Parasellar Granular Cell Tumors

Although symptomatic parasellar granular cell tumors are rare, they are nonetheless the most common primary tumor of the neurohypophysis (1). Historically, these lesions have been subject to a confusing terminology, one in which "choristoma," "granular cell myoblastoma," and "pituicytoma" have been so variably and inconsistently applied that such nomenclature has lost any specific meaning. As incidental autopsy findings, minute granular cell tumors or "tumorlets" are seen with surprising regularity, being present in up to 17% of carefully studied adult autopsy pituitary glands (69). Barely visible macroscopi-cally, these tumorlets assume the form of cryptic aggregates, often multiple, and are equally distributed between the infundibulum and posterior lobe. That such incidental granular cell tumors are rarely present postmortem in individuals younger than 20 yr of age suggests that they are acquired lesions. The most likely progenitor of these tumors is the pituicyte—a glial element that is the dominant cell type of the neurohypophysis.

Symptomatic granular cell tumors are rare. Of reported cases, the majority have occurred during the fourth and fifth decades of life (70-79) . Most symptomatic granular cell tumors arise from the infundibulum and present as suprasellar masses. Less frequently, others originate from the posterior pituitary, causing sellar enlargement and eventual extension to the suprasellar region. Although globular growth in an upward direction is the rule, parasellar and retrosellar extensions are occasionally encountered. Rarely, granular cell tumors wholly situated within the third ventricle have been reported. The clinical presentation is nonspecific; visual loss, hypopituitarism, increased ICP, and DI are all features attributable to the tumor's compressive effects (73). Aside from a single instance, wherein a granular cell tumor occurred in association with acromegaly and the liberation of a GH-secreting peptide was invoked, all other clinically significant examples presented as clinically nonfunctioning sellar/ suprasellar masses. With CT and MR imaging, these lesions appear as large globular well-demarcated homogeneously enhancing suprasellar masses (80). Sellar enlargement may be a feature of those tumors originating below the diaphragma. In those studied by angiography, a vascular blush is characteristically present. Given their globular well-demarcated nature and vascularity a granular cell tumor may mimic a suprasellar meningioma.

Large suprasellar granular cell tumors unaccompanied by sellar enlargement are approached transcranially, usually by a subfrontal or pterional approach. Intraoperatively, they appear as firm pale masses, often with a rubbery texture. As a rule, granular cell tumors are not invasive of surrounding brain, although they are occasionally strongly adherent to it. Given their marked vascularity, bleeding can usually be anticipated during the course of tumor removal. The surgical objective is chiasmal and hypothalamic decompression, although gross total resection may be attempted if it can be easily and safely accomplished. The presence of a ballooned sella in association with a granular cell tumor indicates a tumor of subdiaphragmatic origin. Accordingly, these lesions are best approached transsphenoidally.

Because of their rarity, the natural history of either untreated lesions or those treated with surgery and/or radiotherapy has not been precisely defined. Schaller et al. in their review of 43 cases from the literature, noted that the natural history of symptomatic lesions is unfavorable with conservatively managed patients, most dying as the result of their tumor within 2 to 26 mo (73). Of 19 patients treated with surgery alone, a 12% recurrence rate was recorded at mean time of 46 mo postsurgery. Of 17 patients treated with surgery and radiotherapy, a 7% recurrence rate was seen, occuring at a mean postoperative period of 70 mo. Accordingly, the prognosis for granular cell tumors is generally favorable, with total/subtotal resection generally providing long-term remission (73). Symptomatic recurrences, although uncommon, are managed with repeat resection. In the past, radiation therapy was generally considered unnecessary (79); however, the literature review of Schaller et al. does suggest that radiation therapy delays symptomatic recurrence.

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