Classification

Several authors who attempted to radiographically classify craniopharyngiomas include Rougerie, Pertuiset, Konovalov, Steno, Hoffman, Samii, and Kassam.^5–11 Although none have been universally adopted, these classifications all share the principle of subdividing lesions along the length of extension in the primary vertical axis; the resulting relationship is with the optic chiasm and the third ventricular floor immediately posterior to it.

Histologically, craniopharyngiomas are divided into adamantinomatous, papillary, and mixed. The most common form is adamantinomatous, which is often cystic and filled with dark fluid. Columnar or polygonal squamous cells with nuclear palisading arranged in broad bands, cords, and bridges with nodules of compact keratin and dystrophic calcifications are characteristic of the adamantinomatous type (World Health Organization). The wet keratin contrasts with the lamellar flaky keratin in epidermoid cysts. In contrast, papillary craniopharyngiomas consist of sheets of squamous cells that form papillae, lacking nuclear palisading, wet keratin, calcification, and cholesterol deposits.

Anatomy

Craniopharyngiomas arise in the parasellar space involving the sella, suprasellar space, and third ventricle. Unlike pituitary tumors, they often adhere to the neurovascular structures of the suprasellar space. Perforating vessels, arising from the anterior communicating artery as well as the proximal ICA, coat the tumor capsule anteriorly as they course toward the optic chiasm and anterior perforating substance. On their way to the basal ganglia and thalamus, laterally and posteriorly perforating vessels that originate from the posterior communicating artery and infrequently from the proximal posterior cerebral arteries are found adherent to the tumor capsule. This close anatomic relationship with vascular structures is an important factor that limits the extent of surgical respectability.

Another important limiting factor during surgical resection is the close apposition of craniopharyngiomas to the pituitary infundibulum. This opposition has led some to argue that gross total resection cannot be achieved without the section and removal of the involved part of the infundibulum. Although this point remains contested, the morbidity of sacrificing the infundibulum is significant, particularly in pediatric patients.^12–19 Diabetes insipidus and hypopituitarism after injury to the infundibulum can impact both the physical and mental growth of patients and limit their daily functional capacity.

Treatment Decision Making

The primary treatment of craniopharyngiomas remains surgical. The variability of the tumor extent make is imperative to tailor the surgical approach to the particular lesion. Of several different approaches described, no approach is overall preferred for the majority of the lesions. Adjuvant treatment with radiation therapy is often used; it is necessary in all cases when gross total resection is not achieved and in some tumor recurrences that appear after apparent gross total resection and are likely the result of microscopic residual disease.

Although most patients undergo both surgical and radiation treatments, a number of questions need to be addressed on an individual level. Choice of surgical approach depends primarily on the extent of the lesion along the vertical axis (Fig. 24-1). Lesions that are purely intrasellar are preferably approached through a trans-sphenoidal approach. Microscopic or endoscopic corridors have been well described and mimic the approach to pituitary adenomas. Because intrasellar lesions are often cystic, obliteration of the tumor cavity with fat may not be indicated unless a cerebrospinal fluid (CSF) leak is manifested intraoperatively, effectively allowing for a prolonged outlet that can delay or prevent future reaccumulation of fluid within the cavity. The trans-sphenoidal route can also be used successfully in the presence of significant suprasellar extension in mostly cystic lesions. The recent development of expanded endoscopic trans-sphenoidal approaches to the sella make the resection of the cyst wall possible when vascular adherence is not a significant issue.

FIGURE 24-1 Approaches to the anterior fossa and sellar region include the trans-sphenoidal, extended trans-sphenoidal, bifrontal, interhemispheric, pterional, and supraorbital.

(From Mayfield Clinic, Cincinnati, OH.)

Lesions with significant suprasellar extension, particularly when mostly solid, are preferably approached through intracranial corridors. Although expanded endoscopic trans-sphenoidal approaches can provide effective tumor resection, they are considered alternative approaches because of the dearth of appropriate instrumentation, which can cause difficulty in safely managing intraoperative bleeding. Additionally, the dural opening immediately inferior to the suprasellar cistern has proven to be difficult to seal effectively against CSF leaks. Finally, most lesions that are primarily suprasellar arise superior to the pituitary gland, displacing it inferiorly, making the mobilization of the gland itself a necessity for access to the lesion through a trans-sphenoidal route, a surgical maneuver that can result in hypopituitarism.

Transcranial routes to the suprasellar space range from a supraorbital corridor to the pterional approach (with or without an orbital or orbitozygomatic osteotomy) to the bifrontal craniotomy. Although each one of these approaches provides a similar exposure to lesions in the suprasellar space, they differ in several important ways. The supraorbital craniotomy, which minimizes soft-tissue morbidity and creates a shorter overall incision, is limited by the size of the frontal sinus. Violation of the frontal sinus through the supraorbital approach can cause a CSF leak that is challenging to fix or a rotation periosteal flap is difficult. Additional limitations of the supraorbital craniotomy include the limited vertical exposure and difficulty with effective brain retraction.

The bifrontal subfrontal approach allows for a midline or medial exposure to the suprasellar space and can be the most effective in the presence of a post-fixed chiasm. Conversely, a prefixed chiasm is a limitation that may make access to the lesion all but impossible. Close study of preoperative imaging may give some indication to the location of the chiasm. Specifically, assessment can involve both direct visualization of the chiasm in the absence of severe distortion of normal anatomy and determination of the position of the anterior communicating artery as a surrogate for the location of the chiasm. Nonetheless, large lesions often make it difficult to ascertain the exact position of the chiasm preoperatively; in such cases, this approach can be limiting.

The pterional approach is the most versatile for accessing the majority of craniopharyngiomas. It allows for working channels in between the two optic nerves, between the optic nerve and ICA, and between the ICA and oculomotor nerve. The pterional approach is the one most often used for removal of the optic canal roof and anterior clinoid process, steps often necessary for safe mobilization of the optic nerve. The limitation of this approach relates to the location of the ipsilateral optic nerve in the direct line of sight; that is, resection of a significant part of the tumor deep to the nerve is difficult without substantial mobilization of the nerve itself.

Tumors that extend extensively into the third ventricle or infrequently arise primarily in the third ventricle pose the greatest surgical challenge, particularly when a significant cystic tumor component is absent. The two major corridors to such lesions are the translamina terminalis approach and the transventricular approach. The lamina terminalis forms the superior continuation of the optic chiasm; its fenestration allows for entry into the anterior third ventricle. It provides direct access to the anterior part of the lesion, yet is limited by the amount of retraction of the optic tracts and the anterior communicating artery necessary for visualization into the third ventricle. In large lesions, determination if a plane of safe dissection exists between the lateral walls of the tumor and hypothalamus can also be challenging. This determination is particularly difficult through a pterional approach that leads to blind dissection of the ipsilateral tumor margin.

Transventricular approaches are the most versatile to access large lesions within the third ventricle. A transfrontal or interhemispheric approach can be used to access the lateral ventricle. A transforaminal approach expanded through a subchoroidal extension provides wide access into the third ventricle and good visualization of the lateral margins of the lesion. Limitations of this approach are the significant depth at which the lesion is encountered, the thalamostriate vein that needs to be mobilized, and the potential for injury to the fornices.

Radiation therapy is often used as adjuvant therapy. However, a good indication for its use as primary treatment is the rare case of a solid third ventricular lesion with evidence of poor margins with the hypothalamus in an older patient. The radiation delivery method varies depending on the tumor’s size and characteristics. The usual limitations for radiosurgical treatment, relating to both lesion size and proximity to the optic apparatus, hold true and often lead to the need for fractionated treatment.

For primarily cystic tumors, stereotactic- or endoscopic-transventricular cyst aspiration through an implanted catheter can allow for intracystic instillation of radioactive material or chemotherapy as well as subsequent percutaneous aspirations of fluid re-accumulation.

Surgical Techniques

Trans-Sphenoidal/Expanded Trans-Sphenoidal Approach

The patient is positioned supine; the head in the “sniffing” position allows for elevation above the level of the heart and drainage of bloody material inferiorly away from the surgical field. The traditional trans-sphenoidal approach through a microscopic or endoscopic approach can be used. Intrasellar tumors and mostly cystic craniopharyngiomas even with a significant suprasellar extension are excellent candidates for this approach (Fig. 24-2).

FIGURE 24-2 The trans-sphenoidal approach may be used for craniopharyngiomas that are primarily intrasellar or when the suprasellar component is cystic. A, An endoscope is inserted through one nostril and instruments are passed through the other nostril. A small portion of the posterior nasal septum is removed and the sphenoid sinus is opened. An opening is made in the sella to expose the tumor. Using curettes and suction, the surgeon debulks and removes the solid portion of the craniopharyngioma. B, Dissection into the cystic portion will release the fluid contents, then decompressing the optic nerves and vascular structures in the suprasellar space. C, The sella is lined with Surgicel and filled with fat harvested from the abdomen. Because the sella does not often support primary closure, the sphenoid sinus is obliterated with fat and closed with cartilage or cortical bone

(From Mayfield Clinic, Cincinnati, OH.)

The expanded trans-sphenoidal approach requires significant bony removal superiorly past the tuberculum. Importantly, at the beginning of an expanded trans-sphenoidal approach, consideration should be given to raising a nasoseptal mucosal flap, which will be used during closure.²⁰ Visualization of the superior aspect of the lesion and its relationship to the undersurface of the optic chiasm is feasible with debulking of the tumor. The perforating vessels and the plane with the optic apparatus need to be sharply dissected under direct vision. However, present endoscopic instrumentation creates an obstacle to effective dissection in many patients.

Closure of a traditional or expanded trans-sphenoidal approach has important considerations. Intrasellar lesion resection can be associated with CSF leaks. Obliteration of the sella with abdominal fat grafting is our preferred reconstruction technique; it is reinforced by bone or cartilage obtained during the exposure and by tissue sealant onlay over the entire reconstruction. In the absence of a CSF leak, one may consider leaving the sella open to delay or obviate the re-accumulation of fluid within the cyst. Caution should be used in making this decision depending on the amount of arachnoid descent and herniation within the sella because a delayed CSF leak may ensue.

Although a watertight closure of expanded trans-sphenoidal approaches remains elusive, significant steps have been made during the past several years. Simple fat obliteration proves to be inadequate reconstruction. Multilayer reconstructions and the use of vascularized pedicled mucosal flaps have been promising as an effective reconstruction that can prevent leaks. Use of specialized clips that attempt direct dural reapproximation is an obvious improvement, yet technically very challenging. Deployment of inflatable balloons within the sphenoid sinus can augment the reconstruction. Lumbar subarachnoid drains for temporary CSF diversion offer mechanical advantages but must be balanced by their risk of potential complications, compression of neurovascular structures for the former, and development of pneumocephalus for the latter.

Bifrontal Craniotomy

The patient is positioned supine with the head slightly extended in three-point pin fixation in the Mayfield clamp. Frameless stereotactic guidance is a useful adjunct for accurate localization of the lesion. A bifrontal incision is marked behind the hairline. Ensuring that the lateral limits are close to the zygomas bilaterally then limits the pressure on the skin flap and avoids flap ischemia. Burr holes are placed on either side of the superior sagittal sinus, approximately 5 cm above the nasion and laterally superior to the keyhole, just lateral to the superior insertion of the temporalis muscle, which is elevated in a limited fashion. The inferior bony cut is preferably made just superior to the frontal sinus; however, transgression of the sinus can be fixed easily with the use of a rotational pericranial flap. The dura is opened in a horizontal incision inferiorly and the superior sagittal sinus is divided with medium vascular clips. The falx is incised and the anterior interhemispheric space is explored (Fig. 24-3).

FIGURE 24-3 The bifrontal interhemispheric approach may be used for craniopharyngiomas in the suprasellar space and is most effective when a post-fixed chiasm is found. A, Bilateral burr holes are made at the pterion, and two additional burr holes are made on either side of the superior sagittal sinus. After a bone flap is cut to connect the burr holes, the posterior wall of the frontal sinus is down-fractured and the flap is removed. The dura is opened and the superior sagittal sinus is tied off and cut. The dural cut is extended down the falx until released. B, The frontal lobes are retracted and adhesions to the olfactory tracts separated. C, The anterior cerebral arteries and optic chiasm are identified and tumor is removed. D, If the tumor growth has prefixed the chiasm, entry into the lamina terminalis exposes tumor in the third ventricle. E, If the tumor growth extends inferiorly, the bone of the tuberculum sella can be drilled to access and remove tumor from the sphenoid sinus.

(From Mayfield Clinic, Cincinnati, OH.)

Once the lesion is localized, its relationship to the optic nerves and chiasm is assessed. A prefixed location of the chiasm is a limitation of this approach. In the absence of significant extension into the third ventricle, drilling the tuberculum often allows for increased exposure subchiasmatically. Although exposure is potentially adequate for resection of the lesion, this is a limited corridor for large lesions. Reconstruction of the skull base is crucial for a good outcome.

The anterior interhemispheric approach is perhaps the optimal approach for lesions with extension into the third ventricle. After exposing the chiasm, the surgeon identifies the lamina terminalis, dissects and gently retracts the anterior communicating artery superiorly, and a fenestration into the third ventricle. A midline fenestration at the thinnest area, as far superior to the chiasm as feasible, is most desirable. Correct identification of the optic nerves and optic tracts bilaterally is the safest way to avoid injury to the visual system.

Dissection of the tumor from the third ventricle can be safely achieved through the fenestration of the lamina terminalis. The principles that ensure safety and improved outcome are careful identification of the visual apparatus and careful dissection of the lateral margin of the tumor from the hypothalamus. In cases where the plane between the tumor and the lateral wall of third ventricle is not directly visible or absent, one needs to exercise caution to avoid hypothalamic dysfunction.

Pterional Craniotomy

The traditional frontotemporal or pterional craniotomy is perhaps the most widely used approach for the treatment of craniopharyngiomas. Reduction of the sphenoid wing is a standard part of this approach because it improves exposure superiorly. Once the basal cisterns are opened, there are two major corridors for lesion resection: the subchiasmatic corridor between the two optic nerves and the opticocarotid corridor between the lateral aspect of the ipsilateral optic nerve and ICA (Fig. 24-4).

FIGURE 24-4 The pterional approach is the most versatile to access craniopharyngiomas by allowing the surgeon to work in between the two optic nerves, between the optic nerve and ICA, and between the ICA and oculomotor nerve. A, After a question-mark skin incision is made, a burr hole is placed at the anterior aspect of the superior temporal line. A bone flap is cut with a craniotome and removed. B, View of supraorbital and transorbital keyhole craniotomies. C, The dura is opened and retractors are used to access the optic nerve and chiasmatic cistern. A bipolar is used to coagulate tiny vessels and the lamina terminalis is opened. D, Tumor removal can be accomplished from the third ventricle and suprasellar space with preservation of the pituitary stalk.

(From Mayfield Clinic, Cincinnati, OH.)

This approach is familiar to most neurosurgeons, yet its relative limitation is that the lesion lies posterior to the ipsilateral optic nerve, which often is displaced anteriorly and superiorly as it is splayed over the tumor surface. Manipulation of the ipsilateral optic nerve is a maneuver that endangers visual function. Therefore, one needs to resist the temptation to mobilize the optic nerve for enhanced tumor exposure. Section of the falciform ligament and fenestration of the optic canal, and less often anterior clinoidectomy, are surgical adjuncts that minimize the risk to the ipsilateral vision.

The pterional approach allows for direct visualization of the microvasculature surrounding the lesion in the suprasellar cistern. Careful dissection of perforating vessels from the mesial wall of the ICA and the anterior cerebral artery prevents vascular injury to the anterior perforating substance, basal ganglia, hypothalamus, and visual system. The pterional approach is also a versatile one. An orbital osteotomy allows for wide access and improvement in the superior aspect of the surgical exposure. Dissection along the ipsilateral optic nerve and chiasm allows for fenestration of the lamina terminalis and access to the part of the lesion extending into the third ventricle. Care should be taken to correctly identify the location of the lamina terminalis. The 15- to 45-degree rotation off the vertical axis can disorient the surgeon with respect to midline, particularly at depth. Confirmation of midline anatomically is crucial with respect to the anterior communicating artery as well as with the use of frameless stereotactic guidance. Off-midline fenestration may result in both poor access to the lesion and injury to the visual system and hypothalamus.

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