Resection of a Large Parasellar Craniopharyngioma via the Pterional Route
Craniopharyngiomas typically arise from nests of metaplastic adenohypophyseal cells of the hypophysiopharygneal duct (Rathke’s pouch). Except for the 5% that are purely intraventricular, almost all of these lesions are located within the parasellar chiasmatic cisterns.
Early proliferation of the tumor is contained within the subarachnoid space of the chiasmatic cistern, bordered laterally by the medial carotid cisterns, and posteriorly/superiorly by the interpeducular cistern separated by the diencephalic leaf of the Liliequist’s membrane. Following growth of the tumor mass and subsequent cisternal compression, the tumor infiltrates and fills the surrounding cisterns.
These tumors are often diagnosed at a large size due to their indolent and benign growth pattern. When larger than 4 cm, these tumors are considered giant and often demonstrate proliferation within multiple compartments of the subarachnoid space.
There are two pathologic subtypes of craniopharyngiomas: adamantinomatous and papillary subtypes. Adamantinomatous tumors are the childhood variant which is heterogeneously cystic and solid, containing cholesterol crystals and a dark brown cystic fluid. These tumors adhere to and encase some or all of the following structures: the optic nerves and chiasm, pituitary gland and its stalk, circle of Willis, brainstem, hypothalamus, third ventricle, and the frontal/temporal lobes.
Papillary tumors are seen in both children and adults and are more predominantly solid. This subtype is generally circumscribed and lacks the adherent nature of the adamantinomatous tumors.
Selection of the appropriate surgical approach for resection of a craniopharyngioma takes into account the location of the lesion, size at presentation, encasement of the neurovascular structures, patient’s specific anatomy and the surgeon’s experience.
I have nearly abandoned the transcranial route for resection of craniopharyngiomas in favor of the transnasal route during the past few years. I believe the results of the extent of resection, patient recovery, and postoperative morbidity are in favor of using the direct, minimally invasive transnasal corridor. The relative indications for the transnasal versus the transcranial approaches to this tumor type are discussed below.
Craniopharygniomas account for 1.2% to 4% of all adult intracranial tumors and 6% to 10% of those in the pediatric population. The tumor incidence follows a bimodal distribution with peaks in patients who are 5 to 10 years old and 50 to 60 years old, and carries no gender predilection.
Although generally centered on or near the infundibulum, the clinical presentation of a craniopharyngioma depends on the tumor’s exact location and extent of compression on the surrounding structures: the pituitary gland and stalk, optic apparatus, and the third ventricle and its floor (the hypothalamus).
In adults, visual disturbances and headaches are the most common presenting neurologic findings. Neurocognitive changes due to infiltration of the hypothalamus are also common, although endocrine dysfunction is variable and frequently not clinically significant. Alterations in behavior may also result from compression of the basal frontal lobes, generating a variety of symptoms, including dementia, abulia, apathy, and psychomotor slowing.
Compression of the adjacent ventricular system can result in obstructive hydrocephalus and a subsequent increase in intracranial pressure. In children, elevated intracranial pressure is more common, whereas endocrine dysfunction is usually related to growth hormone insufficiency; occult visual disturbances are also often present in children. Hydrocephalus occurs in one-third of both affected populations.
The primary imaging modality to evaluate a craniopharyngioma is magnetic resonance (MR) imaging. This modality allows characterization of the tumor, which is generally lobulated with heterogeneous signal intensity and large cysts. Computed tomography (CT) is beneficial in studying the anatomy of the underlying skull base and assessing the feasibility of the transnasal operative corridor. Additionally, the adamantinomatous subtype usually contains areas of calcification, whereas the papillary subtype, seen exclusively in adults, commonly lacks calcification.
Given the high incidence of preoperative endocrine dysfunction with these tumors, all patients should undergo a complete endocrinologic evaluation. These tests will also facilitate identification and management of postoperative hormone deficiency.
The order of prevalence for associated endocrine dysfunction from most common to least common is as follows: growth hormone deficiency, follicle-stimulating or luteinizing hormone deficiency, adrenocorticotropic hormone deficiency, thyroid-stimulating hormone deficiency, hyperprolactinemia (due to compression of the inhibitory dopaminergic stalk projections) and diabetes insipidus (<20% preoperatively). However, in the perioperative setting, adrenal insufficiency and diabetes insipidus are the two potential diagnoses of primary importance.
Preoperative formal visual field and a dilated fundoscopic examination are required, both to document a preoperative baseline status and to provide a reference point when monitoring for future tumor recurrence. A complete understanding of any preoperative visual deficit is necessary to fully design the optimal surgical plan.
Vascular studies (CT or MR angiography) will rule out atypical aneurysms and define the surrounding normal vasculature that may be involved in tumors extending anteriorly (anterior cerebral arteries), posteriorly (basilar apex and posterior communicating arteries), or laterally (distal internal carotid arteries and their branches). The finding of a calcified cystic mass associated with the pituitary stalk is almost pathognomonic of a craniopharyngioma.
Preoperative imaging should assess the degree of pituitary stalk involvement. This variable can define the risk of its sacrifice to achieve gross total resection.
Figure 1: Images for two patients with craniopharyngiomas of different sizes and morphology are shown. The images in the upper row show a large somewhat solid craniopharyngioma that can be exposed via a subfrontal route through the lamina terminalis. On the other hand, the images in the middle and lower rows show a typical partially cystic and solid tumor suitable for the transnasal route. Note the nodular calcification found on CT in the right lower image. The significant involvement of both tumors with the pituitary stalk renders salvage of the stalk during resection most likely impossible.
Indications for Surgery
There is minimal evidence regarding observation for these lesions because they are almost always symptomatic at presentation. In older adults with incidental asymptomatic lesions, serial radiographic, endocrinologic, and ophthalmologic monitoring may be appropriate. However, if a diagnosis of craniopharyngioma is entertained, I recommend surgery, and if the diagnosis is confirmed through frozen section, resection and adjuvant radiotherapy are instituted.
The goal of surgery is maximal safe resection. Although a surgical cure is possible with gross total resection, this should not be achieved at the cost of damaging the hypothalamus, because this leads to poor quality of life. Radiotherapy is the main adjuvant treatment modality, and there is an increasing role for radiosurgery and proton beam therapy to protect the surrounding vital structures.
Palliative procedures such as cyst decompression/fenestration or ventricular shunting may improve symptoms, but they generally only temporize the situation without definitively addressing the problem. Other therapy methods such as intracavitary brachytherapy may be chosen in rare recurrent nonoperative cases.
Figure 2: Craniopharyngiomas can have a variable origins within the parasellar region and extend into various ventricular and cisternal spaces. The main image demonstrates the location of an intraventricular craniopharyngioma that is best approached via the transcallosal route. The top inset illustrates a typical tumor with engulfment of the pituitary stalk: I frequently reach this tumor via the endoscopic transnasal transtuberculum corridor. The left lower inset demonstrates a multicompartmental intraventricular tumor that is best resected through the transcallosal route. The last tumor configuration, right lower inset, fills the sella and lends itself to a transnasal expanded transselar approach. The preservation of the floor of the third ventricle is an important factor during selection of the appropriate operative corridor.
The suprasellar anatomy is the major contributor to the complexity of resecting a craniopharyngioma. The intricate arrangement of the subarachnoid planes and cisterns requires the surgeon to appropriately navigate these boundaries. Advanced or complex craniopharyngiomas can involve multiple cisternal compartments; investigation of each of the compartments and their associated neurovascular contents adjacent to the chiasmatic cistern may be necessary during microsurgical exploration.
Figure 3: The anatomy of the basal cisterns with intervening arachnoid membranes is demonstrated. This complex anatomy contributes to the surgical intricacy of the transcranial approach for resecting parasellar lesions (images courtesy of AL Rhoton, Jr). Craniopharyngiomas reside within the subarachnoid space of the chiasmatic cistern, bordered laterally by the medial carotid cistern, and superiorly and posteriorly by the interpenducular cistern separated by the diencephalic leaf of the Liliequist membrane. Following growth of the tumor mass and subsequent cisternal compression, the tumor infiltrates and fills the surrounding cisterns.
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Figure 4: Chiasmatic cistern via the superior exposure (left upper image), anterior exposure (right upper image), and anterolateral exposure (left lower image). The right carotid artery is elevated through the anterolateral exposure of the chiasmatic cistern (right lower image) (images courtesy of AL Rhoton, Jr). Some craniopharyngiomas engulf the pituitary stalk, prohibiting their gross total resection unless the stalk is sacrificed. The intimate attachment of the tumor to the neurovascular structures and specifically the floor of the third ventricle prohibits gross total removal and significantly affects the risk of tumor recurrence.
Surgical Approach for Craniopharyngiomas
Multiple surgical approaches have been designed for resection of craniopharyngiomas. Determining the optimal approach requires a careful consideration of the lesion’s location and expansion, involvement of the surrounding structures, and the surgeon’s expertise.
The first major distinction is the decision to explore the lesion via the transcranial microsurgical or endoscopic transnasal route. For more details on the transnasal route, see the Endoscopic Transnasal Resection of Craniopharyngioma chapter. The commonly used transcranial approaches are discussed in the remainder of this chapter.
Table 1: Surgical Approaches to Craniopharyngiomas by Location
|Frontolateral/orbitozygomatic translamina terminalis
||Endoscopic transnasal translamina terminalis
||Endoscopic transnasal Transselar
As you can see in Table 1, as long as the floor of the third ventricle is affected, the transnasal route would be favored. If the floor of the third ventricle is intact, the translamina terminalis and transcallosal approaches are reasonable.
Retrochiasmatic craniopharyngiomas present a special challenge as there is no safe and effective transcranial corridor to reach them; they are readily exposed via the endoscopic transnasal trajectory.
The Pterional, Frontolateral or Supraorbital and Orbitozygomatic (OZ) craniotomies are traditional subfrontal operative corridors for resection of suprasellar lesions, including craniopharyngiomas. They provide significant versatility and efficacy to justify their use. The pterional approach provides a shorter and more direct trajectory to the parasellar area, whereas the OZ osteotomy facilitates a more inferior-to-superior trajectory to reach the lesions with predominantly vertical growth into the third ventricle.
I will describe the nuances of technique for intradural resection of craniopharyngiomas through these three subfrontal approaches in the following paragraphs. I will also briefly discuss the frontolateral pathway.
The supralateral or supraorbital approach is discussed in its own dedicated chapter in the Cranial Approaches volume. Briefly, the patient is positioned supine with his or her neck extended and rotated 30 degrees contralateral to the side of the craniotomy. An “eye-brow” or hemicoronal skin incision is performed with the lower margin within the axial plane of the orbital root. Next, a 3 to 3.5 cm ✕ 2 to 2.5 cm standard frontolateral craniotomy is performed just lateral to the keyhole and the dura is incised in a semicircular pattern.
Figure 5: For a Soutar or hemicoronal incision, the temporalis muscle is elevated over the keyhole (left image) to protect the frontalis nerve and provide a cosmetic closure. A single burr hole is also used for the craniotomy through the eyebrow incision (right image).
The intradural approach for the subfrontal craniotomies discussed above involves opening of the sphenoidal Sylvian and parasellar cisterns, to release cerebrospinal fluid (CSF) and facilitate tumor resection. Tensionless transsylvian microdissection (see Techniques of Sylvian Fissure Split is the germane step in securing adequate exposure. Next, the intradural trajectory is expanded via dissection of the arachnoid bands around the basal cisterns to expose the ipsilateral internal carotid artery and optic nerve.
Before attempting further dissection of the surrounding structures, it is important to relieve the tension being exerted on the neighboring structures by the mass effect of the tumor. I deflate the cystic tumor by puncturing the cyst in the interoptic space. Alternatively, if the tumor is primarily solid, decompression is attempted along the midline using an ultrasonic aspirator to reduce the mass effect.
Figure 6: In select patients who suffer from significant compromise of their ipsilateral optic nerve, a partial intradural clinoidectomy relieves the tension on the nerve. The falciform ligament is also incised. This maneuver thereby reduces the risk of injury to the nerve during mobilization of the solid tumor components around the nerve. Moreover, the opticocarotid corridor is expanded.
Sufficient decompression is confirmed when the contralateral optic nerve is in view and the regional suprasellar anatomy is more familiar. Further lateral dissection of the tumor from the surrounding structures may then be performed in a tension-free environment.
Prefixed and Postfixed Chiasms
The next operative steps for circumdissection of the tumor capsule and nodule depend on the existence of a prefixed versus a postfixed optic chiasm. These two configurations are determined by the location of the chiasm in the vertical plane relative to the tumor.
Figure 7: An overview of transcranial intradural operative trajectories toward the parasellar craniopharyniomas is illustrated. Note the interoptic, paracarotid (including carotid-oculomotor) and translamina terminalis pathways. The anteriorly displaced prefixed chiasm with short optic nerves limits the subchiasmatic dissection and mandates the use of the translamina terminalis approach. However, the posteriorly displaced postfixed chiasm provides an additional operative corridor within the interoptic space.
A postfixed optic chiasm typically presents with a supraposteriorly displaced chiasm. This configuration is associated with relatively wide interoptic and subchiasmatic spaces that facilitate internal decompression and dissection of the tumor.
The dissection proceeds in the following order and at these planes: the medial and then the inferior surfaces of the ipsilateral optic nerve, medial surface of the internal carotid artery and posterior communicating artery. Next, the contralateral oculomotor nerve can be found while the retrosellar portion of the tumor is dissected free from the basilar artery covered by the membrane of Liliequist.
The resection then targets the contralateral optic nerve and carotid artery. Finally, the hypothalamic attachments of the tumor are released.
The surgeon may consider the use of an angled endoscope to identify occult pockets of tumor, which are particularly present among the adherent adamantinomatous subtype.
If necessary, these trajectories can be augmented via the translamina terminalis approach to reach and resect the intraventricular components of the tumor. Modified forms of this procedure resect the middle fossa extensions of these lesions. To achieve sufficient lateral access within the basal cisterns, I enter the intervening space between the uncus and the internal carotid artery. The close proximity of the adherent anterior choroidal and posterior communicating arteries along with their associated perforating vessels limits gross total resection.
Figure 8: An anterochiasmatic cystic craniopharyngioma (first row of images) was resected via the pterional craniotomy. The ipsilateral optic nerve was decompressed via drainage of the cyst, and the capsule of the cystic components of the tumor was removed (middle row of images). The tumor nodule was sharply released from the hypothalamus (left lower image). The final resection result and the subfrontal operative trajectory are shown. The pituitary stalk (arrow) remained intact (right lower image).
The frontolateral approach to a prefixed optic chiasm for removal of a parasellar craniopharyngioma faces a unique set of challenges because the interoptic and subchiasmatic spaces are significantly more limited compared with a postfixed chiasm. The optic nerves are short and the chiasm is displaced superiorly and anteriorly.
The prefixed chiasmatic lesions commonly demonstrate third ventricular extension and are most effectively resected via the transnasal corridor due to their retrochiasmatic location. If approached via the subfrontal route, these lesions require some modifications of the procedure designed for the postfixed chiasm, such as an initial attempt to reach the tumor via the lamina terminalis cisternal dissection after exposure of the A1 and A2 segments. For details of this route, please see the Subfrontal Translamina Terminalis Approach chapter.
The next steps involve dissection of the ipsilateral optic nerve and A1 segment, while maintaining the integrity of any cortical A1 perforators. The mobile A1 and A2 segments are then mobilized along with the frontal lobe to clear a subfrontal corridor to access the lamina terminalis. These maneuvers allow for a midsagittal entry into the lamina terminalis. Dynamic retraction using the handheld suction device is especially beneficial for this small and deep corridor; the use of fixed retractor blades will demand forceful refraction of the brain.
Next, the lamina terminalis is incised and the contents of the anterior third ventricle examined. If the craniopharyngioma demonstrates mass effect on the ventricle sufficient to generate attenuation of the third ventricular floor or true ventricular extension, a transventricular approach to the posterior aspect of the tumor within the parasellar region is a reasonable strategy. This corridor through the third ventricular floor can facilitate resection of the tumor around the posterior sellar region, inferior segment of the contralateral optic tract, internal carotid artery, posterior communicating artery and retroclival space.
The operative blind spot is wide and is around the ipsilateral structures mentioned above and the posterior aspect of the ventricle. Unfortunately, this restriction in tumor exposure limits the extent of safe resection. The transnasal corridor does not suffer from such a disadvantage and affords an operative trajectory along the long axis of the tumor, respecting one of the very important axioms in tumor surgery.
Last, the paracarotid cisterns are opened to facilitate resection of tumor within the suboptic region. Debulking of the tumor to this point can result in the collapse of the suprasellar tumor components. Finally, the intraventricular extension of the tumor can be removed via the transventricular entrance described above.
During resection of a craniopharyngioma, the surgeon invariably faces the dilemma to sacrifice the pituitary stalk when it is intimately involved with the mass. For lesions that demonstrate partial stalk involvement, a partial section of the stalk may be appropriate to enhance the gross total resection rate.
Figure 9: A left-sided OZ approach via the translamina terminalis pathway to this third ventricular craniopharyngioma is demonstrated. There are numerous operative blind spots through this very limited trajectory that restrict gross total tumor resection.
Craniopharyngioma: Orbitozygomatic Osteotomy/Translamina Terminalis Approach
This approach is best suited for resection of isolated third ventricular craniopharyngiomas with preservation of the third ventricular floor. This approach requires localization of the optic chiasm and associated cerebrovasculature relative to the tumor.
Further details on this approach can be found in the Transcallosal Expanded Transforaminal Transvenous Route chapter. The walls of the third ventricle should be preserved at the expense of subtotal removal of an adherent tumor. The floor of the ventricle is kept out of harm’s way.
Some centers have adopted the use of intraoperative MRI prior to surgical closure to verify the completeness of resection. Evidence suggests that this practice has increased the rates of gross total resection in patients with complex multicompartmental craniopharyngiomas. The experience of the surgeon confounds the results of this practice.
The techniques used in the closure are approach-dependent and are discussed in their corresponding chapters.
After surgery, the patient is observed in the intensive care unit overnight for frequent neurologic evaluations and pain and blood pressure control. Entry into the ventricular system carries a higher risk of postoperative cerebrospinal fluid leak.
A postoperative MRI is obtained to candidly assess the extent of resection and plan for delayed radiotherapy. Prophylactic anticonvulsants are administered.
Diabetes insipidus (DI) is one of the most frequent postoperative complications after craniopharyngioma surgery. This condition can exist preoperatively and worsens postoperatively. The etiology of DI relates to distention or injury of the neurohypophysis or pituitary stalk. Careful monitoring of fluid input/output, urinary osmolality, and frequent serum sodium evaluations are imperative during the immediate postoperative period because serum sodium can rapidly escalate to dangerous levels (>150 mEq/L).
Routine early postoperative diuresis related to frequent intraoperative fluid boluses must be distinguished from DI. This can be achieved through a water deprivation test; early postoperative diuresis will not impact plasma osmolality or sodium. The water deprivation test involves withholding water intake for 6 to 8 hours and checking urine osmolality, which in a patient with DI fails to exceed 200 mOsm/kg due to the patient’s inability to concentrate his or her urine. This will correspond to a normal rise in plasma osmolality, such that it can near 320 to 330 mOsm/kg.
Treatment for DI depends on the patient’s functional status; a conscious patient with intact natural thirst mechanism can maintain plasma osmolality. The patients with severe DI or those who are unconscious can demonstrate dramatic fluctuations in their serum sodium and are managed with desmopressin acetate (DDAVP).
Up to 80% of patients experience transient DI postoperatively, with less than 20% continuing on to permanent DI. Dysregulation of the anterior pituitary hormones is also common.
Hyperphagia leading to morbid obesity is a well-described complication following craniopharyngioma resection that is caused by hypothalamic injury, especially in children. Memory impairments from such an injury are also not uncommon.
Pearls and Pitfalls
- Early central tumor decompression creates room for subsequent extracapsular tumor dissection.
- Sharp and gentle dissection of the arachnoid planes is critical to avoid injuring the fine superior hypophyseal branches that supply the optic chiasm.
- A small part of the floor of the ventricle may be predominantly involved with the tumor and should be considered part of the tumor capsule. However, most of the hypothalamus and other adjacent neural areas must be preserved. If necessary, a small piece of adherent residual capsule may be left behind on the walls or floor of the third ventricle.
Contributor: Benjamin K. Hendricks, MD
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