16 Craniopharyngioma

10.1055/b-0040-177072

16 Craniopharyngioma

Harminder Singh, Walid I. Essayed, and Theodore H. Schwartz

Abstract

Craniopharyngiomas represent up to 4% of pediatric intracranial tumors. Their operative and postoperative management continue to be challenging, particularly in the pediatric population. In this chapter, we discuss the natural history and different management options deployed for the treatment of these tumors, with a specific focus on endoscopic endonasal surgical techniques, and an illustrative case summarizing the different surgical steps. The primary goal of the endoscopic approach is to achieve maximum resection while avoiding hypothalamic and optic apparatus injuries. The pituitary function should be preserved as much as possible, but should not impede gross total resection when achievable.

16.1 Prevalence

Craniopharyngiomas represent between 1% and 4% of diagnosed pediatric tumors and are the most-diagnosed tumors involving the sellar and suprasellar region. ¹ These tumors tend to progress slowly and are often diagnosed between 5 and 14 years of age. ¹ ^, ² Craniopharyngiomas are rare tumors, with less than 100 pediatric cases a year in the United States, ³ making it difficult to evaluate the different treatment strategies applied across institutions.

16.2 Natural History

Craniopharyngiomas are benign epithelial tumors rising from ectopic remnants of Rathke’s pouch. Therefore, they are almost exclusively localized to sellar and suprasellar regions. However, some tumors are purely intrasellar (5%), while others are purely suprasellar (20%). ¹ ^, ⁴ Though benign, these tumors tend to damage surrounding structures by their growth. Opticochiasmatic compression, hypothalamic involvement, and intraventricular progression are the main reasons for presenting symptoms. Pituitary dysfunction is less prominent in pediatric patients, but can often lead to the diagnosis, particularly with linear growth impairment with growth hormone (GH) deficiency, and puberty delay due to follicle-stimulating hormone (FSH)/luteinizing hormone (LH) deficiencies. ⁴ ^, ⁵ Pediatric craniopharyngiomas usually have solid and cystic components, whereas in adults, they tend to be more solid. The cystic dilation of the tumor can be responsible for a rapid increase in the tumor size, inducing life-threatening symptoms (hydrocephalus), and necessitating rapid surgical treatment. ⁶

16.3 Management Options: Medical, Surgical, and Adjuvant

Surgical treatment represents the gold standard of care for craniopharyngiomas. The surgical objective is to achieve gross total resection with minimum morbidity. ⁶ ^, ⁷ ^, ⁸ Classic resection of a craniopharyngioma is done through open transcranial microscopic surgery. Purely intraventricular tumors are usually resected through a transcallosal transventricular approach, while for the other lesions, multiple surgical corridors have been described in the literature. These range from anterior (subfrontal), anterolateral (pterional), to lateral (subtemporal transtentorial, posterior petrosal) approaches, and their different modifications. ⁶ ^, ⁸ Each approach has its advantages and limitations; however, they all require some degree of brain retraction, resulting in an increased risk of contusions and seizures. Moreover, craniopharyngiomas are midline tumors, and lateral approaches can create blind spots, since the surgeon is often working around critical neurovascular structures.

Aggressive resection resulting in bilateral hypothalamic injury can lead to severe functional impairment. Hyperthermia, thirst sensation deficit, hyperphagia leading to morbid obesity, as well as severely debilitating neurocognitive issues are of major concern, particularly in pediatric patients. ⁹ Injury to the mammillary bodies, particularly in retrochiasmatic tumors, can also lead to cognitive and memory disturbances. The lack of infrachiasmatic visualization is shared by all cranial microscopic approaches, putting the optic apparatus at risk for iatrogenic injury or vascular disruption of the optic chiasm. Intraoperative identification of the stalk, superior hypophyseal arteries, and normal pituitary tissue can be challenging, which, together with the frequent infiltration of the stalk, severely impedes postoperative pituitary function.

These unsatisfactory postoperative morbidities, along with the evolution of adjuvant treatment options (radiotherapy, radiosurgery, intracystic treatment, etc.), have led to divergent opinions over the balance between obtaining a complete resection and avoiding postoperative morbidity. No consensus is currently available over management strategies; some authors advocate less invasive procedures in conjunction with adjuvant therapy, in hope to preserve pituitary and hypothalamic function, while others insist on the importance of total resection as a definitive cure for a pathology where reoccurrences are even more delicate to manage. In general, if gross total resection can be achieved without damaging the hypothalamus, it should be attempted, particularly in tumors with infradiaphragmatic origin and no fluid-attenuated inversion recovery (FLAIR) signal in the hypothalamus.

Hypothalamic injuries are difficult to manage. Hypothalamic invasion is frequent and can be found in more than 90% of pediatric patients. ⁵ It is best assessed on MRI on T2 and FLAIR sequences, and if present, can help the surgeon preoperatively plan for a subtotal resection strategy associated with postoperative adjuvant treatment. ¹⁰ On the other hand, pituitary function, even though important, can be intentionally sacrificed to achieve gross total resection. This decision should be guided by thorough preoperative evaluation. Preoperative pituitary deficiencies and transinfundibular growth of the craniopharyngioma, classically signifying invasion of the pituitary stalk, are indicative of a poor postoperative functional preservation outcome. Furthermore, postoperative pituitary insufficiency is relatively frequent even in the subset of patients with subtotal resections. Since pituitary insufficiency can be medically managed, pituitary and stalk preservation should not get in the way of achieving gross total resection.

The adjuvant treatments currently available for postoperative management are mainly based on radiation and intracystic chemotherapy. Multiple radiation therapy algorithms are available with equivalent results in decreasing the recurrence rate in partially resected tumors. ¹ Radiation is also useful if only biopsy was attempted in supposedly unresectable tumors. However, this local control is understandably associated with regional radiation toxicity. Already precarious endocrine equilibrium can be destabilized; visual complications are not uncommon, and long-term neurocognitive impairment is a major concern in pediatric cases, particularly with irradiation of the hypothalamus. Radiation-induced neoplasms and moyamoya can also occur in the pediatric population. ¹ Stereotactic radiosurgery seems to be associated with less morbidity, but long-term results are still under investigation. ¹¹ Accordingly, even though radiotherapy is a useful option, it should be delayed if possible in pediatric patients. Even though secondary surgery is usually more difficult, recurrences judged safe to resect should not be irradiated.

Pediatric craniopharyngiomas are frequently cystic. The cyst can represent the major component of a primitive or recurrent tumor and might display an accelerated growth pattern. Historically, intracystic chemotherapy was first developed in patients with reservoir-drained lesions. Many drugs, such as radioactive isotopes, bleomycin, and interferon, display varying degrees of efficiency but are unfortunately limited to the cystic portion of the tumor. ¹² Currently, intracystic interferon-α instillation via an Ommaya reservoir is one of the most effective therapies. ¹³ Even though treatment modalities are still heterogeneous, multiple reports support the conclusion that intracystic interferon-α provides durable cyst shrinkage beyond the obvious benefit of repeated fluid aspirations. ¹³

16.4 Endoscopic Endonasal Surgery

The anatomically sensitive location of craniopharyngiomas dictates this surgical approach. The position of the tumor in relation to the sellar diaphragm, optic chiasm, third ventricle, and infundibulum is important for the preoperative planning of surgery. Given the midline origin of most craniopharyngiomas, the endoscopic endonasal approach is often the best-suited approach for a majority of craniopharyngiomas. Recent data support the potential of endoscopic endonasal surgery in decreasing previously mentioned morbidities. ¹⁴ Contraindications for the endoscopic approach are tumors extending lateral to the cavernous sinus or carotid bifurcation, where gross total resection is the goal of surgery. Purely intraventricular tumors are a relative contraindication, since the floor of the third ventricle may be intact and violated through the endonasal endoscopic approach. The floor is formed by hypothalamic structures. In most cases, the floor is often extremely attenuated, making the endonasal approach safe. However, the degree of attenuation of the third ventricular floor can be difficult to determine on preoperative MRI scans.

Pediatric considerations should be evaluated preoperatively. The sinus cavities are less developed in children, offering little room during surgery. Adenoidal resection may also be necessary when they limit access to the posterior nasopharynx. Care should be taken to preserve the olfactory epithelium (OE) as well as the maxillary crest growth plate (MCGP) when preparing the nasoseptal flap (NSF) and performing the posterior septostomy. The contralateral septal mucosal flap can then be cut and swung around to cover the denuded septum (from harvesting the NSF) on the ipsilateral side (▶ Fig. 16.1).

Fig. 16.1 The contralateral mucosal “swing” flap is used to cover the denuded septum. The olfactory epithelium (OE) and maxillary crest growth plate (MCGP) should be preserved in pediatric patients.

The infundibulum-based classification is the most pertinent when discussing endoscopic approaches. ⁸ ^, ¹⁰ The amount of skull base bony exposure should be tailored to the size and location of the tumor. ⁹ Transversely, opening the sella “from carotid to carotid” is important to offer maximum room for bimanual dissection. In the sagittal plane, the bony opening can be variable. For a purely intrasellar lesion, a limited classic opening of the anterior wall of the sella may be sufficient. On the other hand, preinfundibular lesions usually grow between the optic chiasm and the pituitary stalk, occupying the suprasellar and infrachiasmatic cisterns, and variably extending into the prechiasmatic cistern. For exposing these lesions, an extension of the drilling through the sphenoidal tuberculum as well as planum is usually necessary. ⁸ ^, ⁹ For transinfundibular tumors, further anterior exposure might be necessary to follow the tumor inside the third ventricle. ⁸ ^, ⁹ Retroinfundibular lesions can be resected by working on either side of the stalk. If the tumor extends into the prepontine cistern behind the dorsum sellae, the bone opening can be extended inferiorly along the clivus with removal of the posterior clinoid process. ⁸ ^, ⁹ ^, ¹⁰

Once the bony opening is completed, the dura is opened, and tumor resection is started. The tumor can usually be quickly identified, allowing for internal debulking of the tumor as the first surgical step. The decompression allows the early identification of neurovascular structures and thus safer tumor dissection. Bimanual technique is employed for gentle and sharp progressive dissection from surrounding structures. Careful dissection of the anterior arterial communicating complex is important when attacking the prechiasmatic extension of the tumor. Preservation of the optic apparatus vasculature is also mandatory when dissecting this anterior extension of the tumor from the optic chiasm. ⁹ The dissection is then carried away from the anterior part, circumferentially to the lateral sides of the tumor, allowing progressive downward retraction to expose its superior aspect. This step is crucial for optimal close evaluation of the extent of hypothalamic invasion. Clear demarcation between the tumor and hypothalamic reactive gliosis can be difficult, but as we emphasized earlier in this chapter, maximal preservation of the hypothalamus is a key factor for maintaining patient functional outcome. Early identification of the pituitary stalk and superior hypophyseal arteries is important when attempting to preserve pituitary function. A branch of this artery can also extend up to the chiasm, which should be preserved. The decision to sacrifice the stalk should be left until the final stage of the resection. The use of angled endoscopes can help evaluate the extent of invasion of the surrounding structures along the resection cavity, and also for final inspection once the tumor is removed.

The progressive improvement in closure techniques have drastically reduced the postoperative rates of cerebrospinal fluid (CSF) leaks in endoscopic endonasal procedures. The systematic use of vascularized nasoseptal flaps in conjunction with postoperative lumbar drainage also helps in decreasing this risk. Various closure tactics have been reported, from the “gasket-seal” technique using MEDPOR and fascia lata ¹⁵ to the “bilayer-button” technique using two pieces of fascia lata stitched together in the center. ¹⁶ Some centers also advocate the use of intrathecal fluorescein to stain the CSF to better identify and repair intraoperative leaks. ¹⁷ Even so, in most craniopharyngioma series, the postoperative CSF leak rates are still around 10 to 15%. ⁹ The most successful closure has been the gasket seal combined with an NSF and a lumbar drain with leak rates on the order of 0 to 3%. ¹⁵ ^, ¹⁸ ^, ¹⁹ Close monitoring for postoperative diabetes insipidus is important, particularly since patients can experience both pituitary dysfunction and hypothalamic thirst deregulation.

16.4.1 Case Example

A 7-year-old boy was diagnosed with a large cystic craniopharyngioma. He underwent endoscopic intraventricular biopsy, cyst fenestration, and placement of a ventriculoperitoneal shunt at an outside institution. However, the patient continued to have increasing memory problems, and the cysts continued to grow in size (▶ Fig. 16.2). Therefore, the decision to proceed with endoscopic endonasal resection of this lesion was made.

Fig. 16.2 Preoperative coronal and sagittal T1-weighted MRI images show an enhancing cystic *suprasellar* lesion with extension into the third ventricle and adherence to the hypothalamus (*blue arrow*). Conchal pattern of pneumatization of the sphenoid is seen (*orange arrow*). Postoperative imaging show subtotal resection (STR) of lesion. The MEDPOR graft used for skull base reconstruction can be visualized (*yellow arrow*), as well as the nasoseptal flap (*green arrow*). Note that some portions of the tumor are adherent to the hypothalamus and are left behind.

The transtuberculum approach, through the transsphenoidal corridor, was used to approach the craniopharyngioma (▶ Fig. 16.3).

Fig. 16.3 The transtuberculum approach, through the transsphenoidal corridor, is used to approach most craniopharyngiomas.

There was incomplete pneumatization (conchal type) of the sphenoid sinus. This soft, cancellous bone was drilled to reach the sella (▶ Fig. 16.4).

Fig. 16.4 Incomplete pneumatization (Conchal type) of the sphenoid is seen. This cancellous bone can be easily drilled to reach the sella.

The bone over the sella and tuberculum was removed to expose the underlying dura, and the underlying intercavernous sinus was visualized. Laterally, the dura was exposed from one cavernous sinus to another for a panoramic exposure of the skull base (▶ Fig. 16.5).

Fig. 16.5 The dura over the sella (S), tuberculum sella (TS), and planum sphenoidale (PS) is exposed. The intercavernous sinus is visualized (*blue arrows*).

The dura was opened above and below the intercavernous sinus, over the sella and the tuberculum sella. The optic chiasm and pituitary gland were visualized. The pituitary stalk was also seen (▶ Fig. 16.6).

Fig. 16.6 The dura is opened above and below the intercavernous sinus, over the sella and the tuberculum sella. The optic chiasm (OC) and pituitary gland (P) are visualized. The pituitary stalk (*) is also seen. The green staining of the cerebrospinal fluid is from the fluorescein dye, which was injected via a lumbar puncture prior to the start of the case.

Working on both sides of the pituitary stalk and under the optic chiasm, the tumor was mobilized from the third ventricle, (▶ Fig. 16.7) and removed in a piecemeal fashion (▶ Fig. 16.8).

Fig. 16.7 The tumor is mobilized from the third ventricle, posterior to the pituitary stalk (*).

Fig. 16.8 The tumor (T) is resected in a piecemeal fashion. The pituitary stalk (*) is indented over the suction.

The majority of the tumor and its capsule was resected in this fashion. Small fragments of the tumor capsule that were adherent to the hypothalamus were left behind to avoid injury to the hypothalamus (▶ Fig. 16.9).

Fig. 16.9 The last few fragments of tumor are removed. The thinned out pituitary stalk (*) is seen. Small fragments of the capsule are stuck to the hypothalamus and are left behind.

A “gasket seal” was used for skull base reconstruction, using fascia lata and MEDPOR graft wedged into the bony opening (▶ Fig. 16.10). The previously harvested pedicled nasoseptal flap was layered over this closure, for a multilayer closure of the skull base.