Rathke Cleft Cyst

Introduction

Rathke cleft cysts are cystic sellar and suprasellar lesions arising from remnants of the embryonic Rathke pouch, a structure of ectodermal origin that folds superiorly from the pharynx during the fourth week of gestation. In the sella, Rathke pouch gives rise to the adenohypophysis anteriorly and intermediate lobe of the pituitary gland posteriorly. In the suprasellar cistern, Rathke pouch gives rise to the pars tuberalis. Failure of embryonic regression results in a persistent remnant of the embryologic Rathke cleft, which, over time, fills with fluid, resulting in the formation of a Rathke cleft cyst. Rathke cleft cysts are typically intrasellar, intrasellar and suprasellar, or suprasellar depending on where exactly the failure in embryonic regression is located ( Fig. 20.1 ).

Most Rathke cleft cysts are incidental findings, found in 4% to 33% of autopsy cases and increasingly found on routine magnetic resonance imaging (MRI). When such a cyst is symptomatic, patients typically present with pituitary dysfunction, visual disturbance, or headache. Asymptomatic Rathke cleft cysts can safely be followed with serial imaging, whereas surgical resection is typically offered for those patients who are symptomatic.

Evolution: Overview

The imaging appearance of Rathke cleft cysts is highly variable. There are variable T1 signal characteristics depending on the protein concentration of the cyst contents. Highly proteinaceous and/or hemorrhagic Rathke cleft cysts typically have hyperintense T1 signal. The T2 signal is also variable, although it is most often hyperintense with the possible presence of a hypointense intracystic nodule centrally or dependently, which is best seen on T2-weighted imaging. Often the size and appearance of this intracystic nodule are variable, with a gradually coalescing T2 hypointense signal abnormality eventually forming the classically reported intracystic nodule throughout the course of follow-up. On postcontrast imaging, there is commonly a thin rim of normal and enhancing displaced pituitary tissue. However, an entirely nonenhancing cyst wall or smooth, thin, discontinuous peripheral enhancement can also be seen.

Evolution: in Greater Depth

The natural history of untreated Rathke cleft cysts is becoming more widely understood with the increased utilization of MRI of the brain. In one series of incidentally discovered Rathke cleft cysts, 69% did not show any growth over a 9-year follow-up period. In another series of incidentally discovered Rathke cleft cysts, only 5.3% had documented growth. It is unclear why these cysts grow. One hypothesis is that there may be an imbalance between the secretion and reabsorption of fluid. Infection or hemorrhage may also occasionally cause growth. Intermittent symptoms may be related to an inflammatory response elicited by the leakage of cyst contents. Rarely, Rathke cleft cyst apoplexy is seen as a cause of spontaneous regression.

As mentioned earlier, surgical treatment is the mainstay of treatment for symptomatic Rathke cleft cysts; it is typically performed via a transsphenoidal approach. Cyst wall fenestration is usually performed with sampling of the cyst wall to confirm the diagnosis. Recurrence is not an unusual finding, with the largest series of cases demonstrating an 18% recurrence at 5 years and 16% recurrence at 2 years postresection.

The imaging appearance of recurrent Rathke cleft cysts is variable, with varying T1 and T2 signal depending on the amount of postsurgical hemorrhagic/proteinaceous change ( Figs. 20.2–20.9 ). The growth rate of recurrent Rathke cleft cysts is also variable, with some recurrent cysts remaining stable and others demonstrating slow growth over several years. Spontaneous regression has also been described.