Rathke cleft cysts (RCC) are intra and/ or suprasellar lesions be lieved to derive from remnants of the Rathke pouch. If ‘microRCCs’ are considered, they represent the most frequent lesions of the sellar region revealed on MRI and have to be evoked first when an incidentaloma is revealed. Characteristic imaging patterns make their diagnosis easy, provided that MRI sequences are carefully selected.
RCC’s can be classified by location, content, and related symptoms.
RCC’s Originate intra— Or Suprasellarly
Intrasellar RCCs are by far the most frequent, diagnosed by their location, just in front and in close contact with the posterior lobe. Most are hyperintense on T1 and can be mistaken for the posterior lobe or even for a fatty dorsum sellae: axial T1 sequence with fat saturation solves the problem. They are strictly mid line and symmetrical with a curved regular anterior border, except when coexisting with a pituitary adenoma (Figure 1). Most intrasellar RCCs are asymptomatic, but can expand into the chiasmatic cistern.
Fig1. Micro Rathke cleft cyst on sagittal T1 (a) and axial T1 Fatsat (b) W images. Coexisting haemorrhagic pituitary adenoma on axial T1- W image on (c).
Suprasellar RCCs are said to originate from the pars tuberalis. They are seen on the upper surface of the pituitary gland or embedded in the pituitary as an egg in an eggcup, on the midline (Figure 2a) very rarely off midline. They can also involve the pituitary stalk and simulate a tumour (Figure 2b). These pituitary stalk RCCs never prevent the normal vasopressin storage within the posterior lobe. Suprasellar RCCs can be hypo- or hyperintense on T1 but usually less hyperintense than when intrasellarly located and more or less hyperintense on T2- weighted sequences. Cyst signal is related to its proteic content and can vary with mucus secretion from its wall and dehydration. Cyst volume can also vary with time; it can increase, decrease, or even dis appear spontaneously. In about 70% of the cases, a T2 hypointense hyperproteinic nodule is able to make the diagnosis of RCC indisputable; this nodule can be tiny or involve the whole RCC (Figure 3). After gadolinium infusion, the thin monocellular cyst wall does not enhance in asymptomatic cysts.
Fig2. Rathke cleft cysts as an egg in an eggcup on coronal T1- W image (a) and of the pituitary stalk in (b) coronal T1- W- enhanced image.
Fig3. Rathke cleft cysts. Hyperproteinic pathognomonic T2 hypointense nodules, small in (a) coronal T2- W image, large and involving the whole cyst in (b) axial T2- W image
We Used to Differentiate Symptomatic from complicated RCCs
Symptomatic RCCs are responsible for mass effects due to their size, mainly visual field defects if the optic chiasm is threatened, head ache, rarely anterior pituitary deficits. Mild hyperprolactinemia due to stalk compression can be encountered. Complicated RCCs can present with haemorrhage, infection or rupture and are mainly responsible for anterior and/ or posterior pituitary deficits, sometimes after one or several short episodes of severe headache, prob ably related to a reactional hypophysitis. These pituitary deficits usually occur in a short period of time. In these cases of complicated RCCs, the cyst wall is thickened and appears enhanced with gadolinium infusion. The distinction between wall enhancement and normal pituitary tissue encircling the cyst has to be made; dynamic imaging could help to this purpose (Figure 4).
Fig4. Rathke cleft cyst wall. (a– c) Coronal T1- W enhanced images. Non- visible and non- enhanced cyst wall in non- complicated RCC (a). Thin and incomplete enhanced wall is also a normal pattern (b). Thick and complete wall enhancement in complicated RCC (c).
The characteristic pattern of RCCs presented here render the differential diagnosis with pituitary adenomas usually simple. Moreover, mass effect, such as enlargement of the sella is less frequent in RCCs than in pituitary adenomas. Finally, the position of the normal pituitary gland is important to consider: unlike what is observed in pituitary adenomas, the normal gland in RCCs can be typically seen between the cyst and the sellar floor.
