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History
Walter Dandy was the first to
undertake a scholarly analysis of surgery in the pineal region. His
supratentorial parafalcine approach to the pineal region was the culmination of
extensive studies first performed on animals. The exact head position that he
used is unclear from his writings, but it seems that some operations were done
in a semi-sitting position while others were done with the hemisphere on the
side of the approach uppermost, retracted against gravity. Once the pineal
region was reached, he sectioned the corpus callosum and dissected the deep
venous system, which unfortunately often resulted in venous damage and central
brain edema. Without an operating microscope, steroids, and sophisticated
anesthesia the surgical mortality rate was prohibitively high. Other, just as
illustrious, neurosurgeons of that era dismissed the feasibility of operative
intervention for pineal tumors because of the technical difficulties encountered
and the probability that most of these tumors could not be removed totally
because of their malignant and invasive characteristics.
It is remarkable that before
Dandy's numerous efforts to surgically treat pineal tumors. Krause (1926)
operated on three patients with lesions in the area of the pineal gland which
were probably astrocytomas (perhaps one was a teratoma). He had no operative
mortality and the operations were done through the posterior fossa over the
cerebellum. Considering the limited instrumentation, lack of microscope or good
lighting and suboptimal anesthesia, these were operative triumphs.
Since that time a number of
different approaches have been advocated, including those around the occipital
lobe and over the tentorium as described by Poppen. The approach through a
dilated lateral ventricle proposed by Van Wagenen was difficult and never gained
wide acceptance. The continued difficulty in achieving successful surgical
results led to a more conservative approach for pineal region tumors consisting
of the insertion of a shunt for hydrocephalus and radiotherapy for presumed
malignancy. Unfortunately, this resulted in numerous articles containing
anecdotal information and an excellent opportunity was lost to study the natural
history of the wide variety of tumor types in the pineal region.
In the 1970s, the increasing use
of the operating microscope rekindled interest in direct surgical approaches to
the pineal region. Both Japanese and American neurosurgeons were active in this
and there was considerable debate as to the best surgical route to the pineal
region. The more important issue, however, was not the route but the fact that
these debates stimulated interest in operating on such tumors to identify their
nature and remove them whenever possible. The most recent development has been
the use of stereotactic biopsy as another option for obtaining tissue for
histologic diagnosis.
Because of these more aggressive
approaches to pineal region tumors, several principles became evident that are
now used to guide the management of pineal region tumors. It is now known that
pineal tumor types exist along an extensive continuum of histologic variance
from benign to highly malignant. Some of these tumors are mixed in nature,
simultaneously containing benign as well as malignant elements or even glial and
pineal cell constituents. The diagnosis from small specimens is often difficult,
even for an experienced pathologist. Despite the advances in radiographic
imaging and increased experience with tumor markers, these preoperative
diagnostic tests are insufficient and accurate determination of histologic
typing requires operative intervention.
Patient Selection
Surgery is indicated for all
patients with symptomatic pineal region masses or patients who are asymptomatic
but have aqueductal compromise and hydrocephalus. This is based on the
assumption that the histologic diagnosis cannot be made without operation and
that open operation provides the best method for dealing with the tumor and
removing it if possible.
Although stereotactic biopsy has
been advocated by some as an initial procedure, it is generally not suitable for
most pineal region tumors for the following reasons:
1. If removal can be
accomplished, then it is best done at the primary operation.
2. Bleeding, if it occurs, can
be controlled better by open operation.
3. A sufficient specimen can be
obtained by open operation, whereas this may not be feasible by stereotactic
biopsy. Frozen tissues are studied by both methods, but the larger specimen
obtained by open surgery makes the identification easier for the
neuropathologist.
4. With modern neurosurgical
techniques, open operations are reasonably safe.
5. Surgical debulking, even
without complete removal, can haw a beneficial effect on the response to
adjuvant therapy.
Because of the relative ease and
safety of stereotactic biopsy, it is generally reserved for those patients who
present with obvious tumor dissemination at the time of diagnosis or those whose
major medical problems contraindicate an open surgical procedure.
With the increasing use of
computed tomography (CT) scanning and especially, magnetic resonance imaging
(MRI), we are now encountering a substantial group of patients with lesions of
the pineal gland that are mostly cystic but contain a small amount of solid
tissue. In most cases the aqueduct has not been compromised and the patients are
not symptomatic from their lesion. Initially such lesions were considered to be
low-grade cystic astrocytomas but, after surgical removal, they were found to be
composed of normal astrocytes and normal pineal cells. Histologically these are
pineal cysts and are normal anatomical variations of the pineal gland. As our
experience with pineal cysts has increased, it is clear that they should be
managed conservatively with serial MRI scans and without surgery. Surgery is
reserved for lesions that are symptomatic, progressing in size or causing
aqueductal obstruction.
Mortality has been most frequent
among a group of highly cellular and extremely vascular malignant pineal cell
tumors. These tumors can sometimes present with an apoplectic spontaneous
haemorrhage. During surgery, obtaining haemostasis can be difficult and
postoperative haemorrhage often accounts for an unfavourable outcome associated
with this group of tumors. The use of stereotactic biopsy has been no less
successful in dealing with this problem. There is hope that specific tumor
markers may be developed that can identify these tumors non invasively to avoid
such complications.
Diagnosis
The standard diagnostic workup
includes CT and MRI scans without and with the administration of a contrast
agent and measurement of beta human chorionic gonadotropin and alpha fetoprotein
in both the serum and the cerebrospinal fluid (CSF). MRI has proven to be the
most accurate diagnostic examination and provides information on tumor
characteristics and the anatomic relationships of the tumor with its
surroundings. Angiography is only performed if the MRI suggests a vascular
lesion such as a vein of Galen aneurysm or arteriovenous malformation. However,
despite this broad diagnostic armamentarium, the exact histologic nature of the
tumor cannot be determined reliably with surgery.
Certain tumors can be suspected
from the appearance of the scans, particularly teratomas that contain multiple
germ layers. The radiographic workup does provide relevant information about the
following:
1. Size of the tumor, especially
its lateral and superior extent.
2. Vascularity of the lesion and
the nature of its contents (whether homogenous or heterogeneous).
3. Irregularities of margination
and the probability of invasion.
4. Most importantly, the
anatomic relationships of the tumor and the surrounding structures. These
include tumor involvement of the third ventricle and its position within the
third ventricle, extension of the tumor into or above the corpus callosum,
superior-lateral extension of the tumor into the region of the ventricular
trigone, involvement or compression of the quadrigeminal region and aqueduct by
the tumor relationship of the tumor to the anterior cerebellar vermis, and
location of the deep venous system.
Anatomy
The vast majority of tumors
arise in the region of, and are attached to, the undersurface of the velum
interpositum, which includes the choroid plexus, deep venous system, and
choroidal arteries. If the tumor invades these important midline
structures, the attachment may be minimal or extensive. Tumors rarely extend
above the velum interpositum for any significant distance. Therefore, the blood
supply comes from within the velum interpositum, mainly through the posterior
medial and lateral choroidal arteries, with an anastomosis to the pericallosal
arteries and quadrigeminal arteries.
Some tumors extend to the
foramen of Monro, but most are centered at the pineal gland, extending
anteriorly to the midportion of the third ventricle and posteriorly to compress
the anterior portion of the cerebellum. In rare instances, the internal
cerebral veins are ventral to the tumor and this can be recognized through the
MRI. Mostly, however, the vein of Galen, internal cerebral veins,
basal veins of Rosenthal and precentral cerebellar vein surround or cap the
periphery of these tumors. The quadrigeminal plate may give rise to an exophytic
astrocytoma or be infiltrated by the more malignant tumors of the pineal region,
encompassing the aqueduct in the course of tumor growth. Most tumors are not
highly vascular, with the exception of malignant pineocytomas,
hemangioblastomas and hemangiopericytoma. The most important aspects of the
anatomy, which can be gleaned by radiologic imaging, are the relationship of the
tumor to the third ventricle and quadrigeminal cistern, and the lateral and
superior extent of the tumor. These features determine the route of the
operation and the degree of difficulty that may be encountered during surgery .
Hydrocephalus
Most patients present with
hydrocephalus. It is generally preferable to place a ventriculoperitoneal shunt
3 to 7 days prior to the definitive tumor surgery to allow the ventricles
sufficient time to gradually decompress. Although ventriculoperitoneal shunting
carries the risk of peritoneal seeding in the presence of malignant pineal
tumors, this occurs only rarely. On occasions where a complete tumor removal
is anticipated and a permanent shunt may not be necessary, the hydrocephalus can
be managed with a ventricular drain placed at the time of tumor surgery. This
ventricular drain can be removed or converted to a permanent shunt on
postoperative day 2 or 3, depending on which circumstances prevail.
Surgery
Operative Considerations
Common approaches to the pineal
region include infratentorial supracerebellar, occipital transtentorial and
transcallosal interhemispheric approaches. The best approach to use depends on
the anatomic location or spread of the tumor, along with a degree of familiarity
and confidence that the surgeon has with a given approach.
The
infratentorial supracerebellar approach is most commonly used for several reasons:
1. The approach is to the center
of the tumor, which begins at the midline and grows eccentrically.
2. The approach is ventral to
the velum interpositum and the deep venous system. to which the tumor is often
adherent. This minimizes the risk of damage to the vascular drainage of this
critical region.
3. The exposure in the sitting
position is comparable to that of other routes.
4. No normal tissue is violated
on route to the tumor.
5. If the tumor is not removed completely, a shunt
catheter can be placed from the third ventricle, over the cerebellum, to the
cisterna magna as a modification of Torkildsen's procedure. If the incisura is
not blocked by tumor, this may be sufficient to control hydrocephalus.
Either the transcallosal
interhemispheric or occipital transtentorial approach is used under the
following circumstances:
1. Tumors that extend
superiorly, involving or destroying the posterior aspect of the corpus callosum
and deflecting the deep venous system in a dorsolateral direction.
2. Tumors that extend laterally
to the region of the trigone.
3. In rare cases where the tumor
displaces the deep venous system in a ventral direction (often seen with
meningiomas).
Under these circumstances the
transcallosal interhemispheric approach can provide extensive exposure,
although the subtentorial portion of the tumor on the contralateral side of the
approach is not easily visualized. This approach requires retraction of the
parietal lobe and the disruption of bridging veins between the parietal lobe and
the sagittal sinus, creating the potential for venous infarction and retraction
injury. Additionally, the veins of the deep venous system usually overlie the
tumor, forcing the surgeon to work around them to avoid injury. Like the
transcallosal approach, the occipital transtentorial approach has the
disadvantage of encountering the deep venous system overlying the tumor, but
usually there are no draining veins to the SSS. Once
the tentorium is divided, however, this approach permits a wide view of the
pineal region with particularly good visualization of the quadrigeminal plate.
A major drawback is the high frequency of visual field deficits associated with
this approach.
Various positions have been
described for these approaches. The sitting-slouched position is used most often
for the infratentorial supracerebellar and occipital transtentorial
approaches. This position enables gravity to work in the surgeon's favour by
helping tumor dissection from the roof of the third ventricle and minimizing
blood pooling in the operative field. It does carry the risk of venous air
embolism, and of ventricular and cortical collapse with the subsequent
collection of blood or air in the subdural space. However, with proper
precautions these complications are infrequent. The occipital transtentorial
approach often utilizes the three-fourths prone-lateral decubitus position,
which, although avoiding many of the complications of the sitting position, does
not allow gravity to work in the surgeon's favour. The Concorde position was
developed to combine aspects of both the prone and semi-sitting positions but
still has the disadvantage of blood pooling in the operative field.
Infratentorial Supracerebellar
Approach
The infratentorial
supracerebellar approach is a modification of the technique proposed by Krause,
the approach being made through the posterior fossa over the cerebellum. The
position of the patient is critical to the smooth performance of this operation.
The patient is placed in a sitting-slouched position with the head flexed and
held forward by a pin-vise type of head holder so that the body conforms to a
C-configuration. The aim is to position the patient's tentorium as close to the
horizontal as possible.
Because of the depth of the
exposure and the need for magnification and proper illumination, the operative
microscope is essential to this operation. The angled eyepieces are reversed
and a 275-mm objective is the most utilitarian. To avoid fatigue. armrests are
needed for the surgeon, who is seated during the operation.
A midline incision is used and a
craniotomy is performed, leaving the foramen magnum intact but extending at
least to the upper edge of the transverse sinuses and torcular to allow slight
upward retraction upon the midline of the tentorium. If a craniotomy is to be performed, the
sinuses must first be exposed before the bone over them is traversed with the craniotome.
The cerebellum must be
completely relaxed, without any dural tension. This can be accomplished by
mannitol administration, shunt insertion or ventricular drainage. The dura is
opened in a three-flap fashion and the upper flaps are reflected upward. The central flap is the most critical to maximizing exposure. This
allows visualization of the upper surface of the entire cerebellar hemispheres
and vermis. The bridging veins across the upper surface of the cerebellum are
cauterized and divided to relax the cerebellum. We have not encountered oedema or
permanent cerebellar damage from interrupting these numerous bridging veins.
Once the veins are divided. the cerebellum drops down because of gravitational
forces. After protecting the superior surface of the cerebellum with cottonoid, one self-retaining retractor is placed over the
vermis, pulling it posteriorly and inferiorly. The operating microscope is
brought in at this point and is initially angled upward. An irrigating system
using an 18-gauge spinal needle on the retractor arm is directed to the pineal
region and connected to a syringe containing irrigating solution.
With the operative microscope in
place, the rostral portion of the vermis is visualized. The
arachnoid of the quadrigeminal cistern is often thickened in the presence of
tumor and must be opened widely. while damage to the precentral cerebellar vein
is avoided. This vein is usually in the midline but can be rostral, caudal or
displaced to one side. It is easily identified as the thickened arachnoid is
opened. The arachnoid is opened close to the cerebellar edge: this opening is
then extended laterally and the free edge of the tentorial incisura is pursued.
This exposes small arteries of the choroidal group supplying the posterior
surface of the tumor. Laterally, the large veins of Rosenthal are also exposed.
At this point the microscope
trajectory is modified horizontally or angled slightly downward to avoid opening
the vein of Galen. Cauterizing and dividing the precentral cerebellar vein will
expose the large posterior surface of the tumor. With further opening of the
arachnoid and cauterization of the choroidal arteries to the tumor, the exposure
becomes quite generous. The retractor is moved forward to retract the anterior
vermis downward and posteriorly. If the tumor is large, the quadrigeminal plate
may be obscured. The tumour's vascularity and degree of encapsulation should be
noted and a biopsy taken for frozen-tissue analysis. If the tumor is cystic, its
contents may be aspirated with a spinal needle to further decompress the area.
If a further superior view is required, a retractor may be placed under the
tentorium to elevate it slightly using a self-retaining system.
For tumor removal, we use a
group of instruments that have been modified to be longer than normal. These
include cautery forceps, dissectors, suction tips. the long-curved tip of the
ultrasonic aspirator, tumor forceps and transsphenoidal instruments. Depending
on the composition of the tumor, it may be decompressed internally with tumor
forceps, suction and cautery, or the ultrasonic aspirator. With gradual
decompression of an encapsulated tumor, the margins may be folded into the
decompressed area, The superior borders are often adherent, sometimes invading
the velum interpositum. These connections must be cauterized and divided without
injuring the deep venous system. Inferiorly, the quadrigeminal plate tends to
remain obscure and is difficult to expose or dissect from the tumor. Gravity is
now working against the surgeon at this point and the tumor must be lifted with
either suction or tumor forceps to develop this plane if feasible. With further
tumor removal, the interior of the dilated third ventricle is exposed. The tumor
may be attached to the wall of the third ventricle. specifically the medial
nuclei of the thalamus and the pulvinar. Occasionally there is dense attachment
to the quadrigeminal plate. In benign and encapsulated tumors, attachment is
rarely a problem and a complete resection is usually possible. At the completion
of tumor resection, haemostasis is secured with cautery and various
haemostatic agents.
The dura is closed in as
water-tight fashion as possible to avoid extradural CSF accumulation and pseudo
meningocele formation. The muscles and fascia are closed in appropriate layers.
The patient is extubated and sent to the intensive care unit in a semi-sitting
position.
Transcallosal Interhemispheric
Approach
When a supratentorial approach
is desirable, the patient is operated on in the sitting-slouched position with an
approach from the non-dominant posterior parietal region. A parietal craniotomy
is performed, extending across the midline. The dura is opened in a U-shaped
fashion and flapped toward the superior sagittal sinus. The hemisphere is
separated from the sagittal sinus and the falx. The trajectory is toward the
apex of the tentorium and the posterior portion of the corpus callosum. With
large tumors, the corpus callosum is generally thin and is resected over an area
of about 2 cm from its posterior aspect. This allows visualization of the
dorsal surface of the tumor. If the tumor extends into the posterior fossa, the
tentorium is incised from the leading edge posteriorly to the limit of the
tumor. On occasions when it is desirable to reach the side opposite to the
exposure. a suture may be placed in the tentorium adjacent to the straight sinus
to rotate the straight sinus and tentorium until the opposite portion is
visualized. With large tumors, the deep venous system is generally displaced
laterally to the region of the trigone. Some authors, sometimes divide
one of the internal cerebral veins. At its best this exposure provides for a
comprehensive view of the entire roof of the third ventricle, laterally to both trigones and down the posterior
fossa in the region of the anterior medullary vellum.
Occipital Transtentorial
Approach
The occipital transtentorial
approach as advocated by Clark and others involves an occipital craniotomy and
sectioning of the tentorium. It is usually performed in the
lateral or three-fourths prone position with the operative approach on the
dependent side so that the occipital lobe falls away from the falx. Occasionally
one or two bridging veins between the occipital lobe and the superior sagittal
sinus must be divided, which can sometimes lead to visual problems. Optimal
exposure is gained by sectioning the tentorium adjacent to the straight sinus.
This approach brings the surgeon under the splenium of the corpus callosum. It
does have the disadvantage that the surgeon must work around the deep venous
system, but it provides excellent exposure of the quadrigeminal region. The high
incidence of hemianopsia from retraction of the occipital lobe and the
eccentric exposure of the bulk of the tumor, limit its usefulness. The
principles of the tumor removal are the same as with the supracerebellar
infratentorial approach. The tumor is debulked internally and the capsule is
then dissected away from the surrounding structures.
Complications of Surgery
Serious complications of pineal
tumor surgery, regardless of the route used, are related to the nature of the
tumor and its potential for intra- or postoperative hemorrhage. Haemorrhage
has played a major role in most of the surgery-related deaths and can occur with
a delay of up to several postoperative days. This phenomenon is most prevalent
with pineal cell tumors (pineoblastoma and pineocytoma), which tend to be soft
and highly vascular. Haemostasis is difficult both at operation and in the
postoperative period. Haemorrhage can occur prior to surgery as a so-called
"pineal apoplexy" or can be associated with stereotactic biopsy.
Complications of the sitting
position, particularly with the posterior fossa approach, include venous air
embolism, hypotension and cortical collapse when hydrocephalus of significant
degree is relieved by tumor removal. The incidence of cortical collapse can be
reduced by preoperative shunting to allow the ventricular system a chance to
accommodate over several days before the major operation. This phenomenon can
occur in varying degrees and, although striking on the postoperative CT scan,
gradually improves without major neurologic complications for the patient.
Subdural shunting is rarely required to relieve chronic hygromas resulting from
this complication.
There are unusual and
unexpected complications related to the cervical spinal cord and indirectly to
the flexed position of the head in the sitting position, especially if the patient
has local problem in the neck, which could lead
postoperatively to a permanent quadriplegia. Another complication could be in an
individual with an arteriovenous malformation of the pineal gland which could
cause
quadriparesis, presumably due to spinal cord stretching from the intraoperative
posture.
The complications of the
interhemispheric approach are related to retraction of the parietal lobe, with
transient sensory or stereognostic deficits on the opposite side. These have
not been serious or permanent. Unlike the occipital transtentorial approach,
the interhemispheric approach has not been associated with visual field defects.
Regardless of the operative
approach used, various pupillary abnormalities, difficulty focusing or
accommodating, internuclear ocular palsies and limitation of upward gaze can be
expected when the tumor is dissected from the quadrigeminal region. These
deficits improve gradually but may last for many months or up to a year before
normal function returns. Manipulation of the brain adjacent to the third
ventricle can lead to impaired consciousness. The fourth cranial nerve is
generally caudal to the tumor and is rarely identified. Of all the cranial
nerves in the region, however, it is the closest and injury may result in a
specific extraocular palsy. Ataxia has been minimal and usually transient. The
incidence and severity of deficits is increased with prior radiation therapy,
the presence of symptoms preoperatively, and a high degree of malignant and
invasive tumor characteristics.
Shunt malfunction can occur in
up to 20 percent of patients following surgery. To minimize this problem, with
the infratentorial approach a catheter can be left from the opening in the
third ventricle over the cerebellum to the cisterna magna to provide additional
CSF diversion.
Postoperative Management
All patients with malignant
pineal cell tumors, germ cell tumors and ependymomas should have postoperative
staging to look for spinal metastasis. Spinal MRI with
contrast is the procedure of choice. We also perform CSF
cytology but have not found this to be particularly helpful for guiding
management decisions.
All patients with malignant
pineal region tumors should receive 4000 cGy to the whole brain with an
additional 1500 cGy to the pineal region. The only exceptions to this
include the occasional pineal cell tumor or ependymoma with a histologically
benign appearance that has been completely excised. In these cases a
decision may be made for close follow-up with serial MRI scans while withholding
radiation therapy unless the tumor recurs. We do not routinely give spinal
radiation unless there is radiographic evidence of tumor seeding.
Chemotherapy is reserved for
those patients with nongerminomatous malignant germ cell tumors. In these
patients, it is advisable to give chemotherapy first, before radiation therapy.
Although some studies have suggested that chemotherapy may be useful for
pineal cell tumors and as an adjunct in the treatment of germinomas to reduce
the amount of radiation necessary, these results are still preliminary.
Because some tumors may be of a
mixed cell type, such as benign teratoma with a small inclusion of germ cell
malignancy, detailed and comprehensive evaluation of the specimen is necessary
to determine the appropriate mode of therapy. A report of one patient who had a
removal of what was considered to be a germinoma. After receiving radiation to
the entire neuroaxis, he then returned with massive seeding and recurrence of
what was now an embryonal cell carcinoma. The radiation had eliminated the
germinoma while a small nidus of embryonal carcinoma (tumor more appropriately
treated with chemotherapy) was permitted to run rampant.
Results
An excellent surgical outcome occurs in
more than 90 percent of the time. Operative mortality around 4 percent, which in
nearly all instances is related to complications of postoperative haemorrhage.
Morbidity, mostly involving extraocular dysfunction is minor and usually
temporary. Permanent major morbidity occurs in 3 percent of patients. Not
surprisingly, risk factors for increased operative morbidity and mortality
included malignant tumors, prior radiation therapy and the presence of
significant preoperative neurological impairment.
The most common tumors are
astrocytomas and germinomas, each representing about 16 percent of all pineal
tumors. One-third of all tumors are benign and have been nearly always
completely resectable and curable with surgery alone. Among all tumors, benign
and malignant, a gross total resection is possible 45 percent of the time. A
histologic diagnosis can be made in all patients.
Surgery for all pineal region
tumors with removal of benign encapsulated tumors and debulking of malignant
tumors is recommended. Large specimens are necessary for accurate histologic
typing. Advances in surgical management have led to improved surgical outcome.
Additional therapy is based on operative findings, including histologic
diagnosis as well as tumor staging for metastatic disease.
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