Parasellar Gliomas

Mass lesions involving parasellar structures occasionally arise from glial tissues (1). This is especially true in the pediatric population wherein the possibility of a glial tumor is commonly considered in the differential diagnosis of a suprasellar mass. The majority of these are astrocytomas, whose anatomic origins include the optic nerve/chiasm, hypothalamus, and third ventricular walls. In many instances, however, assignment of a precise anatomic origin is difficult, if not impossible, given the infiltrative nature of most astrocytic tumors and the sleek anatomic continuity of the third ventricular floor, hypothalamus, and optic chiasm. Rarely, astrocytomas may arise from the infundibular stalk and even more rarely from the posterior pituitary (48-52). Finally, occasional glial tumors, such as ependymomas or choroid plexus papillomas, arise within the anterior third ventricle, secondarily descending into the suprasellar space.

Collectively, visual pathway and hypothalamic gliomas account for approx 5% of all pediatric intracranial tumors, with most occurring during the first decade of life. Most of these lesions are low-grade astrocytomas of pilocytic type; low-grade fibrillary variants also occur, but less frequently. Rarely, and notably in the adult patient, gliomas located here tend to be higher grade lesions—ones assuming the histology and behavior of glioblastoma multiforme. Between 15% and 35% of patients with visual pathway gliomas will also have neurofibromatosis (NF-1) (53). Whether tumors occurring in the presence of NF-1 behave differently from sporadic ones remains uncertain.

The clinical presentation of these lesions depends primarily on their location. Diagnostic features of intraorbital tumors and intracranial tumors confined to the optic nerve include decreased visual acuity, optic atrophy, proptosis, and, in the young child, strabismus and/or nystagmus. Chiasmatic-hypothalamic lesions also present with visual loss, often with bilateral field deficits. In addition, these lesions may also be accompanied by hydrocephalus and elevated ICP as the result of ventricular obstruction.

Endocrine dysfunction is frequently reported with these lesions, assuming the form of growth failure, precocious puberty, and occasionally the diencephalic syndrome. Generally occurring in infants, the last is fairly specific to processes involving the anterior hypothalamus and is characterized by failure to thrive, emaciation, hyperkinesis, nystagmus, and inappropriate euphoria. The anatomic diagnosis is best provided by MRI. The presence of a suprasellar lesion with contiguous optic nerve and/or optic tract thickening is characteristic.

The optimal management of these lesions remains a subject of ongoing debate. The necessity of tissue diagnosis, the indications for treatment, and the timing and form of intervention are all issues steeped in controversy. Much of the uncertainty stems from the seemingly erratic natural history of these tumors. In many instances, their natural history is one of quiescence and negligible growth over long periods of time (53). In a significant yet uncertain proportion of cases, however, their behavior is unpredictable, with periods of quiescence abruptly giving way to progressive growth, visual and neurologic compromise, and eventually death (32,54-58). In nonprogressive lesions—ones in which the radio-logic diagnosis of glioma is near certain and the patient remains neurologicly stable—careful observation is often prescribed as the wisest course. In progressive lesions, such as those associated with increasing neuroendocrine deficits and ICP elevations, some form of intervention is required. Therapeutic options include surgery, irradiation, or chemotherapy. The main indication for surgical resection is in the circumstance of disfiguring proptosis or severe visual loss occurring with a tumor confined to the optic nerve. In this situation, en bloc excision of the involved optic nerve-associated tumor is generally curative. This is achieved by either a transcranial approach through the orbital roof or a lateral orbitotomy, depending on the precise location and extent of the tumor.

For chiasmatic-hypothalamic gliomas, surgery, irradiation, and chemotherapy have all been applied as either primary or adjuvant therapy. A surgical debulking procedure carried out through a variety of transcranial approaches has proven beneficial in some circumstances; visual improvement, ICP reduction, and amelioration of hydrocephalus have all been observed, sometimes with involution of the residual tumor (32,54-58). By delaying the time to disease progression, surgical intervention may also postpone the need for immediate radiation therapy—an issue important in the young child (59). Furthermore, surgical therapy has a definite beneficial role in the management of recurrent postirradiation tumors. The devastating neuroendocrine and developmental consequences of cranial radiation in young children notwithstanding, radiation therapy does have a beneficial antitumor effect for these lesions. In one report, radiation therapy increased the median time to tumor progression by 40 mo and led to clinical and radiologic improvement in 45% of patients (58). Chemotherapy is emerging as an increasingly used option in young children in whom there is a desire to defer the deleterious effects of radiation. In one report, actinomycin D and vincristine induced remission in 63% of patients during a median follow-up of 4.3 yr (57). In several of these, tumor shrinkage was also demonstrated. Petronio and colleagues, using several nitrosurea-based cytotoxic regimens, induced clinical remission, stabilization/improvement in visual and neurologic deficits, and tumor shrinkage in up to 88% of patients during a median follow-up period of 18 mo (60). Chemotherapy may also have a role in the management of recurrent postirradiation tumors. The overall 5-yr survival rate of patients with chiasmatic-hypothalamic gliomas has been variably reported between 40% and 88% (32).

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