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Rathke cleft cyst

Rathke cleft cysts (also known as pars intermedia cysts) are non-neoplastic, sellar or suprasellar epithelium-lined cysts arising from the embryologic remnants of Rathke’s pouch in the pituitary gland. They are common lesions and usually incidentally identified. 

Epidemiology

Rathke cleft cysts are common and are found in 11-22% of autopsies. Although the underlying substrate is congenital, they appear to enlarge during life, as they are rare in childhood 2. There is a recognised female preponderance with a female to male ratio of approximately 2:1.  

Clinical presentation

The vast majority of Rathke cleft cysts are asymptomatic, and are incidentally found when the pituitary is imaged for other reasons. 

If large, they may cause:

  • visual disturbances: due to compression of the optic chiasm 
  • pituitary dysfunction
    • due to compression of adjacent pituitary tissue and distortion of the pituitary stalk
    • present in up to 69% of symptomatic cases 10
  • headaches 3

Pathology

Rathke’s pouch forms during the 4th week of embryologic development as a rostral outpouching from the roof of the primitive oral cavity.  The anterior wall of the pouch gives rise to the anterior lobe of the pituitary (pars distalis).  The posterior wall of the pouch does not proliferate and remains as the intermediate lobe of the pituitary (pars intermedia). The lumen of the pouch narrows to form a cleft (Rathke’s cleft) that normally regresses.  Persistence of this cleft with expansion is believed to be the origin of a Rathke’s cleft cyst.

The wall of the cyst is typically lined by a single columnar cell layer of epithelium, often containing goblet cells, and is often ciliated. An intraluminal nodule which macroscopically appears white and is often adherent to the cyst wall (although it may be free floating) is composed of solid tissue that represented desquamated cellular debris 3,10.

Radiographic features

On imaging a Rathke’s cleft cyst is seen as a well defined non enhancing midline cyst within the sella arising between the anterior and intermediate lobes of the pituitary. 40% are purely intrasellar and 60% have suprasellar extension. Purely suprasellar location, although reported, is rare.

CT 

Non contrast: it is typically non-calcified and of homogenous low attenuation.  Uncommonly it may be of mixed iso- and low-attenuation, or contain small curvilinear calcifications in the wall (seen in 10-15% of cases).

Post contrast: typically non enhancing although the cyst wall may enhance in some cases 8.

MRI 

The signal characteristics vary according to the cyst composition which may be mucoid or serous.  

  • T1
    • 50% are hyperintense (high protein content)
    • 50% are hypointense
  • T2
    • 70% are hyperintense
    • 30% are iso or hypointense
  • T1 C+ (Gd)
    • no contrast enhancement of the cyst is seen, however a thin enhancing rim of surrounding compressed pituitary tissue may be apparent 9-10

In 70-80% of cases a small non-enhancing intracystic nodule can be identified which is virtually pathognomic of a Rathke’s cleft cyst. When seen it is hyper intense to surrounding fluid on T1 and hypointense on T2. Depending on the signal of the surrounding fluid it may be inapparent on one or other sequence.

Occasionally, a fluid-fluid level may be seen (particularly if there has been a haemorrhage).

Differential diagnosis

The main differential diagnoses are:


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