The usual spinal meningocele or
meningomyelocele is an obvious posterior protrusion of meningeal-neural elements
out of the spinal canal, most commonly in the lumbosacral area. However, lateral
or anterior spinal meningoceles also occur, albeit much less frequently.
Typically, lateral and anterior meningoceles are occult lesions that are not
visible externally. Yet, patients with these unusual lesions come to medical
attention in characteristic ways, and the diagnosis can be confirmed readily by
myelography and postmyelographic computed tomography (CT) or by MRI, if the
physician simply thinks of it.
An anterior defect can form in
the vertebral column as a result of faulty embryogenesis. Such faulty
development also can result in coexisting abnormalities in the skin,
subcutaneous tissues, spine, and internal organs. For example, when one
considers the close embryologic associations of the caudal end of the spinal
cord, the adjacent notochord, the tailgut, and the cloaca, one can understand
the greater than chance simultaneous occurrence of two or more developmental
defects, such as sacral agenesis, anterior sacral meningocele, imperforate anus,
duplication of the ureter and renal pelvis and duplication of the vagina and
uterus. In like fashion, one or more of these conditions may be associated with
a presacral or sacral epidermoid, dermoid, or teratomatous tumour. One can also
understand how in some instances such associated abnormalities can be found
within the same family, apparently transmitted genetically.
Another important factor that
can influence the development of anterior and lateral spinal meningoceles is the
balance between both the hydrostatic pressure and the pulsations of the
cerebrospinal fluid (CSF), and the resistance of the arachnoid and dura mater to
deformation by such pressure, especially at the intervertebral foramina. If
there is a developmental bony defect in the sacrum, the dura and arachnoid may
bulge out through it. especially since the hydrostatic pressure of the CSF at
this level is increased when the individual is sitting or standing. von
Recklinghausen's disease can lead to both bony dysplasia and dural ectasia,
permitting the development of a meningocele at an intervertebral foramen,
particularly in the thoracic area. Similarly, Marfan's syndrome can also result
in dural ectasia and a lateral meningocele.
As a generalization. an anterior
vertebral meningocele may be viewed as the result of an embryologic
malformation, and a lateral vertebral meningocele as the result of structural
weakness related to dysplasia. especially in the setting of neurofibromatosis or
Marfan's syndrome. Occasionally, an anterior or lateral spinal meningocele
results from trauma or surgery. These are actually, however. pseudomeningoceles
formed by a connective tissue response to cerebrospinal fluid that has escaped
through a tear in the arachnoid and dura mater, they are dealt elsewhere.
Anterior (Lateral) Sacral
Meningocele; Intrapelvic Meningocele
The first such lesion was
recognized in 1837, and more than 227 were reported in the medical literature
through 1988. Anterior sacral meningoceles have been discovered in women almost
three times as often as in men. Of the patients reported through 1988 for whom
the sex was specified, 165 were female and 60 were male (an 8: 3 ratio). In
women, this type of meningocele has been diagnosed primarily during the
childbearing years, and especially during the third decade of life; in males,
the diagnosis has been made primarily during the first decade.
An anterior sacral meningocele
is a unilocular or multilocular extension of the dura mater and arachnoid out of
the sacral spinal canal into the retroperitoneal and infraperitoneal space,
either anteriorly through the body of the sacrum or anterolaterally through an
enlarged intervertebral foramen or coalesced foramina. It contains CSF, which in
some of the reported cases has been discolored slightly yellow and has had an
elevated protein content. Its wall is composed of fibrous connective tissue,
which may contain some of the adjacent sacral nerve fibers and which
occasionally contains poorly differentiated neuroglial tissue. It may be covered
by a network of epidural veins.
The anterior sacral meningocele
is accompanied by some type of bony defect in the anterior surface of the
sacrum, varying in severity from an enlarged intervertebral foramen to complete
agenesis of the lower sacrum and coccyx. Usually the first and second sacral
segments are spared, and the bony pelvic ring remains intact. The most
distinctive sacral abnormality is a lateral defect in the lower sacrum that is
accompanied by a sickle-shaped deformity of the remaining sacrum and coccyx.
This is sometimes referred to as a scimitar sacrum because of the resemblance to
In cases reported through 1988
in which the side of the anterior sacral defect was specified, 70 occurred
solely or primarily on the right side, 49 on the left side, and 24 in the
midline or in bilateral 10cations.l~ The pedicle of the anterior meningocele is
often smaller in diameter than the bony defect, but it involves the same portion
of the sacrum.
Other vertebral abnormalities,
such as hemivertebra and posterior spina bifida also occur occasionally in
association with an anterior sacral meningocele. A posterior bony sacrococcygeal
defect is common, usually in the same general location as the anterior defect,
but through 1971 a coexisting intrasacral meningocele had been described in only
two cases, and a posterior sacral meningocele in just one case.
It must be pointed out, however,
that partial or total sacral agenesis may occur in the absence of an anterior
sacral meningocele, and is itself frequently associated with neurological
deficits in the distribution of the sacral nerves with posterior
myelomeningocele and other vertebral anomalies. and with congenital
abnormalities in the genitourinary apparatus, rectum and anus. The combination
of sacral agenesis and a presacral mass does not always mean an anterior sacral
meningocele. Similarly, an anterior vertebral defect (anterior spina bifida) may
occur at any level of the vertebral column without an anterior meningocele; it
may instead be accompanied by a neurenteric or enterogenous cyst.
Among the other
abnormalities exhibited by 227 reported patients with anterior sacral
meningocele, there were 25 instances of anal atresia or stenosis or an
imperforate or covered anus ( 11.0 percent); 24 instances of a presacral or
sacrococcygeal epidermoid, dermoid or teratomatous tumour ( 10.6 percent):
17 instances of a bicornuate or double uterus (7.5 percent); 13 instances of
duplication of the renal pelvis or ureter (5.7 percent) and 8 instances of
vaginal duplication (3.5 percent). Four patients (1.8 percent) had
neurofibromatosis and five (2.2 percent) had Marfan's syndrome or a
Most of the reported cases
haw been sporadic. but familial occurrence also has been reported. For
example. Thomas et al. reported 10 documented cases of anterior sacral
meningocele within five generations of one family. Yates et a!. reported a
family in which 11 members of three generations had partial sacral agenesis
and either an anterior sacral meningocele (5) a presacral teratoma (4). or
Because of its occasional
appearance in infancy and its frequent association with other congenital
defects in adjacent tissues, the anterior sacral meningocele is thought to
arise as an embryologic maldevelopment of the anterior bony sacrum and
meninges. The meningocele may then enlarge with time, probably as the result
of the hydrostatic pressure of the CSF within it. This enlargement, if it
does occur, is usually slow, and the meningocele may not give rise to
symptoms until adult life.
As it develops, the anterior
sacral meningocele compresses the rectum, uterus and bladder from behind and
becomes a spaceconsuming mass within the pelvis. It may also extend up into
the abdomen, pushing the peritoneum ahead of it, and may bulge out in the
retroanal region. Rarely, the meningocele may extend out o( the pelvis
posteriorly into the gluteal area through the greater sciatic foramen.
In 14 of 122 reported cases
cited by Wilkins and Odom in 1978, the patient was brought to medical
attention because of an abdominal mass in 5 because of a retroanal or pelvic
mass, and in 3 because of a gluteal mass. In virtually all of the 122 cases,
a retrorectal pelvic mass was detected by pelvic or rectal examination, but
the patient was usually not aware of the presence of the mass per se.
The symptoms experienced by
female and male patients are similar (e.g. constipation or difficult
defecation; pain in the low back, pelvis or abdomen; urinary frequency or
obstruction; or a mass in the abdomen, perineum or buttock). However, in
addition, some women experience dystocia or menstrual irregularities, and it
is not uncommon for an intrapelvic meningocele to be discovered during
pregnancy or childbirth.
The presence of an anterior
sacral meningocele may be suspected in a patient presenting the symptoms
listed above, especially if a congenital abnormality of the genitourinary
apparatus or anus is also present. Physical examination will add further
evidence if a presacral cystic mass can be detected by pelvic and rectal
examination. and radiographic evaluation of the sacrum will then virtually
establish the diagnosis if an anterior sacral defect can be demonstrated.
However, the coexistence of
a cystic presacral mass with a defect in the bony sacrum does not guarantee
that the lesion is an anterior sacral meningocele. A variety of symptomatic
cystic tumors, many of them congenital in origin, may develop between the
sacrum and rectum. And furthermore, these tumours may be associated with
abnormalities in the adjacent pelvic viscera and with defects in the
anterior surface of the sacrum.
pyelography, cystography, proctoscopy, barium enema examination and hysterosalpingography have all been employed as diagnostic aids in cases of
suspected anterior sacral meningocele. These tests may verify the location
and size of the lesion and document its pressure effects on the adjacent
pelvic viscera. and they may demonstrate the presence of associated
abnormalities in the genitourinary system and rectum, but they do not
establish the diagnosis of meningocele.
Aspiration of the presacral
cyst has also been used on a number of occasions, but this procedure involves
a significant risk of meningitis, especially when performed through the vagina, rectum
or perineum. Myelography with postmyelographic CT scanning
is the one test that, more than any other, will verify that a presacral mass
is a meningocele (or myelomeningocele). This may be performed with either a
positive or a negative contrast medium. In the cases in which a very narrow
pedicle connects the meningocele sac with the subarachnoid space, a positive
contrast medium and delayed filming may be necessary to demonstrate filling
of the sac. MRI and ultrasonography can also be used to visualize an
intrapelvic meningocele. but they will not demonstrate the bony anatomy as
well as CT myelography and may not document the anatomic and physiologic
connection between the sacral subarachnoid space and the meningocele.
The anterior sacral
meningocele is one of the few remediable developmental malformations of the
CNS, but attempted treatment may result in death if it is not properly
performed. Since this type of meningocele usually causes symptoms, involves
relatively young and healthy individuals, and tends to enlarge with time,
its surgical correction is ordinarily justified. However, among the first 13
reported patients who were treated by aspiration or surgical resection, nine
died (primarily of meningitis), two recovered from meningitis, and only two
were cured. Even in recent years, mistakes in management have occasionally
resulted in unnecessary morbidity and mortality. The most common mistake is
that the true nature of the anterior sacral meningocele is not recognized
until it has been aspirated, often through a contaminated area. or exposed
surgically. An awareness of the condition and radiologic proof of its
existence will prevent this error.
Sacral laminectomy with
aspiration of the meningocele through its pedicle, followed by closure of the
pedicle, is an excellent method of treatment if the meningocele pedicle is small
enough and the dura mater is firm enough to permit a water-tight closure.
Otherwise the meningocele will refill.
Exposure of the meningocele sac
by an abdominal or retroanal approach may allow a better closure of the pedicle
since the walls of the pedicle and sac can be used to bridge larger defects. But
an abdominal or retroanal operation is somewhat more difficult for at least
three reasons: the sac of the meningocele is often closely adherent to the
rectum, and the surgical separation of the two is somewhat hazardous because of
the risk of bacterial contamination if the rectal wall is inadvertently opened;
the epidural veins over the sac may cause annoying or dangerous bleeding during
or after the operation; and the blood or serum that collects in the presacral
space left after the meningocele has been excised is an excellent culture medium
for the bacteria that may enter from the rectum or through postoperative drains.
It seems that the most logical
surgical treatment involves the water-tight closure of the meningocele pedicle.
by whatever approach (including endoscopy), with prior aspiration but not
excision of the meningocele sac. This should be performed with strict aseptic
technique, and surgical drains should be avoided.
Lateral or Anterior Lumbar
Through 1987, only about 21
lateral or anterior lumbar meningoceles had been reported. In general,
these fall into two categories. The first type is a single large
retroperitoneal meningocele that presents as an abdominal or lumbar paravertebral mass, frequently in an infant or young child and that usually is
associated with other congenital anomalies, especially involving the spinal
column at the level of the meningocele. The second. more common, type is a
lateral lumbar meningocele that involves a relatively small meningeal herniation
or herniations, at one or several levels on one or both sides, causing back or
loin pain in an adolescent or young adult, who may have neurofibromatosis.
Perhaps in these second cases an underlying weakness in the vertebral bones and
connective tissues allows a gradual herniation of the meninges to occur under
the influence of CSF pressure.
Among the 21 patients reviewed
by Wilkins and Rossitch, the main meningoceles were right-sided in 10 patients,
left-sided in 5. and bilateral in 4. Additional vertebral abnormalities were
present in at least 12 of the 21 patients. Of the 21 patients, 8 presented
during the first decade of life. and 3 during the second decade; among these 11
patients, only one had neurofibromatosis. In contrast, among the 10 patients who
presented after the age of 20, 7 had neurofibromatosis. Overall, the patient's
sex was given for 19 patients: 12 were female and 7 were male.
As is true with the intrapelvic
meningocele. plain roentgenograms. ultrasonography. and MRI are useful in
establishing the diagnosis. but the key diagnostic test is myelography combined
with postmyelographic CT. If the symptoms are sufficient to justify surgical
treatment, either an anterior or posterior approach can be made, with the goal
being a water-tight closure of the neck of the meningocele.
Lateral or Anterior Thoracic
Meningocele; Intrathoracic Meningocele
More than 150 cases of
intrathoracic meningocele have been reported since 1933. One hundred such cases
were reviewed in 1978, and 45 more were collected from the literature through
1988. An intrathoracic meningocele is
a unilocular or multilocular herniation of the dura mater and arachnoid out of
the spinal canal into the retropleural space in the region of the posterior
mediastinum. The lateral meningocele typically exits from the
spinal canal through a single enlarged intervertebral foramen or two coalesced
foramina. whereas the less common anterior meningocele extends through or
between the vertebral bodies.
When a kyphoscoliosis is
present, the lateral meningocele usually arises at the apex of the deformity.
on its convex side. Of 137 cases of intrathoracic meningocele compiled by
Wilkins and Odom and Wilkins and Rossitch for whom lateralization data were
available, 66 were on the right. 52 were on the left. and 13 were bilateral. The
remaining 6 extended anteriorly in the midline. At least 99 of the total group
of 145 patients had a single intrathoracic meningocele. The meningoceles were
fairly evenly distributed from T1 to T12.
With time. the intrathoracic
meningocele usually increases in size. This has been well documented in at least
20 cases by repeated roentgenograms of the chest over periods ranging from 2
months to 28 years. If the lateral thoracic
meningocele does enlarge, it usually erodes the ipsilateral bony structures
adjacent to the intervertebral foramen, such as the posterior and lateral
aspects of the vertebral bodies, the pedicles, the transverse processes and the
ribs immediately superior and inferior to the foramen. It also stretches the
adjacent nerves and vessels over its dural surface. In addition. the vertebral
canal and the proximal intercostal space may be widened at the level of the
The meningocele finally assumes
the form of a mushroom with a narrow stalk (pedicle) and a rounded intrathoracic
sac. The wall of the sac is covered by parietal pleura. It is composed of dura
mater and arachnoid with varying numbers of epidural veins. intercostal nerves, intercostal vessels and sympathetic chains coursing between the pleura
and dura. Occasionally a neurofibroma is also present in the wall of the
meningocele. The sac is filled with CSF that
usually communicates freely with the spinal subarachnoid space. However, in two
of the reported cases, the fluid within the sac had a yellow or brown tint.
In 1979. Erkulvrawatr et al.
reviewed 88 cases of intrathoracic meningocele and found that 75 (85 percent) of
them had evidence of neurofibromatosis. In one review of 145 cases, at least 89
(61.4 percent) of the patients with intrathoracic meningocele also had cutaneous
neurofibromatosis. This figure may be compared to the incidence of
neurofibromatosis among 227 patients with intrapelvic meningocele (1.8
percent). 2I patients with lateral or anterior lumbar meningocele (38 percent).
and 5 patients with lateral or anterior cervical meningocele (60 percent).
Vertebral abnormalities not
ordinarily associated with neurofibromatosis were present in a few of the
reported patients with intrathoracic meningocele. Anomalies were noted
occasionally in a number of other organ systems as well, but not to the same
extent as in patients with an intrapelvic meningocele. In the majority of cases. the
lateral thoracic meningocele appears to be a gradual outpouching of the dura
mater and arachnoid through a weakened area in the vertebral column. This
weakening seems to be due to a regional dysplasia related to neurofibromatosis,
but its exact nature remains a subject for debate.
In a few of the reported cases.
in which the intrathoracic meningocele was discovered during infancy or was
noted to project anteriorly in the midline, it seems more likely that the
meningocele was a congenital malformation similar to a posterior meningocele. In
these patients there was no evidence of neurofibromatosis and at least four of
them had other congenital anomalies.
Of the reported cases of lateral
or anterior thoracic meningocele in which the patient's sex was specified. 85
(60.7 percent) were females and 55 (39.3 percent) were males. The peak age
at diagnosis for both sexes was in the fourth and fifth decades.
Many patients with intrathoracic
meningoceles are asymptomatic. Of the 100 patients reviewed by Wilkins and
Odom 40 had no symptoms. The presence of a mass in the chest was detected
by chest roentgenograms made in conjunction with a preemployment physical
examination as a routine study during hospitalization or for some other
unrelated reason. Another 30 patients had chest or back pain, which was often
radicular in nature (probably due to the distortion of the intercostal nerves
adjacent to the meningocele). Symptoms of pulmonary compression (dyspnoea,
cyanosis) were present in 17 cases and cough in 7. Although many of the
patients had some degree of kyphosis or scoliosis, this was the presenting
symptom of eight patients. Myelopathy or leg weakness was present in 11 cases,
but these did not seem to be caused by the meningocele itself.
Intraspinal neoplasms of various
kinds develop occasionally in patients with neurofibromatosis. Among these is a
dumbbellshaped neurofibroma or schwannoma having intrathoracic and intraspinal
masses connected by a cylindrical stalk that lies within (and expands) an
intervertebral foramen. In many of the reported cases of intrathoracic
meningocele. the meningocele was thought initially to be this type of tumour
until myelography or thoracotomy was performed.
Diagnosing an intrathoracic
meningocele usually involves establishing the true nature of a symptomatic or
asymptomatic posterior mediastinal mass that has been demonstrated by a
roentgenogram of the chest. A wide variety of neoplasms and cysts occur in this
location, some of which may be encountered in association with von
Percutaneous aspiration of the
intrathoracic mass. with analysis of the contained fluid and with the
introduction of a positive or negative contrast medium for roentgenographic
examination will confirm the diagnosis of a meningocele. However, it is
ordinarily easier and safer to establish the diagnosis by myelography aided by
postmyelographic CT scanning. MRI is also a useful diagnostic procedure.
Intrathoracic meningoceles are
often asymptomatic, so the fact that one exists does not necessarily mean that
it should be treated. The probability of its gradual enlargement with time and
the possibility that it may cause pain and dyspnoea must be weighed against the
risks of anaesthesia and surgery. which may be significant in a cachectic patient
with severe kyphoscoliosis and poor pulmonary ventilation.
If surgical correction of the
meningocele is decided upon, the surgeon's primary goal should be the closure of
its pedicle. This is usually easier to perform from an anterolateral approach
via thoracotomy or from a posterolateral approach than by means of a
laminectomy. It is usually also feasible to excise the sac of the meningocele,
but, of course care must be taken not to injure important adjacent structures.
For example, if the sympathetic chain is damaged in a high thoracic meningocele.
a Horner syndrome may result.
Lateral or Anterior Cervical
In their 1978 review, Wilkins
and Odom could find no reports of such lesions. Between 1978 and 1986. at
least four cases were documented. In addition, a case originally categorized
in 1976 as a meningeal diverticulum along the left C7 nerve root can be
classified as a lateral cervical meningocele. In all five cases, these were
lateral meningoceles. As with the intrathoracic meningoceles, they involved
females more often than males (3: 2) and the right side more often than the left
(3:1). Three of the five patients had evidence of von Recklinghausen's
neurofibromatosis, and in these cases there were multiple lateral meningoceles.
Spinal meningoceles and
meningomyeloceles most often occur as posterior lesions that are obvious at
birth. However, a meningocele may form at a lateral or anterior defect in the
vertebral column. The lateral defect ordinarily involves a single intervertebral
foramen or coalesced adjacent foramina. The anterior opening usually represents
a developmental defect in one or more vertebral bodies and intervertebral discs.
Patients with lateral meningoceles often have neurofibromatosis, and those with
anterior vertebral defects often have other associated embryologic
Overall, female patients are
more often affected than male patients [8: 3 in the sacral region; 3:2 in the
lumbar, thoracic, and cervical regions; roughly 11:5 overall (265: 124)]. More
of the meningoceles are on the right (149) than on the left (107) or in the
midline (25). Although the majority are solitary lesions, many patients have
multiple unilateral or bilateral meningoceles. Among the cases surveyed, the
incidence of neurofibromatosis ranged from 1.8 percent of the patients with an
intrapelvic meningocele, to 38 percent of those with a lateral lumbar
meningocele, to 60 percent of those with a lateral cervical meningocele. to 61
percent of those with an intrathoracic meningocele.
In general, lateral and anterior
meningoceles gradually enlarge with time. The diagnosis can be verified easily
by myelography. In the individual case, the decision about surgical treatment
must be based on the severity of the symptoms and signs. the likelihood of
clinical progression, and the risks posed by the operation. The key to
successful surgical treatment is a water-tight closure of the meningocele
pedicle. If that can be achieved, the symptoms and signs caused by the mass
effect of the meningocele often can be relieved.