Abstract
Craniopharyngioma is an uncommon, benign but locally aggressive intracranial tumor. Management of this entity is challenging and requires a multidisciplinary approach. Microsurgical resection remains the mainstay of treatment. However, it carries significant risks due to the deep-seated midline location and the proximity to important neurovascular structures. The most common surgical complications are endocrinologic abnormality, visual deficit, cranial nerve palsy, obesity, and neuropsychological disturbances. In this chapter, the relevant anatomy of the arterial and venous systems, third ventricle, hypothalamus and optic chiasm is discussed. This is followed by the classifications of tumor locations, which aid surgeons to choose the appropriate surgical approach for individual patients. The indications and nuances in operative techniques of the common surgical approaches (midline anterior, frontolateral, and transcallosal or transventricular intraventricular) are explained. Finally, the management for complications specific to craniopharyngioma surgery (fusiform dilatation of the internal carotid artery, hypothalamic dysfunction and morbid obesity, and ectopic recurrence) is discussed.
Keywords
craniopharyngioma, circle of Willis, optic chiasm, hypothalamus, lamina terminalis, endocrinologic abnormality, fusiform dilatation
Highlights
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Endocrinologic abnormality, visual deficit, cranial nerve palsy, obesity, and neuropsychological disturbances are the most common surgical complications in transcranial microsurgery for craniopharyngioma.
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Careful study of preoperative imaging is essential for deciding the most appropriate microsurgical approach, assessing hypothalamic involvement, and anticipating the relationship between the tumor and surrounding neurovascular structures.
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The tumor capsule and the Liliequist’s membrane provide safe tissue planes for dissection.
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Similar medium-term outcome between gross total resection versus subtotal resection with adjuvant radiotherapy means that patients’ functional outcome should not be compromised to achieve complete section.
Background
Craniopharyngioma is an uncommon tumor arising from the embryonic squamous cells of the craniopharyngeal duct (Rathke’s pouch) at the suprasellar region. It is benign but locally aggressive. Management of this entity is challenging and requires a multidisciplinary approach. Surgical resection remains the mainstay of treatment. However, it carries significant risks due to the deep-seated midline location and the proximity to important neurovascular structures. There has been an increased use of the extended endoscopic endonasal approach in the last two decades. However, transcranial microsurgery continues to be an important approach for large tumors with lateral extension, vascular encasement, and significant peripheral calcification and in children less than 3 years of age whose sphenoid sinus is conchal and not fully pneumatized and the basicranium is small. The transcranial approaches are broadly divided into midline anterior (interhemispheric, unilateral subfrontal/bifrontal) and frontolateral (pterional-frontotemporal and modified orbitozygomatic), lateral (combined petrosal and subtemporal), and transcallosal or transventricular intraventricular approaches. Posterior approaches for retrochiasmatic tumor have been described, and stereotactic aspiration and decompression surgery with Ommaya reservoir are routinely used for cystic tumors, but these will not be discussed in further detail. All transcranial approaches carry the risks of brain retraction, vascular injury, pituitary stalk disturbance, optic nerve (ON) manipulation for tumor exposure, and difficulty of accessing the infrachiasmatic portion, superior pole, and posterior fossa extension of the tumor. In large series, the proportion of patients experiencing at least one complication ranges between 53% and 79.4%. The main intra- and postoperative complications include: endocrinologic, electrolyte, ophthalmologic, neurologic, vascular, metabolic, infective, hydrocephalus, long-term cognitive impairment, and nonneurosurgical complications. Historically, complete excision was advocated because it offered the best outcome. However, the 10-year outcome is not different between gross total resection versus subtotal resection followed by adjuvant radiotherapy. Therefore, microsurgery with the aim of debulking and sparing important anatomic structures, thereby reducing morbidities, is a safe and efficacious treatment option.
Anatomic Insights
Arterial
The suprasellar arterial relationships are complex because this region contains all the parts of the circle of Willis ( Fig. 29.1A ). The anterior part of the craniopharyngioma is usually supplied by perforators from the anterior communicating artery (AComA) and the proximal anterior cerebral artery (ACA), the lateral part from the posterior communicating artery (PComA), and the intrasellar part from intracavernous meningohypophyseal arteries. It is not usually supplied by the posterior cerebral (PCA) and basilar arteries (BA).
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Internal carotid artery : The ICA courses inferior, then lateral to the ON and chiasm, sending perforating branches to the ON, chiasm, tract, and the floor of the third ventricle. These branches can be obstacles to the surgical approach through the triangle formed by the ICA, ACA, and the ON. The ICA also gives rise to the superior hypophyseal artery, which courses medially toward the tuber cinereum to form a ring around the infundibulum with its opposite mate ( Fig. 29.1A ).
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Posterior communicating artery : The PComA branches penetrate the floor between the optic chiasm and the cerebral peduncle to supply the thalamus, hypothalamus, subthalamus, and internal capsule.
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Anterior cerebral artery : The origin and the course of the ACA are highly variable. Normally, it arises from the ICA inferior to the anterior perforated substances (APS) and courses anteromedially superior to the ON and chiasm toward the interhemispheric fissure, where it joins the opposite ACA via the AComA. The AComA is usually related to the chiasm. Displacement of the chiasm against the anterior ACAs can lead to visual impairment before that caused by direct compression by the tumor. The perforating branches from the ACA and AComA supply the anterior wall of the third ventricle, hypothalamus, fornix, septum pellucidum, and striatum. The recurrent branch enters the APS.
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Middle cerebral artery : The MCA originates at the medial end of the sylvian fissure, lateral to the optic chiasm. It courses 1 cm posterior and parallel to the sphenoid ridge, sending the lenticulostriate arteries to the APS.
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Anterior perforating arteries : Of all the arterial systems at risk, the anterior perforating arteries are perhaps the most feared if interrupted during craniopharyngioma surgery. These arteries are the group that enters the brain through the APS ( Fig. 29.1A −C), arising from the ICA, anterior choroidal artery, ACA, and MCA. There are minimal anastomoses and overlap between these groups of arteries, and thus their preservation during surgery is important.
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Basilar artery : The BA bifurcates to form the two PCAs. Proximally, they send thalamoperforating arteries to supply the posterior part of the third ventricular floor and the lateral walls.
Venous
The veins in the suprasellar region drain mainly to the bilateral basal veins. They are generally small and do not usually present as obstacles to operative approaches to the suprasellar region and the lower part of the third ventricle. The internal cerebral vein originates at the foramen of Monro and courses in the velum interpositum, which forms the roof of the third ventricle.
Because the anatomy is highly variable between individuals, and because it can be distorted by the expansile craniopharyngioma, the vascular relationships should be studied carefully from cross-sectional imaging.
Third Ventricle and Hypothalamus
The inferior lateral walls and the floor of the third ventricle are formed by the hypothalamus. Thus, manipulation of the walls can cause hypothalamic dysfunction, including altered consciousness, metabolic disturbance, temperature control, and hypophyseal secretion. Injury to the columns of the fornix in the walls can lead to memory impairment. The roof is formed by four layers: one neural layer formed by the fornix and two membraneous layers of tela choroidea, which contains the layer velum interpositum, where the internal cerebral veins reside.
Position of Optic Chiasm to the Sella
The “normal” optic chiasm overlies the diaphragma sellae and pituitary gland (70%), the prefixed chiasm overlies the tuberculum sellae (10%); and the postfixed chiasm overlies the dorsum sellae (10%) ( Fig. 29.2 ). Several anatomic configurations limit the exposure to the suprasellar region in the transcranial approach: (1) a prefixed chiasm, (2) a normal chiasm with a small window between the tuberculum and the chiasm, and (3) a superior protruding tuberculum sellae. There are several surgical strategies to circumvent these obstacles. A transfrontal-transsphenoidal exposure is achieved by opening through the tuberculum and planum sphenoidale. If the chiasm is prefixed and the tumor is identified through a thinned-out anterior third ventricular wall, it can be accessed by opening the lamina terminalis. An expanded space between the ICA and ON caused by a lateral or parasellar extension of tumor can also provide a surgical corridor.
A good understanding of the relationship between the ON, the ICA, and the anterior clinoid process (AC) is essential for craniopharyngioma surgery in the sellar/parasellar regions. Both the ON and the ICA are medial to the ACP. The ICA exits from the cavernous sinus and courses posterolaterally, whereas the ON travels posteromedially toward the chiasm.
Classifications for Tumor Locations
Craniopharyngiomas are found typically in the infundibulo-hypophyseal axis in the sella and suprasellar area, and may grow in any direction. Several systems have been described to classify their location and anatomy. Most are topographically based and aid surgeons in choosing the optimal operative approaches. Some also have predictive value in surgical outcome.
The classifications are mostly based on (1) the vertical extension of the tumor or (2) its relation with normal anatomic structures including the sella turcica, optic chiasm, infundibulum, and ventricles. The main classifications are listed in Table 29.1 , and Fig. 29.2 is the diagrammatic representation of Yaşargil et al.’s classification. A prechiasmatic tumor extends from the sella into the subfrontal spaces. A retrochiasmatic tumor displaces the pituitary stalk anteriorly and the chiasm anterosuperiorly, resulting in a falsely prefixed ON. A subchiasmatic tumor displaces the chiasm superiorly and the pituitary stalk posteriorly. However, because the tumor growth pattern is often complex, not every tumor fits into a group neatly, and the suggested surgical approach by the scheme does not replace the careful study of the preoperative images.
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Prefixed chiasm
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Large tumor with lateral extension
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Tumor encasing the ICA
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Tumor adherent to the pituitary stalk
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Hypothalamic infiltration
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Recurrent tumor
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Previous radiation therapy
| Authors and Year | Basis of Classification | Classification |
|---|---|---|
| Ciric and Cozzens 1980 | Developmental and microsurgical relation. |
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| Konovalov 1983 | In relation to surgical management. |
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| Yaşargil et al 1990 | Relation with diaphragm sellae and ventricle. |
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| Hoffman 1994 | Relation with sella turcica and chiasm. |
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| Samii and Tatagiba 1997 | Anatomic, radiologic. |
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| Samii and Samii 2000 | Tumor vertical extension. |
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| Matsuo et al 2014 | Relation with anatomic structures. | Relation with diaphragm:
Relation with stalk:
Relation with optic nerve:
Sphenoid sinus:
|
| Pascual et al 2004 | Relation with third ventricle floor, only applicable to tumors involving the third ventricle area. |
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| Wang et al 2005 | Level of origin and the competence of the diaphragm sellae. |
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| Kassam et al 2008 | Relation with infundibulum, relevant to expanded endonasal approach. |
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| Fatemi et al 2009 | Anatomic extension of tumor, for comparison of endonasal and supraorbital approaches. |
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| Pan et al 2011 | Intraoperative and histologic classification of intraventricular tumor, third ventricle floor anatomy; no preoperative MRI correlation. |
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| Qi at al 2011 | Histologic findings and intraoperative tumor-membrane relationship around the pituitary stalk, leading to a proposed theory of four basic growth patterns. Aim to supplement existing classifications. |
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| Šteňo et al 2014 | Relation to sellae and third ventricle. |
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| Pan et al 2016 | Site of tumor origin and tumor development. This simplifies the earlier classification by Qi et al 2011 and is more practical. |
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| Jeswani et al 2016 | Based on Kassam et al 2008. |
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