Craniopharyngioma (Endonasal Approach)
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Craniopharyngiomas typically arise from nests of metaplastic adenohypophyseal cells of the pituitary stalk. Except for the 5% that are purely intraventricular, most of these lesions originate from the parasellar space with their nodule and extend their cystic section into the third ventricle. These tumors adhere to and encase some or all of the following structures: the optic nerves and chiasm, pituitary gland and stalk, circle of Willis, brainstem, hypothalamus, third ventricle, and the frontal/temporal lobes.
A relatively safe corridor of approach is available from below through the subchiasmatic route. These tumors and their predominantly third ventricular counterparts are most often retrochiasmatic in location; this feature makes them suitable candidates for endoscopic transnasal surgery as there is no practical transcranial route to access the retrochiasmatic space.
I have nearly abandoned the transcranial route for resection of craniopharyngiomas in favor of the transnasal route for the past few years. I believe the results of the extent of resection, patient recovery, and postoperative morbidity are in favor of the direct minimally invasive transnasal corridor. The indications for the transnasal versus transcranial approaches for this tumor type are discussed below.
Although generally centered on or near the infundibulum, the clinical presentation of a craniopharyngioma depends on the tumor’s exact location relative to structures surrounding it: the pituitary gland and stalk, optic apparatus, and the third ventricle and its floor (the hypothalamus).
In adult patients, visual disturbances and headaches are the most common presenting neurologic findings. Neurocognitive changes due to infiltration of the hypothalamus are also common, although endocrine dysfunction is variable and frequently not clinically significant. In children, elevated intracranial pressure is more common, while endocrine dysfunction is usually related to growth hormone insufficiency; occult visual findings are also often present in children. Hydrocephalus occurs in one-third of both populations.
The primary modality to evaluate a craniopharyngioma is magnetic resonance imaging (MRI). This imaging modality allows characterization of the tumor, which is generally lobulated with heterogeneous signal intensity and large cysts. Computed tomography (CT) is necessary to evaluate the anatomy of the underlying skull base to assess its feasibility as an operative corridor. Additionally, the adamantinomatous subtype usually contains areas of calcification, whereas the papillary subtype, seen exclusively in adults, lacks calcification.
Given the high incidence of preoperative endocrine dysfunction with these tumors, all patients should undergo a complete endocrinologic evaluation. These tests will also facilitate management of postoperative hormone deficiency. In the perioperative setting, adrenal insufficiency and diabetes insipidus are the two potential diagnoses of primary importance and demand appropriate treatment.
Preoperative formal visual field and a dilated fundoscopic examination are required, both to document a preoperative baseline status and to provide a reference point when monitoring for future tumor recurrence. A complete understanding of any preoperative visual deficit is necessary to fully design the optimal surgical plan.
Other suprasellar lesions include a variety of pathologies that can be extrinsic (meningioma, germ cell tumor, metastasis, epidermoid cyst), intrinsic (hypothalamic or optic glioma, pituitary macroadenoma), or bony (giant cell tumor, aneurysmal bone cyst). Vascular studies (CT or MR angiography) will rule out atypical aneurysms and define the surrounding normal vasculature that may be involved in tumors extending anteriorly (anterior cerebral arteries), posteriorly (basilar apex and posterior communicating arteries), or laterally (distal internal carotid arteries and their branches). The finding of a calcified cystic mass associated with the pituitary stalk is almost pathognomonic of a craniopharyngioma.
Preoperative imaging should assess the degree of pituitary stalk involvement; this variable can potentially define the risk of its sacrifice to achieve a gross-total resection.
Indications for Surgery
There is minimal evidence regarding observation for these lesions as they are almost always symptomatic at presentation. In older adults with incidental asymptomatic lesions, serial radiographic, endocrinologic, and ophthalmologic monitoring may be appropriate. However, if the diagnosis of craniopharyngioma is likely, I recommend surgery, and if the diagnosis is confirmed through frozen section, resection and adjuvant radiotherapy are instituted.
The goal of surgery is maximal safe resection. Although a surgical cure is possible with gross total resection, this should not be achieved at the cost of damaging the hypothalamus, as this leads to poor quality of life. Radiotherapy is the main adjuvant treatment, and there is an increasing role for radiosurgery or proton beam therapy to protect the surrounding vital structures.
Palliative procedures such as cyst decompression/fenestration or ventricular shunting may improve symptoms, but they generally only temporize the situation without definitively addressing the problem. Other methods of therapy such as intracavitary brachytherapy may be chosen in rare recurrent nonoperative cases.
Preoperative evaluation includes neuro-ophthalmologic tests with special attention to visual fields and endocrinologic testing. Neuropsychological evaluation is often helpful for lesions causing mass effect, especially those affecting the frontal or medial temporal lobes.
The majority of craniopharyngiomas (75%) have a significant suprasellar component, and the pathologic expansion of the suprasellar space defines the main operative corridor. Moreover, the extent and size of the paranasal sinuses, the involvement of surrounding vascular structures, and the expansion of the tumor lateral to the carotid arteries or into the posterior fossa determine the transcranial versus transnasal choice of approach.
Specifically, rare tumor types that are purely intraventricular may not be ideal for an endonasal approach because the intact third ventricle floor has to be preserved. Tumors that are largely solid or have a large extension lateral to the carotid bifurcation are suitable for a transcranial corridor (Figure 2). Purely intrasellar lesions, although rare, may require minimal parasellar bony exposure. Based on involvement of the hypothalamus, a preoperative plan for a gross total versus subtotal resection should be designed. Hypothalamic involvement by the tumor usually is best seen on coronal fluid attenuated inversion recovery (FLAIR) sequences.
ENDOSCOPIC TRANSNASAL MICROSURGICAL RESECTION OF CRANIOPHARYNGIOMAS
The technical nuances for skull base parasellar craniotomy/osteotomy are discussed in the Endoscopic Expanded Transnasal Approach chapter. Please refer to this chapter for information regarding the initial and final stages of the operation, including exposure and closure. The open transcranial approaches for resection of this tumor type are discussed in the Craniopharyngioma (Transcranial) chapter.
Prior to dural opening, a circumferential bony edge should be mucosa-free to allow placement of the mucosal nasoseptal flap at the end of the operation, and epidural dissection for a layered closure may also be performed. Ultrasonography may be used to guide the dural opening and help the surgeon avoid injuring the carotid arteries.
Upon opening the dura, preinfundibular tumors are immediately visible. There is often a thin layer of arachnoid covering the tumor that should be opened sharply. It is important to identify the stalk and the superior hypophyseal arteries as early as possible during surgery to facilitate their preservation for as long as possible until it is determined that gross total resection necessitates the sacrifice of the pituitary function.
This patient presented with visual decline and was diagnosed with a suprasellar craniopharyngioma of moderate size.
Meticulous closure is necessary to avoid postoperative CSF leakage that can spoil a good resection result.
The patient is observed in the intensive care unit overnight for frequent neurologic evaluations and pain and blood pressure control. Entry into the ventricular system carries a higher risk of postoperative cerebrospinal fluid leak. Therefore, lumbar drainage is used for 3-4 days after surgery; the patient is then mobilized.
The best timing for the initiation of lumbar drainage is controversial. Some operators delay drainage for 4-6 hours after surgery while others start drainage immediately. I wait for the CT scan on the first postoperative day to exclude significant pneumocephalus that can worsen with CSF drainage. Stress dose steroids are continued postoperatively until endocrinologic status can be assessed in detail.
A postoperative MRI is obtained to assess the extent of resection and plan for delayed radiotherapy. I do not use prophylactic anticonvulsants unless cortical disruption was noted intraoperatively. Standard precautions to the patient are recommended; including avoidance of nose-blowing, using a straw to drink, and unnecessary bearing down.
Diabetes insipidus (DI) is one of the more frequent postoperative complications after transsphenoidal surgery, which can exists preoperatively and worsens postoperatively. The etiology of DI relates to distention or injury of the neurohypophysis or pituitary stalk. Careful monitoring of fluid input/output, urinary osmolality and frequent serum sodium evaluations are imperative during the immediate postoperative period as serum sodium may rapidly escalate to dangerous levels (>145mEq/L).
Routine early postoperative diuresis related to frequent intraoperative fluid boluses must be distinguished from DI. This can be achieved with a water deprivation test: early postoperative diuresis will not impact plasma osmolality or sodium. The water deprivation test involves withholding water intake for 6-8 hours and checking urine osmolality, which in the setting of DI fails to exceed 200mOsm/kg due to the patient’s inability to concentrate his or her urine. This will correspond to a rise in plasma osmolality, such that it can near 320 to 330 mOsm/kg.
Treatment for DI depends on the patient’s functional status; a conscious patient with intact natural thirst mechanism can maintain plasma osmolality. The patients with severe DI or those who are unconscious can be managed with desmopressin (DDAVP).
Approximately 60% of patients can experience transient DI postoperatively, with less than 10% continuing on to permanent DI. Dysregulation of the anterior pituitary hormones is also common.
Hyperphagia leading to morbid obesity is a well-described complication following craniopharyngioma resection that is caused by hypothalamic injury, especially in children.
Pearls and Pitfalls
- Early central decompression creates room for subsequent extracapsular tumor dissection, especially of cystic components.
- Sharp and gentle dissection of the arachnoid planes is critical to avoid injuring the fine superior hypophyseal branches that supply the optic chiasm.
- Angled endoscopes allow thorough inspection and further resection of residual tumors in the difficult-to-reach locations under direct vision.
- A small part of the floor of the ventricle may be predominantly involved with the tumor and should be considered part of the tumor capsule. However, most of the hypothalamus and other adjacent neural areas must be preserved. If necessary, a small piece of adherent residual capsule may be left behind on the walls or floor of the third ventricle.
Contributor: Charles Kulwin, MD
Conger AR, Lucas J, Zada G, Schwartz TH, Cohen-Gadol AA. Endoscopic extended transphenoidal resection of craniopharyngiomas: nuances of neurosurgical technique. Neurosurgical Focus. 37:E10, 2014.
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