There are a variety of different types of cysts that may be seen within the pituitary. Although some pituitary tumors can have cystic components, most cysts are not true neoplasms (tumors) and instead are developmental in origin. The most common cyst is a Rathke’s cleft cyst (RCC). Other cysts seen in the pituitary include arachnoid cysts, Pars Intermedia cysts and epidermoid cysts.
Rathke’s Cleft Cysts
Rathke’s cleft is a normal part of the developing pituitary gland in the fetus. The cleft actually begins as a pouch (Rathke’s pouch), which can be seen in the human fetus beginning in the 4th week of development. Part of the pouch goes on to form the anterior pituitary gland and part becomes the intermediate lobe of the pituitary (which sits between the anterior and posterior pituitary). As the anterior and intermediate lobes of the pituitary form, what was a pouch becomes a cleft and ultimately the cleft regresses. However, in some people the cleft does not fully regress and the space becomes filled with liquid. Those people are said to have Rathke’s cleft cysts.
Although the majority of cysts are small and asymptomatic, some are noticed, either incidentally or because of specific symptoms, including headaches, visual deficits and pituitary hormone deficiency.
The most common symptom is headache. Because there is no headache that is specific to a cyst, it can be challenging to distinguish what is a headache from the cyst and what is anther type of headache.
If the cyst is large and extends above the pituitary, it may put pressure on the optic chiasm. Pressure on the optic chiasm from below typically affects the peripheral vision in both eyes.
Pituitary hormone deficiency can cause a wide variety of symptoms. The pituitary hormones that are most sensitive to the effects of a mass lesion are those controlling gonadal function. In women of childbearing years, this will affect menstrual cycles. Men more often will report a decrease in libido, or sex drive.
Although magnetic resonance imaging (MRI) provides the most detailed imaging evaluation of the pituitary, Rathke’s clefts cysts can have a wide variety of appearances on MRI. The MRI appearance of a Rathke’s cleft cyst can be indistinguishable from other types of cysts within the pituitary. However, specific sequences can be used to diagnose epidermoid cysts. At times, computed tomography (CT) scanning can be useful to help distinguish a Rathke’s cleft cyst from a cystic craniopharyngioma.
A patient with suspected Rathke’s cleft cyst should have an assessment of pituitary function. Although lab tests can confirm the function of the pituitary, a detailed history and physical examination is just as important. Patients with compression of the optic chiasm by the tumor should have a detailed visual exam, including a visual field testing.
Because most people with Rathke’s cleft cysts do not have symptoms, most do not need surgery. However, there is a wide variety of cyst sizes and potential symptoms that contribute to the decision making for specific treatments.
While a small Rathke’s cleft cyst in a well person who has no problems (visual or endocrine) requires no therapy, those with large cysts who have visual deficits should be treated with surgery.
The main treatment dilemmas are in people who are diagnosed with a Rathke’s cleft cyst during an evaluation for headaches. When the only symptom is headache and the cyst is limited to the pituitary (does not compress the optic chiasm), a trial of medical therapy for the headaches is warranted. Follow-up imaging is often performed to confirm that the cyst is not growing.
Virtually all Rathke’s cleft cysts can be operated on through the nasal passages without an external incision on the skin (transsphenoidal surgery). The surgeon may either attempt to remove the entire cyst wall or drain the cyst and remove only a portion of the wall. There are advantages and disadvantages of each type of removal. Although complete removal of the cyst wall is associated with the lowest chance of recurrence, this technique places pituitary function at risk. Also, cyst drainage and fenestration are associated with a higher chance of recurrence but a lower chance of injuring the pituitary gland. Simple cyst drainage and fenestration may be the best choice for most patients.
There is no medical therapy that has been shown to be effective in the treatment of Rathke’s cleft cysts, pars intermedia cysts, arachnoid cysts or epidermoid cysts.
Radiation therapy is not considered to be effective in the treatment of Rathke’s cleft, pars intermedia, arachnoid or epidermoid cysts.
There is no preventive therapy known for Rathke’s cleft, pars intermedia, arachnoid or epidermoid cysts.