Introduction

 

Controversy has surrounded the craniopharyngiomas as it has almost no other tumor affecting the brain; the origin, natural history, operative removability, response to radiation, and optimal therapy of the lesion have all been topics of debate. Many of these questions remain unresolved, and the conclusions  must be regarded as only tentative.

 

Origin

 

At the end of the nineteenth century, pathologists were intrigued by a strange group of epithelial tumors encountered above and within the sella turcica. Mott and Barrett, in 1899, postulated that these tumors might arise from the hypophyseal duct or Rathke's pouch. This amazingly prescient theory, based on three cases of third-ventricular tumor, continues to be widely held. Histologic characteristics of these tumors were well described in 1904 by Erdheim, who pointed out similarities between craniopharyngiomas and adamantinomas, tumors known to be primitive neoplasms of buccal origin. He thought this close resemblance proved that craniopharyngiomas arose from ectoblastic remnants of Rathke's duct. In addition, the anterior wall of Rathke's pouch forms both the pars tuberalis and the anterior lobe of the pituitary, the most common sites for craniopharyngiomas. Since that time, craniopharyngiomas have been found along the path of development of Rathke's pouch from the pharynx to the floor of the sella,  as well as above and within the sella.

However, while craniopharyngiomas and adamantinomas have a similar appearance, the histologic picture differs greatly between a Rathke's cleft cyst and a craniopharyngioma, although these entities are postulated to have a common origin. The Rathke's cleft cyst may be a simple cystic enlargement and may lack the changes induced by neoplastic transformation found in craniopharyngiomas.

Some investigators have demonstrated histologic differences between adult and childhood craniopharyngiomas that might indicate separate origins. They stress that almost half the adult tumors are made up of squamous epithelium, often with a papillary form, without palisading or other adamantinomatous characteristics of the childhood tumor. These differences are not confirmed in some series. In one series 17 percent of patients had the papillary type of tumor; these patients ranged in age from 26 to 54 years. In the same series, adamantinomatous tumors were found in patients ranging in age from I to 69 years. Other workers have tried to predict the behavior and clinical likelihood of recurrence on the basis of these pathologic differences and have found that both the outcome of surgery and the recurrence rate were slightly better for papillary tumors than for the adamantinomatous variety.

Squamous epithelial rests in the hypophysis were described in autopsy material by Carmichael more than 70 years ago. However, these cell rests are found in only 3 percent of neonates and are found with increasing frequency in each succeeding decade. This finding suggests that an embryonic origin need not be postulated for such cells, which may appear later in life because of cellular alteration or metaplasia of pituitary cells, which are also of ectodermal origin.

 

Incidence

 

Craniopharyngiomas are variously reported to constitute between 2.5 and 4 percent of all brain tumors. Since almost half these tumors occur in childhood, their incidence in children is higher; they constituted 9 percent of Matson' s series of childhood tumors, in which craniopharyngioma was the most common nonglial tumor. When the differential diagnosis is limited to tumors of the sellar-chiasmatic region, craniopharyngiomas constitute a majority in children (54 percent) but only 20 percent in adults.  However, craniopharyngiomas may become symptomatic at any age, with the oldest in this series being 71 at the time of operation. The tumor occurs with equal frequency in both sexes throughout life. Although a male preponderance in children has been reported,it is not supported by other reports of large series of children with equal sex distribution.

Symptoms and Signs

Although lesions that expand in the suprasellar region have a high potential for producing neurological deficits, there may be some variation in presenting complaints, and adults and children have dissimilar clinical syndromes. These differences are summarized in Tables-1 and 2. Since craniopharyngiomas are slow­growing, extra-axial tumors, they may grow quite large before causing symptoms, especially in children. Many of these tumors in children obstruct the flow of cerebrospinal fluid (CSF) and present with increased intracranial pressure. In addition, children will tolerate a surprising degree of visual loss without complaint and may continue school and watch television without arousing the suspicions of parents or teachers despite severe deficits (in one case, complete visual loss in one eye and a major field cut in the other).

Adults are much more sensitive to visual impairment, and it is almost uniformly a complaint of adult patients. A notable exception are patients with purely intrasellar lesions. In institutions treating large numbers of women with complaints of amenorrhea or infertility, a higher proportion of intrasellar tumors is now found than was reported in series of even a decade ago.

Psychiatric symptoms are difficult to diagnose in children, and most examples are found in adults, usually in association with hydrocephalus. Decreases in mentation (especially memory), apathy, incontinence, depression, and hypersomnia may be noted. Long-standing mentation deficits or depression are associated with a poor prognosis. Kahn and coworkers found the marked mental changes of Korsakoff's syndrome in 3 of 12 adult patients

 

Diagnostic Procedures

Almost all craniopharyngiomas have a common origin from cells in the infundibular region. Despite this common site of origin, the growth pattern of the tumor varies enormously. To select the proper operative approach and identify tumors that will require staged operations, it is preferable to have complete radiologic tumor visualization in three planes. Both computed tomography (CT) and magnetic resonance imaging (MRI) are used in the evaluation of these tumors. Both types of scanning will demonstrate the mass of the tumor, outline the ventricular system. and show where the tumor abuts CSF spaces. Enhancement with an appropriate contrast agent will often bring out the solid portions of the tumor and allow better definition of cyst walls. The use of various MRI sequences often allows correct definition of cystic portions of craniopharyngiomas, which may appear solid on CT scanning. The density of cysts varies widely, depending on the content of protein and blood and the presence of keratin and calcium salts.

Sagittal MRI views have proved most useful. They show the relationship between the tumor and the optic nerves and chiasm, pituitary stalk, and basilar artery. In particular. tumors that look intraventricular on axial CT scans may be shown by the sagittal MRI view to abut the basal cisterns. Approaching the tumor through the basal cisterns may allow removal by entirely extra­axial pathways. Although MRI has been the most useful modality for defining the geometry and extension of craniopharyngiomas, it may fail to reveal solid, calcified portions of the tumor. Similarly. small calcifications that remain after surgery may not be appreciated on MR scans. We have found a combination of MRI and CT to be useful preoperatively and postoperatively.

Some authors have advocated preoperative angiography in the diagnostic workup of these tumors. However. the relationship between the tumor wall and the major vessels of the circle of Willis can be defined on MR scans, and MR angiography can be used as well. Scanning techniques have made preoperative angiography unnecessary in our practice for more than tow decades. Vessels that directly supply the craniopharyngioma are quite small and difficult to demonstrate on angiography. and even the perforating vessels that must be saved are not well seen.

Changes in the structure in the bone at the base of the skull may be identified by CT or plain radiograph and are characteristic in craniopharyngiomas. Two-thirds of the adults and almost all of the children will show bone changes on these studies. Half of all patients have an enlarged sella. Tumors with a suprasellar component may cause erosion of the dorsum sellae and anterior clinoids. Tumor calcification is found in approximately 85 percent of childhood tumors and 40 percent of those in adults.

Endocrine assessment is usually performed preoperatively. These tests are not diagnostic but indicate those patients at higher risk endocrinologically. Both hypoadrenalism and hypothyroidism may contribute to poor intra- or postoperative results. Hypoadrenalism is correctable and is adequately treated by the high dosages of steroid used in contemporary cranial surgery. Hypothyroidism takes longer to correct and correction should be attempted preoperatively if the patient shows clinical manifestations of decreased thyroid function or has mentation deficits and if the need for surgical intervention is not pressing. If endocrine results are not available and if there is an urgent need to decrease intracranial pressure, CSF shunting or external drainage may be employed. and the major operation deferred.

 

Control of Hydrocephalus

Hydrocephalus is a complicating factor found in 15 to 30 percent of craniopharyngioma patients. Proper management of the enormous positional shifts that occur when treating the tumor and hydrocephalus simultaneously will help to avoid major complications. When the patient's symptoms and signs are solely related to

increased intracranial pressure, treatment of hydrocephalus is indicated as a first step. However, decompression of the hydrocephalus may allow the tumor to change position. For example, a tumor located beneath the optic chiasm can cause greater stretching of the chiasm and a larger bitemporal field cut when the lateral ventricles are decompressed. Very rapid decompression of hydrocephalus may allow the cortex to fall away from the inner table, creating subdural hygromas or hematomas or even leading to venous thrombosis. Installing a shunting device preoperatively may make it difficult to control the rate of decompression. For this reason, valve-regulated external drainage may be useful for carefully controlling the rate of decompression.

Occasionally it may be useful to decompress the hydrocephalus and a cystic tumor simultaneously. In a recent case, a huge cyst filling the third ventricle caused hydrocephalus. Catheters placed in the cyst and ventricular system for 24 h allowed controlled decompression of both spaces, making the operation easier and facilitating total removal of the tumor.

 
  

 

 

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