Key points

A video of endoscopic endonasal resection of a supra sellar craniopharyngioma accompanies this article at www.oto.theclinics.com/

Introduction

Craniopharynigoma are rare, benign tumors of the central nervous system. Thought to arise from remnants of Rathke pouch in the sellar region, they represent less than 1% of all primary central nervous system tumors. Despite their benign histology, these tumors have posed a significant treatment challenge. Their central location in the sellar and suprasellar region and frequent invasion into critical neurovascular structures, such as the pituitary gland, hypothalamus, and optic apparatus, makes gross total resection (GTR) challenging. Although tumors may still recur after GTR the likelihood increases dramatically with subtotal resection. Nevertheless, significant controversy exists regarding the optimal treatment strategy, with some groups pursuing conservative subtotal resection with either upfront or salvage radiotherapy or radiosurgery to lessen the risks of aggressive surgical resection.

As these treatment paradigms have evolved, so too have the surgical techniques and approaches to craniopharyngioma, with the goal of maximizing resection and minimizing collateral damage. Traditional transcranial approaches require some degree of brain retraction and manipulation of cerebrovascular structures that lay between the surgeon and the pathology. The transsphenoidal approach offers a more direct route to the sellar/suprasellar region and if performed with the operating microscope provides only a limited field of view, which often precludes safe and complete resection of these lesions. The use of the transsphenoidal corridor was broadened with the development of expanded approaches, which offered a safe alternative method for reaching suprasellar craniopharyngioma. The incorporation of the endoscope was the next step on the evolutionary ladder. By virtue of an improved field of view and superb illumination, this allowed for further expansion of the endonasal corridor. Finally, the development of a variety of complementary multilayer techniques to repair the skull base minimized the risk of postoperative cerebrospinal fluid (CSF) leak. Several groups have now published their series incorporating these innovations into a fully endoscopic, endonasal, extended transsphenoidal approach for sellar and suprasellar craniopharyngioma.

Radiologic and Pathologic Characteristics

There are two major subtypes of craniopharyngioma. The adamantinomatous subtype is more prevalent in children and is thought to arise from neoplastic transformation of epithelial rests within the craniopharyngeal duct. The papillary subtype is almost exclusively found in adults and is thought to derive from metaplastic changes of epithelial cells within the pituitary stalk. Craniopharyngioma are characterized as a World Health Organization grade I neoplasm ( Fig. 1 ).

Resection from a 63-year-old woman with a sellar/suprasellar mass. Hematoxylin and eosin stained sections at low ( A ) and high ( B ) power reveal classic adamantinomatous histology with squamous epithelium, palisaded columnar cells, islands of wet keratin, stellate reticulum, and calcifications.

Most craniopharyngioma range in size from 2 to 4 cm, but can be significantly larger. They often have irregular borders and cystic components (46%–64%). The cystic components tend to be hyperintense on T2-weighted MRI. Enhancement of the cyst wall and heterogeneous enhancement of the solid portions is common. The adamantinomatous variant is frequently calcified. Close review of preoperative imaging is crucial to identify the relationships between the lesion and the chiasm, adjacent vasculature, pituitary stalk, and third ventricle ( Fig. 2 ).

MRI of craniopharyngioma. ( A ) Preoperative axial FLAIR. ( B ) Preoperative sagittal with gadolinium contrast. ( C ) Preoperative coronal with gadolinium contrast. ( D ) Postoperative axial FLAIR, note the absence of fluid attenuated inversion recovery (FLAIR) signal normally associated with retraction injury. ( E ) Postoperative sagittal with gadolinium contrast. ( F ) Postoperative coronal with gadolinium contrast.

Introduction

Craniopharynigoma are rare, benign tumors of the central nervous system. Thought to arise from remnants of Rathke pouch in the sellar region, they represent less than 1% of all primary central nervous system tumors. Despite their benign histology, these tumors have posed a significant treatment challenge. Their central location in the sellar and suprasellar region and frequent invasion into critical neurovascular structures, such as the pituitary gland, hypothalamus, and optic apparatus, makes gross total resection (GTR) challenging. Although tumors may still recur after GTR the likelihood increases dramatically with subtotal resection. Nevertheless, significant controversy exists regarding the optimal treatment strategy, with some groups pursuing conservative subtotal resection with either upfront or salvage radiotherapy or radiosurgery to lessen the risks of aggressive surgical resection.

As these treatment paradigms have evolved, so too have the surgical techniques and approaches to craniopharyngioma, with the goal of maximizing resection and minimizing collateral damage. Traditional transcranial approaches require some degree of brain retraction and manipulation of cerebrovascular structures that lay between the surgeon and the pathology. The transsphenoidal approach offers a more direct route to the sellar/suprasellar region and if performed with the operating microscope provides only a limited field of view, which often precludes safe and complete resection of these lesions. The use of the transsphenoidal corridor was broadened with the development of expanded approaches, which offered a safe alternative method for reaching suprasellar craniopharyngioma. The incorporation of the endoscope was the next step on the evolutionary ladder. By virtue of an improved field of view and superb illumination, this allowed for further expansion of the endonasal corridor. Finally, the development of a variety of complementary multilayer techniques to repair the skull base minimized the risk of postoperative cerebrospinal fluid (CSF) leak. Several groups have now published their series incorporating these innovations into a fully endoscopic, endonasal, extended transsphenoidal approach for sellar and suprasellar craniopharyngioma.

Radiologic and Pathologic Characteristics

There are two major subtypes of craniopharyngioma. The adamantinomatous subtype is more prevalent in children and is thought to arise from neoplastic transformation of epithelial rests within the craniopharyngeal duct. The papillary subtype is almost exclusively found in adults and is thought to derive from metaplastic changes of epithelial cells within the pituitary stalk. Craniopharyngioma are characterized as a World Health Organization grade I neoplasm ( Fig. 1 ).

Resection from a 63-year-old woman with a sellar/suprasellar mass. Hematoxylin and eosin stained sections at low ( A ) and high ( B ) power reveal classic adamantinomatous histology with squamous epithelium, palisaded columnar cells, islands of wet keratin, stellate reticulum, and calcifications.

Most craniopharyngioma range in size from 2 to 4 cm, but can be significantly larger. They often have irregular borders and cystic components (46%–64%). The cystic components tend to be hyperintense on T2-weighted MRI. Enhancement of the cyst wall and heterogeneous enhancement of the solid portions is common. The adamantinomatous variant is frequently calcified. Close review of preoperative imaging is crucial to identify the relationships between the lesion and the chiasm, adjacent vasculature, pituitary stalk, and third ventricle ( Fig. 2 ).

MRI of craniopharyngioma. ( A ) Preoperative axial FLAIR. ( B ) Preoperative sagittal with gadolinium contrast. ( C ) Preoperative coronal with gadolinium contrast. ( D ) Postoperative axial FLAIR, note the absence of fluid attenuated inversion recovery (FLAIR) signal normally associated with retraction injury. ( E ) Postoperative sagittal with gadolinium contrast. ( F ) Postoperative coronal with gadolinium contrast.

Treatment goals and planned outcomes

Although histologically benign, these lesions are locally aggressive and mandate intervention for the prevention and/or amelioration of neurologic symptoms. Surgical resection is a critical component of the treatment algorithm for craniopharyngioma. For many years attempted GTR was believed to be paramount to successful management of these lesions, and evidence suggests that recurrence rates are significantly improved when GTR is obtained. With the advent of modern microsurgical techniques, imaging modalities, and improved endocrine management, GTR became feasible with reasonably low morbidity and mortality. Nevertheless, some groups contend that a conservative surgical approach, achieving subtotal resection, followed by radiation therapy should be considered the preferred treatment strategy. The rationale is to avoid potential surgical morbidity that would adversely affect quality of life. This is especially true in children, in whom endocrinologic and hypothalamic injury can be devastating. There is no level 1 or level 2 evidence that supports one management paradigm over the other. Our general philosophy is one that aims to maximize tumor resection while minimizing postoperative complications. In most cases this means an attempt at complete resection with an endoscopic, endonasal approach followed by observation if successful or adjuvant therapy, such as radiation, if residual tumor remains.

The transsphenoidal corridor and endoscopic, endonasal technique can be used to resect sellar and suprasellar craniopharyngioma. A key aspect of this technique is the expansion of the operative field by incorporation of the transtuberculum and transplanum approaches. This approach is adapted for use in tumors extending into the third ventricle, and those extending into the prepontine cistern. The primary limitation of the transsphenoidal approach is its lateral reach, and as a general rule, this approach should not be applied to tumors extending more than a centimeter beyond the lateral limits of the exposure.

Preoperative planning and preparation

Relevant anatomy from preoperative MRI should be reviewed in detail. Particular attention should be paid to the location of the optic nerves/chiasm, internal carotid, anterior cerebral, and middle cerebral arteries, and the pituitary gland/stalk. In addition, a detailed neurologic examination should be performed before any intended surgical intervention. Patients with optic chiasm compression should undergo comprehensive neuro-ophthalmologic evaluation, including formal visual field testing. All patients should undergo neuroendocrine assessment, including measurement of pituitary hormones.