Chapter 39 Craniopharyngiomas and Suprasellar Tumors

• Craniopharyngiomas with different points of origin of tumor growth have substantially different topographical relationships with surrounding structures determining their surgical resectability and the outcome of treatment; originally infradiaphragmatic tumors are the most amenable for safe radical removal, which is the best treatment of craniopharyngiomas.

• The majority of craniopharyngiomas growing inside and outside the cavity of the third ventricle have started to grow as intrapial tumors, thus acquiring direct and intimate contact with hypothalamic structures.

• If the floor of the third ventricle cannot be seen directly on preoperative magnetic resonance imaging (MRI) scans, the topographical relationship of the tumor with hypothalamic structures may be predicted according to its relation with the chiasm and the presence or absence of hydrocephalus.

• The nature and intensity of the tumor adherence to surrounding structures vary in different cases within each topographical group. Decisions about the optimal extent of tumor removal may thus be made only at surgery.

• The natural history of craniopharyngiomas is unpredictable, the growth potential of the tumor or its residual tumor may differ significantly, and therefore radiotherapy should be indicated in case of tumor progression.

The region above the sella contains anatomical structures of the hypothalamus-pituitary system (hypothalamic structures and infundibulum with its pars compacta named also the pituitary stalk), the structures of the visual pathways (optic chiasm and adjacent portions of the optic nerves and the optic tracts), and important blood vessels. The tumors affecting the suprasellar region may belong to (a) tumors of dysembryogenetic origin (craniopharyngioma, epidermoid cyst, dermoid cyst, hamartoma, germ cell tumors, Rathke’s cleft cyst), (b) tumors originating from the tissues of suprasellar structures (gliomas of the visual pathways and hypothalamus, pituicytoma, granular cell tumor of the neurohypophysis, meningioma), (c) tumors extending into the suprasellar space secondarily, most often from the cavity of the sella (pituitary adenoma, Rathke’s cleft cyst, and other cysts), and (d) systemic tumors affecting the central nervous system (CNS metastasis, lymphoma, leukemia).¹^–³

The most common tumors of the region are craniopharyngiomas and chiasmatic/hypothalamic gliomas. Differential diagnosis has to be made first of all between the craniopharyngiomas and other cystic tumors and between chiasmatic/hypothalamic gliomas and other solid lesions. The majority of these tumors are presented in this chapter.

The structures of optic pathways and the hypothalamus-pituitary system may be involved also by suprasellar meningiomas or large and giant pituitary adenomas. The latter may severely displace the floor of the third ventricle upward and may also lead to atrophy of the pia and invade the hypothalamus.⁴ Suprasellar meningiomas originating from the lower leaf of the diaphragm can mimic nonfunctioning pituitary adenomas.⁵ Extremely rare is a meningioma originating from the pituitary stalk having no connection to surrounding dura.⁶

Craniopharyngiomas

Craniopharyngiomas, benign extra-axial epithelial tumors, often follow an aggressive clinical course resulting in significant morbidity and shortened life expectancy. Incomplete tumor removal is followed by progression of the remnants in virtually all patients. Damage to the structures of utmost functional importance due to repeated tumor recurrences and subsequent therapeutic procedures substantially deteriorates the patient’s condition. The most logical treatment seems to be a total tumor removal and thus cure of the patient.

The intention to remove the craniopharyngioma totally whenever technically possible emerged in the past in conjunction with therapeutic and diagnostic improvements: steroid hormone replacement, microsurgery, magnetic resonance imaging.⁷^–¹⁶ Another attitude to management of craniopharyngiomas, namely, intentional incomplete removal and radiotherapy, has been advocated in order to lower the surgical morbidity rate.¹⁷^–²³ However, radiotherapy cannot prevent recurrences in many instances²⁴ and causes adverse effects.¹⁶ A compromise solution has been elaborated: radical removal was recommended only for the patients harboring the tumors not involving the hypothalamus.²⁵ Nevertheless, the definition of “involvement of the hypothalamus” is not clear. Radiological signs of retrochiasmatic growth of the tumor in the direction of the hypothalamus and the impossibility of identifying the latter²⁶ as a distinct form of the tumor do not indicate whether the hypothalamus is compressed or invaded.²⁷

The management of craniopharyngiomas presented in this chapter is based on the results of our morphological studies,²⁸ the results of the correlation of morphological data with neuroradiological and operative findings,²⁷ and our clinical experience.

Incidence

Craniopharyngiomas account for 1% to 4.6% of all intracranial tumors and 13% of suprasellar tumors. Their incidence represents 0.5 to 2.5 new cases per 1 million population per year, being more frequent in Nigerian (18% of all CNS tumors) and Japanese children, with an annual incidence of 5.25 cases per 1 million per year. Papillary craniopharyngiomas occur virtually exclusively in adults, at a mean age of 40 to 55 years. A bimodal age distribution of adamantinomatous craniopharyngiomas is observed with peaks in children aged 5 to 15 years and in adults aged 40 to 55 years.²⁹ In children, craniopharyngiomas account for 2.5% to 13% (average 7.5%) of all tumors and 56% of the sellar-chiasmatic tumors.³⁰

Tumor Development

According to the widely accepted embryogenetic theory of Erdheim, craniopharyngiomas take their origin from the remnants of the craniopharyngeal duct or Rathke’s pouch. Epithelial cell rests have been reported to occur in the “nests” most frequently along the anterior part of the infundibulum near its origin from the brain and the anterosuperior surface of the adenohypophysis.^29,³¹ When the cells of the vanishing hypophyseal duct are brought into immediate contact with the infundibular area before the primitive pia mater has developed, they will be intimately adherent to the neuroepithelium and subsequently developed pia mater will incorporate them into the subpial space.³² Alternatively, when the cell rests do not come into immediate contact with the neuroepithelium they will remain extrapial (Fig. 39.1). On the basis of histological findings, Grekhov³³ distinguished four groups of craniopharyngiomas according the point of their original growth: infrasellar, intrasellar (intrasellar and suprasellar), pituitary stalk, and infundibular craniopharyngiomas. Intimate contact of the cells of tumor origin with neural elements probably accounts for the manner in which many of these tumors appear to blend with the tuber cinereum, so as to form an intrinsic portion of that structure, or even to replace it.³⁴ These developmental concepts represent the clue to understanding the topographical variations of craniopharyngiomas.

FIGURE 39.1 The remnants of the craniopharyngeal duct. Arrow a, below the embryonic base of the anterior pituitary (ap); arrow b, below the primitive pia mater (A). B, embryonic base of the posterior pituitary.

The metaplastic theory postulates that the nests of squamous epithelium are derived from mature cells of adenohypophysis which undergo metaplasia.³⁵ However, these nests were not found in persons in their first decade, and rarely in those in the second; according to Kernohan³⁶ these observations failed to support the origin of craniopharyngiomas from such cells. The theory explains the craniopharyngioma spectrum, attributing the adamantinomatous type (typical for childhood) to embryonic remnants, and the papillary type (common in adult age) to metaplasia.¹⁴

Pathology and Surgical Anatomy

Microscopic Anatomy

The adamantinomatous craniopharyngioma is a histologically complex epithelial lesion resembling the enamel pulp of developing teeth. A pronounced feature is a palisading of peripheral layer of epithelium. The inner layer often undergoes hydropic vacuolation. This loose stellate reticular zone contains nodules of plump keratinocytes (“wet” keratin) with frequent dystrophic calcification. Areas of cholesterol deposits may be found. Papillary craniopharyngiomas are composed of simple squamous epithelium, which rests on a villous fibrovascular stroma forming papillae.

The brain parenchyma that surrounds both variants of craniopharyngioma is typically gliotic and often shows a profuse number of Rosenthal fibers.^29,³⁴ Tumor tissue, gliosis, and brain parenchyma may form one layer of tissue with a common vascular network. Finger-like protrusions of the tumor into the surrounding gliosis or even into the adjacent brain parenchyma are characteristic of adamantinomatous craniopharyngiomas.³⁷ On histological sections, these outgrowths appear as isolated islands of epithelium in the zone of intense gliosis.^34,³⁶

The intraventricular and extraventricular location of the craniopharyngiomas, according to a widespread idea, is a consequence of the disruption of a stretched and thinned-out floor of the third ventricle. This mechanism, which may also be occasionally observed in giant pituitary adenomas,⁴ is rather rare. More commonly, it is caused by the mechanism described previously. Our morphological^27,²⁸ and clinical observations showed that the structures of the third ventricular floor undergo atrophy of different degrees. The most affected structure is the tuber: its central part (postinfundibular eminence) is usually absent, and its remnants, the lateral eminences, are located on the lateral or lateral-basal surface of the tumor. The infundibulum (median eminence) is destroyed less frequently, whereas compressed mammillary bodies covering the posterior pole of the tumor can be found in all IEVCs.²⁷

The IEVCs are commonly located exclusively behind the optic chiasm. In some cases, presumably with premorbid long optic nerves, a small part of the tumor may occasionally extend below the chiasm or even between the optic nerves.

Some tumors classified in the literature as intraventricular craniopharyngiomas have been described as protruding into the interpeduncular cisterns.³⁸ We classified such tumors as IEVCs, reserving the term intraventricular for rare craniopharyngiomas lying entirely within the ventricular cavity covered from below by the floor of the third ventricle.³⁹^–⁴¹ Such a tumor is attached to a partially atrophied floor of the third ventricle while it may only touch its lateral walls (Figs. 39.2 and 39.3). This observation²⁸ has also been confirmed by others.⁴² We have seen only one such tumor in our clinical series.

FIGURE 39.3 Anatomical specimen with the intraventricular craniopharyngioma not adhering to the lateral walls of the third ventricle.

Clinical Presentation

The most common signs and symptoms include endocrine deficiencies (over 90%) more frequently in children, and visual disturbances (up to 96%) more frequently in adults. Among hypothalamic disorders in children obesity is prevalent, and mental disorders occur in both age groups.⁴³ Increased intracranial pressure is the most frequent presenting symptom in children.

Patients with craniopharyngioma generally present late, and visual symptoms are often preceded by a long history of systemic symptoms.⁴⁴ Children rarely become aware of visual problems and often present after almost complete visual damage has taken place.⁴⁵

Involvement of the optic pathway manifests itself by the defects of the visual fields and lowering of the visual acuity. Many different varieties of the visual field defects are found, among them bitemporal hemianopia, homonymous hemianopia, concentric contractions of fields, and central or paracentral scotomas.⁴³ The commonest field defect is asymmetrical bitemporal hemianopia, as a result of the compression of the chiasm, whereas homonymous visual field defects are caused by the tumors located behind the chiasm. The structures of the optic pathway may be compressed not only by the tumor but also by the arteries of the anterior part of the circle of Willis. The tumors growing below the chiasm push the optic structures upward against the anterior cerebral arteries (A1) and the anterior communicating artery (AComA). A strangulation groove may be found on the upper surface of the chiasm or on the terminal portion of the optic nerves. Retrochiasmatic tumors push the chiasm forward and downward below the A1-AComA complex. Strangulation grooves may be found on the most anterior parts of the optic tracts (Figs. 39.4 and 39.5). In the most severe case of our series we observed practically complete amputation of the optic tract from the chiasm.⁴⁶ Decompression of the optic pathway in such a case cannot be expected to improve the visual functions. Visual impairment may also be caused by compression of the lower chiasmatic arteries, branches of the internal carotid arteries (ICAs) between the upper surface of the tumor and the stretched chiasm. The decussating fibers in the central chiasm receive their arterial supply solely from this inferior group of vessels.^47,⁴⁸ Visual defects caused by ischemia may rapidly resolve after surgical decompression.

FIGURE 39.4 Relationship of the suprasellar extraventricular (A to C) and intraventricular and extraventricular (D to F) craniopharyngiomas with the optic nerves (1), chiasm (2, open arrow), optic tracts (3), internal carotid (4), and anterior communicating (arrows) arteries.

FIGURE 39.5 1, Internal carotid artery, displaced anteriorly, strangulating the right optic tract (2). 3, Chiasm; 4, optic nerve; 5, extraventricular portion of the tumor (see text); 6, posterior communicating artery; 7, posterior cerebral artery; 8, crus cerebri; 9, oculomotor nerve.

Long-standing intracranial hypertension causing atrophy of the optic disks may lead to concentric narrowing of the visual fields. Vision may also worsen after the surgery.

Endocrinopathies represented the most common manifestation at diagnosis (68%) in pediatric series of Di Rocco and associates.¹⁶ However, they are rarely the reason for referral. Growth deceleration and diabetes insipidus are often overlooked;⁴⁹ gonadotropic deficiency cannot be observed in small children. Delayed puberty in appropriate age was observed in all children with craniopharyngiomas.⁴⁹ Adults complain of decreased sexual drive and almost 90% of men complain of impotence, and most women complain of amenorrhea. Growth hormone deficiency in a large group of mostly adult patients was found in 82%.⁵⁰ The frequency of presurgery diabetes insipidus varies from 8% to 35%.^16,^49,^51,⁵² Compression of the pituitary stalk by a suprasellar mass causes hyperprolactinemia, which can be detected in more than 40% of patients with craniopharyngiomas.⁵³ Obesity is present in up to 25% of the patients.⁵¹ Its evolution before and after surgery is related to the severity of the involvement of the hypothalamus.^54,⁵⁵ Growth hormone insufficiency can also lead to increased body fat.⁵⁶

Signs of increased intracranial pressure from obstructive hydrocephalus, headache and vomiting, are more frequent in pediatric patients.⁵¹ This may be explained by the more common occurrence of the IEVCs causing hydrocephalus in children (73%) more frequently than in adults (49%). Extraventricular tumors, even large or giant, usually do not cause complete obstruction of the cerebrospinal fluid (CSF), as can be assumed according to the absence of enlargement of the lateral ventricles.

Cognitive impairment and personality changes occur more often in adults. In a series with the patients over 40 years of age, more than half suffered from impairment of memory.⁴³ Memory disturbances are attributed to a lesion of the mammillary bodies or of their connections with the hippocampal system, the fornix, and the mammillary-thalamic tract.^57,⁵⁸

Radiographic Diagnosis

Infradiaphragmatic craniopharyngiomas (intrasellar, infrasellar, and suprasellar) enlarge the sella similar to pituitary adenomas. Supradiaphragmatic tumors displace the diaphragm and the pituitary downward and the sella is shallow with depressed tuberculum, acquiring a J or a pear shape on plain radiography. Calcifications are present in about 85% of childhood and 40% of adult craniopharyngiomas, and are more readily detected by computed tomography (CT). Calcium deposits are present in most adamantinomatous tumors. Eggshell-like calcification of the wall of a cystic tumor may occasionally delineate the entire lesion (Fig. 39.6). Cyst fluid is usually of low density; however, cystic portions may appear dense or solid if they contain a sufficient quantity of suspended calcium salts (Fig. 39.7). Solid tumor tissue and the cyst walls show contrast enhancement.

FIGURE 39.6 Eggshell-like calcification of the capsule of intrasellar ane suprasellar craniopharyngioma.

FIGURE 39.7 Computed tomography (CT) (A) and magnetic resonance imaging (MRI) (B and C) scans of predominantly cystic intraventricular craniopharyngiomas with different cysts (see text). X, corresponding part of tumor.

The heterogeneous nature of the craniopharyngiomas is best displayed by magnetic resonance imaging (MRI). Solid parts of the tumor are most often isointense on T1-weighted images and show contrast enhancement. Hyperintense ring enhancement of the cyst wall is common. The high signal of the cyst fluid seen on T1 images in some tumors is related to high protein content or blood breakdown products. MRI provides information on the topography essential for planning the surgical approach. A different relation to the sella and its diaphragm may be seen on coronal scans (Fig. 39.8). In a tumor of a large or a giant size, the chiasm and the structures of the floor of the third ventricle often cannot be identified. The position of the chiasm may be detected indirectly as the AComA is always located in its immediate vicinity, most often at its upper posterior surface (see Fig. 39.4). Furthermore, the relation of the tumor with the chiasm and presence or absence of hydrocephalus may indicate the relation of the tumor to the floor and the cavity of the third ventricle with a high degree of probability.²⁷

FIGURE 39.8 Intrasellar and suprasellar (A), suprasellar extraventricular (B), craniopharyngioma on coronal magnetic resonance imaging (MRI) scans.

Modalities and Options for Treatment

The benign histological nature and aggressive clinical course of craniopharyngiomas together with technically difficult surgery led to two different attitudes to the initial management of this neoplasm: (a) radical surgical excision or (b) intentional incomplete (subtotal or partial) excision and radiotherapy.

The argument for radical surgery is the recurrence rate, which is considerably lower after complete tumor removal compared to subtotal or partial tumor resection, reaching 0% to 43% and 40% to 100%, respectively, and a worse outcome of secondary surgery.^9,^10,^{12–16,59–63} The authors advocating conservative surgery and subsequent radiotherapy stress lower incidence of endocrine deficit, hypothalamic insufficiency, major disability, and even higher rate of local tumor control after more conservative management.¹⁷^–²² There is almost general agreement on decreasing the number of recurrences and progression of residual tumors after radiotherapy. The recurrence rate in children after incomplete removal reaching 44% to 100% lowered to 16% to 37.5% after radiotherapy.^60,^64,⁶⁵ The recurrence-free survival rate representing 38% after partial surgery increased to 77% after radiotherapy.⁶⁶ Even a 100% progression-free survival rate after radiotherapy without previous surgery has been reported.¹⁷ Some other studies, however, found no relation between recurrence and adjuvant radiotherapy—neither globally nor in patients with incomplete resection.²⁴

There is no agreement concerning the timing of radiation. Lin and colleagues ⁶³ could prevent the recurrence in all cases with radiotherapy applied initially; if radiotherapy was applied at relapse the tumor subsequently recurred in 22%. Some authors therefore recommend routine administration of postoperative radiation.^18,^22,⁶⁷ On the other hand, residual tumor may remain stable for a very long period of time; therefore, others prefer the wait-and-see policy and do not recommend radiotherapy in stable residual tumor.¹⁶

Irradiation may be applied in fractions as conventional radiation therapy or by means of more advanced techniques: three-dimensional conformal radiation treatment, intensity modulated radiation therapy, or stereotactic radiotherapy. The tolerance of the optic chiasm is 54 Gy in 30 fractions.¹⁷ Gamma Knife stereotactic radiosurgery delivers to a tumor margin a dose from 9.5 to 35 Gy.⁶⁸^–⁷⁰ Close tumor relationship to visual pathways, however, is a limiting factor. For targeted single high-dose irradiation the dose to the optic chiasm should not exceed 8 Gy.⁶⁹

Shrinking of a cystic craniopharyngioma may be achieved by means of instillation of the solution of beta particle–emitting radioactive isotopes of yttrium-90, gold-198, or phosphorus-32. Long-term results after yttrium-90 colloid irradiation led to reduction of the initial cyst volume of 79%; in 47 patients in the reduction was more than 80%.⁷¹

Different modalities of irradiation (conventional external radiation therapy, Gamma Knife or linear accelerator radiosurgery, radioactive yttrium implantation) in our clinical series succeeded in local tumor control in 6 of 11 patients. It failed to prevent the recurrence or progression of residual tumor in another 5 patients, occurring from 6 to 60 months after irradiation.

All modalities of radiotherapy may cause damage to the pituitary, the hypothalamus, and the visual structures, and it may cause moyamoya syndrome, cavernous malformation, and secondary malignant astrocytoma.^16,⁷²^–⁷⁵ Most often affected is the function of the anterior pituitary.¹⁸ Deterioration of vision after instillation of beta wave emitters, attributed to irradiation and as the result of tumor progression, reached 22.5% to 52%.^76,⁷⁷ New neuro-ophthalmological deficits after yttrium-90 colloid irradiation occurred in 5.8%.⁷¹ The latter was comparable to 6.1% of visual deterioration after radiosurgery.⁶⁸ Damage to the carotid was reported after yttrium-90 treatment.⁷¹ In our autopsy series of craniopharyngiomas, the occlusion of the supraclinoid ICA was noted in a 15-year-old boy 6 years after intracystic instillation of 5 mCi of yttrium-90 and 2 years after additional external radiotherapy.

Our policy for the past 20 years is to recommend radiation therapy either by fractionated or a single-dose technique only to progressively growing tumors considered nonremovable at the previous surgery (primary or secondary) performed by us.

Chemotherapy with bleomycin has been used in cystic craniopharyngiomas. It causes thickening of the tumor capsule, and the cyst contracts, pulling away from brain structures, which facilitates cyst removal.⁷⁸ However, bleomycin is highly toxic for neural structures if it is allowed to leak from the cyst. In a review of 16 articles⁷⁹ at least one severe toxic effect, including visual or hearing impairment, personality changes, seizures, somnolence, or even death, occurred in 19% of patients. A combination of intracystic bleomycin and phosphorus-32 used in nine patients led to an even higher rate of complications.⁸⁰

Other surgical techniques are sometimes used in patients with primary or recurrent craniopharyngiomas. Ventriculoperitoneal shunt or even external ventricular drainage (EVD) may be inserted in cases with severe intracranial hypertension. We have had severe acute intracranial hypertension necessitating EVD in one patient. Some patients have had shunts implanted before referring to us for a tumor removal. Our policy is to restore the patency of the CSF pathways by removal of the tumor. Stereotactic technique is sometimes used for evacuation of a cyst or for instillation of radioisotopes or bleomycin into the tumor cyst.^21,^70,⁸¹ A repeatedly enlarging large cystic tumor may be treated by the implantation of an Ommaya reservoir, enabling simple evacuation of the cystic contents.

Cyst evacuation, different forms of irradiation, and chemotherapy are recommended mostly as an adjuvant treatment. We believe the best management of craniopharyngiomas is radical tumor removal whenever safely possible. A lower quality of life was observed after radical removal of craniopharyngiomas “involving the hypothalamus.”^25,²⁶ However, in cases with “hypothalamus no longer identifiable” on MRI scans the tumor may just compress the floor of the third ventricle and not invade it.^27,²⁸ It may be a good decision to remove the tumor radically in cases of extraventricular craniopharyngiomas and consider it contraindicated when the tumor is intraventricular.⁸² Nevertheless, the nature and intensity of the adherence of the tumor to diencephalic structures may differ within any of the topographical groups. Imaging studies do not show directly whether the tumor is simply compressing the hypothalamus or invading it, without a plane of cleavage. Therefore, the final decision about the extent of safe tumor removal cannot be made before the operation.

Surgery

Surgical strategy and tactics are based on the answers to two questions: Where to begin, and when to stop tumor removal? The answer to the first question is related to the choice of the optimal surgical approach. It should respect the topographical relationship of the tumor with the surrounding structures and at the same time it must provide sufficient tumor exposure. The answer to the second question is related to the fact that accessibility of a craniopharyngioma does not mean its resectability. Hypothalamic structures should be avoided during surgical approach and tumor resection (Fig. 39.9). There are two factors limiting preoperative assumption of the tumor–third ventricular floor relationship on rare occasions. First, it may be impossible to find out whether a retrochiasmatic supradiaphragmatic tumor not reaching the foramina of Monro and not causing hydrocephalus lies below the floor of the third ventricle or is embedded inside the infundibulum and the tuber cinereum. Distinction in such an MRI finding is possible only if the structures of the floor of the third ventricle are directly delineated. Second, besides the majority of tumors with expressed topographical features characteristic for one of the described groups, there are transitional types of craniopharyngiomas displaying the features of two topographical groups.

FIGURE 39.9 Schematic representation of the relationship of the intrasellar and suprasellar (A), suprasellar extraventricular (B), intraventricular and extraventricular (C), and intraventricular (D) craniopharyngiomas with the floor of the third ventricle (black) and surgical approaches (arrows) avoiding the hypothalamic structures.

Intrasellar and Intrasellar and Suprasellar Craniopharyngiomas

For intrasellar craniopharyngiomas the only appropriate approach is the transsphenoidal route, which exposes the entire tumor and allows identification of the remnants of the pituitary gland located anterior to the tumor or posterior to it.⁸³ The transsphenoidal approach is suitable also for the intrasellar and suprasellar craniopharyngiomas, with the exception of giant tumors and the tumors of a dumbbell or multinodular shape, which are rather rare in intrasellar and suprasellar craniopharyngiomas (Fig. 39.10). These tumors can be resected through the extended transsphenoidal approach, which allows removing even supradiaphragmatic craniopharyngiomas.^84,⁸⁵ In our series of 43 infradiaphragmatic tumors, 4 were intrasellar and 39 extended above the sellar diaphragm. Some of them were large or even giant tumors.

FIGURE 39.10 Intrasellar and suprasellar craniopharyngiomas, dumbbell (A and B) and multilobulated (C, D), resected via the subfrontal approach.

To expose the tumor via the transsphenoidal route we use the unilateral paraseptal, usually sublabial, approach performed under the operative microscope from the first incision. In order to get sufficient exposure of intrasellar contents a large opening of the sphenoid sinus and the sellar floor is mandatory.⁸³ The anterior wall of the sphenoid sinus and the sellar floor is resected under neuronavigation guidance. In a majority of our cases in which a compressed pituitary gland was found (one third of the intrasellar and suprasellar tumors), it could be detected at the sellar floor immediately after dural incision. The gland, which was identified at the floor of the enlarged sella, was split in the midline and displaced to the side so the tumor capsule could be identified (Fig. 39.11). The capsule always adheres to surrounding dura covering the sellar cavity; nevertheless, the tumor does not invade the cavernous sinus as the pituitary adenomas do. The capsule is separated from the dura by pulling it into the sellar cavity and detaching it by blunt microdissection, although sometimes sharp dissection is necessary. If the capsule is thin and fragile, care must be taken not to lose its continuity as later on it may not be identified and may be unintentionally left in place. On the other hand, if there is a thick firmly adhering capsule, it may not be possible to dissect it free and a part of it may have to be left in place.

FIGURE 39.11 Intrasellar and suprasellar craniopharyngioma removed transsphenoidally with preservation of the pituitary and no endocrinological deficiency.

The capsule may contain eggshell-like calcification which may be sharp like a blade so that maximum caution is necessary during its removal. Adherence of the capsule to the diaphragm is always extensive, and its removal is sometimes not possible without resection of the diaphragm and transsection of the pituitary stalk. Preservation of the pituitary stalk necessitates leaving the piece of the capsule in some cases.

Suprasellar Extraventricular Craniopharyngiomas

Superior displacement of the chiasm and partial prechiasmatic extension of a great majority of the SECs allow tumor removal through the (1) prechiasmatic space between the optic nerves, anterior angle of the chiasm, and the sellar tubercle; (2) opticocarotid triangle between the lateral margin of the optic nerve and chiasm, supraclinoid carotid artery, and the A1 segment of the anterior cerebral artery; and (3) laterally to the carotid. All these extracerebral routes to the tumor are accessible by the unilateral subfrontal approach, which is our most commonly used craniotomy in craniopharyngiomas (Fig. 39.12). Removal of an extraventricular tumor through the lamina terminalis would jeopardize hypothalamic structures of the floor of the third ventricle covering the upper surface of the tumor. Therefore, with rare SECs growing exclusively behind the optic chiasm we approach below and behind the chiasm through pterional craniotomy (Figs. 39.13 and 39.14). Skull base approaches enabling an approach to the tumor more from below, such as the orbitozygomatic or transpetrosal approach, may be of great help in these cases.⁸⁶ In a giant multicystic tumor a bifrontal craniotomy was necessary (Fig. 39.15).

FIGURE 39.12 A, Intraoperative view of a suprasellar extraventricular craniopharyngioma (t) removed via right subfrontal approach (B). s, pituitary stalk; x, basilar artery behind the Liliequist’s membrane; 1, right optic nerve.

FIGURE 39.13 Retrochiasmatic suprasellar extraventricular craniopharyngioma located behind the pituitary stalk, removed via the frontotemporal approach. Preserved pituitary stalk, no endocrine deficiency.

FIGURE 39.14 Retrochiasmatic suprasellar extraventricular craniopharyngioma removed via the frontotemporal approach. Preserved pituitary stalk. A to C, Intraoperative photographs. Preoperative (D) and postoperative (E) magnetic resonance imaging (MRI) scans. ba, basilar artery; ch, chiasm; ic, internal carotid artery; oc, oculomotor nerve (left); on, optic nerve; p1, p2, segments of the posterior cerebral artery; t, tumor.

FIGURE 39.15 Giant suprasellar extraventricular craniopharyngioma removed via bifrontal craniotomy (A and B). Magnetic resonance imaging (MRI) scans 2 days (C and D) and 5 years (E and F) after surgery.

For both subfrontal and pterional approaches we perform frontotemporal skin incision just behind the hair line, beginning from the midline medially and continuing laterally to the zygoma, preferably on the nondominant side. The extent of the bone flap in the subfrontal approach includes the convexity of the frontal bone as its merges with the supraorbital rim at its middle and lateral portions. In cases of a large frontal sinus the latter may be opened and then closed by the periostal flap before opening the dura. After evacuation of the CSF by lumbar drain and opening the dura, the sellar region is approached below the frontal lobe with the forceps in one hand and the sucker in the other without a spatula. The carotid and chiasmatic cisterns are opened for more CSF evacuation, and then the medial part of the Sylvian fissure is opened to relieve the pressure on the frontal lobe. Removal of the tumor starts by opening and evacuation of the cyst if visible. The subarachnoid space around the exposed tumor is blocked by cottonoids before opening the cyst to prevent leakage of the cyst contents into the CSF space. A brain spatula is used in later stages of surgery to support the relaxed brain if necessary.

Solid parts of the tumor are removed in a piecemeal fashion. The capsule is then detached from the optic nerves, the optic chiasm, the carotid arteries, and their branches. At this stage the capsule may be dissected from the pituitary stalk located on the posterosuperior tumor surface or displaced by the tumor toward one side. In some cases the dissection of the tumor capsule from the pituitary stalk is relatively easy, whereas in others, its lower part fades into the capsule and cannot be traced down to the sella.

The tumor may adhere to large blood vessels. Intraoperative damage to the internal carotid artery has been reported. Removal of a calcified portion of the tumor from the wall of the carotid in children may be especially dangerous.^8,⁸⁷ We found such extensive calcifications more commonly in the IEVCs. The SECs could be dissected safely from the adventitia even if they completely envelop the large arteries at the base of the brain. Extreme care must be taken to look for the minute perforating vessels, the branches of the supraclinoid carotid, and the posterior communicating arteries supplying the visual pathways and the hypothalamus. It is important to dissect these tiny vessels from the capsule of the tumor because they often bifurcate, with one branch supplying the tumor and the other continuing to its original destination. The vessel may be occluded only after confirming that it does not supply adjacent neural structures. The branches of the A1 and the AComA come in such close contact only with the tumors growing in front of the chiasm. If the perforators adhere firmly and cannot be safely detached from the tumor surface, a part of the capsule is left attached to the vessels.

A more common cause of an incomplete removal of the SECs is the adherence of the upper pole of the tumor to the pia mater of the superiorly displaced floor of the third ventricle, or more rarely of the chiasm. If the capsule cannot be dissected without disruption of the pial vascular network, then part of it or even a small piece of a tumor tissue has to be left in place. On rare occasions the distended floor of the third ventricle falls down during removal of the upper pole of the tumor. In a majority of the cases we delineate the condition of the ventricular floor by angled endoscope. Unintentionally left tumor remnants may be removed, but those firmly adhering to the pia of the hypothalamus have to be left in place (Fig. 39.16).