Intracranial Cysts and Cyst-Like Lesions

CHAPTER 27 Intracranial Cysts and Cyst-Like Lesions

Non-neoplastic, noninfectious intracranial cysts are uncommon benign lesions of variable etiology and pathogenesis. The nomenclature for these lesions can be confusing. Single entities often have multiple names. Lesions with similar embryologic origins and histologic findings may be designated differently in different locations.

At present there is no established classification for intracranial cysts. Instead, they are often classified by their anatomic location and/or the nature of their lining membrane. In this chapter, we classify these cysts based on pathology as (1) cysts derived from endoderm, which include neurenteric cysts, Rathke’s cleft cysts, and colloid cysts; (2) cysts derived from neuroectoderm, such as glioependymal cysts, ependymal cysts, and choroid plexus cysts; (3) congenital inclusion cysts, which include dermoid, epidermoid, and arachnoid cysts; and (4) pineal cysts.

Most of these cysts are asymptomatic. In symptomatic cases the clinical presentations are often related to the cyst’s size and location. Most of these cysts have contents resembling cerebrospinal fluid (CSF), so their CT density and MR signal intensity will parallel that of CSF. The density and MR signal intensity of a cyst may be different from that of CSF when there is increased protein, other chemical compounds, or hemorrhage causing increase of CT attenuation or shortening of T1 and T2 relaxation times. Among these, the cysts with an endodermal lining have a tendency to retain secretory function. Their contents may cause marked increase in density and shortening of the T1 and T2 relaxation times, resulting in hyperdensity in precontrast CT and hyperintensity on T1-weighted (T1W) images.

Although some cysts have (nearly) specific features (e.g., a colloid cyst), the degree of confidence for preoperative diagnosis in the majority of these cysts is low. Diffusion-weighted imaging (DWI) is helpful to differentiate epidermoid cysts from other intracranial cysts and to increase detection of choroid plexus cysts.

Correct diagnosis of these cysts requires histologic examination, particularly immunohistochemistry, which can demonstrate the embryonic origin of the lesion. Ectodermal markers such as S-100 and glial fibrillary acidic protein (GFAP) are not present in an endodermal cyst. Endodermal-derived cysts typically stain positively for endodermal markers such as epithelial membrane antigen, cytokeratin, mucicarmine, periodic acid–Schiff, and carcinoembryonic antigen.


A neurenteric cyst is a benign malformative endodermal cyst of the central nervous system (CNS). Alternate names include enterogenous cyst, enteric cyst, endodermal cyst, gastroenterogenous cyst, gastrocytoma, intestinoma, and archenteric cyst.1


Neurenteric cysts exhibit no age or gender predominance. They are rarely found intracranially, with fewer than 60 reported to date.2 Neurenteric cysts occur approximately three times more commonly in the spine than in the intracranial space.


Intracranial neurenteric cysts are typically sharply demarcated, round to oblong lesions with smooth or lobulated margins. Size varies from 1 to 9 cm. Supratentorial cysts are generally larger than their posterior fossa counterparts.3

Most intracranial neurenteric cysts (72%) are extra-axial masses of the low posterior fossa, especially the cerebellopontine angle and the midline pontomedullary junction. About 28% of intracranial neurenteric cysts are supratentorial. These are commonly related to the frontal lobes and most frequently lie away from the midline.3 Neurenteric cysts have also been found in the septum pellucidum, third ventricle, parasellar region, orbital apex, superior orbital fissure, optic nerves, and oculomotor nerves. Intraventricular neurenteric cysts are very rare.3 Unlike spinal neurenteric cysts, intracranial neurenteric cysts are rarely associated with bony anomalies.


Rathke’s cleft cyst is a non-neoplastic cyst arising from remnants of the embryonic Rathke’s cleft.

Clinical Presentation

Most Rathke’s cleft cysts are asymptomatic. A few cause symptoms by compression of intrasellar or suprasellar structures, leading to hypopituitarism, amenorrhea, galactorrhea, headache, and visual field defects. Rarely, symptoms result from hemorrhage into or around the cyst.7

In 53 symptomatic patients with Rathke’s cleft cysts, headache was the most common presenting symptom (81%) and was often accompanied by other symptoms.8 Other findings were visual impairment (47%); hormonal abnormalities such as hyperprolactinemia, hypocortisolism, hypothyroidism, hypogonadism, or panhypopituitarism (38%); and other endocrine disturbances such as diabetes insipidus, galactorrhea, amenorrhea, or oligomenorrhea (30%).8 Pituitary apoplexy was present in 4 patients (7.5%).


Rathke’s cleft cysts typically appear as well-demarcated rounded or ovoid intrasellar-suprasellar lesions located exactly in the midline between the anterior and posterior pituitary lobes (Fig. 27-1). They usually exhibit a smooth contour, homogeneous density/signal intensity within the lesion, and no calcification. Blood products and debris may, however, cause inhomogeneity of cyst texture and signal. Contrast enhancement within the surrounding pituitary gland often delimits the cyst as a filling defect within the gland, but the cyst contents show no enhancement.

Rathke’s cleft cysts range in size from 5 to 40 mm (mean, 17 mm). Only 40% are completely intrasellar; 60% to 70% involve both intrasellar and suprasellar regions simultaneously (Fig. 27-2). Atypical locations include purely suprasellar, intrasphenoid, and nasopharyngeal sites (Fig. 27-3).


As on CT, Rathke’s cleft cysts are similarly variable on MRI, because the MR signal depends on the presence and concentration of cyst protein, mucopolysaccharides, chronic hemorrhage, cholesterol, and cellular debris from the cyst wall. High concentrations of these materials shorten the T1 and T2 relaxation times, leading to high signal intensity on T1W and low signal intensity on T2W imaging.

Rathke’s cleft cysts can be classified into three types on the basis of their signal intensity. Type 1 cysts show low signal intensity on T1W images and high signal intensity on T2W images.11 This is the most common group. Type 2 cysts show high signal intensity on both T1W and T2W images. The amount of mucopolysaccharide in the mucoid material influences the signal intensity in type 2 cysts. This is the second most common group. Type 3 cysts show high signal intensity on T1W images and low signal intensity on T2W images. This pattern most likely results from prior hemorrhage.12 Small cysts are usually homogeneous in signal intensity, whereas other lesions such as cystic craniopharyngiomas and hemorrhagic adenomas more frequently have heterogeneous signal intensity.

The wall of the cyst shows thin rim enhancement in 28% of lesions studied by MRI but only 9% studied by CT.8 This rim has been ascribed, variably, to compressed, peripherally displaced pituitary tissue or to changes due to squamous metaplasia, inflammation, or deposition of hemosiderin or cholesterol crystals.

Like CSF, Rathke’s cleft cysts appear hypointense on echoplanar DWI.13 ADC maps show markedly increased ADC in all cases. In one report, the average ADC value of Rathke’s cleft cysts was 2.12 ± 0.29 (range, 1.60-2.48) × 103 mm2/s and the average relative ADC of Rathke’s cleft cysts was 2.61 ± 0.37 (range, 1.95-3.18), a value similar to that of the CSF.14


Colloid cysts are congenital benign epithelium-lined cysts that nearly always arise in the anterior third ventricle. The name derives from the Greek word kollodes, resembling glue, in reference to the cyst’s contents. It is also called a paraphyseal cyst.


Colloid cysts are found in approximately three individuals per million per year and account for approximately 1% of all intracranial masses.15 They are the most common intracranial neuroepithelial cysts and most common third ventricular tumor. Most colloid cysts present in the third to fifth decades of life. Fewer than 40 cases have been described in children.16 No gender predilection is known. Rare cases of familial colloid cysts are reported.17

Clinical Presentation

Most colloid cysts are asymptomatic and found incidentally. In symptomatic patients, the most common complaint (68%-100%) is headache that is initiated, exacerbated, or relieved by a change in position and lasts from seconds to minutes.18 Other symptoms include progressive dementia, cognitive impairment, and spells of transient loss of consciousness, related to hydrocephalus. In children, the most common symptoms are headache, nausea, vomiting, papilledema, and diplopia.19

Colloid cysts may cause acute hydrocephalus and sudden death.20 Such acute deterioration may result from downward movement of the cyst after lumbar puncture.21 In rare cases, hemorrhage into the cyst may cause acute enlargement of the cyst and obstruct CSF flow.22 Cyst size is not a reliable predictor of outcome, because even small cysts may cause sudden death.23


Colloid cysts originate when ectopic endodermal elements migrate into the velum interpositum during development of the CNS.24 Immunohistochemically, colloid cysts are similar to the respiratory mucosa of the trachea and sphenoidal sinus, suggesting an endodermal origin.24 Ultrastructural analysis reveals ciliated cells, nonciliated cells with microvilli, goblet cells with secretory granules, basal cells, and undifferentiated cells with scanty organelles. The type and topographic arrangement of the cells again resemble respiratory epithelium and suggest that colloid cysts have an endodermal lineage.25 For these reasons, some consider colloid cysts, neurenteric cysts, and Rathke’s cleft cysts to represent the same lesion at different locations.26


The most nearly characteristic feature of colloid cysts is their location in the anterior third ventricle. Rarely, however, true colloid cysts are found within the lateral ventricles, fourth ventricle, brain stem, prepontine cistern, suprasellar region, and cerebral convexity. The cysts are typically smooth-walled, rounded masses measuring 3 to 40 mm in diameter (occasionally larger) (Figs. 27-4 and 27-5).


Most colloid cysts are slightly hyperdense with respect to the brain, but they may appear hypodense or isodense (see Fig. 27-4).28 Contrast enhancement may show a thin enhancing rim that is thought to represent the cyst capsule. Calcifications are rare. Because CT density reflects the hydration state of the cysts, colloid cysts that are hypodense on CT scans (watery) may be aspirated successfully29 whereas cysts that are hyperdense on CT (and therefore more viscid) are likely to fail stereotactic aspiration.


About 50% of colloid cysts are hyperintense on T1W images. The rest are either isointense or hypointense with respect to brain. On T2W imaging, most colloid cysts are isointense to hypointense with respect to the brain. Most commonly, colloid cysts appear hyperintense on T1W images and isointense to hypointense on T2W images. Although the central T2 hypointensity was believed to result from hemorrhage and the paramagnetic effects of metal ions within the fluid, more recent studies suggest that cholesterol contents and paramagnetic substances are responsible for the MRI appearance.19 Isointense cysts may be more difficult to detect with MR images as compared with CT scans.22 Some cysts nearly indetectable on T1W and T2W images are readily displayed on proton density–weighted images. Occasionally intracystic fluid levels are present. Vascularity in the outer cyst wall may appear as a thin rim of peripheral enhancement, However, central enhancement suggests an alternate diagnosis of solid tumor, because colloid cysts do not contain intrinsic central soft tissue. On DWI, colloid cysts may show elevated water diffusion.30 It is expected that DWI and ADC maps will ultimately show the same variations in cyst hydration already known from pathology, CT, and MRI.


This is a benign epithelial-lined CNS cyst that is also referred to as a neuroglial cyst.


The origin of glioependymal cysts is uncertain. Supratentorial intraparenchymal glioependymal cysts may arise from the lining of the embryonic neural tube, sequestered in some way within the developing white matter. Subarachnoid glioependymal cysts may derive from subarachnoid neuroglial heterotopias.31 Posterior fossa glioependymal cysts are thought to arise from remnants of Blake’s pouch32 (a diverticulum of the roof of the fourth ventricle)33 or from the tela choroidea.34 Glioependymal cysts may be associated with agenesis of the corpus callosum, gray matter heterotopias, and other cortical dysplasias.


Glioependymal cysts appear anywhere along the neural axis but are more common in the frontal lobes. They are rounded, smooth, unilocular cysts ranging in size from a few millimeters to several centimeters. They contain clear fluid that resembles CSF (Figs. 27-6 and 27-7).

Jan 22, 2016 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Intracranial Cysts and Cyst-Like Lesions
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