FINAL DIAGNOSIS: Rathke's Cleft Cyst
Remnants of Rathke's cleft persist as microcysts at the interface of the adenohypophysis and neurohypophysis. They are usually incidental postmortem or radiographic findings (3) Occasionally they may enlarge and become symptomatic in the form of headaches, visual disturbances, or pituitary dysfunction. Symptomatic cysts have usually been reported in adults, and rarely in the pediatric population (4).
Radiographically, Rathke's cleft cysts usually are smooth bordered, homogeneous, and do not contrast enhance. High signal intensity on T1 weighted MRI images has been reported in cysts with hemorrhage, hemosiderin pigment, and cholesterol clefts (6). Rathke's cleft cysts may enhance peripherally as the result of inflammation and granulation tissue within the cyst wall (2,4,6). Others have disputed this, and claim the peripheral enhancement is due to a peripherally displaced rim of pituitary tissue (5).
The inflammatory process seen in some cases may represent a foreign body reaction to leakage of cyst contents, such as mucin, from partial rupture of the cyst (1,7). Other rare inflammatory lesions of the sellar region include lymphocytic hypophysitis, tuberculosis, syphilis, and sarcoidosis (8). Rathke's cleft cysts have been reported in association with abscess formation, in which the cysts were infected by the hematogenous spread of bacteria (2).
The pre-operative differential diagnosis in this case, based on clinical data and imaging, was pituitary adenoma or craniopharyngioma. There was no evidence of epithelial lobules with peripheral palisading, dystrophic calcification, or necrobiotic squamous debris, to suggest the diagnosis of craniopharyngioma. The finding of cholesterol crystals and hemosiderin pigment should alert the pathologist to carefully exclude the diagnosis of craniopharyngioma, although a ruptured Rathke's cleft cyst should also be considered.
Contributed by Thomas J Cummings MD, Charleen T Chu MD, PhD, Christine M Hulette MD