You are in: eMedicine Specialties > Radiology > BRAIN/SPINE Brain, Colloid CystArticle Last Updated: Sep 19, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 8
  Author: Andrew L Wagner, MD, Assistant Professor of Radiology, Instructional Faculty, University of Virginia School of Medicine; Director of Neuroradiology, Department of Radiology, Rockingham Memorial Hospital Andrew L Wagner is a member of the following medical societies: American College of Radiology, American Roentgen Ray Society, American Society of Neuroradiology, and Radiological Society of North America Editors: Lucien M Levy, MD, PhD, Director of Neuroradiology, Professor of Radiology, Department of Radiology, George Washington University Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; L Gill Naul, MD, Professor and Head, Department of Radiology, Texas A&M University College of Medicine; Chair, Department of Radiology, Chief, Section of Magnetic Resonance Imaging, Scott and White Memorial Hospital and Clinic Author and Editor Disclosure Synonyms and related keywords: epithelium-lined cysts, intracranial tumors, neuroepithelial cysts, foramen/foramina of Monro/Monroe, CSF obstruction, obstructed CSF flow, ventricular outflow obstruction, intraventricular outflow obstruction INTRODUCTIONSection 2 of 8
  BackgroundColloid 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 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. PathophysiologyThe 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.4 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. FrequencyUnited StatesColloid cysts account for approximately 1% of all intracranial tumors. Mortality/MorbidityAlthough colloid cysts are histologically benign, they can acutely obstruct both foramina of Monro, resulting in sudden loss of consciousness, coma, and death.2, 3 RaceNo racial predilection is known. AgeColloid 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. AnatomyApproximately 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. Clinical DetailsTypically, 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 symptoms5: (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.6 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 ExaminationEither CT scanning or MRI may help in diagnosing a colloid cyst, although MRI has a few advantages.7 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 TechniquesAlthough MRI has the advantage of multiplanar imaging, CT scanning is usually adequate for the diagnosis of a colloid cyst. DIFFERENTIALSSection 3 of 8
Astrocytoma, Brain Brain, Metastases Cysticercosis, CNS Germinal Matrix Hemorrhage Other Problems to Be ConsideredIntraventricular 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. CT SCANSection 4 of 8
FindingsCT scan findings include a round mass with high attenuation at the anterior third ventricle. Rarely, colloid cysts may be isoattenuating or hypoattenuating relative to brain parenchyma. The typical high attenuation likely results from proteinaceous fluid. Hydrocephalus, which can be severe, results when the cyst obstructs the lateral ventricles at the foramen of Monro. This finding can be intermittent, as the cyst can act as a ball valve. Patients may then present with intermittent positional headaches. Degree of ConfidenceA nonenhancing area of high attenuation in the typical location is almost diagnostic of a colloid cyst, but most clinicians confirm the diagnosis with MRI. False Positives/NegativesNo normal variants are commonly confused with a colloid cyst. MRISection 5 of 8
FindingsColloid cysts are well demonstrated on MRIs and are found near the foramen of Monro, just posterior to the fornices in the anterosuperior third ventricle. The MRI signal intensity of colloid cysts is notoriously variable, with any combination of T1- and T2-signal intensities described.7, 8 The most common appearance is hyperintensity with T1-weighted sequences and isointensity to hypointensity with T2 sequences.4 This variation is believed to be a result of the proteinaceous fluid, as well as the paramagnetic effects of the metal ions in the fluid and hemorrhage. El Khoury et al found that low signal intensity of colloid cysts on T2-weighted images corresponded to difficult percutaneous aspiration in 100% of cases, whereas most of the cysts with high T2-signal intensity were considered easy to aspirate.9 Rarely, inspissated debris may form a dependent nodule that can be seen on MRIs and CT scan images. Colloid cysts do not have intrinsic enhancement; the presence of enhancement suggests a solid tumor. Peripheral enhancement may be present because of vascularity in the outer wall.4 Degree of ConfidenceThe diagnosis of a colloid cyst is made based on the classic location, appearance, and signal intensity. Central contrast enhancement suggests an alternative diagnosis, but most other pathologies that occur in this location are easily distinguishable from colloid cysts. False Positives/NegativesNo normal variants are commonly confused with a colloid cyst. INTERVENTIONSection 6 of 8
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MULTIMEDIASection 7 of 8
REFERENCESSection 8 of 8
Article Last Updated: Sep 19, 2007 | |||||||||||||||||||||||||||||||||||
