Colloid cyst of the third ventricle
A colloid cyst of the third ventricle is a benign epithelial lined cyst with characteristic imaging features. Although usually asymptomatic, they can present with acute and profound hydrocephalus.
Colloid cysts account for 0.5-3% of primary brain tumours and 15-20% of intraventricular masses 1-3. They are located at the foramen of Monro in 99% of cases 1.
The majority of cases are identified in early middle age (30-40 years of age) although 8% of cases may be diagnosed in paediatric age 3.
In the vast majority of cases, colloid cysts are found incidentally and are asymptomatic. Their position in the roof of the third ventricle immediately adjacent foramen of Monro can on occasion result in sudden obstructive hydrocephalus and can present with a thunderclap headache or unconscious collapse. The headaches tend to be positional, and patients may learn how to relieve symptoms.
Colloid cysts originate from abnormal folding of the primitive neuro-epithelium (the paraphysis elements) 2-3. They contain mucin, old blood (haemosiderin), cholesterol, and various ions, accounting for the wide range of imaging appearance.
These cysts are lined by a single layer of columnar epithelium which produces mucin, which appears as a thick yellow green fluid when the cyst is open.
Cross-sectional imaging usually enables the diagnosis to be made with confidence. MRI is superior to CT in fully characterising the lesion.
On all modalities colloid cysts appear as a rounded, sharply demarcated lesion at the foramen of Munro, which range in size from a few millimetres to 3-4cm 3.
Typically seen as a well defined, rounded lesion at the roof of the 3rd ventilcle
- typically hyperdense
- isodense and hypodense cysts are uncommon
- calcification is uncommon 2
MR signal characteristics include
- T1 - typically high T1 signal (short T1) - can be variable
- T1 C+ (Gd) - only rarely demonstrates thin rim enhancement, but usually this represents enhancement of the adjacent and stretched septal veins 3
- T2 - typically low T2/T2* signal (short T2) - can be variable
Treatment and prognosis
They tend to gradually increase in size over time and if resection is required, this can be performed via a transcallosal approach or more recently endoscopically. When large and or symptomatic the decision to operate is relatively straight forward, as it can be life saving. For small lesions without symptoms attributable to them, the careful discussion between the patient and treating surgeon is required to weigh up the pros and cons of surgical intervention.
There are usually no differential diagnoses for a colloid cyst. In atypical cases it is worth considering other masses which arise in the region of the foramen of Monro, including:
- calcified / hyperdense meningioma
- giant cell astrocytoma
- pilocytic astrocytoma
- blood in the region of foramen of Monro
For a more complete list please refer to masses in the region of the foramen of Monro.
- 1. Osborn AG, Preece MT. Intracranial cysts: radiologic-pathologic correlation and imaging approach. Radiology. 2006;239 (3): 650-64. doi:10.1148/radiol.2393050823 - Pubmed citation
- 2. Waggenspack GA, Guinto FC. MR and CT of masses of the anterosuperior third ventricle. AJR Am J Roentgenol. 1989;152 (3): 609-14. AJR Am J Roentgenol (abstract) - Pubmed citation
- 3. Kornienko VN, Pronin IN. Diagnostic Neuroradiology. Springer Verlag. (2008) ISBN:3540756523. Read it at Google Books - Find it at Amazon
- 4. Armao D, Castillo M, Chen H et-al. Colloid cyst of the third ventricle: imaging-pathologic correlation. AJNR Am J Neuroradiol. 2000;21 (8): 1470-7. AJNR Am J Neuroradiol (full text) - Pubmed citation
Synonyms & Alternative Spellings
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