Introduction
Background
Colloid cysts are benign, congenital epithelium-lined cysts that almost always arise in the anterior third ventricle. However, rare reports describe cysts in other locations. The cysts are believed to derive from either primitive neuroepithelium of the tela choroidea or from endoderm.1 See the images of colloid cysts below.
Sagittal nonenhanced T1-weighted magnetic resonance image. This image demonstrates a round area of increased signal intensity in the anterosuperior portion of the third ventricle (arrow).
Axial fluid-attenuated inversion recovery magnetic resonance image. This image shows a bright mass.
Axial contrast-enhanced T1-weighted magnetic resonance image. This image demonstrates a small amount of peripheral enhancement but no discernible central enhancement. Note the location of the colloid cyst near the foramina of Monro.
Computed tomography scan in a 65-year-old man who had acute onset of headache. This image demonstrates a round area of increased attenuation at the foramina of Monro, with hydrocephalus. The image is degraded because of motion artifact, as the patient was in severe pain at the time of imaging.
Axial computed tomography scan in a 50-year-old man who was transported to the emergency department after falling down while lifting weights; he later had cardiopulmonary arrest. This image demonstrates a hyperattenuating colloid cyst at the foramina of Monro, with marked hydrocephalus.
The diagnosis is usually made by assessing the typical location and appearance of the cyst. Colloid cysts account for approximately 1% of all intracranial tumors and are the most common type of the neuroepithelial cysts, as well as the most common tumor in the third ventricle. Typically, patients are asymptomatic, although colloid cysts may cause symptoms by obstructing the foramen of Monro, which results in sudden death in rare cases.2,3
For excellent patient education resources, visit eMedicine's Dementia Center and Headache Center. Also, see eMedicine's patient education articles Normal Pressure Hydrocephalus, Migraine Headache, and Cluster Headache.
Recent studies
Denby et al studied the effects on memory of colloid cyst removal in 38 patients. They used quantitative MRI volume measures of the mammillary bodies, because of their association with mnemonic problems, and established the superiority of 0.8-mm-volume scans over standard isotropic 1.0-mm-thick-volume scans. Compared with 20 age-matched controls, the patients who underwent colloid cyst removal showed significant mammillary body atrophy. According to the authors, each of the colloid cyst patients had a mammillary body volume below the control mean, and the majority had a volume decrease of more than 1 SD. The atrophy appeared to be caused partly by a loss of temporal lobe projections in the fornix.4
Shapiro et al described the long-term results of an interhemispheric, transcallosal, subchoroidal, fornix-sparing approach to gross-total resection of colloid cysts. In 57 colloid cysts, total removal was achieved via a 3 x 3-in paramedian craniotomy flap and a microscopic interhemispheric, transcallosal, subchoroidal approach sparing the ipsilateral fornix. According to the investigators, at 1 year after surgery, CT or MR imaging confirmed gross-total resection, with no infection, hemiparesis, seizures, or disconnection syndrome. There were no deaths or recurrences. One surgery was complicated by bilateral subdural hematomas, which were successfully treated; 3 patients required a permanent ventriculoperitoneal shunt; and 1 patient with permanent short-term memory loss presented with a herniation syndrome, requiring emergency ventriculostomy. Mean hospital stay was 4.8 days. The authors noted that the results were superior to those seen with endoscopy.5
Sampath et al performed a retrospective review of 10 patients who underwent microsurgical colloid cyst resection. All 10 patients had complete excision, mean cyst size was 1.6 cm, mean operative time was 124 minutes, and median postoperative stay was 3.5 days. Mean operative time from cyst visualization to complete excision was 18 minutes. There were no recurrences; and symptoms of headache, visual problems, and balance problems improved significantly in 70% of patients, according to the authors. Postoperative cognitive performance, including memory, remained the same in 8 patients and worsened in 2 patients. The bone flap was removed in 1 patient for wound dehiscence; hemiparesis in another patient resolved before discharge; and a patient with loculated ventricles and multiple previous shunt revisions had unresolved hydrocephalus after cyst excision.6
Pathophysiology
The term colloid cyst refers to only neuroepithelial cysts that arise in the anterosuperior third ventricle, near the foramina of Monro. The cysts are lined by a single layer of epithelial cells and are typically filled with a thick, viscous mucus that has an array of ingredients, including blood products, macrophages, cholesterol crystals, and numerous metallic ions, such as copper, iron, magnesium, aluminum, and phosphorus. Some colloid cysts may be filled only with thin serous fluid, and the composition of each cyst dictates its imaging characteristics, especially with magnetic resonance imaging (MRI). Microscopically, the cyst wall has a thin inner layer of cuboidal cells and an outer layer of vascular connective tissue, which explains why the wall may enhance on MRI.7
Most colloid cysts are discovered incidentally, and if follow-up imaging is performed, the cysts usually demonstrate slow or no growth. Clinical symptoms, when present, are caused by obstruction of cerebrospinal fluid (CSF) flow in the foramen of Monro, resulting in hydrocephalus. Patients may become symptomatic when the tumor enlarges rapidly enough to cause notable CSF flow disruption. The obstruction may be positional because of the shape of the colloid cyst.
Frequency
United States
Colloid cysts account for approximately 1% of all intracranial tumors.
Mortality/Morbidity
Although colloid cysts are histologically benign, they can acutely obstruct both foramina of Monro, resulting in sudden loss of consciousness, coma, and death.2,3
Race
No racial predilection is known.
Age
Colloid cysts are typically found in adults, usually in the fifth to sixth decade. However, in rare cases, they occur in children. Younger patients have an increased risk of developing symptoms.
Anatomy
Approximately 500 mL of CSF is made each day in the choroid plexus, most of it in the lateral ventricles. To reach the remainder of the subarachnoid space, the CSF must exit the lateral ventricles through the foramina of Monro, which are small openings that lead to the third ventricles. When a colloid cyst obstructs this pathway, no other means of egress exists for the CSF, and hydrocephalus ensues.
Presentation
Typically, colloid cysts are clinically silent and are found incidentally when patients are imaged for other reasons. When patients are symptomatic, they typically experience chronic headaches, which may be intermittent and positional because of transient CSF obstruction. On rare occasions, a colloid cyst may completely and irreversibly obstruct the foramen of Monro, resulting in sudden loss of consciousness and, if patients are not treated, in coma and death.2,3
Pollock et al reviewed 155 cases of colloid cyst and found 4 factors that were associated with colloid cyst-related clinical symptoms8 : (1) younger patient age, (2) increased cyst size (average of 13 mm in symptomatic patients vs 8 mm in asymptomatic patients), (3) ventricular dilatation (although 31% of asymptomatic patients had this finding), and (4) increased signal intensity on T2-weighted MRIs. These findings suggest that slowly growing colloid cysts may allow for compensation by the brain, thus avoiding symptoms. In addition, findings of high T2 signals in symptomatic patients suggest that the more-serous colloid cysts enlarge the fastest.
In another large study, 58 asymptomatic patients with colloid cysts were followed up for a mean of 79 months. The results showed a 0% incidence of symptoms up to 5 years and an 8% incidence at 10 years. None of the patients died suddenly during the follow-up period, suggesting that the lesions may be monitored safely.
When patients are symptomatic, treatment consists of surgical removal, either by flexible endoscopic means or by using rigid catheters. Computed tomography (CT) scan guidance is useful in reducing postsurgical complications, the most frequent of which is forniceal injury.
The appearance of a colloid cyst on CT scans and MRIs is important in planning treatment because the success rate after percutaneous aspiration is lower in colloid cysts that have high attenuation on CT scans and decreased MRI T2-signal intensity than in the cysts that have fluid characteristics.9 Interestingly, the cysts with high T2-signal intensity are easier to treat with minimally invasive surgical techniques; however, these cysts are also the ones that are most likely to cause clinical symptoms.
Preferred Examination
Either CT scanning or MRI may help in diagnosing a colloid cyst, although MRI has a few advantages.10 The multiplanar capabilities of MRI optimally demonstrate the location of the cyst, and typical signal intensities in the cyst help to confirm the diagnosis. T2-weighted MRI sequences may be useful to assess the nature of the intracystic contents and to predict the difficulty of aspiration during endoscopic or stereotactic procedures.
Limitations of Techniques
Although MRI has the advantage of multiplanar imaging, CT scanning is usually adequate for the diagnosis of a colloid cyst.
Differential Diagnoses
Astrocytoma, Brain
Brain, Metastases
Cysticercosis, CNS
Germinal Matrix Hemorrhage
Other Problems to Be Considered
Intraventricular hemorrhage occasionally mimics a colloid cyst on CT scans and MRI.
Subependymomas, central neurocytomas, and subependymal astrocytomas may occur in the same area as a colloid cyst on imaging studies, but these entities can be distinguished by their shape, contrast enhancement, and signal intensity.
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References
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Further Reading
Related eMedicine topics
Colloid Cysts
Neoplasms, Brain
Brain Metastasis
Hydrocephalus
Keywords
epithelium-lined cysts, intracranial tumors, neuroepithelial cysts, foramen/foramina of Monro/Monroe, CSF obstruction, obstructed CSF flow, ventricular outflow obstruction, intraventricular outflow obstruction
