Colloid cysts are rare, benign intracranial neoplasms most often located within the third ventricle, in close proximity to the foramen of Monro. It is then referred to as colloid cyst of the third ventricle.
Most patients diagnosed with CC are asymptomatic, at least with regards to this neoplastic lesion. CC may be coincidental findings on magnetic resonance images obtained for any other reason.
However, CC may also cause insidious and/or intermittent symptoms like headaches, nausea, and vomiting. Usually, these are related to an increase in intracranial pressure due to mechanical obstruction of the third ventricle. Headaches are reported by the vast majority of symptomatic CC patients; they are typically of acute onset and very intense, last seconds to minutes . Relief may be found by adopting certain head positions or lying down. Patients may experience asymptomatic periods, and because CC are slow growing tumors, the frequency of headaches and other symptoms may rise gradually.
In some cases, peracute exacerbation, loss of consciousness and sudden death may be observed. To date, it is not clear how such events are triggered and if there are any prognostic parameters that indicate an imminent deterioration.
Anamnesis and clinical presentation will rarely prompt a suspicion of CC but should allow deducting the patient is suffering from a brain lesion that may be visualized by means of magnetic resonance imaging or computed tomography scans.
Both techniques will depict a well-demarcated, homogeneous, non-calcified mass measuring up to 4 cm in diameter in close proximity to the foramen of Monro.
With regards to magnetic resonance imaging, in T1- and T2-weighted images, CC may appear hyper-, iso- or hypointense when compared to the adjacent brain tissue. Presumably, variance in intensity results from different contents of cholesterol, protein, and water. Of note, high contents of cholesterol correspond to hyperintensity in T1-weighted images and hypodensity in T2-weighted images. These features are observed in most cases. Peripheral regions may be enhanced.
Similarly, the depiction of CC in images obtained during computed tomography scans varies with the composition of their content. CC with high contents of cholesterol appear as hyperdense areas; they are most common. Density is considerably lower in cases of liquid cyst content. Assessment of viscosity may be of interest when deciding for an aspiration or surgical resection .
Empiric data indicate that magnetic resonance imaging is superior to computed tomography if the aim is to confirm a tentative diagnosis of CC. Computed tomography, in contrast, is the method of choice to evaluate the density of a cyst's content.
In some cases, CC may be incidental findings of brain imaging, and these tumors don't necessarily require any treatment . Affected individuals should, however, undergo regular follow-ups to detect tumor growth or interference with the cerebrospinal fluid flow before symptoms manifest.
If the decision for an intervention is taken, the following methods may be helpful:
Cysts which present hyperintense in T2-weighted images and iso- or hypodense in computed tomographic images are likely candidates for aspiration or fenestration. These techniques are generally preferred over surgical resection because their respective complication rates are lower. If complete resection is required, endoscopic methods should be applied whenever possible. The length of operation and recovery is shorter, associated morbidity and mortality are lower. On the other hand, complete resection carries the lowest risk of recurrence .
CC are slow growing tumors. In many cases, surgical interventions may not be indicated if cyst size and intracranial pressure are monitored in regular follow-ups . Today, surgery is associated with minor risks and most patients achieve complete recovery unless they don't receive medical attention until advanced stages of the disease . Here, mortality rates may exceed 10%  - which is still much better than what has been reported not too long ago .
CC tend to be more aggressive in pediatric patients, a fact that indicates the necessity of very close monitoring and an eventual decision for surgery.
As has been indicated above, some scientists assume CC to be congenital lesions. This theory would be supported if it could be proven that CC develop from remnant embryonic structures - a hypothesis that has in fact been proposed about a hundred years ago. It was based on morphological similarities between cells lining CC and those isolated from the respective embryonic brain structures. However, CC have subsequently been reported to obstruct lateral ventricles, the fourth ventricle, connecting ducts or be even located outside of the ventricular system . These findings argue strongly against the aforementioned hypothesis of congenital CC originating from embryonic tissues located in the midline.
This applies unless one considers the possibility of CC of the third ventricle differing from those detected in other brain regions. Such has been diagnosed in a pediatric patient who suffered from three cysts, one of them obstructing the third ventricle, the other two developing in the supratentorial subarachnoid space . Here, a neuroepithelial origin has only been shown for those cysts outside of the third ventricle. The CC of the third ventricle has been proposed to consist of endodermal tissue. In detail, it has been suggested that this cyst originated from the cleft of Rathke's pouch. This would argue for CC being congenital lesions that originate from embryonic structures.
For a long time, it has been assumed that CC are of neuroepithelial origin. Indeed, to this day, they are commonly referred to as neuroepithelial cysts. This theory has been refuted when cells covering CC have been shown to bear considerable similarities to respiratory epithelium but not to choroid plexus or ependyma . Later, it could be demonstrated that those distinct cell types that compose the capsule of a CC correspond in further respects to respiratory epithelium: morphologic features, cytoplasmic cell organelles and cell junctions remind of mucous membranes lining the respiratory tract.
Although it may seem that the mystery of CC histogenesis has been resolved, evidence supporting the aforementioned theories is still provided . In sum, the origin of these benign tumors is a matter of ongoing debate.
The annual incidence of CC has been estimated to be at least 3 per 1,000,000 inhabitants . CC account for only 2% of primary brain tumors but are rather common in patients presenting with intraventricular lesions. The vast majority of CC is located in the medial, anterior portion of the third ventricle, at the foramen of Monro .
CC are most frequently diagnosed in adults aged 20 to 50 years, but these tumors have also been described in many pediatric patients. In fact, CC may be congenital lesions that don't provoke any clinical symptoms until well into adulthood.
Predilections regarding race or gender have not been reported.
CC are round, smooth masses that usually measure a few millimeters in diameter but that may grow to several centimeters. They are well demarcated, both with regards to diagnostic imaging and to the naked eye. CC grow very slowly and may not cause any symptoms at all, during years or even throughout life. However, CC patients often present with intermittent but intense headaches that result from an increased intracranial pressure due to obstruction of cerebrospinal fluid drainage. Under physiological conditions, the liquid flows from the lateral ventricles through the foramina of Monro into the third ventricle, fourth ventricle, and subarachnoid spaces. Even though the passage into the third ventricle is blocked by a CC, production of cerebrospinal fluid in the lateral ventricles continues: The patient can develop hydrocephalus.
The most feared complication of CC is sudden death. Although hydrocephalus may cause brain herniation, symptom onset is rarely acute. To date, it is not clear which pathomechanisms cause sudden death in CC patients. They may or may not be related with hydrocephalus; a correlation with tumor size could not be proven.
The cyst is surrounded by a thin capsule and contains gelatinous material. Presumably, active secretory cells in the capsule release further mucus into the interior of the cyst. This may be the mechanism of "tumor growth" and in this scenario, the capsule would merely adjust to pressure increase instead of growing in an uncontrolled manner. The amorphous content of the cyst may also contain cell debris and cholesterol. The latter may be visualized by means of magnetic resonance imaging.
No specific measures can be recommended to prevent CC.
Colloid cysts (CC) are rare intracranial lesions of neoplastic origin. They are almost exclusively located in the anterior portion of the third ventricle and thus, most affected individuals are diagnosed with the colloid cyst of the third ventricle . Only isolated cases of CC obstructing the lateral ventricles, the fourth ventricle or connecting structures have been reported.
CC are benign tumors consisting of a thin, presumably epithelial capsule and gelatinous, more or less liquid content. Their origin is still a matter of debate. Although CC are most commonly diagnosed in adulthood, they may also be encountered in pediatric patients. It has thus been speculated that CC are congenital lesions , but this theory is difficult to prove if they are only detected in adulthood.
Historically, CC were associated with high mortality rates. These neoplasms exert local mass effects, obstruct the third ventricle and may compromise adjacent brain tissue. Mechanical impairment of cerebrospinal fluid drainage results in acute hydrocephalus, a life-threatening condition. The subsequent increase in intracranial pressure may cause brain herniation and death.
Diagnosis of CC was very complicated when techniques like magnetic resonance imaging and computed tomography were not yet widely available. CC-related symptoms are unspecific with intermittent, severe headaches being the most frequent cause of presentation. Patients may present a variety of other, presumably psychiatric, ophthalmologic or endocrinologic anomalies. None of them are pathognomonic for CC. In contrast, imaging findings are very characteristic for this disease and detection of a round, smooth mass in the anterior portion of the third ventricle is considered diagnostic.
Treatment consists in either aspiration or resection of the cyst. Because such procedures are not without risks, some physicians prefer to monitor patients diagnosed with CC and not to intervene unless growth or progressive ventricular obstruction with hydrocephalus are observed .
Colloid cysts are slow-growing, benign brain tumors. They are most commonly located in the anterior portion of the third ventricle and thus, most patients are diagnosed with the colloid cyst of the third ventricle.
The third ventricle belongs to a system of liquid-filled cavities within the brain. Cerebrospinal fluid is mainly produced in both lateral ventricles, passes through the foramina of Monro into the third ventricle, flows to the fourth ventricle and finally to the subarachnoid space from where it is drained and reabsorbed. Any mass obstructing the ventricular system - a colloid cyst of the third ventricle, for instance - may cause hydrocephalus and an increase of intracranial pressure. These and associated symptoms are dreaded complications of a colloid cyst.
Most patients, however, present with less specific symptoms:
A colloid cyst is diagnosed by means of magnetic resonance imaging and/or computed tomography scans. Physicians are able to identify and localize the cyst, assess its size and the viscosity of its content. This information is required for therapeutic planning. The decision between aspiration or resection, stereotactic, endoscopic or surgical intervention is taken individually.
Unless colloid cysts are diagnosed very late, the prognosis is very good. Most patients achieve complete recovery.