The pineal region can harbor highly diverse histologic tumor subtypes. Because optimal therapeutic strategies vary with tumor type, an accurate diagnosis is the foundation of enlightened management decisions. Either stereotactic biopsy or open surgery is essential for securing tissue for pathologic examination. Biopsy has the advantage of ease and minimal invasiveness but is associated with more sampling errors than open surgery. The emergence of endoscopic techniques and stereotactic radiosurgery provide complementary options to improve pineal tumor management, and will assume greater importance in the neurosurgeon’s armamentarium.
Surgical strategy for pineal region tumors is affected not only by anatomic considerations but by pathologic features as well. The varied pathologies that occur in this region can dictate a range of surgical strategies from gross total resection or debulking to biopsy or medical management.
History of pineal region surgery
Since its birth in the early twentieth century, surgery of the pineal region has matured, reflecting an understanding of the region’s varied pathologies as well as evolution of surgical technologies and techniques, creating a modern, nuanced, multidisciplinary approach to these tumors.
Among the earliest descriptions of operative approaches to pineal tumors, published in 1913, were interhemispheric transcallosal, an approach modified by Dandy in the 1920s. Pineal tumor surgery in the 1910s through the early 1930s was dangerous for a multitude of reasons beyond the anatomic challenges, including the lack of experience, operative microscope, and adequate lighting. In 1931, Van Wagenen introduced a transcortical transventricular approach through the right parietal lobe and right lateral ventricle. Horrax reported a variation on Dandy’s approach involving resection of the occipital lobe to afford better exposure of large tumors. Through the 1940s and 1950s, use of these and Dandy’s original approach did little to improve outcomes for these patients, with perioperative mortality of 20% to 70%.
In the 1960s, Poppen first described the occipital transtentorial approach, though during this same period radiotherapy became the first-line treatment, as these patients fared better than surgery patients in the aggregate. However, as only half of pineal tumors are radiosensitive, at least half of all pineal tumor patients received unnecessary whole brain radiation, particularly those with benign or low-grade lesions, who should have the best prognosis. The need for tissue diagnosis thus became clear, and a modern pathology-driven management strategy was born. Stein’s infratentorial supracerebellar approach adapted from Krause and Jamieson’s experience with Poppen’s approach, both published in 1971 and using the operative microscope, ushered in the modern era of safer radical pineal surgery, and allowed the effective treatment of all types of pineal pathology.
The 1970s also saw reports of stereotactic biopsy, stereotactic radiosurgery, and endoscopic biopsy of pineal tumors, a practice that became commonplace by the 1990s, often coupled with endoscopic third ventriculostomy for treatment of hydrocephalus.
Indications for surgery
The pineal region produces an unrivaled variety of neoplastic and nonneoplastic masses, half of which are radiosensitive. Therefore, indication for surgical management of pineal tumors depends on tumor markers, pathologic findings on biopsy, and the degree and chronicity of associated hydrocephalus. Contrast magnetic resonance imaging (MRI) is indicated prior to any nonurgent management, but does not reliably differentiate among histologic subtypes; its utility is thus to plan the operative approach, identify the relationships between the tumor and other anatomic structures, and determine whether total resection can be attempted safely.
Tumor Markers
Considering the attendant morbidity of pineal region surgery or even biopsy, noninvasive means of obtaining an accurate diagnosis of a radiosensitive tumor should always be attempted. Detection of β-human chorionic gonadotropin (β-HCG) or α-fetoprotein, or both, in the serum or cerebrospinal fluid (CSF) suggests a malignant germ cell tumor and is an indication for radiotherapy and chemotherapy without resection or biopsy, though management of hydrocephalus is still usually warranted. CSF can be obtained during external ventricular drain placement, endoscopic third ventriculostomy, shunting, or via low-volume lumbar puncture. It must be noted that pineal masses cause obstructive hydrocephalus, and lumbar puncture in this setting could precipitate herniation.
Hydrocephalus Management
Most patients with pineal region tumors present with hydrocephalus, and in their preoperative evaluation, the acuity of the situation is primarily dictated by the degree of hydrocephalus and clinical presentation. If urgent, bedside placement of a temporizing external ventricular drain can be performed until definitive treatment strategy is determined. In the event of subsequent resection, some patients may not require continued CSF diversion. This strategy can be employed in nonurgent cases as well, particularly in the setting of mild hydrocephalus with a simple cyst or well-encapsulated tumor.
Optimal surgical strategy usually involves endoscopic third ventriculostomy, as these tumors create an obstructive hydrocephalus, and some can be biopsied through the posterior third ventricle during the same procedure, if indicated. The procedure is safe and effective, and is preferred over ventriculoperitoneal shunting unless tumor occupies the floor of the third ventricle, or mass effect distorts anatomy thus making the relationship of the basilar artery with the floor of the third ventricle unfavorable. Ventriculoperitoneal shunting is also an acceptable means of CSF diversion, though it is associated with higher rates of infection, malfunction, overshunting, subdural hematoma, and peritoneal metastasis.
Biopsy Versus Resection
The decision between biopsy alone or resection should take into account the treatment objectives as well as the risks of each of the possible procedures. The primary objective in the surgical management of pineal region tumors is to establish accurate pathologic diagnosis, which dictates further surgical strategy, adjuvant therapy, metastatic workup, prognosis, and follow-up plans. The secondary objective is resection, whether partial or complete.
Considering the diversity of histologic findings in pineal masses, in the absence of positive tumor markers accurate tissue diagnosis is essential. The most reliable strategy for accurate diagnosis is adequate tissue sampling, which is limited in stereotactic and endoscopic biopsy, and much more feasible in open procedures.
A major advantage of open microsurgical techniques is resection. Approximately one-third of pineal tumors are benign, and resection affords the best opportunity for long-term recurrence-free survival. For malignant tumors, the clinical impact of maximal tumor resection is less well documented, though several reports have correlated extent of tumor resection with improved response to adjuvant therapy and increased survival. Other advantages of more aggressive resection include the potential to control hydrocephalus without a second procedure and reduced risk of postoperative hemorrhage into residual tumor bed.
These advantages of open surgery are contingent on avoidance of complications. Favorable results are achievable, but are considerably dependent on the experience and judgment of the surgeon, beyond what is typically necessary for an intracranial tumor operation. Indeed, the risk-benefit balance may shift depending on the surgeon as much as the anatomy.
The primary advantage of stereotactic biopsy over open microsurgical tissue sampling is that the stereotactic procedure carries a lower morbidity through limited invasiveness and ability to avoid general anesthesia. However, the deep venous system, choroidal arteries, and multiple pial surfaces to be traversed during the procedure, as well as limited ability of nearby brain to tamponade even minor bleeding, makes this area among the most hazardous in the brain for stereotactic biopsy.
Endoscopic biopsy of pineal tumors through the ventricles has been reported as an alternative method for securing a tissue diagnosis. In addition to sampling error, a major drawback of this procedure is that the tumor is biopsied along its ventricular surface, where there is no tissue turgor to tamponade the bleeding. Even minor bleeding within the CSF space can be difficult to manage, a problem that is compounded by the highly vascular properties of many pineal tumors. This procedure typically is combined with a ventriculostomy. However, even with flexible endoscopes it is difficult to perform a biopsy simultaneously with a ventriculostomy because the trajectory required is different for each procedure. The rigid endoscope is not easily maneuverable without risk of damage to the fornix and the septal and thalamostriate veins at the foramen of Monro. A suitable entry point through the forehead might allow the use of a rigid scope, but this offers no advantage over a simple stereotactic biopsy. More typically, endoscopes have been used to aspirate pineal cysts; however, the benefits of this approach are equivocal.
Indications for surgery
The pineal region produces an unrivaled variety of neoplastic and nonneoplastic masses, half of which are radiosensitive. Therefore, indication for surgical management of pineal tumors depends on tumor markers, pathologic findings on biopsy, and the degree and chronicity of associated hydrocephalus. Contrast magnetic resonance imaging (MRI) is indicated prior to any nonurgent management, but does not reliably differentiate among histologic subtypes; its utility is thus to plan the operative approach, identify the relationships between the tumor and other anatomic structures, and determine whether total resection can be attempted safely.
Tumor Markers
Considering the attendant morbidity of pineal region surgery or even biopsy, noninvasive means of obtaining an accurate diagnosis of a radiosensitive tumor should always be attempted. Detection of β-human chorionic gonadotropin (β-HCG) or α-fetoprotein, or both, in the serum or cerebrospinal fluid (CSF) suggests a malignant germ cell tumor and is an indication for radiotherapy and chemotherapy without resection or biopsy, though management of hydrocephalus is still usually warranted. CSF can be obtained during external ventricular drain placement, endoscopic third ventriculostomy, shunting, or via low-volume lumbar puncture. It must be noted that pineal masses cause obstructive hydrocephalus, and lumbar puncture in this setting could precipitate herniation.
Hydrocephalus Management
Most patients with pineal region tumors present with hydrocephalus, and in their preoperative evaluation, the acuity of the situation is primarily dictated by the degree of hydrocephalus and clinical presentation. If urgent, bedside placement of a temporizing external ventricular drain can be performed until definitive treatment strategy is determined. In the event of subsequent resection, some patients may not require continued CSF diversion. This strategy can be employed in nonurgent cases as well, particularly in the setting of mild hydrocephalus with a simple cyst or well-encapsulated tumor.
Optimal surgical strategy usually involves endoscopic third ventriculostomy, as these tumors create an obstructive hydrocephalus, and some can be biopsied through the posterior third ventricle during the same procedure, if indicated. The procedure is safe and effective, and is preferred over ventriculoperitoneal shunting unless tumor occupies the floor of the third ventricle, or mass effect distorts anatomy thus making the relationship of the basilar artery with the floor of the third ventricle unfavorable. Ventriculoperitoneal shunting is also an acceptable means of CSF diversion, though it is associated with higher rates of infection, malfunction, overshunting, subdural hematoma, and peritoneal metastasis.
Biopsy Versus Resection
The decision between biopsy alone or resection should take into account the treatment objectives as well as the risks of each of the possible procedures. The primary objective in the surgical management of pineal region tumors is to establish accurate pathologic diagnosis, which dictates further surgical strategy, adjuvant therapy, metastatic workup, prognosis, and follow-up plans. The secondary objective is resection, whether partial or complete.
Considering the diversity of histologic findings in pineal masses, in the absence of positive tumor markers accurate tissue diagnosis is essential. The most reliable strategy for accurate diagnosis is adequate tissue sampling, which is limited in stereotactic and endoscopic biopsy, and much more feasible in open procedures.
A major advantage of open microsurgical techniques is resection. Approximately one-third of pineal tumors are benign, and resection affords the best opportunity for long-term recurrence-free survival. For malignant tumors, the clinical impact of maximal tumor resection is less well documented, though several reports have correlated extent of tumor resection with improved response to adjuvant therapy and increased survival. Other advantages of more aggressive resection include the potential to control hydrocephalus without a second procedure and reduced risk of postoperative hemorrhage into residual tumor bed.
These advantages of open surgery are contingent on avoidance of complications. Favorable results are achievable, but are considerably dependent on the experience and judgment of the surgeon, beyond what is typically necessary for an intracranial tumor operation. Indeed, the risk-benefit balance may shift depending on the surgeon as much as the anatomy.
The primary advantage of stereotactic biopsy over open microsurgical tissue sampling is that the stereotactic procedure carries a lower morbidity through limited invasiveness and ability to avoid general anesthesia. However, the deep venous system, choroidal arteries, and multiple pial surfaces to be traversed during the procedure, as well as limited ability of nearby brain to tamponade even minor bleeding, makes this area among the most hazardous in the brain for stereotactic biopsy.
Endoscopic biopsy of pineal tumors through the ventricles has been reported as an alternative method for securing a tissue diagnosis. In addition to sampling error, a major drawback of this procedure is that the tumor is biopsied along its ventricular surface, where there is no tissue turgor to tamponade the bleeding. Even minor bleeding within the CSF space can be difficult to manage, a problem that is compounded by the highly vascular properties of many pineal tumors. This procedure typically is combined with a ventriculostomy. However, even with flexible endoscopes it is difficult to perform a biopsy simultaneously with a ventriculostomy because the trajectory required is different for each procedure. The rigid endoscope is not easily maneuverable without risk of damage to the fornix and the septal and thalamostriate veins at the foramen of Monro. A suitable entry point through the forehead might allow the use of a rigid scope, but this offers no advantage over a simple stereotactic biopsy. More typically, endoscopes have been used to aspirate pineal cysts; however, the benefits of this approach are equivocal.
Surgical approaches
Operative Procedures
Several variations on approaches to the pineal region exist, but essentially they are categorized as supratentorial or infratentorial. Supratentorial approaches include transcallosal interhemispheric, occipital transtentorial, and the rarely used transcortical transventricular. The infratentorial approach is through a natural corridor created between the tentorium and the cerebellum ( Fig. 1 ). Many of these approaches are interchangeable, although the surgeon’s experience and several anatomic caveats play a role in the choice of approach. Supratentorial approaches afford greater exposure than do infratentorial approaches, allowing access to large tumors that extend supratentorially or laterally to the trigone, but they have the disadvantage of forcing the surgeon to work around the convergence of the vein of Galen and internal cerebral veins. The midline infratentorial location of most pineal tumors gives the infratentorial supracerebellar approach several natural advantages. It is performed with the patient in the sitting position, whereby gravity allows the cerebellum and the tumor to drop downward. As the deep venous system is dorsal to pineal tumors, it and the velum interpositum can easily be dissected off the tumor by this approach. With appropriate extra-long instruments, even tumors extending anteriorly into the third ventricle can be removed.
Patient Positioning
Numerous patient positions have been described for these approaches, each having advantages and disadvantages.
Sitting position
The sitting position is usually preferred for the infratentorial supracerebellar approach. Gravity works in the surgeon’s favor by reducing pooling of blood in the operative field and by facilitating dissection of the tumor from the deep venous system. The risks for air embolism, pneumocephalus, or subdural hematoma associated with cortical collapse can be anticipated and managed with proper precautions. Precordial Doppler monitoring or a drop in end-tidal CO 2 can detect air emboli, and a central venous catheter can be used to remove entrapped air if necessary. Optimization of the sitting position involves lowering the table to the floor and bringing the patient to position by manipulating the table. The head is flexed so that the tentorium is approximately parallel to the floor. At least 2 fingerbreadths of space are needed between the patient’s chin and sternum to avoid compromising the airway and venous return. The patient’s legs should be elevated to assist venous return. A 3-point vise type of head holder keeps the head immobile.
Lateral position
The lateral decubitus position with the dependent, nondominant right hemisphere down is another useful approach. The head is raised approximately 30° above the horizontal in the midsagittal plane, especially for the transcallosal approach. For the occipital transtentorial approach, the head should be positioned with the patient’s nose rotated 30° toward the floor, or the three-quarter prone position can be used, which is essentially an extension of the lateral position except that the head is at an oblique 45° angle with the nondominant hemisphere dependent. The nondominant hemisphere is easily retracted with the help of gravity. Surgeon fatigue is reduced because the surgeon’s hands are not extended to the degree they are with patients in the sitting position.
Prone position
The prone position is simple and safe for supratentorial approaches, and is generally comfortable for the surgeon but can be cumbersome for the infratentorial approach. This position is useful when two surgeons work together through an operative microscope and is often useful in the pediatric population. When desired for infratentorial approaches in infants, the position of the head can be rotated 15° away from the craniotomy side in a variation known as the Concorde position.
Operative Approaches
Infratentorial supracerebellar approach
The infratentorial supracerebellar approach is usually performed with the patient in the sitting position. If necessary, a ventricular drain can be placed in the trigone of the lateral ventricle through a burr hole in the midpupillary line at the lambdoid suture.
A suboccipital exposure is begun through a linear midline incision extending from just above the torcular and external occipital protuberance down to the level of the C4 spinous process. A single low-profile, self-retaining retractor is used to retract the muscles and fascia of the suboccipital region for exposure of the suboccipital bone. The craniotomy is centered just below the torcular. The bony opening must be sufficient to provide access for the surgical instruments and adequate light from the operating microscope.
A craniotomy is preferred over a craniectomy because it reduces the incidence of postoperative aseptic meningitis, fluid collections, and discomfort. Slots are drilled over the sagittal sinus, above the torcular, over both transverse sinuses, and approximately 1 or 2 cm above the foramen magnum in the midline. A craniotome is used to connect the slots. Sufficient bone should be removed above the transverse sinus to ensure that the view along the tentorium is not obscured. Any bone edges should be carefully waxed, and all venous bleeding should be controlled to avoid air emboli.
The dura is opened in a semilunar curve extending from the lateral aspects of the exposure and reflected upward on slight tension. If the posterior fossa is tight, fluid can be removed from a ventricular drain or by opening the cisterna magna.
To open the infratentorial corridor, the arachnoid adhesions and midline bridging veins between the dorsal surface of the cerebellum and the tentorium are cauterized and carefully divided, preserving any veins found laterally. Cauterizing the bridging veins and dividing them midway can minimize the nuisance of bleeding from the sinus. The cerebellum then drops away from the tentorium to provide an excellent corridor with minimal brain retraction. Additional adhesions and bridging veins can be divided when they become visible near the anterior vermis as the cerebellum is retracted. With the retractor in place, the opalescent arachnoid covering the pineal region can be seen. The operating microscope is brought in at this time.
Under the microscope, the arachnoid overlying the quadrigeminal plate is sharply opened; this is generally an avascular plane, and minimal cautery is necessary. The precentral cerebellar vein is identified as it courses from the anterior vermis to the vein of Galen and should be carefully dissected, cauterized, and divided ( Fig. 2 ). Although this vein can be taken without difficulty, it is not advisable to cauterize any other veins of the deep venous system. With the posterior surface of the tumor exposed, the central portion is cauterized and opened with a long-handled knife or bayonet scissors. Specimens can be taken from within the capsule and sent for frozen diagnosis.
The tumor is then internally debulked with a variety of instruments such as suction, cautery, tumor forceps, and a Cavitron ultrasonic aspirator if necessary. Most tumors are soft and can generally be suctioned with a large-bore Japanese-style suction device with variable control. As the tumor is decompressed, the capsule can be separated from the surrounding thalamus. Most of the vessels along the wall of the capsule are choroidal vessels and need not be preserved. The dissection continues until the third ventricle is encountered. The tumor is then carefully dissected inferiorly off the brainstem. This stage is often the most difficult of the tumor dissection, and can be facilitated by retracting the tumor superiorly and dissecting it bluntly off the brainstem under direct vision. Finally, the tumor is removed superiorly after separating the attachments along the velum interpositum and the deep venous system. Flexible mirrors can be useful for examining the inferior portion of the tumor bed to verify the extent of resection and to avoid leaving any blood clots. Fig. 3 depicts preoperative and postoperative MRI scans from a patient with a tumor suited for this approach.
Transcallosal interhemispheric approach
This approach between the falx and hemisphere of the brain involves a corridor along the parieto-occipital junction. Any of the previously described patient positions can be used for this approach, although the prone or sitting position is generally preferred. Positioning of the bone flap depends on where the tumor is centered in the third ventricle. A U-shaped scalp flap extending across the midline and reflected laterally followed by a wide craniotomy roughly 8 cm in length generally over the vertex provides flexibility in determining the corridor and avoiding bridging veins whenever possible. The craniotomy should extend 1 to 2 cm to the left of the sagittal sinus.
The dura is opened in U-shaped fashion and reflected medially toward the sagittal sinus. The bridging veins are inspected, and an approach is chosen that will minimize the number of veins sacrificed. It is unlikely that sufficient exposure can be achieved without sacrificing at least one bridging vein, although sacrifice of more than one should be avoided if possible. Because these tumors are deeply seated, even a small opening provides a wide angle of deep exposure. The parietal lobe is gently retracted, as is the falx, which may be divided inferiorly to provide further retraction; this is generally a nonvascular corridor with few adhesions between the falx and the cingulate gyrus. The corpus callosum is easily identified with the operating microscope by its striking white appearance. The pericallosal arteries are retracted either to one side or with separate retractors to each side. The opening into the corpus callosum, centered over the maximal bulge of the tumor, is generally about 2 cm, which is not likely to lead to disconnection syndrome or cognitive impairment. Even more posterior openings in the splenium have been performed routinely without deficits. The corpus callosum is generally thin and can be opened with gentle suction and cautery. The lateral extent of the opening is determined by the amount that is sufficient to expose the tumor and avoid damage to the pericallosal arteries. If necessary, the tentorium and falx can be divided to provide additional exposure.
Once through the corpus callosum, the dorsal surface of the tumor can be seen, and the veins of the deep venous system must be identified. Whether one vein can be sacrificed safely is questionable, but certainly interruption of two would have a devastating result. Once the tumor is exposed, it is debulked and then dissected as described previously. Leaving a ventricular drain in place for 1 or 2 days is optional.
Occipital transtentorial approach
A three-quarter prone position is generally preferred for the occipital transtentorial approach. Although some find orientation difficult intraoperatively, stereotactic guidance can be helpful. By dividing the tentorium, excellent exposure of the quadrigeminal plate is achieved, thus making it particularly useful for tumors that extend inferiorly. A U-shaped right occipital scalp flap is reflected inferiorly, with the medial vertical limb beginning just to the left of midline at about the level of the torcular. A burr hole is placed in the midline over the sagittal sinus just above the torcular, along with another burr hole 6 to 10 cm above this, followed by a generous craniotomy extending 1 to 2 cm left of midline. Gravity helps with retraction of the nondominant occipital lobe, which is also facilitated by the lack of bridging veins near the occipital pole. Mannitol and ventricular drainage are useful for relaxing the brain and minimizing the risk for hemianopsia from excessive occipital lobe retraction.
Under the operating microscope, the straight sinus is identified so that the tentorium can be divided adjacent to it. A retractor can be placed over the falx for exposure. The inferior sagittal sinus and falx can be divided to facilitate further falcine retraction ( Fig. 4 ). At this point, the arachnoid overlying the tumor and the quadrigeminal cisterns can be seen. Tumor removal proceeds as described earlier while taking care to avoid injury to the deep venous system. Fig. 5 depicts preoperative and postoperative MRI scans from a patient with a tumor suited for this approach.
Related posts:
On the Surgery of the Seat of the Soul: The Pineal Gland and the History of Its Surgical Approaches
Preoperative Evaluation of Pineal Tumors
Stereotactic Biopsy Considerations for Pineal Tumors
Minimally Invasive Approaches to the Pineal Region
Clinical Outcomes after Treatment of Germ Cell Tumors
Contemporary Management of Pineocytoma
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