Tumor-like lesions composed of neurons can, on rare occasions, present as symptomatic masses in the sellar region (1). Although the nomenclature of these lesions has been confusing, including designations such as hamartoma, gangliocytoma, and choristoma, the basic lesions in all cases are the same: mature neurons of varying size clustered among axons and astroglial elements. Because of their benign nature, uniformly slow growth, and histologic resemblance to fully differentiated hypothalamic tissue, they are generally considered hamar-tomatous. In some instances, the neuronal elements of these lesions secrete hypophysiotropic factors, producing a clinically manifest hypersecretory state. Hamartomas of the sellar region are distinguished according to their state of origin. Those arising in the hypothalamus are referred to as hypothalamic neu-
ronal hamartomas, whereas those arising in the sella are designated as adenohy-pophyseal neuronal choristomas.
When carefully sought, ectopic foci of hypothalamic tissue are not unusual as autopsy findings, appearing as minute macroscopic masses attached to the ventral hypothalamus, the adjacent pia, or on the surface of the proximal posterior cerebral arteries. Although such hamartomatous nodules are clinically insignificant, on occasion they may be several centimeters, extend into the third ventricle, descend into the sella, or hang in the interpeduncular cistern, producing a variety of com-pressive and endocrinologic effects. Most symptomatic examples occur in young males, in whom precocious puberty is the best known manifestation (61). The latter features may simply be the result of hypothalamic compression; however, in some instances, these lesions contain gonadotropin-releasing hormone (GnRH), thus providing an endocrine basis for accelerated sexual maturation. Other hypothalamic neuronal hamartomas liberate growth hormone-releasing hormone (GHRH), which may induce GH cell hyperplasia and GH adenomas in the pituitary, with acromegaly being the clinical result (62-68). Aside from other features, hypothalamic hamartomas are associated with a peculiar form of epilepsy—one characterized by laughing fits (gelastic seizures).
As a rule, hypothalamic hamartomas are generally quiescent lesions; however, others may be slowly progressive, causing visual and neurologic deficits and death. Given their eloquent hypothalamic origins, the management of these lesions is often difficult. Establishing a histologic diagnosis is an important initial objective, thus excluding inflammatory conditions and other tumors that may be radiosensitive (germinomas, possibly gliomas). Large masses are often amenable to significant surgical debulking—a procedure generally reserved for those lesions having documented radiologic or clinical progression and one that occasionally provides marked symptomatic benefit.
This lesion is histologically similar to the hypothalamic variant but has a primary intrasellar origin, lacks anatomic continuity with the hypothalamus, and is almost invariably associated with a hypersecretory pituitary adenoma. The basic lesion consists of neurons and associated neuropil interspersed within the substance of a pituitary adenoma. It has been proposed that by way of paracrine mechanisms, choristomas release hypothalamic trophic hormones, which may induce a change in adjacent adenohypophyseal cells. Of reported cases, most have occurred in the context of acromegaly, wherein the neuronal choristoma contains GHRH and is associated with a GH-producing pituitary adenoma (62,63,66,67). Similar lesions producing corticotroph-releasing hormone (CRH) have also been associated with corticotroph adenomas in the context of Cushing's disease (CD) (1).
Because of their near-uniform association with a hypersecretory state, adeno-hypophyseal neuronal choristomas are always preoperatively mistaken for functioning pituitary macroadenomas, both clinically and radiographically. Their diagnosis is revealed only after pathologic examination of the surgical specimen. Given the limited number of cases reported, the long-term outcome of these lesions is uncertain but is likely to be comparable to that of the hypersecretory tumors with which they are associated.
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