits and cholesterol clefts may be found. The connective
tissue capsule of those cysts that are attached to, or are located within. the
spinal cord are frequently surrounded by a zone of reactive gliosis. The cavity
of an epidermoid cyst is filled with white keratinized debris shed from the
epithelial lining. The material in a dermoid cyst also contains hair and
glandular secretions, and because of the latter the cyst contents may be
yellowish with a buttery consistency. More complex cysts lined with stratified
squamous epithelium can also be seen.
The contents of both epidermoid
and dermoid cysts are quite irritating. If such material enters the spinal
subarachnoid space, for example. during a surgical resection of the cyst, it may
produce a sterile meningitis followed by a dense chronic arachnoiditis.
Many of the intraspinal
epidermoid or dermoid cysts that arise "spontaneously" are seen in association
with other congenital anomalies of the spinal cord, the vertebrae and the soft
tissues overlying them posteriorly. Posterior spina bifida occulta is common:
and posterior dermal sinuses. hypertrichosis. and other dermal abnormalities
are also occasionally encountered. Because of these associations, it is thought
that solitary intraspinal epidermoid and dermoid cysts probably occur through an
error in embryologic development, such as the inadvertent inclusion of cutaneous
ectoderm during closure of the neural tube heteroplasia of prospective neural
tissue or deficient closure of the posterior portions of an early neurenteric
However, there is also evidence
that some intraspinal epidermoid cysts (especially multiple lumbar cysts in the
same patient) may have their origin from fragments of skin that are implanted
into the spinal canal. such as by lumbar punctures performed without a stylette
in the needle. This assertion is supported by several types of evidence. First,
the cysts in these cases have rarely been associated with spina bifida occulta.
dermal sinus tracts or other congenital anomalies. Second. the cysts have
frequently been multiple, have virtually always been extramedullary, and have
occurred at the levels of previous lumbar punctures. Third, similar
intraspinal epidermoid and dermoid cysts have been encountered in patients who
have had epidermis implanted into the spinal canal during the surgical closure
of a meningomyelocele. Fourth, it has been shown that fragments of epidermis
will lodge within open needles. And finally, epidermoid and dermoid cysts have
been produced in experimental animals by the introduction of tiny fragments of
skin into the spinal subarachnoid space.
Takeuchi et al. analyzed the reports of 84 intraspinal
dermoids and 114 intraspinal epidermoids from the literature.28 Wilkins and
Rossitch added 24 intraspinal dermoids and eight intraspinal epidermoids from
three other reports. Among the patients whose sex was stated, there were 52
males and 52 females with dermoid cysts, and there were 71 males
and 49 females with epidermoid cysts. Of 104 patients with dermoid cysts, 33
were less than 10 years old and 17 were between 10 and 19 years of age: thus,
about half presented during the first two decades of life. Similarly, of 120
patients with epidermoid cysts, 30 were less than 10 years old and 24 were
between 10 and 19 years of age, again, almost half presented during the first
two decades of life.
Using the same sources, it is apparent that most intraspinal
dermoid and epidermoid cysts involve the thoracic or lumbar area. Only 15 of 108 dermoid cysts and 6 of 122 epidermoid cysts were
located totally or partially within the cervical spine. In contrast, at least 67
of the dermoid cysts and 79 of the epidermoid cysts occurred at or below the
thoracolumbar junction. Of 104 intraspinal dermoids, at least 31 were wholly or
partially intramedullary in location. Of 114 intraspinal epidermoids, at least
31 were wholly or partially intramedullary.
In regard to associated defects,
25 of 100 patients with dermoid cysts and 17 of 85 patients with epidermoid
cysts had posterior spina bifida, and 34 of 100 patients with dermoid cysts and
12 of 85 patients with epidermoid cysts had a posterior dermal sinus tract. When
a patient presents with a dermal sinus tract in the lumbosacral or thoracic
area, it is likely that the tract extends to an intradural congenital tumour.
Among the cases collected by Wright, 11 of 12 sinus tracts in the thoracic
region terminated in such a tumour (9 dermoids. 1 epidermoid, and 1 teratoid
tumour). as did 31 of 72 lumbosacral sinus tracts.
Epidermoid and dermoid cysts
tend to grow slowly within the spinal canal and are usually associated with a
long latent period followed by gradually increasing neurological symptoms and
signs that are appropriate to the specific location of the cyst. Scoliosis may
develop as the cyst enlarges in a child. Frequently, these tumors occur at the
level of the conus medullaris and cauda equina. and in addition to the usual
symptoms and signs may cause lower spinal rigidity accompanied by spinal hyperlordosis. In these cases, pain is produced if the patient attempts to
flatten his back. flex his trunk. or extend his legs. When associated with a
dermal sinus, the cysts are usually diagnosed earlier in life, either through
investigation of the obvious sinus tract or because of repeated bouts of
Plain roentgenograms may reveal
associated vertebral anomalies and will also frequently demonstrate focal
enlargement of the spinal canal with pedicular erosion and scalloping of the
posterior surfaces of the vertebral bodies. In cases in which the cysts are
thought to be of iatrogenic origin from lumbar punctures, plain x-ray films are
more likely to be normal. Ultrasonography, myelography, CT scanning. and MRI
have all proved useful in the diagnostic workup of this lesion.
The treatment of intraspinal
epidermoid and dermoid tumors is surgical, although antibiotics and
glucocorticosteroids may also be necessary for the management of any concurrent
bacterial or chemical meningitis. When a dermal sinus is present, the optimal
treatment is complete excision of the entire tract, utilizing prophylactic
antibiotics. This is usually best accomplished early in life, before infection
has occurred and before any associated intraspinal cyst has reached extensive
proportions. The sinus should not be probed or injected because of the danger of
introducing bacteria or dermal debris into the spinal canal. If infection is
present and there is no significant neurological deficit, operation should be
deferred until the infection has been treated adequately. Since dermal sinus
tracts in the lumbosacral area may lead upward to a cyst within the conus
medullaris, the surgeon should be prepared to follow to that level and to
operate intradurally if this is indicated.
Most intraspinal epidermoid and
dermoid cysts are located intradurally. A large percentage are intramedullary,
but even those which are extramedullary are frequently firmly attached to the
spinal cord or cauda equina. especially if the cyst has been previously
infected. The cyst should be evacuated, with care taken not to spill its
contents into the subarachnoid space. and the accessible portions of the cyst
wall should be excised. It is usually wiser to leave any adherent portion rather
than risk the neurological damage that may result from attempts to dissect it
free. This conservative approach is usually followed by marked and prolonged
improvement. even though the cyst may recur years later.
Diverticula and Cysts
Developmental intradural spinal
arachnoidal diverticula and cysts have been recognized as pathologic entities
since at least 1898. They are composed of normal or slightly thickened arachnoid
and are filled with a clear colorless fluid that is most likely
normal cerebrospinal fluid. There is debate about the origin of these
diverticula and cysts, but it is likely that most arise from congenital
"faults" in the distribution of the arachnoidal trabeculae, especially in the
septum posticum, which divides the posterior spinal subarachnoid space
longitudinally in the cervical and thoracic areas. Despite this apparent
developmental origin. it is unusual for intraspinal arachnoidal diverticula and
cysts to be associated with spinal dysraphism or other congenital anomalies.
They rarely occur in families or as part of a congenital syndrome.
The arachnoidal diverticula are
common anatomic variations that ordinarily cause no symptoms. They are
encountered incidentally. The noncommunicating arachnoidal cysts are much less
common but also are usually located posterior to the spinal cord. This type of
cyst probably originates from the closure of a previously patent diverticulum.
(In the present classification scheme, intradural arachnoidal cysts that form as
a response to inflammation caused by spinal trauma or surgery, by the presence
of blood or a myelographic contrast medium within the subarachnoid space, by
bacterial infection, etc. are grouped in a separate category.) As it expands.
the developmental spinal intradural arachnoidal cyst can cause progressive
spinal cord compression.
The symptoms and signs of a
patient with a noncommunicating intradural arachnoidal cyst typically progress
over several years. Occasionally. kyphoscoliosis will develop as the cyst
enlarges. Sometimes radiographic evidence of enlargement of the spinal canal may
be seen. Myelography and postmyelographic CT demonstrate these cysts as nonfilling mass lesions. MRI is now the procedure of choice for the diagnosis of
an intradural spinal arachnoid cyst.
Wilkins and Odom collected 67
cases of symptomatic developmental spinal intradural arachnoidal diverticula
and cysts from the medical literature through 1971. Of the 66 patients whose
sex was specified, 34 were male and 32 were female. The peak age of occurrence
was in the fifth decade: only four patients presented in the first decade and
only eight in second. Of the 50 cases in which the location of the lesion was
specified. 47 were in the posterior or posterolateral aspect of the spinal
canal. Only three were in an anterior or anterolateral location, and none was
intramedullary. The most common area of the spine affected was the thoracic
region, and the second most common area was the cervical region. Other reports
of similar diverticula and cysts have appeared since 1971.
Treatment ordinarily consists of
a laminectomy with resection of as much of the cyst wall as possible. A portion
of the cyst wall may be fused with or consist of the pia mater, making
attempts at its complete excision unwise. The patient usually improves and it
is unusual for the cyst to recur. However, delayed deterioration of neurological
function after initial improvement may occur, perhaps on the basis of spinal
cord ischemia or spinal instability. If the cyst extends along many spinal
segments is anterior to the cord or recurs after surgical resection, it may be
treated to better advantage by shunting its contents into another space such as
the peritoneal cavity. Whether the cyst wall is resected or the cyst fluid is
shunted, histologic examination of a part of the cyst wall should be performed
to establish the diagnosis, because what appears by gross inspection to be an
arachnoidal cyst may prove to be a neurenteric or neuroepithelial cyst.
Miscellaneous Spinal Intradural
Other more unusual types of
intradural spinal cyst include inflammatory arachnoidal cyst, ependymal
(neuroepithelial) cysts, cystic dilatation of the terminal ventricle, cystic
spinal subdural haematoma, spinal cysticercosis, cystic neurilemoma and spinal
subdural cysts of undetermined type.