Rathke Cleft Cyst: Symptomatic and Complicated

Abstract

Rathke cleft cysts (RCCs) are a very common incidental finding: with the improvement in MRI techniques, their frequency in living patients is now approaching that seen at autopsy. Most are millimetric and located either intrasellarly on the midline, between anterior and posterior pituitaries, or lying on the upper surface of the gland at the level of the distal end of the pituitary stalk (Fig. 19.1). They have to be considered as anatomical variants and do not warrant any follow-up. RCC may become symptomatic either by mass effect or through complications. Mass effect (chronic headache, visual field defect, pituitary deficiency) may appear with an increase in cyst size when mucus production exceeds absorption. Complications may include inflammation, infection, hemorrhage, apoplexy, or rupture. RCCs 4–8 mm in diameter are frequent and cannot be usually held responsible for symptoms unless it can be demonstrated that a cyst has shrunk, as can be observed in some patients with pituitary insufficiency seen late after the onset of symptoms (Fig. 20.1). In these cases, the exact nature of the “complication” can remain unknown. Nevertheless, the natural history of these 4–8-mm asymptomatic cysts is unpredictable (Fig. 20.2), and the obvious fact that a symptomatic RCC one day was asymptomatic must be kept in mind. Our policy, in the setting of such an incidental finding, is to monitor these cysts at 1 year with strictly the same MRI projections. Serial MRI are then spaced out, but only if there is no change of size or signal of the cyst and if there is no postgadolinium enhancement of the cyst wall. Of course the nearer is the cyst to the optic chiasm, the more careful will be the monitoring. RCCs 1 cm and larger can be symptomatic or asymptomatic (Figs. 20.3 and 20.4), so their responsibility in the setting of chronic or repeated episodic headaches can be difficult to assert unless inflammation is demonstrated. Cyst wall inflammation appears on MRI as rim enhancement after gadolinium injection (Fig. 20.5). Such an inflammation could be related to an intermittent foreign-body reaction caused by mucinous contents, and therefore is more frequently observed with T1-hyperintense RCC. Inflammation of the cyst wall may increase mucus secretion and, therefore, cyst volume. It can extend to the surrounding anterior pituitary tissue, giving rise to a secondary hypophysitis with gonadotropin, ACTH, TSH, and/or GH deficiencies and hyperprolactinemia (Fig. 20.6). Diabetes insipidus is also frequent and can be isolated. In patients with repeated episodic headaches and demonstration of cyst wall enhancement, i.e., inflammation, some authors have proposed surgical treatment of RCC to avoid hypophysitis and its hormonal consequences. Partial or even complete cyst shrinkage can occur spontaneously with time, leading to an erroneously termed “empty sella.” In our experience, a complicated RCC represents a not infrequent cause of pituitary insufficiency or diabetes insipidus of “unknown origin.” Cyst infection and bacterial meningitis occur principally in mucinous RCC (Fig. 20.7). The shared venous drainage of the sellar content and the sphenoid sinus has been proposed as a mechanism of secondary infection. Intracystic hemorrhage is rare except in patients with coagulation disorders. It is represented by a fluid-fluid level better seen on sagittal and axial sequences. Depending of the RCC protein concentration and, therefore, of the T1 signal intensity, the hemorrhagic compartment can appear more or less intense than the rest of the cyst. In some cases, diagnosis of cyst hemorrhage can be difficult on T1WI, but the presence of a fluid level on T2WI is characteristic of a hemorrhagic event. Sudden hemorrhage can lead to rapid extension of cyst or even cyst rupture, possibly responsible for chemical meningitis (Fig. 20.8). The term “RCC apoplexy” (hemorrhagic or nonhemorrhagic) is used in the literature for different pathologies: symptomatic RCC hemorrhage or pituitary apoplexy in contact with an RCC or true RCC apoplexy. Hemorrhagic RCC apoplexy (Fig. 20.9) is very rare; its mechanism is presumed to be the repeated bleeding from the thin blood vessels in the cyst wall or from the hypophyseal blood vessels by compression or shearing stress. The mechanism of nonhemorrhagic RCC apoplexy is not clearly understood. In fact, the term “RCC apoplexy” refers to a symptomatology of acute severe headache and possibly meningismus, visual disturbance, oculomotor nerve palsies, and impairment of pituitary function. Clinical and imaging features can be very similar to those observed with pituitary apoplexy. Sphenoidal mucosal thickening is often present in both pituitary and RCC apoplexy, although intracystic nodules are found only in RCC. The largest RCCs, up to 30–40 mm in diameter, are mostly T1 hypointense (Fig. 20.10). Symptoms are related to mass effect and include frontal headache (though not always) and visual field defect and/or optic nerve impairment. Oculomotor nerves palsies are more commonly observed in case of acute cyst enlargement. Cyst recurrences are frequent after cyst puncture, and MR follow-up is mandatory in all cases (Fig. 20.11).