The epithelial cyst is a rare lesion, and its relation to the suprasellar cyst is questionable but in the past they have usually been grouped together with the thought that all are perhaps in some way derived from remnants of Rathke's pouch. The pouch itself closes early in embryonic life, but its apical extremity persists in postnatal life as a cleft between the anterior and posterior lobes of the hypophysis (Fig. 1). The cleft is lined with cuboidal or columnar epithelium often ciliated in places and at times it also contains mucous goblet cells (Fig. 2). Thus the background is set for the development of a cyst within this cleft. Epidermoid cysts at the level of the stalk, however, have been traced to small nests of squamous cells, also remnants of Rathke's pouch. This is understandable in view of the rotation of the anterior pituitary upward and forward early in its development.
Several anatomists and pathologists—among them Russell and Rubenstein,7 Hunter,4 and Willis12 have given attention to the development of cystic change in Rathke's cleft. Shanklin,8–10 in his several papers on the subject, cited Luschka's description in 1860 of epithelial areas in the capsule of the human hypophysis which resembled oral mucosa. Shanklin examined 100 pituitary glands and actually found cysts in 13 of these. The glands were taken from persons who ranged in age from 11 to 20 years. He classified the cysts as cystic clefts (partial or complete) and follicular cysts (simple, compound or multiple). One of us (H. C.) examined 40 pituitary glands obtained at necropsy and found 2 which contained cystic change. One was a dilatation of the cleft lined by low cuboidal epithelium and the other appeared within the anterior lobe (Fig. 3).
However, cysts of macroscopic dimension projecting upward from the sella have been reported very infrequently in the clinical literature, and one wonders whether they have perhaps been more prevalent and were erroneously diagnosed as craniopharyngiomas. Frazier and Alpers3 made the distinction in their case. The cyst wall was a bluish membrane; 8 cc. of brownish fluid was evacuated and no solid tissue was found within the cyst. The lining was composed of ciliated columnar epithelium in a single layer. In a subsequent review, these authors specifically included mucoid epithelial cysts which they referred to as cysts of Rathke's cleft. Bailey1 included mucoid epithelial cysts in his classification of pituitary lesions. Smith and Bucy11 provided a clinical and pathologic description of a mucoid cyst treated by surgery, and Rowbotham and Clarke6 subsequently reported a similar case. The most recent case was that reported by Fairburn and Larkin;2 their patient had a typical chiasmal syndrome. At operation a large, intrasellar cyst was found. Thick, purulentlooking material was evacuated, following which a smooth-walled cystic cavity was found to occupy practically all of the pituitary fossa. The patient made a full recovery and was well at the time of their report 4 years later. It is important to note that in this, as well as in most of the other cases, the cyst wall itself was not removed except for the biopsy portion. Love and Kernohan5 mentioned one case, but most of the reports dealing with epidermoid tumors and craniopharyngiomas do not differentiate these from epithelial cysts, although instances of the latter may quite possibly be included in some of these series.
In 1963 a patient came to our attention whose lesion resembled several others seen in recent years, and stimulated a closer look at these cases which had been variously diagnosed as cyst of a craniopharyngeal remnant, epithelial inclusion cyst, epithelial unclassified cyst, and mucocele.
Shanklin W. M. The incidence and distribution of cilia in the human pituitary with a description of micro-follicular cysts derived from Rathke's cleft. Acta Anat.195111: 361–382.Shanklin W. M. The incidence and distribution of cilia in the human pituitary with a description of micro-follicular cysts derived from Rathke's cleft. Acta Anat.11: 361–382.