H. ZAGHOUANI, N. EZZAIRI, A.BEN ABDALLAH,S. YAHYAOUI, S. MAJDOUB,T. RZIGUA, L. BEN CHRIFA,H. AMARA, D. BEKIR, CH. KRAIEM Departement of radiology, Hospital of Farhat Hached, Sousse, Tunisia NR37

 Rathke’s cleft cysts (RCCs) are benign congenital, non- neoplastic sellar and/ or suprasellar lesions originating from epithelial remnants of Rathke’s pouch.  These cysts are extremely common, found during routine autopsies in 13% to 22% of normal pituitaries.

 In 1913, Goldzieher described the first case of RCC as an incidental postmortem finding.  The description of RCC has expanded since the advent of computed tomography (CT) scanning and magnetic resonance imaging (MRI), showing that the incidence of this disease wich discovery was only by autopsy, was underestimated.

The aim of this work is to emphasize the value of MRI in the positive and differential diagnosis of this disease through a retrospective study of 5 cases of Rathke’s cleft cyst with a literature review.

 We retrospectively analyzed the records of five patients with Rathke’s cleft cysts collected in the service of radiology in the hospital of Farhat Hached Sousse.  A brain MRI was performed for all patients. All the cysts were discovered incidentally.

 There were two female and three male patients ranging in age from 14 to 48 years.  MR examinations were performed using 1.5-T imagers.  Axial and coronal T1-weighted images were obtained without administration of gadolinium.  With axial and coronal FSE T2-weighted images.  Section thickness was 4 mm, with intersection spacing of 0%.

 The signal, shape, size, seat and reports of the lesions were analyzed.  It showed in all cases a cystic formation of the sellar region with variable signals and sizes.  The localization of the cysts was strictly intrasellar in 4 cases and extended to the suprasellar region in one case.  Of the five MR scans reviewed, the lesions were of low signal intensity in T1-weighted images, there was no enhancement in post-gadolinium sequences.They were recorded to be of high intensity T2-weighted images.

Coronal T1 MR image Coronal T2 MR image Coronal postcontrast T1 MR image Coronal postcontrast T1 MR image Sagittal post contrast T1-weighted MR image Sagittal post contrast T1-weighted MR image

 Rathke’s cleft cyst (RCC) was first incidentally reported by Lushka in 1860 as ‘an epithelial area in the capsule of the human hypophysis resembling oral mucosa’.  The first symptomatic RCC case was described by Goldzieher in 1913.

 RCCs have been referred to by a variety of names including pituitary cyst, mucoid epithelial cyst, intrasellar epithelial cyst, Rathke’s pouch cyst, and colloid cyst of the pituitary.  Not until 1934 did Frazier and Alpers propose its contemporary name of tumor of Rathke’s cleft.

 As Voelker and colleagues have stated, the most common theory about the origin of RCCs is that the cysts are derived from true remnants of the embryologic Rathke pouch.  On or about the 24th day of embryonic life, the Rathke pouch arises as a dorsal diverticulum from the stomodeum; it is lined with epithelial cells of ectodermal origin.

 At approximately the same time, the infundibulum forms as a downgrowth of the neuroepithelium from the diencephalon.  By the fifth week, the Rathke pouch comes into contact with the infundibulum, and the neck of the pouch becomes occluded at the buccopharyngeal junction.  During the sixth week, the Rathke pouch separates from the oral epithelium. Subsequently, the pars distalis of the pituitary gland develops from the anterior wall of the pouch.

 The posterior wall does not proliferate and remains as the poorly defined pars intermedia.  The residual lumen of the pouch is reduced to a narrow Rathke cleft, which generally regresses. The persistence and enlargement of this cleft is considered to be the cause of the RCC.  Other authors have different theories regarding the formation of RCCs, suggesting instead that the cells of origin are derived from the neuroepithelium or the endoderm, or that they come from metaplastic anterior pituitary cells.

 Rathke cleft cysts are smoothly marginated cysts that vary in size from a few millimeters to 1–2 cm.  The contents vary from clear CSF-like fluid to thick mucoid material.  Microscopically, they are similar to other endodermal cysts (neurenteric and colloid). They are lined by pseudostratified or single-layered columnar or cuboidal epithelium.

 Cilia and scattered mucin-secreting goblet cells are common. Many cysts have squamous differentiation, and cornified squamous pearls are occasionally identified.  The intracystic nodule consists of mucinous material at histologic examination. Biochemical analysis of this material is consistent with cholesterol and protein.

 Forty percent are completely intrasellar, while 60% have some suprasellar extension through the cleft of the diaphragma sella.  Completely suprasellar cysts are rare.

 RCCs often produce no symptoms and so are usually discovered incidentally, when radiographic or necropsy findings are reviewed.  Symptomatic RCCs are uncommon, but cysts can enlarge and cause symptoms secondary to compression of the pituitary gland, pituitary stalk, optic chiasm, or hypothalamus.  Symptomatic RCCs vary in presentation: headache, visual and/or endocrine disturbance.

 MRI is the modality of choice in the detection of RCCs. It is superior to CT scanning for evaluating RCC mass extension.  Sagittal and coronal MRI scans provide reliable information concerning the relationship of the mass to the optic nerves, optic chiasm, and hypothalamus.

 Coronal MRI is also helpful in the evaluation of the lateral extension of the sellar cyst and its relationship to the internal carotid arteries and cavernous sinuses. MRI also has superior multiplanar capabilities and contrast resolution compared with those of CT scanning.  The advantage of CT scanning is that it is superior to MRI in depicting small amounts of calcium.

 This advantage can be important, because the presence of calcification tends to indicate an alternative diagnosis, such as craniopharyngioma, although small calcifications are observed in some cases of RCC. CT scanning is also superior to MRI in the evaluation of associated bony remodelin g.

 Rathke cleft cysts (RCCs) frequently appear as well- circumscribed, hypo-attenuating, cystic sellar masses that may have suprasellar extension.As a result of the different cystic contents, RCCs may appear iso- attenuating or hyperattenuating relative to the brain parenchyma.  RCCs usually have a thin wall that may enhance.

 Variability in CT scan contrast enhancement among individual cysts may reflect squamous metaplasia in the wall or a peripherally displaced rim of pituitary tissue.  Extravasation of cystic contents may inflame nearby structures, resulting in enhancement.  Calcification characteristically is not depicted on CT scans, although Shin and colleagues have described this finding in a number of cases.Complex cysts may have septations.  Large cysts may cause bony remodeling.

 The best imaging clue is a non enhancing non calcified intra- and/or suprasellar cyst with an intracystic nodule. While this is the typical picture, the imaging characteristics vary widely.  Approximately half are hyperintense on T1- weighted images, while half are hypointense. On T2-weighted images, 70% are hyperintense and 30% are iso- or hypointense.

 Although no characteristic MRI features have been identified, many RCCs are in 1 of the following 2 groups: Rathke cleft cysts (RCCs) with low signal intensity on T1-weighted images and high signal intensity on T2- weighted images. RCCs with high signal intensity on T1-weighted images and variable signal intensity on T2-weighted images. The cystic contents of the first group resemble those of cerebrospinal fluid (CSF). In the second group, an increase in the signal on T1-weighted images has been

related to the high content of mucopolysaccharides, which is believed to result from an increase in the number of mucin- secreting cells in the cyst wall, as well as from an increase in the activity of these cells. Uncommon cases with high signal intensity on T1-weighted images and low signal intensity on T2-weighted images have been suggested to result from a combination of factors, including the presence of mucopolysaccharides, chronic hemorrhage, a high cholesterol content, and cellular debris from the cyst wall.

 A small nonenhancing intracystic nodule is considered a virtually pathognomonic sign of a Rathke cleft cyst. These nodules show high signal intensity on T1- weighted images and low signal intensity on T2- weighted images, and they do not enhance.  Rathke cleft cysts do not enhance after contrast material administration, although an enhancing rim of displaced compressed pituitary gland is present in approximately half of the cases.

 The report's authors went on to conclude that, with regard to RCCs, DWI-SSFSE with apparent diffusion co-efficient (ADC) values provides objective information for differentiation from other sellar cysts. DWI-SSFSE with ADC values can also be employed in the differentiation of RCCs from craniopharyngiomas and hemorrhagic pituitary adenomas. All the RCCs are hypo-intense relative to the normal brain parenchyma (restricted diffusion).

 The differential diagnosis for Rathke cleft cysts includes craniopharyngioma, cystic pituitary adenoma, or other non neoplastic cysts ( arachnoid cysts or epidermoids).  Unlike Rathke cleft cysts, craniopharyngiomas typically demonstrate calcification and approximately 90% have nodular, globular, or rim enhancement.

 The presence of solid enhancing nodules in the cyst wall also favors the diagnosis of craniopharyngioma.  The rare noncalcified cystic nonenhancing craniopharyngioma, a finding more common in adults than in children, may be impossible to distinguish from Rathke cleft cyst with imaging findings alone.

 The most common approach in the treatment of RCCs is transsphenoidal surgery, in which the cyst is partially excised and drained.  This method is effective and helps to preserve pituitary function.  Radical excision can cause additional and unnecessary pituitary damage; therefore, it is not the treatment of choice.  In transsphenoidal surgery, the cyst is opened, a biopsy specimen is obtained from the wall, and the cyst is drained into the sphenoid sinus.

 An interesting aspect of treatment is the decrease in the size of the cyst after high-dose steroid therapy. Although the pathophysiologic mechanism is not clear, the steroids are assumed to have an effect on the secretion or absorption of cystic fluid. This finding suggests that steroid therapy may be useful in some patients with an RCC and inflammatory changes. Further study in this area is needed to gauge its effectiveness is the treatment of RCCs.

 The MRI is effecticient in the positive and especially the differential diagnosis of these cysts, and to guide the therapeutic decision.Once the diagnosis is considered, a spaced clinical and MRI monitoring is adopted in cases of asymptomatic cyst, while a surgical treatment is proposed for the rare symptomatic cysts.