Rathke's cleft cyst is an epithelial cyst apparently derived from remnants of Rathke's pouch, the embryologic anlage of the anterior pituitary (1). At approx wk 4 of gestation, Rathke's pouch arises as a stomadeal evagination that extends cranially to form the craniopharyngeal duct and later the anterior lobe of the pituitary gland. The eventual obliteration of the craniopharyngeal duct is normally accompanied by involution of Rathke's pouch. In some pituitary glands, however, discontinuous cystic remnants of the pouch may persist within the pars intermedia—the interface between the anterior and posterior lobes of the gland. Such cystic remnants, usually only of microscopic dimensions, are readily identified in up to 25% of autopsy pituitaries as incidental clinically insignificant findings (122). Occasionally, such cysts, presumably by way of progressive accumulation of colloidal material, attain sufficient size to be clinically relevant. When symptomatic, such a cyst usually manifests itself between the third and fifth decades, and a slight female preponderance has consistently been noted.
Most symptomatic Rathke's cleft cysts arise within and remain confined to the sella turcica, causing sellar enlargement and compression of the pituitary gland and stalk (123) (Fig. 4).
An additional third of cases exhibit significant suprasellar extension, causing visual loss, hypothalamic dysfunction, and, if sufficiently large, hydrocephalus. On rare occasions, pure suprasellar Rathke's cleft cysts have also been documented (124-126). Local compressive effects are the usual basis for presentation in symptomatic cases, with headache, partial hypopituitarism, low-grade hyperprolactinaemia, visual disturbance, and, rarely, DI being the principal clinical features. Unusual complications include chemical meningitis arising from the leakage of irritative cyst contents into the CSF and infection with abscess formation. The characteristic radiologic appearance of Rathke's cleft cysts is not particular. Sellar enlargement is a common feature, except in those wholly suprasellar in location. On CT scanning, most, but not all, appear as homogeneous noncalcified low-density nonenhancing lesions. Their MR signal characteristics are variable, depending on the composition and consistency of their fluid contents. Nonetheless, in many instances a presumptive diagnosis of Rathke's cleft cyst can be made on radiologic grounds. The difficulty arises in the occasional
case having a heterogeneous fluid content, particularly one in which cellular debris is abundant. In such cases the imaging characteristics may resemble craniopharyngioma, cystic pituitary adenoma, or other suprasellar tumors. It is of great practical importance to distinguish Rathke's cleft cysts from other tumors, particularly craniopharyngiomas, because the therapeutic strategies are quite different. Such distinctions can sometimes by made only by gross inspection at the time of surgery or by biopsy.
Symptomatic Rathke's cleft cysts are treated by surgical decompression (7,14,123,127-130). Once a diagnosis of craniopharyngioma or other tumor has been excluded with an intraoperative biopsy of the cyst wall, simple transsphenoidal drainage with conservative partial resection of the cyst wall usually effects a cure. Because most patients have dramatic resolution of symptoms and because few will recur, more aggressive surgical approaches are unjustified. The outcome for this lesion is generally favorable. In their recent review, El-Mahdy and Powell restored visual deficits in almost 70% of cases, normalized prolactin (PRL) levels in 63%, and restored one or more axes of preoperative hormone deficiency in 15-20% of cases (128). No patient experienced recurrence over the period of this study. The issue of recurrence was, however, highlighted by Mukherjee et al. who noted recurrence in fully one third of patients (127). However, we have not encountered so high rate of symptomatic reexpansion. This may, in part, result from our strategy of marsupializing such cysts and maintaining a communication between the cyst and the sphenoid sinus without reconstruction of the sellar floor. We believe this to be important in preventing symptomatic intracranial reexpansion of such cysts.
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